- Email: [email protected]
Natural fiber-reinforced polymer composites
Natural fiber-reinforced polymer composites: application in marine environments
3
Deepak Verma1 and Kheng Lim Goh2 1 Department of Mechanical Engineering, Graphic Era Hill University, Dehradun, Uttarakhand, India, 2Newcastle Research & Innovation Institute (NewRIIS), Singapore
3.1
Introduction
Composite materials can be developed by incorporating various reinforcements, such as fibers and particulates, into the polymer matrix, whether they are synthetic or biodegradable types. With the correct selection, these composite materials can be found to be suitable for various applications, such as marine applications, which resist the various chemical attacks. As we already aware, seawater composition changes with respect to the location—this can be because of the watercourses which ultimately carry eroded materials and agricultural run-off into the sea. As per Kester et al. [1], the composition of 1 kg of seawater consists of around 19.4 g Cl2, 10.8 g Na1, 2.7 g SO422, 1.3 g Mg21, 0.4 g Ca21, 0.4 g K1, 0.1 g HCO32, 0.1 g Br2, and other chemicals (at lower levels). As per the given composition of seawater, it has been observed that the salt water environment is found to be corrosive to most engineering metals and, in addition, marine animals, for example, naval shipworm (Teredo navalis), and gribble (Limnoriidae), can result in rapid decay of wood. The utilization of composite materials and their structures in marine industries is growing, as in other industries. For example, sandwich composite panels having glass or carbon skins with a polymeric core have been found to be one of the most used advanced composites for the development of entire hulls and structures of marine craft. It has been noticed that the composite materials and their structures show various advantages/benefits as compared to the conventional metallic materials, for example [2]: G
G
G
G
G
Light in weight; Good corrosion resistance; Nonmagnetic structure; Lower acoustic and thermal signatures; and High blast resistance.
It has been observed that the seawater environment generally consists of combinations of various parameters. Some of the primary parameters are: Biomass, Biopolymer-Based Materials, and Bioenergy. DOI: https://doi.org/10.1016/B978-0-08-102426-3.00003-5 © 2019 Elsevier Ltd. All rights reserved.
52
G
G
G
G
Biomass, Biopolymer-Based Materials, and Bioenergy
Hydrostatic pressure; Seawater; Temperature; Water currents
In the case of marine sandwich structures [36], FRPs (i.e., carbon fiber, aramid fiber, and glass fiber reinforcement in a polymeric matrix) are primarily utilized as skin materials and polymer foams (i.e., specifically polystyrene or PVC foam) as core materials. It is also seen that the composite materials, that is, sandwich structures, show greater advantages as compared to steel structures. If the structure is light in weight then it validates a larger cargo capacity, savings in fuel, greater acceleration, improved stability of the ship, greater specific strength and stiffness, and buoyancy, etc. These composites also provide resistance to marine environments and have nonmagnetic properties. It has been observed that these composite structures showed higher corrosion resistance, need low maintenance, and permit more design flexibility. One disadvantage of composite sandwich structures is the high production cost as compared to conventional materials (i.e., steel or wood), as their manufacture is a labor-intensive process. The selection of the ideal manufacturing method for every part is strategic, as there are many choices specifically for raw materials, processing methods, and stacking sequence (for sandwich structures) that are available for design and manufacturing engineers for the development of each specific part/ component. The various parameters, such as production rate, cost, strength, size, and shape of the structure, can be taken into account for the selection of a specific part/component. In this chapter, we discuss the different types of natural fibers and their reinforcements in the polymer matrix, specifically for application in the marine industries. We also discuss the effect of the seawater environment on the polymermatrix composites, that is, specifically in terms of moisture absorption by marine biocomposites. The different methods for moisture measurement are also reported in this chapter. The different mechanical properties of the natural fiber-reinforced biocomposites are also been discussed, specially focusing on the marine applications. It has been observed that there is a good utilization of nondestructive testing (NDT) methods by marine industries. Therefore, based on this, we have also included a brief introduction to some of the NDT methods used by marine industries. Different types of morphological methods and their past studies are also included in the chapter. At the end of the chapter, we describe the advantages and disadvantages of the marine composites.
3.2
Effect of seawater on polymer matrix composites
The exposure of the composites to the liquid environment resulted in the absorption of the water molecules. The reason behind the absorption is the diffusion process which can be monitored by weight gain with respect to time. The diffusion process
Natural fiber-reinforced polymer composites: application in marine environments
53
is slow and is mostly affected by the equivalent coefficient of diffusion of the composite material. The diffusion coefficient depends upon the type of reinforcing fiber (e.g., glass vs carbon), type of resin (e.g., epoxy vs vinyl ester), and type of manufacturing process. The moisture absorption resulted in detrimental effects associated with lower adhesion between the fiber and the matrix, and ultimately a deterioration in the properties of the composites [711]. Also, the moisture, in combination with the temperature, resulted in changes to material properties, such as the glass transition temperature, Tg, of composites [8,12]. Diffusion can be defined as a process by which matter is transported/diffused from one part of a system to another by random molecular motions. Diffusion is considered to be a time-dependent process, where D is the diffusion coefficient. Assume a continuous mass distribution m (x,t), the steady-state flux (J) is controlled by Fick’s first law [13]. J 52D
@m @x
(3.1)
Under general conditions (unsteady state), applicable to polymer composites, diffusion can often be described by Fick’s second law: @m @2 m 5D 2 @t @x
(3.2)
The degradation of the properties is due to fluids, which may be recoverable, and difference between them can be observed by the weight gain data. Fig. 3.1 shows the five schematic curves of fluid sorption in polymers and polymeric composites relating weight gain to Ot . The solid curve showed the linear Fickian (LF) behavior. Curves “A” and “B” show the typical variations with reference to both neat polymers and fiber-reinforced composites having recoverable fluid-induced deterioration of some material properties. The curve of type A variation shows a case where weight gain is at nonequilibrium phase, and the type B curve shows the state of two-stage diffusion. On the other hand, curves “C” and “D” are generally obtained for polymeric composites only. Also, “C” shows the case of speedily increasing fluid content, generally associated with damage growth resulting in material break down and large failure rates. Curve “D” shows the weight loss that is referred to the chemical or physical break down of the material. The authors invented an experimental method to permit measurement of moisture uptake through adsorption kinetics with a highly precise gravimetric microbalance system as represented in Fig. 3.2. The setup contains a high-sensitivity microbalance (Cahn Digital Recording Balance, DRB-200), tailor-made sampling and gas-handling system, and a data acquisition system. A quartz chamber 750 mm long and 75 mm inner diameter is fixed to the balance on the sampling side. A nickelchromium wire mesh is used to attach the sample pan to minimize the mass transfer resistance between solidfluid phases. This sample pan is kept inside the quartz chamber, which does not absorb moisture. The quartz chamber consists of an
A
C
LF
M(t*) M(∞)
1.00 B
D
0.62
0.0 0.0
0.567
1.320 t*
Figure 3.1 Schematic curves representing a solid line, designated by LF, corresponds to linear Fickian diffusion and four possible categories of non-Fickian weight gain sorption data. Source: Reproduced with permission from Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:821828.
Figure 3.2 Setup of a gravimetric microbalance system coupled with a DAQ system. Source: Reproduced with permission from Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:821828.
Natural fiber-reinforced polymer composites: application in marine environments
55
inlet gas port at the bottom side and some exit ports along its length. The gas generation system has ultrahigh pure N2, which acts as a carrier gas. The carrier gas is firstly passed through a gas desiccator, having anhydrous CaSO4, which ultimately removes any traces of gas moisture. The gas flow rates are controlled by mass flow controllers. A part of the carrier gas is permitted to purify by double-distilled water in a fritted glass bubbler which forms a saturated vapor of carrier gas. Afterwards, the wet carrier gas is again mixed with the leftover dry carrier gas to form controlled water vapor concentrations. The water vapor concentration is observed by a relative humidity probe above the sample pan which ultimately gives the feedback control for the flow rates of wet and dry streams to keep to the target relative humidity at the sample position. The gravimetric balance is combined with a data acquisition system that congregates mass, time, and temperature data.
3.3
Effect of moisture on the properties of marine composites
Moisture intrusion in composites is governed by three different mechanisms. These are [14,15]: 1. Diffusion of water molecules into the microgaps between polymer chains; 2. Capillary movements into the cracks or gaps and defects available at the interface between fibers and the matrix phase; and 3. Transportation of water in the matrix comes from the swelling of fibers.
Moisture absorption with reference to the postconsolidated composites can be mainly distinguished by comparative absorptivity values, which can be found by Fick’s law (as reported in Eqs. 3.1 and 3.2). However, diffusion is the main mechanism for moisture intrusion and may occur due to the presence of voids in the matrix phase resulting in blistering and in the case of gel coats, it is mainly related to interfacial seepage between fibers and matrix [16]. According to the diffusion principle, water diffusion into polymer composites includes the displacement of fluid molecules from high concentration regions to lower concentration regions [17].
3.3.1 Fickian diffusion behavior Water absorption is usually a two-step process, as shown in Fig. 3.3. In the first step, rapid seepage takes place as water perforates mainly between the matrix phases, and advances at a constant rate. The second step includes a noticeable reduction as the material achieves saturation and is due to the component swelling and attainment of the final equilibrium [18].
56
Biomass, Biopolymer-Based Materials, and Bioenergy
Mt (%)
t Figure 3.3 Fickian diffusion curve. Source: Reproduced with permission from Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine Composites. Marine Applications of Advanced Fibre-Reinforced Composites. Woodhead Publishing. Eds Edited by J. GrahamJones and J. Summerscales, 2016, pp. 103124.
3.3.2 Non-Fickian or anomalous diffusion behavior In some conditions, the non-Fickian behavior is noticed for some definite materials and situations whereby plots did not match classic absorption properties. NonFickian effects are generally categorized in accordance with their nature in water absorption plots. The exemplary non-Fickian behavior may be categorized into three separate behavior types as described below.
3.3.2.1 Two-stage absorption This type of absorption is regularly found in non-Fickian behaviors. The two-stage curves consists of two distinct plateaus (Fig. 3.4). At the starting stage of absorption, Fickian behavior is noticed which consists of both the linear and plateau regions. This is succeeded by gradual non-Fickian absorption, which generally consists of a linear initial period and eventual plateau. This second stage is described by moisture-strengthened structural relaxation possibly creating voids and blisters, which ultimately retain water. The two-stage curve can be obtained from Eq. (3.3) as shown below [19] ( 0:75 ) pffi Dx t Mt 5 MN0 ð1 1 k tÞ 1 2 exp½ 2 7:3 h2
(3.3)
57
Mt(%)
Natural fiber-reinforced polymer composites: application in marine environments
t Figure 3.4 Two-stage absorption curve. Source: Reproduced with permission from Bao L, Yee AF. Moisture diffusion and hygrothermal ageing in bismaleimide matrix carbon fibre composites part I: uni-weave composites. Compos Sci Technol 2002;62:20992110.
where, h is the thickness of the sample and the other terms are as explained above. The term (1 1 kOt) in Eq. (3.3) shows the relaxation controlled second stage and the parameter k is the rate of relaxation.
3.3.2.2 Sigmoidal absorption The next conventional non-Fickian behavior is sigmoidal absorption. This is shown by the S-shaped curves in Fig. 3.5. This type of behavior is due to phase void formation during water intrusion and localized saturation. These attributes mostly depend on the environmental conditions and materials selection for the particular composite [18].
3.3.3 Moisture diffusion measurements Moisture diffusivity is considered to be an important characteristic that should be taken into account while designing composite materials for marine environments/ applications. This is essential for the evaluation of the dispersion rate of water in the composite throughout its initial advancement from a high-concentration to a low-concentration area. The moisture diffusivity behavior of polymeric composites can be obtained using Eq. (3.4).
Biomass, Biopolymer-Based Materials, and Bioenergy
Mt(%)
58
t Figure 3.5 Sigmoidal absorption curve. Source: Reproduced with permission from Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine Composites. Marine Applications of Advanced Fibre-Reinforced Composites. Woodhead Publishing. Eds Edited by J. GrahamJones and J. Summerscales, 2016, pp. 103124.
N X Mt 8 2 Dx ð2n11Þ2 π2 t 512 exp 2 h2 MN n50 ½ð2n11Þπ
(3.4)
where Mt is the mass of absorbed moisture at the time, (t); MN is the saturated mass of absorbed moisture; h is the thickness of the sheet in dry condition; and D is the diffusion coefficient or diffusivity. The mass uptake (Mt) can be represented by Eq. (3.5): Mt 5 k:tn
(3.5)
where t is the time, k is the initial slope of the Mt versus Ot curve and n is the constant, then Fickian absorption n 5 0.5. The percentage of water absorption in the polymer composites is determined by the weight difference between the immersed samples and the dry samples using Eq. (3.6) Mt 5
Wt 2 W0 3 100 W0
(3.6)
where Mt is moisture uptake, and W0 and Wt are the mass of the specimen before and during aging, respectively.
Natural fiber-reinforced polymer composites: application in marine environments
59
The coefficient of diffusion is a significant parameter in Fick’s law. The following relation is used for the evaluation of the diffusion coefficient: rffiffiffiffiffiffiffiffi Dx t Mt 5 4MN πh2
(3.7)
Rearranging the above equation and solving for the diffusion coefficient (Dx) gives the following equation: " #2 π Mt Dx 5 2 16MN Ot=h
(3.8)
where MN is the equilibrium moisture content (maximum water uptake) of the sample. The graph of weight gain versus time can be plotted with the help of the weight gain data of the material with respect to time. The water diffusion coefficient is the rate at which water transports from the surface to the core of the specimens. Again, the diffusion coefficient can be calculated by modifying Eq. (3.9) from the slope of moisture content versus square root time as follows: Dx 5 π
h 4MN
2
M2 2M1 2 pffiffiffiffi pffiffiffiffi t2 2 t1
(3.9)
The diffusion properties of composites explained by Fick’s laws are assessed by the weight gain measurements of immersed samples in water by taking into account the slope of the first portion of the weight gain graph versus square root time. For values MMNt lower than approximately 0.6, the initial portion of the curve can be detailed as: Mt 4 5 h MN
rffiffiffiffiffi Dt π
(3.10)
This method gives good approximations of absorption evaluation where the gradient of the curve is found to be greater than 0.6 [19].
3.4
NDT of marine composites: a brief overview
This section describes the utilization of NDT (nondestructive techniques) for the inspection or testing of marine composites. It has been observed that only ultrasonics and radiography techniques have shown significant applications for the inspection of marine composites. Eddy-current testing and eddy electromagnetic techniques are utilized for the inspection of high-density and highly conductive materials. The fluorescent penetrant/dye is used for the detection of considerable
60
Biomass, Biopolymer-Based Materials, and Bioenergy
weathering at the surface of glass fibre reinforced polymer (GFRP) composites. In this process, the dye is rapidly absorbed in a porous matrix and shows a large reflection to the UV light source as compared to a fresh fabricated panel [20].
3.4.1 Vibration analysis Vibration analysis also played a significant role in the analysis of the acoustic response of a structure over a wide frequency/spectrum. Vibrational techniques also helpful for the dynamic analysis of the structures at specified intervals and, in particular, the response of these structures will change with respect to time because of the changes in structural stiffness [21]. The vibration analysis is generally performed at very low elastic-wave frequencies (,20 kHz).
3.4.2 Mechanical impedance analysis Mechanical impedance analysis is another evaluation test. In this method, a metallic probe tip at a particular frequency of around 210 kHz, loads the structure and then measures the variations in terms of the amplitude and phase of the probe. This test attains moderately sound penetration as compared to the resonance technique. The pitch-catch technique utilizes two dry-coupled transducers which contact at a fixed distance and transmit and receive frequencies in the range of 10100 kHz along the surface.
3.4.3 Conventional ultrasonics Ultrasonic testing (UT) uses the piezoelectric effect, in which a permanently polarized crystal can be utilized to generate elastic waves at particular frequencies, and then convert these waves into electrical energy. The original transducers used quartz crystals, which were then replaced by piezo-ceramics, for example, barium titanate and lead zirconate titanate (“PZT”). Generally, pulses of ultrasound are repeatedly introduced into the structure at a very high rate, and in timber structures, the range of the ultrasound is 20 kHz, and 50 MHz in high-stiffness metallic alloys [22]. However, in the case of marine composites, the inspections are generally carried out at a frequency range of 0.52.25 MHz. When ultrasound waves strike a composite structure it scatters them and shows a mismatch of acoustic impedance between glass fibers and the polymer matrix. Therefore, glass is found to be highly reflective to ultrasound.
3.4.4 Advanced ultrasonics A major criticism of UT has been the severe bottlenecks it can create, both in manufacturing facilities and in costly maintenance downtime for in-service components. A range of modifications has been developed to overcome this problem, mainly by introducing ultrasound into the structure using alternative means, as outlined below.
Natural fiber-reinforced polymer composites: application in marine environments
61
3.4.4.1 Air-coupled UT It is very difficult to establish a coupling between the transducer and test component for ultrasonic testing. This can be done by water coupling, by immersing the transducers along with the test part in a water tank, or by a water-squirter arrangement. Localized or point inspections or testing are attained by using a water-based gel. The constant coupling can be maintained by these methods with substantial time to complete the UT inspection. Air-coupled UT is achieved without any acoustic couplants, maximizing the inspection efficiency. Solving the problem of the high-impedance mismatch that appears at the transducer/air and subsequent air/ component interfaces is not superficial, and needs further modifications. In marine composites of considerable thickness (approximately 50 mm), the aircoupled testing is mainly suitable for the detection of disbonds and voids present in low-density foam-sandwich structures [23].
3.4.4.2 Laser-based ultrasound High-frequency pulsed lasers are utilized for the production of elastic waves of ultrasonic wavelength, for the use of high-frequency pulsed lasers usually solidstate neodymium-doped yttrium aluminum garnet (“Nd:YAG”), which taps the surface at megahertz frequencies. Noncontact inspection is found to be more advantageous and is rarely applied as the ultrasonic waves produce thermoelastic waves via laser ablation, as localization of the laser causes melting of the surface. High power may cause overheating of the polymer matrix, resulting in macroscopic destruction of the surface. The ultrasound detection function can be implemented by lasers; the arrangement is shown in Fig. 3.6 and is known as a heterodyne Michelson interferometer. On the other hand, robotic laser UT became a traditional NDT method for the analysis of aerospace composites [24].
3.4.4.3 Infrared thermography Infrared thermography is another advanced NDT method that uses electromagnetic radiation over the infrared spectrum at wavelengths of around 700 nm to 1 mm. As the name implies, this bandwidth is felt by the human body as “warmth,” and the method has found very good application in industries for the detection of overheating in electrical circuits and in pipes of petrochemical processing plants. Such evaluations can be performed indifferently, as the IR radiation is generated by the source in its standard operating state. However, inadequate heat is dissipated by the internal structure of a composite which permits measurements to be performed on composite structures, and an active heating source is needed to carry out an accurate investigation of these structures. The major limitation of thermography is its limited utilization related to thick structures. The physical limitation of heat transfer in most of the structures resulted in a quick decrease in sensitivity of components [25].
62
Biomass, Biopolymer-Based Materials, and Bioenergy
Optical detector Interference filter Variable attenuator
Laser
Oscillator Acousto-optic cell M1
M4
Beam splitter M3
Ultrasound emission
M5 L1
L2
M2
Figure 3.6 Laser-based ultrasonic detection using a heterodyne Michelson interferometer detection method. Source: Reproduced with permission from Borum KK. Evaluation of the quality of thick fibre composites using immersion and air-coupled ultrasonic techniques. In: 9th European Conference on Non-destructive Testing, ECNDT, 2529 September 2006, Berlin, Germany, 2006.
3.4.4.4 Radiography and tomography X-ray radiography is one of the most feasible NDT methods. X-rays are also used in the medical field for inspection of diseases. Apart from this, radiography has shown correspondingly less applications for the testing of composite materials. With this technique, thin structures can be inspected [26], where large air voids are easily detectable. It has been observed that, in the lateral plane, it is hard to detect the delamination as porosity and fiber volume fraction investigation are considered to be a complex proposition [27]. The main disadvantage of X-ray radiation is that it is very harmful to humans.
3.4.4.5 Electrical and magnetic techniques A variety of NDT techniques that utilize electrical conductivity are available for composite inspection. These techniques require an electrically conductive (i.e., carbon fiber) composite. The following are some of the methods for the inspection of these composites.
3.4.4.6 Eddy-current testing Eddy-current testing is the less successful technique for the inspection of composites, and requires electromagnetic induction of electrical current on the component surface. This is generally used to detect the aerospace surface crack inspection. Prakash and Owston used this technique for the characterization of ply-orientation in carbon fiber-reinforced plastics. This can be possible by correlating the plyorientation and the electrical conductivity, although as composite laminates have different layers of polymer and fibers, this process may give inaccurate measurements.
Natural fiber-reinforced polymer composites: application in marine environments
63
3.4.4.7 Capacitive imaging In this process, two charged electrodes are used, which emit and receive an electric field on a material volume which they interact with. This method may be utilized in a broad range of material applications as compared to the eddy-currents, and provides fairly good indications of cracks and impacts, damage by heat, and dampness. However, the nonintuitive feature of the volume-averaged field measurement excludes its utilization for quantitative analysis. Yacht surveyors generally used such devices as a moisture meter for the inspection of GFRP hulls [28].
3.4.4.8 Nuclear magnetic resonance Nuclear magnetic resonance (NMR) has been successfully applied in the medical industry as magnetic resonance imaging, functioning as a 3D computed system. The sensitivity of NMR to the availability of water gives an idea of drying rates in various composites, with physically absorbed or chemically bound moisture. It has been observed that this technique is useful for moisture-related investigation in low-conductivity composites, for example, glass-fiber [29].
3.5
Mechanical properties of polymer marine biocomposites: a past study
It is well known that exposure to seawater for a long duration ultimately affects the mechanical properties of composites. The degradation of composites can be dynamically related to the water absorption feature of composites. From Fig. 3.7 we can see the connection between the glass/polyester composite water absorption (moisture) and disparity of tensile strength, flexural strength, and flexural modulus. It has
Figure 3.7 Water intake versus mechanical properties glass/polyester composite at 17 C and 30 C. Source: Reproduced with permission from Gu H. Behaviours of glass fibre/unsaturated polyester composites under seawater environment. Mater Des 2009;30:13371340.
64
Biomass, Biopolymer-Based Materials, and Bioenergy
already been reported that the moisture saturation of glass/polyester composite B is found to be 0.58% [30]. After the attainment of the moisture saturation level (approximately 30 days), deterioration of the tensile slope decreases and then becomes steady. However, the flexural variation slope increases just at the moisture saturation level of the polyester composite (1.25% for 65 days). Veazie et al. [31] performed double-cantilever beam (DCB) tests and describe a considerable (approximately more than 50%) decrease in interfacial fracture toughness due to the formation of cracks induced following the “wet” exposure. Although, the specimens that already contained cracks before the “wet” exposure, the interfacial fracture toughness was again reduced (approximately another 50%). It is generally observed that specimens exposed to the “wet” environment show degradation because of seawater absorption, mainly through the facesheet/core interface. The fracture toughness of the nanocomposites was characterized by investigating the effect of nanosilica with different periods of saltwater immersion. CT tests at room temperature for each material were performed and are shown in Fig. 3.8, which represents the ideal load-crack opening displacement (COD) curves. It is noted that both neat epoxy and composite specimens subjected to fracture in a brittle manner at the maximum load conditions, and obviously the maximum loads for the nanocomposite are greater than those of the corresponding neat counterpart [32]. The fatigue life of the cross-ply laminate (with four testing environments) is shown in Fig. 3.9, with the four-point bending test performed on both dry and wet specimens, at 90% UFS, and it was observed that all specimens failed at no more than 106 cycles. However, the immersed specimen represents a lower cycle count as compared to those without immersion. At about 80% UFS, all of the dry specimens showed infinite fatigue life (i.e., more than 3 3 106 cycles) in the same testing conditions. In contrast, all the immersed specimens failed [33].
Figure 3.8 Typical load-crack opening displacement (COD) curves for neat epoxy (EP) and nanosilica-enhanced epoxy composite (SEP) with different periods of immersion of 0, 7, and 30 days. Source: Reproduced with permission from Han W, Chen S, Campbell J, Zhang X, Tang, Y. Fracture toughness and wear properties of nano silica/epoxy composites under marine environment. Mater Chem Phy 2016;177:147155.
Natural fiber-reinforced polymer composites: application in marine environments
65
Infinite life 100% 95% 90% UFS
85%
Dry-3P
80%
Dry-4P
75%
Wet1-4P
70% 65% 60% 1.0E+05
Wet2-4P
1.0E+06 Cycle
1.0E+07
Figure 3.9 Fatigue life of CP laminate. The fatigue cycle is plotted as a logarithm scale. Wet1-4P: immersed specimen, covered with a wet sponge while undergoing four-point bending fatigue testing; Wet2-4P: immersed specimen, without wet sponge cover while undergoing testing. Source: Reproduced with permission from Meng M, Le H, Grove S, Rizvi MJ. Moisture effects on the bending fatigue of laminated composites. Comp Struct 2016;154:4960.
Three-point bending tests were performed to determine the flexural strength and modulus of the composites at various environmental exposures. It has been noticed from Fig. 3.10 that all exposure conditions represent an unsubstantial effect on longitudinal flexural modulus of specimens in contrast to the flexural modulus of dry specimens within the experimental error. A great decline in longitudinal flexural modulus was observed for the specimens, which were exposed to 2000 hours, in addition to the UV radiation and salt spray in environmental chambers (7%). The result shows that the longitudinal flexural strength noticeably diminishes for distinct types of exposure (Fig. 3.11). The noticeable decrease in longitudinal flexural strength (because of the moisture absorption) is due to the failure of the fibermatrix interface, resulting in swelling and loss of coalition in carbon fiber vinyl ester composites [34]. Dayakar Penumadu et al. [35] focused on the effect of confinement and studied one-sided seawater confinement of composites specifically for the determination of the cyclic fatigue behavior of carbon fiber-reinforced vinyl ester composites, used as facings materials for naval sandwich structures. It has been observed from the experimental results in the case of matrix dominated [ 6 45]2x laminates of carbon fiber-reinforced vinyl ester composites, that the failure occurs after a fewer number of cycles and when fatigued under immersed conditions in the water (not in air), a drop of approximately 80% occurs in the number of cycles to failure. Again, when fatigued with the conditions of one-sided confinement to water, the composite failed in less than 50% of loading cycles as compared to the samples without water
66
Biomass, Biopolymer-Based Materials, and Bioenergy
(A)
Indoor immersion 6 month 1 year
Longitudinal flexural modulus (GPa)
120
–5%
–4.8%
100 80
–6.3% –3.3%
–4.6%
–5.5%
60 40 20 0 Virgin
Distilled
Salt water
Sea water
Longitudinal flexural modulus (GPa)
(B) Outdoor exposure 1 year 6 month
120
–0.06%
–1.4%
100
–3.8%
–5.8%
80 –2.1%
60
1.4%
–4.1%
–3.8%
40 20 0
Virgin
Row 1
Row 2
Row 3
Row 4
Longitudinal flexural modulus (GPa)
(C) Environmental chamber 800 hours 2000 hours
120
–4.8%
–2.6%
–3.1%
100
–4.7%
80 –4.2%
–2.1%
0.06%
–7%
60 40 20 0
Virgin
Heat and UV-Heat Humidity and Humidity
Salt Spray
UV-Salt Spray
Figure 3.10 The longitudinal flexural modulus of CFVE composites exposed to (A) indoor immersion, (B) outdoor environmental exposure, and (C) conditioning in environmental chambers. Source: Reproduced with permission from Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:8085.
Natural fiber-reinforced polymer composites: application in marine environments
Longitudinal flexural strength GPa
(A)
Indoor immersion
2.5
6 month 2.0
1 year –15.3%
–16%
–17.1%
1.5 –15%
–14.4%
–13.1%
1.0 0.5 0.0 Virgin
(B) Longitudinal flexural strength GPa
Outdoor exposure 2.5
1 year
6 month –4.1%
2.0
–9.1%
–13.8% –17.7%
1.5 1.0
–12.4%
–13.8% –16.8%
–31%
0.5 0.0
Virgin
(C) Longitudinal flexural strength (GPa)
Distilled Salt water Sea water
Row 1
Row 2
Row 3
Row 4
Environmental chamber
2.5
800 hours –6.7%
2
2000 hours
–4.6%
–7.8%
–7.7%
1.5 –11.7%
1
–11.9%
–13%
–17.1%
0.5 0
Virgin
Heat and UV-Heat Humidity and Humidity
Salt Spray
UV-Salt Spray
Figure 3.11 The longitudinal flexural strength of CFVE composites exposed to (A) indoor immersion, (B) outdoor environmental exposure, and (C) conditioning in environmental chambers. Source: Reproduced with permission from Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:8085.
67
68
Biomass, Biopolymer-Based Materials, and Bioenergy
Stress (MPa)
Figure 3.12 Average number of cycles to failure of dry and wet [ 6 45]2s sample in air and under one-sided exposure conditions under cyclic loading at 1 Hz frequency. Source: Reproduced with permission from Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:9498.
Last cycle of wet immersed sample
90 80 70 60 50 40 30 20 10 0
First cycle of dry, wet immersed and one-sided wet immersed samples
Last cycle of one-side wet sample
Last cycle of dry sample
0
0.01
0.02
0.03
0.04
0.05
0.06
True strains (mm/mm) Figure 3.13 Comparison of the last cycle true strains on [ 6 45]2s dry sample in air and wet immersed and one-sided immersed. Source: Reproduced with permission from Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:9498.
confinement (in air). These results are represented in Figs. 3.12 and 3.13, respectively. Alkhader et al. [36] showed the stiffness and stress distributions for both UV and moisture aging conditions as illustrated in Fig. 3.14. This figure shows that the
Dimensionless thickness (2z/h)
Natural fiber-reinforced polymer composites: application in marine environments
0 1 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 –100
Flexural modulus (GPa) 2 4 6
Flexural stress Flexural modulus –50 0 50 Flexural stress (MPa)
69
8
1 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 100
Figure 3.14 Distribution of transverse modulus and stress, showing variation across the laminate thickness for the laminate exposed to UV and moisture. Plots created using the force level at the onset of failure. Source: Reproduced with permission from Afshar A, Alkhader M, Korach CS, Chiang F-P. Effect of long-term exposure to marine environments on the flexural properties of carbon fibre vinyl ester composites. Compos Struct 2015;126:7277.
stiffness deviated distinctly inside the damaged zone, and at the commencement of failure, it is noticed that the stress in the damaged zone is much lesser as compared to the value expected by utilizing the adequate lamina properties assumption (i.e., 61.81 MPa). On the other hand, it is found that the maximum stress inside the aged specimen (i.e., 64.66 MPa) is approximately the same as the 61.81 MPa value, nevertheless, it remains in the interior of the specimen only and not on the surface. Xu et al. [37] studied the durability and dynamic failure properties that are considered to be the evaluative parameters for naval composite ships in a seawater environment. Other authors have carried out a low-speed impact experiment of the composite laminates. The impact damage resulted in a noticeable surface damage in lieu of a quick failure pattern. Impact damage was performed by using an Instron test machine [6]. All the developed samples were subjected to the same impact energy (60 joules) having a 16-mm (5/800) diameter hemisphere impactor. This hemisphere impactor was lifted to a specific height (for the achievement of the desired impact energy) and then dropped freely. The impact force was then recorded by the test machine. Fig. 3.15A and B shows the damage zones of the impacted samples.
70
Biomass, Biopolymer-Based Materials, and Bioenergy
Figure 3.15 Typical impact damage on the front and back surfaces (A and B). Source: Reproduced with permission from Bar-Cohen Y, Crane RL. NDE of hygrothermal affected glass fiber-reinforced plastics. In: ASNT Spring Conference, March 1980. American Society for Nondestructive Testing, Philadelphia, PA, USA, 1980.
3.6
Advantages and disadvantages of marine composites
The following are the advantages of marine composites: G
G
G
G
G
The great strength of the weight attribute; Resistance to corrosion applicable for different applications; Complex-shaped structures can be developed easily as compared to the conventional methods; Low maintenance cost; Improved stiffness.
The following are some noticeable disadvantages of marine composites: G
G
G
G
Low impact resistance; Low heat tolerance; Low UV resistance, which is of utmost important in the marine environment; Very initial cost as compared to some conventional materials [38].
3.7
Conclusion
Recently, substantial progress has been made to understand the different attributes of composite materials and their structures in the marine environment. It is also observed that presently processing and production areas have given more attention to ensuring the potential for the development of intricate, large assemblies to withstand heavy loads. However, the prime challenges for employing composites as a marine application include the optimum capital expenditure and operation costs of boats and ships developed using composites. Nowadays, novel composites, for example, epoxy-based composites with carbon nanotubes, are found to be more favored, with increasing concern for high-performance marine structures. Certainly, light structure, fast production, durability, and strength facilitate composites in playing an important role in marine applications/environments.
Natural fiber-reinforced polymer composites: application in marine environments
71
References [1] Kester DR, Duedall IW, Connors DN, Pytkowicz RM. Preparation of artificial seawater. Limnol Oceanogr 1967;12(1):1769. [2] Sierakowski RL, Newaz GM. Damage tolerance in advanced composites. USA: Technomic Publishing Company; 1995. [3] Di Bella G, Calabrese L, Borsellino C. Mechanical characterisation of a glass/polyester sandwich structure for marine applications. Mater Des 2012;42:48694. [4] Mouritz AP, Gellert E, Burchill P, Challis K. Review of advanced composites structures or naval ships and submarines. Compos Struct 2003;53:2141. [5] Kolat K, Neser G, Ozes C. The effect of seawater exposure on the interfacial fracture of some sandwich systems in marine use. Compos Struct 2007;78:1117. [6] Ulven CA, Vaidya UK. Post-fire low-velocity impact response of marine grade sandwich composites. Compos Part A 2006;37:9971004. [7] Kootsookos A, Mouritz AP. Seawater durability of glass- and carbon-polymer composites. Compos Sci Technol 2004;64(1011):150311. [8] Yu Y, Yang X, Wang L, Liu H. Hygrothermal ageing on pultruded carbon fibre/vinyl ester resin composite for sucker rod application. J Reinf Plast Compos 2006;25 (2):14960. [9] Gellert EP, Turley DM. Seawater immersion ageing of glass-fibre reinforced polymer laminates for marine applications. Compos A Appl Sci Manuf 1999;30(11):125965. [10] Siriruk A, Jack Weitsman Y, Penumadu D. Polymeric foams and sandwich composites: material properties, environmental effects, and shear-lag modelling. Compos Sci Technol 2009;69(6):81420. [11] Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:8218. [12] Akbar S, Zhang T. Moisture diffusion in carbon/epoxy composite and the effect of cyclic hygrothermal fluctuations: characterization by dynamic mechanical analysis (DMA) and interlaminar shear strength (ILSS). J Adhes 2008;84:585600. [13] Weitsman YJ. Effects of fluids on mechanical properties and performance fluid effects in polymers and polymeric composites. Berlin: Springer; 2012. [14] Espert A, Vilaplana F, Karlsson S. Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties. Compos A 2002;35:126776. [15] Dhakal HN, Zhang ZY, Richardson MOW. Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites. Compos Sci Technol 2007;67:167483. [16] Searle TJ, Summerscales J. Review of the durability of marine laminates. In: Pritchard G, editor. Reinforced plastics durability. Cambridge: Woodhead Publishing; 1998. p. 21966 (Chapter 7), ISBN: 1-85573-320-X. [17] Assarar M, Scida D, El Mahi A, Poilane C, Ayad R. Influence of water ageing on mechanical properties and damage events of two reinforced composite materials: flaxfibres and glass-fibres. Mater Des 2011;32:78895. [18] Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine composites. In: Graham-Jones J, Summerscales J, editors. Marine applications of advanced fibre-reinforced composites. Woodhead Publishing; 2016. p. 10324. Edited by.
72
Biomass, Biopolymer-Based Materials, and Bioenergy
[19] Bao L, Yee AF. Moisture diffusion and hygrothermal ageing in bismaleimide matrix carbon fibre composites part I: uni-weave composites. Compos Sci Technol 2002;62:2099110. [20] Shen CH, Springer G. Moisture absorption and desorption of composite materials. J Compos Mater 1999;10:220. [21] Bar-Cohen Y, Crane RL. NDE of hygrothermal affected glass fiber-reinforced plastics. In: ASNT Spring Conference, March 1980. American Society for Nondestructive Testing, Philadelphia, PA, USA, 1980. [22] Cawley P, Adams RD. A vibration technique for non-destructive testing of fibre composite structures. J Compos Mater 1979;13(2):16175. [23] Emerson RN, Pollock DG, Mclean DI, Fridley KJ, Ross RJ, Pellerin RF. Nondestructive testing of large bridge timbers. In: 11th International Symposium on Nondestructive Testing of Wood, September 911, 1998. Forest Products Society, Madison, WI, 1999. [24] Borum KK. Evaluation of the quality of thick fibre composites using immersion and air-coupled ultrasonic techniques. In: 9th European Conference on Non-destructive Testing, ECNDT, 2529 September 2006, Berlin, Germany, 2006. [25] Jones TS, Lindgren EA. Thermographic inspection of marine composite structures. International conference on thermal sensing and imaging diagnostic applications. SPIE; 1994. p. 1735. [26] Baidya KP, Ramakrishna S, Rahman M, Ritchie A. Quantitative radiographic analysis of fiber reinforced polymer composites. J Biomater Appl 2001;15(3):27989. [27] Prakash R. Non-destructive testing of composites. Composites 1980;11(4):21724. [28] Summerscales J. Non-destructive measurement of the moisture content in fibre reinforced plastics. Br J Nondestr Test 1994;36:6472. [29] Green Jr. RE. Nondestructive evaluation of thick-composite fatigue damage. Nondestructive evaluation of aging maritime applications. Oakland, CA, USA: SPIE; 1995. 68 June 1995. [30] Gu H. Behaviours of glass fibre/unsaturated polyester composites under seawater environment. Mater Des 2009;30:133740. [31] Veazie DR, Robinson KR, Shivakumar K. Effects of the marine environment on the interfacial fracture toughness of PVC core sandwich composites. Compos Part B 2004;35(461):466. [32] Han W, Chen S, Campbell J, Zhang X, Tang Y. Fracture toughness and wear properties of nano silica/epoxy composites under marine environment. Mater Chem Phy 2016;177:14755. [33] Meng M, Le H, Grove S, Rizvi MJ. Moisture effects on the bending fatigue of laminated composites. Comp Struct 2016;154:4960. [34] Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:805. [35] Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:948. [36] Afshar A, Alkhader M, Korach CS, Chiang F-P. Effect of long-term exposure to marine environments on the flexural properties of carbon fibre vinyl ester composites. Compos Struct 2015;126:727. [37] Xu LR, Krishnan A, Ning H, Vaidya U. A seawater tank approach to evaluating the dynamic failure and durability of E-glass/vinyl ester marine composites. Comp Part B 2012;43:24806. [38] https://www.azom.com/article.aspx?ArticleID 5 8155.
Natural fiber-reinforced polymer composites: application in marine environments
73
Further reading Monchalin J-P. Optical detection of ultrasound. IEEE Trans Ultrason Ferroelectr Freq 1986;33(5):48599. Scruby CB, Drain LE. Laser ultrasonics: techniques and applications. New York: Taylor & Francis Group; 1990.
3
Deepak Verma1 and Kheng Lim Goh2 1 Department of Mechanical Engineering, Graphic Era Hill University, Dehradun, Uttarakhand, India, 2Newcastle Research & Innovation Institute (NewRIIS), Singapore
3.1
Introduction
Composite materials can be developed by incorporating various reinforcements, such as fibers and particulates, into the polymer matrix, whether they are synthetic or biodegradable types. With the correct selection, these composite materials can be found to be suitable for various applications, such as marine applications, which resist the various chemical attacks. As we already aware, seawater composition changes with respect to the location—this can be because of the watercourses which ultimately carry eroded materials and agricultural run-off into the sea. As per Kester et al. [1], the composition of 1 kg of seawater consists of around 19.4 g Cl2, 10.8 g Na1, 2.7 g SO422, 1.3 g Mg21, 0.4 g Ca21, 0.4 g K1, 0.1 g HCO32, 0.1 g Br2, and other chemicals (at lower levels). As per the given composition of seawater, it has been observed that the salt water environment is found to be corrosive to most engineering metals and, in addition, marine animals, for example, naval shipworm (Teredo navalis), and gribble (Limnoriidae), can result in rapid decay of wood. The utilization of composite materials and their structures in marine industries is growing, as in other industries. For example, sandwich composite panels having glass or carbon skins with a polymeric core have been found to be one of the most used advanced composites for the development of entire hulls and structures of marine craft. It has been noticed that the composite materials and their structures show various advantages/benefits as compared to the conventional metallic materials, for example [2]: G
G
G
G
G
Light in weight; Good corrosion resistance; Nonmagnetic structure; Lower acoustic and thermal signatures; and High blast resistance.
It has been observed that the seawater environment generally consists of combinations of various parameters. Some of the primary parameters are: Biomass, Biopolymer-Based Materials, and Bioenergy. DOI: https://doi.org/10.1016/B978-0-08-102426-3.00003-5 © 2019 Elsevier Ltd. All rights reserved.
52
G
G
G
G
Biomass, Biopolymer-Based Materials, and Bioenergy
Hydrostatic pressure; Seawater; Temperature; Water currents
In the case of marine sandwich structures [36], FRPs (i.e., carbon fiber, aramid fiber, and glass fiber reinforcement in a polymeric matrix) are primarily utilized as skin materials and polymer foams (i.e., specifically polystyrene or PVC foam) as core materials. It is also seen that the composite materials, that is, sandwich structures, show greater advantages as compared to steel structures. If the structure is light in weight then it validates a larger cargo capacity, savings in fuel, greater acceleration, improved stability of the ship, greater specific strength and stiffness, and buoyancy, etc. These composites also provide resistance to marine environments and have nonmagnetic properties. It has been observed that these composite structures showed higher corrosion resistance, need low maintenance, and permit more design flexibility. One disadvantage of composite sandwich structures is the high production cost as compared to conventional materials (i.e., steel or wood), as their manufacture is a labor-intensive process. The selection of the ideal manufacturing method for every part is strategic, as there are many choices specifically for raw materials, processing methods, and stacking sequence (for sandwich structures) that are available for design and manufacturing engineers for the development of each specific part/ component. The various parameters, such as production rate, cost, strength, size, and shape of the structure, can be taken into account for the selection of a specific part/component. In this chapter, we discuss the different types of natural fibers and their reinforcements in the polymer matrix, specifically for application in the marine industries. We also discuss the effect of the seawater environment on the polymermatrix composites, that is, specifically in terms of moisture absorption by marine biocomposites. The different methods for moisture measurement are also reported in this chapter. The different mechanical properties of the natural fiber-reinforced biocomposites are also been discussed, specially focusing on the marine applications. It has been observed that there is a good utilization of nondestructive testing (NDT) methods by marine industries. Therefore, based on this, we have also included a brief introduction to some of the NDT methods used by marine industries. Different types of morphological methods and their past studies are also included in the chapter. At the end of the chapter, we describe the advantages and disadvantages of the marine composites.
3.2
Effect of seawater on polymer matrix composites
The exposure of the composites to the liquid environment resulted in the absorption of the water molecules. The reason behind the absorption is the diffusion process which can be monitored by weight gain with respect to time. The diffusion process
Natural fiber-reinforced polymer composites: application in marine environments
53
is slow and is mostly affected by the equivalent coefficient of diffusion of the composite material. The diffusion coefficient depends upon the type of reinforcing fiber (e.g., glass vs carbon), type of resin (e.g., epoxy vs vinyl ester), and type of manufacturing process. The moisture absorption resulted in detrimental effects associated with lower adhesion between the fiber and the matrix, and ultimately a deterioration in the properties of the composites [711]. Also, the moisture, in combination with the temperature, resulted in changes to material properties, such as the glass transition temperature, Tg, of composites [8,12]. Diffusion can be defined as a process by which matter is transported/diffused from one part of a system to another by random molecular motions. Diffusion is considered to be a time-dependent process, where D is the diffusion coefficient. Assume a continuous mass distribution m (x,t), the steady-state flux (J) is controlled by Fick’s first law [13]. J 52D
@m @x
(3.1)
Under general conditions (unsteady state), applicable to polymer composites, diffusion can often be described by Fick’s second law: @m @2 m 5D 2 @t @x
(3.2)
The degradation of the properties is due to fluids, which may be recoverable, and difference between them can be observed by the weight gain data. Fig. 3.1 shows the five schematic curves of fluid sorption in polymers and polymeric composites relating weight gain to Ot . The solid curve showed the linear Fickian (LF) behavior. Curves “A” and “B” show the typical variations with reference to both neat polymers and fiber-reinforced composites having recoverable fluid-induced deterioration of some material properties. The curve of type A variation shows a case where weight gain is at nonequilibrium phase, and the type B curve shows the state of two-stage diffusion. On the other hand, curves “C” and “D” are generally obtained for polymeric composites only. Also, “C” shows the case of speedily increasing fluid content, generally associated with damage growth resulting in material break down and large failure rates. Curve “D” shows the weight loss that is referred to the chemical or physical break down of the material. The authors invented an experimental method to permit measurement of moisture uptake through adsorption kinetics with a highly precise gravimetric microbalance system as represented in Fig. 3.2. The setup contains a high-sensitivity microbalance (Cahn Digital Recording Balance, DRB-200), tailor-made sampling and gas-handling system, and a data acquisition system. A quartz chamber 750 mm long and 75 mm inner diameter is fixed to the balance on the sampling side. A nickelchromium wire mesh is used to attach the sample pan to minimize the mass transfer resistance between solidfluid phases. This sample pan is kept inside the quartz chamber, which does not absorb moisture. The quartz chamber consists of an
A
C
LF
M(t*) M(∞)
1.00 B
D
0.62
0.0 0.0
0.567
1.320 t*
Figure 3.1 Schematic curves representing a solid line, designated by LF, corresponds to linear Fickian diffusion and four possible categories of non-Fickian weight gain sorption data. Source: Reproduced with permission from Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:821828.
Figure 3.2 Setup of a gravimetric microbalance system coupled with a DAQ system. Source: Reproduced with permission from Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:821828.
Natural fiber-reinforced polymer composites: application in marine environments
55
inlet gas port at the bottom side and some exit ports along its length. The gas generation system has ultrahigh pure N2, which acts as a carrier gas. The carrier gas is firstly passed through a gas desiccator, having anhydrous CaSO4, which ultimately removes any traces of gas moisture. The gas flow rates are controlled by mass flow controllers. A part of the carrier gas is permitted to purify by double-distilled water in a fritted glass bubbler which forms a saturated vapor of carrier gas. Afterwards, the wet carrier gas is again mixed with the leftover dry carrier gas to form controlled water vapor concentrations. The water vapor concentration is observed by a relative humidity probe above the sample pan which ultimately gives the feedback control for the flow rates of wet and dry streams to keep to the target relative humidity at the sample position. The gravimetric balance is combined with a data acquisition system that congregates mass, time, and temperature data.
3.3
Effect of moisture on the properties of marine composites
Moisture intrusion in composites is governed by three different mechanisms. These are [14,15]: 1. Diffusion of water molecules into the microgaps between polymer chains; 2. Capillary movements into the cracks or gaps and defects available at the interface between fibers and the matrix phase; and 3. Transportation of water in the matrix comes from the swelling of fibers.
Moisture absorption with reference to the postconsolidated composites can be mainly distinguished by comparative absorptivity values, which can be found by Fick’s law (as reported in Eqs. 3.1 and 3.2). However, diffusion is the main mechanism for moisture intrusion and may occur due to the presence of voids in the matrix phase resulting in blistering and in the case of gel coats, it is mainly related to interfacial seepage between fibers and matrix [16]. According to the diffusion principle, water diffusion into polymer composites includes the displacement of fluid molecules from high concentration regions to lower concentration regions [17].
3.3.1 Fickian diffusion behavior Water absorption is usually a two-step process, as shown in Fig. 3.3. In the first step, rapid seepage takes place as water perforates mainly between the matrix phases, and advances at a constant rate. The second step includes a noticeable reduction as the material achieves saturation and is due to the component swelling and attainment of the final equilibrium [18].
56
Biomass, Biopolymer-Based Materials, and Bioenergy
Mt (%)
t Figure 3.3 Fickian diffusion curve. Source: Reproduced with permission from Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine Composites. Marine Applications of Advanced Fibre-Reinforced Composites. Woodhead Publishing. Eds Edited by J. GrahamJones and J. Summerscales, 2016, pp. 103124.
3.3.2 Non-Fickian or anomalous diffusion behavior In some conditions, the non-Fickian behavior is noticed for some definite materials and situations whereby plots did not match classic absorption properties. NonFickian effects are generally categorized in accordance with their nature in water absorption plots. The exemplary non-Fickian behavior may be categorized into three separate behavior types as described below.
3.3.2.1 Two-stage absorption This type of absorption is regularly found in non-Fickian behaviors. The two-stage curves consists of two distinct plateaus (Fig. 3.4). At the starting stage of absorption, Fickian behavior is noticed which consists of both the linear and plateau regions. This is succeeded by gradual non-Fickian absorption, which generally consists of a linear initial period and eventual plateau. This second stage is described by moisture-strengthened structural relaxation possibly creating voids and blisters, which ultimately retain water. The two-stage curve can be obtained from Eq. (3.3) as shown below [19] ( 0:75 ) pffi Dx t Mt 5 MN0 ð1 1 k tÞ 1 2 exp½ 2 7:3 h2
(3.3)
57
Mt(%)
Natural fiber-reinforced polymer composites: application in marine environments
t Figure 3.4 Two-stage absorption curve. Source: Reproduced with permission from Bao L, Yee AF. Moisture diffusion and hygrothermal ageing in bismaleimide matrix carbon fibre composites part I: uni-weave composites. Compos Sci Technol 2002;62:20992110.
where, h is the thickness of the sample and the other terms are as explained above. The term (1 1 kOt) in Eq. (3.3) shows the relaxation controlled second stage and the parameter k is the rate of relaxation.
3.3.2.2 Sigmoidal absorption The next conventional non-Fickian behavior is sigmoidal absorption. This is shown by the S-shaped curves in Fig. 3.5. This type of behavior is due to phase void formation during water intrusion and localized saturation. These attributes mostly depend on the environmental conditions and materials selection for the particular composite [18].
3.3.3 Moisture diffusion measurements Moisture diffusivity is considered to be an important characteristic that should be taken into account while designing composite materials for marine environments/ applications. This is essential for the evaluation of the dispersion rate of water in the composite throughout its initial advancement from a high-concentration to a low-concentration area. The moisture diffusivity behavior of polymeric composites can be obtained using Eq. (3.4).
Biomass, Biopolymer-Based Materials, and Bioenergy
Mt(%)
58
t Figure 3.5 Sigmoidal absorption curve. Source: Reproduced with permission from Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine Composites. Marine Applications of Advanced Fibre-Reinforced Composites. Woodhead Publishing. Eds Edited by J. GrahamJones and J. Summerscales, 2016, pp. 103124.
N X Mt 8 2 Dx ð2n11Þ2 π2 t 512 exp 2 h2 MN n50 ½ð2n11Þπ
(3.4)
where Mt is the mass of absorbed moisture at the time, (t); MN is the saturated mass of absorbed moisture; h is the thickness of the sheet in dry condition; and D is the diffusion coefficient or diffusivity. The mass uptake (Mt) can be represented by Eq. (3.5): Mt 5 k:tn
(3.5)
where t is the time, k is the initial slope of the Mt versus Ot curve and n is the constant, then Fickian absorption n 5 0.5. The percentage of water absorption in the polymer composites is determined by the weight difference between the immersed samples and the dry samples using Eq. (3.6) Mt 5
Wt 2 W0 3 100 W0
(3.6)
where Mt is moisture uptake, and W0 and Wt are the mass of the specimen before and during aging, respectively.
Natural fiber-reinforced polymer composites: application in marine environments
59
The coefficient of diffusion is a significant parameter in Fick’s law. The following relation is used for the evaluation of the diffusion coefficient: rffiffiffiffiffiffiffiffi Dx t Mt 5 4MN πh2
(3.7)
Rearranging the above equation and solving for the diffusion coefficient (Dx) gives the following equation: " #2 π Mt Dx 5 2 16MN Ot=h
(3.8)
where MN is the equilibrium moisture content (maximum water uptake) of the sample. The graph of weight gain versus time can be plotted with the help of the weight gain data of the material with respect to time. The water diffusion coefficient is the rate at which water transports from the surface to the core of the specimens. Again, the diffusion coefficient can be calculated by modifying Eq. (3.9) from the slope of moisture content versus square root time as follows: Dx 5 π
h 4MN
2
M2 2M1 2 pffiffiffiffi pffiffiffiffi t2 2 t1
(3.9)
The diffusion properties of composites explained by Fick’s laws are assessed by the weight gain measurements of immersed samples in water by taking into account the slope of the first portion of the weight gain graph versus square root time. For values MMNt lower than approximately 0.6, the initial portion of the curve can be detailed as: Mt 4 5 h MN
rffiffiffiffiffi Dt π
(3.10)
This method gives good approximations of absorption evaluation where the gradient of the curve is found to be greater than 0.6 [19].
3.4
NDT of marine composites: a brief overview
This section describes the utilization of NDT (nondestructive techniques) for the inspection or testing of marine composites. It has been observed that only ultrasonics and radiography techniques have shown significant applications for the inspection of marine composites. Eddy-current testing and eddy electromagnetic techniques are utilized for the inspection of high-density and highly conductive materials. The fluorescent penetrant/dye is used for the detection of considerable
60
Biomass, Biopolymer-Based Materials, and Bioenergy
weathering at the surface of glass fibre reinforced polymer (GFRP) composites. In this process, the dye is rapidly absorbed in a porous matrix and shows a large reflection to the UV light source as compared to a fresh fabricated panel [20].
3.4.1 Vibration analysis Vibration analysis also played a significant role in the analysis of the acoustic response of a structure over a wide frequency/spectrum. Vibrational techniques also helpful for the dynamic analysis of the structures at specified intervals and, in particular, the response of these structures will change with respect to time because of the changes in structural stiffness [21]. The vibration analysis is generally performed at very low elastic-wave frequencies (,20 kHz).
3.4.2 Mechanical impedance analysis Mechanical impedance analysis is another evaluation test. In this method, a metallic probe tip at a particular frequency of around 210 kHz, loads the structure and then measures the variations in terms of the amplitude and phase of the probe. This test attains moderately sound penetration as compared to the resonance technique. The pitch-catch technique utilizes two dry-coupled transducers which contact at a fixed distance and transmit and receive frequencies in the range of 10100 kHz along the surface.
3.4.3 Conventional ultrasonics Ultrasonic testing (UT) uses the piezoelectric effect, in which a permanently polarized crystal can be utilized to generate elastic waves at particular frequencies, and then convert these waves into electrical energy. The original transducers used quartz crystals, which were then replaced by piezo-ceramics, for example, barium titanate and lead zirconate titanate (“PZT”). Generally, pulses of ultrasound are repeatedly introduced into the structure at a very high rate, and in timber structures, the range of the ultrasound is 20 kHz, and 50 MHz in high-stiffness metallic alloys [22]. However, in the case of marine composites, the inspections are generally carried out at a frequency range of 0.52.25 MHz. When ultrasound waves strike a composite structure it scatters them and shows a mismatch of acoustic impedance between glass fibers and the polymer matrix. Therefore, glass is found to be highly reflective to ultrasound.
3.4.4 Advanced ultrasonics A major criticism of UT has been the severe bottlenecks it can create, both in manufacturing facilities and in costly maintenance downtime for in-service components. A range of modifications has been developed to overcome this problem, mainly by introducing ultrasound into the structure using alternative means, as outlined below.
Natural fiber-reinforced polymer composites: application in marine environments
61
3.4.4.1 Air-coupled UT It is very difficult to establish a coupling between the transducer and test component for ultrasonic testing. This can be done by water coupling, by immersing the transducers along with the test part in a water tank, or by a water-squirter arrangement. Localized or point inspections or testing are attained by using a water-based gel. The constant coupling can be maintained by these methods with substantial time to complete the UT inspection. Air-coupled UT is achieved without any acoustic couplants, maximizing the inspection efficiency. Solving the problem of the high-impedance mismatch that appears at the transducer/air and subsequent air/ component interfaces is not superficial, and needs further modifications. In marine composites of considerable thickness (approximately 50 mm), the aircoupled testing is mainly suitable for the detection of disbonds and voids present in low-density foam-sandwich structures [23].
3.4.4.2 Laser-based ultrasound High-frequency pulsed lasers are utilized for the production of elastic waves of ultrasonic wavelength, for the use of high-frequency pulsed lasers usually solidstate neodymium-doped yttrium aluminum garnet (“Nd:YAG”), which taps the surface at megahertz frequencies. Noncontact inspection is found to be more advantageous and is rarely applied as the ultrasonic waves produce thermoelastic waves via laser ablation, as localization of the laser causes melting of the surface. High power may cause overheating of the polymer matrix, resulting in macroscopic destruction of the surface. The ultrasound detection function can be implemented by lasers; the arrangement is shown in Fig. 3.6 and is known as a heterodyne Michelson interferometer. On the other hand, robotic laser UT became a traditional NDT method for the analysis of aerospace composites [24].
3.4.4.3 Infrared thermography Infrared thermography is another advanced NDT method that uses electromagnetic radiation over the infrared spectrum at wavelengths of around 700 nm to 1 mm. As the name implies, this bandwidth is felt by the human body as “warmth,” and the method has found very good application in industries for the detection of overheating in electrical circuits and in pipes of petrochemical processing plants. Such evaluations can be performed indifferently, as the IR radiation is generated by the source in its standard operating state. However, inadequate heat is dissipated by the internal structure of a composite which permits measurements to be performed on composite structures, and an active heating source is needed to carry out an accurate investigation of these structures. The major limitation of thermography is its limited utilization related to thick structures. The physical limitation of heat transfer in most of the structures resulted in a quick decrease in sensitivity of components [25].
62
Biomass, Biopolymer-Based Materials, and Bioenergy
Optical detector Interference filter Variable attenuator
Laser
Oscillator Acousto-optic cell M1
M4
Beam splitter M3
Ultrasound emission
M5 L1
L2
M2
Figure 3.6 Laser-based ultrasonic detection using a heterodyne Michelson interferometer detection method. Source: Reproduced with permission from Borum KK. Evaluation of the quality of thick fibre composites using immersion and air-coupled ultrasonic techniques. In: 9th European Conference on Non-destructive Testing, ECNDT, 2529 September 2006, Berlin, Germany, 2006.
3.4.4.4 Radiography and tomography X-ray radiography is one of the most feasible NDT methods. X-rays are also used in the medical field for inspection of diseases. Apart from this, radiography has shown correspondingly less applications for the testing of composite materials. With this technique, thin structures can be inspected [26], where large air voids are easily detectable. It has been observed that, in the lateral plane, it is hard to detect the delamination as porosity and fiber volume fraction investigation are considered to be a complex proposition [27]. The main disadvantage of X-ray radiation is that it is very harmful to humans.
3.4.4.5 Electrical and magnetic techniques A variety of NDT techniques that utilize electrical conductivity are available for composite inspection. These techniques require an electrically conductive (i.e., carbon fiber) composite. The following are some of the methods for the inspection of these composites.
3.4.4.6 Eddy-current testing Eddy-current testing is the less successful technique for the inspection of composites, and requires electromagnetic induction of electrical current on the component surface. This is generally used to detect the aerospace surface crack inspection. Prakash and Owston used this technique for the characterization of ply-orientation in carbon fiber-reinforced plastics. This can be possible by correlating the plyorientation and the electrical conductivity, although as composite laminates have different layers of polymer and fibers, this process may give inaccurate measurements.
Natural fiber-reinforced polymer composites: application in marine environments
63
3.4.4.7 Capacitive imaging In this process, two charged electrodes are used, which emit and receive an electric field on a material volume which they interact with. This method may be utilized in a broad range of material applications as compared to the eddy-currents, and provides fairly good indications of cracks and impacts, damage by heat, and dampness. However, the nonintuitive feature of the volume-averaged field measurement excludes its utilization for quantitative analysis. Yacht surveyors generally used such devices as a moisture meter for the inspection of GFRP hulls [28].
3.4.4.8 Nuclear magnetic resonance Nuclear magnetic resonance (NMR) has been successfully applied in the medical industry as magnetic resonance imaging, functioning as a 3D computed system. The sensitivity of NMR to the availability of water gives an idea of drying rates in various composites, with physically absorbed or chemically bound moisture. It has been observed that this technique is useful for moisture-related investigation in low-conductivity composites, for example, glass-fiber [29].
3.5
Mechanical properties of polymer marine biocomposites: a past study
It is well known that exposure to seawater for a long duration ultimately affects the mechanical properties of composites. The degradation of composites can be dynamically related to the water absorption feature of composites. From Fig. 3.7 we can see the connection between the glass/polyester composite water absorption (moisture) and disparity of tensile strength, flexural strength, and flexural modulus. It has
Figure 3.7 Water intake versus mechanical properties glass/polyester composite at 17 C and 30 C. Source: Reproduced with permission from Gu H. Behaviours of glass fibre/unsaturated polyester composites under seawater environment. Mater Des 2009;30:13371340.
64
Biomass, Biopolymer-Based Materials, and Bioenergy
already been reported that the moisture saturation of glass/polyester composite B is found to be 0.58% [30]. After the attainment of the moisture saturation level (approximately 30 days), deterioration of the tensile slope decreases and then becomes steady. However, the flexural variation slope increases just at the moisture saturation level of the polyester composite (1.25% for 65 days). Veazie et al. [31] performed double-cantilever beam (DCB) tests and describe a considerable (approximately more than 50%) decrease in interfacial fracture toughness due to the formation of cracks induced following the “wet” exposure. Although, the specimens that already contained cracks before the “wet” exposure, the interfacial fracture toughness was again reduced (approximately another 50%). It is generally observed that specimens exposed to the “wet” environment show degradation because of seawater absorption, mainly through the facesheet/core interface. The fracture toughness of the nanocomposites was characterized by investigating the effect of nanosilica with different periods of saltwater immersion. CT tests at room temperature for each material were performed and are shown in Fig. 3.8, which represents the ideal load-crack opening displacement (COD) curves. It is noted that both neat epoxy and composite specimens subjected to fracture in a brittle manner at the maximum load conditions, and obviously the maximum loads for the nanocomposite are greater than those of the corresponding neat counterpart [32]. The fatigue life of the cross-ply laminate (with four testing environments) is shown in Fig. 3.9, with the four-point bending test performed on both dry and wet specimens, at 90% UFS, and it was observed that all specimens failed at no more than 106 cycles. However, the immersed specimen represents a lower cycle count as compared to those without immersion. At about 80% UFS, all of the dry specimens showed infinite fatigue life (i.e., more than 3 3 106 cycles) in the same testing conditions. In contrast, all the immersed specimens failed [33].
Figure 3.8 Typical load-crack opening displacement (COD) curves for neat epoxy (EP) and nanosilica-enhanced epoxy composite (SEP) with different periods of immersion of 0, 7, and 30 days. Source: Reproduced with permission from Han W, Chen S, Campbell J, Zhang X, Tang, Y. Fracture toughness and wear properties of nano silica/epoxy composites under marine environment. Mater Chem Phy 2016;177:147155.
Natural fiber-reinforced polymer composites: application in marine environments
65
Infinite life 100% 95% 90% UFS
85%
Dry-3P
80%
Dry-4P
75%
Wet1-4P
70% 65% 60% 1.0E+05
Wet2-4P
1.0E+06 Cycle
1.0E+07
Figure 3.9 Fatigue life of CP laminate. The fatigue cycle is plotted as a logarithm scale. Wet1-4P: immersed specimen, covered with a wet sponge while undergoing four-point bending fatigue testing; Wet2-4P: immersed specimen, without wet sponge cover while undergoing testing. Source: Reproduced with permission from Meng M, Le H, Grove S, Rizvi MJ. Moisture effects on the bending fatigue of laminated composites. Comp Struct 2016;154:4960.
Three-point bending tests were performed to determine the flexural strength and modulus of the composites at various environmental exposures. It has been noticed from Fig. 3.10 that all exposure conditions represent an unsubstantial effect on longitudinal flexural modulus of specimens in contrast to the flexural modulus of dry specimens within the experimental error. A great decline in longitudinal flexural modulus was observed for the specimens, which were exposed to 2000 hours, in addition to the UV radiation and salt spray in environmental chambers (7%). The result shows that the longitudinal flexural strength noticeably diminishes for distinct types of exposure (Fig. 3.11). The noticeable decrease in longitudinal flexural strength (because of the moisture absorption) is due to the failure of the fibermatrix interface, resulting in swelling and loss of coalition in carbon fiber vinyl ester composites [34]. Dayakar Penumadu et al. [35] focused on the effect of confinement and studied one-sided seawater confinement of composites specifically for the determination of the cyclic fatigue behavior of carbon fiber-reinforced vinyl ester composites, used as facings materials for naval sandwich structures. It has been observed from the experimental results in the case of matrix dominated [ 6 45]2x laminates of carbon fiber-reinforced vinyl ester composites, that the failure occurs after a fewer number of cycles and when fatigued under immersed conditions in the water (not in air), a drop of approximately 80% occurs in the number of cycles to failure. Again, when fatigued with the conditions of one-sided confinement to water, the composite failed in less than 50% of loading cycles as compared to the samples without water
66
Biomass, Biopolymer-Based Materials, and Bioenergy
(A)
Indoor immersion 6 month 1 year
Longitudinal flexural modulus (GPa)
120
–5%
–4.8%
100 80
–6.3% –3.3%
–4.6%
–5.5%
60 40 20 0 Virgin
Distilled
Salt water
Sea water
Longitudinal flexural modulus (GPa)
(B) Outdoor exposure 1 year 6 month
120
–0.06%
–1.4%
100
–3.8%
–5.8%
80 –2.1%
60
1.4%
–4.1%
–3.8%
40 20 0
Virgin
Row 1
Row 2
Row 3
Row 4
Longitudinal flexural modulus (GPa)
(C) Environmental chamber 800 hours 2000 hours
120
–4.8%
–2.6%
–3.1%
100
–4.7%
80 –4.2%
–2.1%
0.06%
–7%
60 40 20 0
Virgin
Heat and UV-Heat Humidity and Humidity
Salt Spray
UV-Salt Spray
Figure 3.10 The longitudinal flexural modulus of CFVE composites exposed to (A) indoor immersion, (B) outdoor environmental exposure, and (C) conditioning in environmental chambers. Source: Reproduced with permission from Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:8085.
Natural fiber-reinforced polymer composites: application in marine environments
Longitudinal flexural strength GPa
(A)
Indoor immersion
2.5
6 month 2.0
1 year –15.3%
–16%
–17.1%
1.5 –15%
–14.4%
–13.1%
1.0 0.5 0.0 Virgin
(B) Longitudinal flexural strength GPa
Outdoor exposure 2.5
1 year
6 month –4.1%
2.0
–9.1%
–13.8% –17.7%
1.5 1.0
–12.4%
–13.8% –16.8%
–31%
0.5 0.0
Virgin
(C) Longitudinal flexural strength (GPa)
Distilled Salt water Sea water
Row 1
Row 2
Row 3
Row 4
Environmental chamber
2.5
800 hours –6.7%
2
2000 hours
–4.6%
–7.8%
–7.7%
1.5 –11.7%
1
–11.9%
–13%
–17.1%
0.5 0
Virgin
Heat and UV-Heat Humidity and Humidity
Salt Spray
UV-Salt Spray
Figure 3.11 The longitudinal flexural strength of CFVE composites exposed to (A) indoor immersion, (B) outdoor environmental exposure, and (C) conditioning in environmental chambers. Source: Reproduced with permission from Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:8085.
67
68
Biomass, Biopolymer-Based Materials, and Bioenergy
Stress (MPa)
Figure 3.12 Average number of cycles to failure of dry and wet [ 6 45]2s sample in air and under one-sided exposure conditions under cyclic loading at 1 Hz frequency. Source: Reproduced with permission from Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:9498.
Last cycle of wet immersed sample
90 80 70 60 50 40 30 20 10 0
First cycle of dry, wet immersed and one-sided wet immersed samples
Last cycle of one-side wet sample
Last cycle of dry sample
0
0.01
0.02
0.03
0.04
0.05
0.06
True strains (mm/mm) Figure 3.13 Comparison of the last cycle true strains on [ 6 45]2s dry sample in air and wet immersed and one-sided immersed. Source: Reproduced with permission from Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:9498.
confinement (in air). These results are represented in Figs. 3.12 and 3.13, respectively. Alkhader et al. [36] showed the stiffness and stress distributions for both UV and moisture aging conditions as illustrated in Fig. 3.14. This figure shows that the
Dimensionless thickness (2z/h)
Natural fiber-reinforced polymer composites: application in marine environments
0 1 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 –100
Flexural modulus (GPa) 2 4 6
Flexural stress Flexural modulus –50 0 50 Flexural stress (MPa)
69
8
1 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1 100
Figure 3.14 Distribution of transverse modulus and stress, showing variation across the laminate thickness for the laminate exposed to UV and moisture. Plots created using the force level at the onset of failure. Source: Reproduced with permission from Afshar A, Alkhader M, Korach CS, Chiang F-P. Effect of long-term exposure to marine environments on the flexural properties of carbon fibre vinyl ester composites. Compos Struct 2015;126:7277.
stiffness deviated distinctly inside the damaged zone, and at the commencement of failure, it is noticed that the stress in the damaged zone is much lesser as compared to the value expected by utilizing the adequate lamina properties assumption (i.e., 61.81 MPa). On the other hand, it is found that the maximum stress inside the aged specimen (i.e., 64.66 MPa) is approximately the same as the 61.81 MPa value, nevertheless, it remains in the interior of the specimen only and not on the surface. Xu et al. [37] studied the durability and dynamic failure properties that are considered to be the evaluative parameters for naval composite ships in a seawater environment. Other authors have carried out a low-speed impact experiment of the composite laminates. The impact damage resulted in a noticeable surface damage in lieu of a quick failure pattern. Impact damage was performed by using an Instron test machine [6]. All the developed samples were subjected to the same impact energy (60 joules) having a 16-mm (5/800) diameter hemisphere impactor. This hemisphere impactor was lifted to a specific height (for the achievement of the desired impact energy) and then dropped freely. The impact force was then recorded by the test machine. Fig. 3.15A and B shows the damage zones of the impacted samples.
70
Biomass, Biopolymer-Based Materials, and Bioenergy
Figure 3.15 Typical impact damage on the front and back surfaces (A and B). Source: Reproduced with permission from Bar-Cohen Y, Crane RL. NDE of hygrothermal affected glass fiber-reinforced plastics. In: ASNT Spring Conference, March 1980. American Society for Nondestructive Testing, Philadelphia, PA, USA, 1980.
3.6
Advantages and disadvantages of marine composites
The following are the advantages of marine composites: G
G
G
G
G
The great strength of the weight attribute; Resistance to corrosion applicable for different applications; Complex-shaped structures can be developed easily as compared to the conventional methods; Low maintenance cost; Improved stiffness.
The following are some noticeable disadvantages of marine composites: G
G
G
G
Low impact resistance; Low heat tolerance; Low UV resistance, which is of utmost important in the marine environment; Very initial cost as compared to some conventional materials [38].
3.7
Conclusion
Recently, substantial progress has been made to understand the different attributes of composite materials and their structures in the marine environment. It is also observed that presently processing and production areas have given more attention to ensuring the potential for the development of intricate, large assemblies to withstand heavy loads. However, the prime challenges for employing composites as a marine application include the optimum capital expenditure and operation costs of boats and ships developed using composites. Nowadays, novel composites, for example, epoxy-based composites with carbon nanotubes, are found to be more favored, with increasing concern for high-performance marine structures. Certainly, light structure, fast production, durability, and strength facilitate composites in playing an important role in marine applications/environments.
Natural fiber-reinforced polymer composites: application in marine environments
71
References [1] Kester DR, Duedall IW, Connors DN, Pytkowicz RM. Preparation of artificial seawater. Limnol Oceanogr 1967;12(1):1769. [2] Sierakowski RL, Newaz GM. Damage tolerance in advanced composites. USA: Technomic Publishing Company; 1995. [3] Di Bella G, Calabrese L, Borsellino C. Mechanical characterisation of a glass/polyester sandwich structure for marine applications. Mater Des 2012;42:48694. [4] Mouritz AP, Gellert E, Burchill P, Challis K. Review of advanced composites structures or naval ships and submarines. Compos Struct 2003;53:2141. [5] Kolat K, Neser G, Ozes C. The effect of seawater exposure on the interfacial fracture of some sandwich systems in marine use. Compos Struct 2007;78:1117. [6] Ulven CA, Vaidya UK. Post-fire low-velocity impact response of marine grade sandwich composites. Compos Part A 2006;37:9971004. [7] Kootsookos A, Mouritz AP. Seawater durability of glass- and carbon-polymer composites. Compos Sci Technol 2004;64(1011):150311. [8] Yu Y, Yang X, Wang L, Liu H. Hygrothermal ageing on pultruded carbon fibre/vinyl ester resin composite for sucker rod application. J Reinf Plast Compos 2006;25 (2):14960. [9] Gellert EP, Turley DM. Seawater immersion ageing of glass-fibre reinforced polymer laminates for marine applications. Compos A Appl Sci Manuf 1999;30(11):125965. [10] Siriruk A, Jack Weitsman Y, Penumadu D. Polymeric foams and sandwich composites: material properties, environmental effects, and shear-lag modelling. Compos Sci Technol 2009;69(6):81420. [11] Siriruk A, Penumadu D, Weitsman Y. Effect of sea environment on interfacial delamination behaviour of polymeric sandwich structures. Compos Sci Technol 2009;69:8218. [12] Akbar S, Zhang T. Moisture diffusion in carbon/epoxy composite and the effect of cyclic hygrothermal fluctuations: characterization by dynamic mechanical analysis (DMA) and interlaminar shear strength (ILSS). J Adhes 2008;84:585600. [13] Weitsman YJ. Effects of fluids on mechanical properties and performance fluid effects in polymers and polymeric composites. Berlin: Springer; 2012. [14] Espert A, Vilaplana F, Karlsson S. Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties. Compos A 2002;35:126776. [15] Dhakal HN, Zhang ZY, Richardson MOW. Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites. Compos Sci Technol 2007;67:167483. [16] Searle TJ, Summerscales J. Review of the durability of marine laminates. In: Pritchard G, editor. Reinforced plastics durability. Cambridge: Woodhead Publishing; 1998. p. 21966 (Chapter 7), ISBN: 1-85573-320-X. [17] Assarar M, Scida D, El Mahi A, Poilane C, Ayad R. Influence of water ageing on mechanical properties and damage events of two reinforced composite materials: flaxfibres and glass-fibres. Mater Des 2011;32:78895. [18] Dhakal HN, Mac Mullen J, Zhang ZY. Moisture measurement and effects on properties of marine composites. In: Graham-Jones J, Summerscales J, editors. Marine applications of advanced fibre-reinforced composites. Woodhead Publishing; 2016. p. 10324. Edited by.
72
Biomass, Biopolymer-Based Materials, and Bioenergy
[19] Bao L, Yee AF. Moisture diffusion and hygrothermal ageing in bismaleimide matrix carbon fibre composites part I: uni-weave composites. Compos Sci Technol 2002;62:2099110. [20] Shen CH, Springer G. Moisture absorption and desorption of composite materials. J Compos Mater 1999;10:220. [21] Bar-Cohen Y, Crane RL. NDE of hygrothermal affected glass fiber-reinforced plastics. In: ASNT Spring Conference, March 1980. American Society for Nondestructive Testing, Philadelphia, PA, USA, 1980. [22] Cawley P, Adams RD. A vibration technique for non-destructive testing of fibre composite structures. J Compos Mater 1979;13(2):16175. [23] Emerson RN, Pollock DG, Mclean DI, Fridley KJ, Ross RJ, Pellerin RF. Nondestructive testing of large bridge timbers. In: 11th International Symposium on Nondestructive Testing of Wood, September 911, 1998. Forest Products Society, Madison, WI, 1999. [24] Borum KK. Evaluation of the quality of thick fibre composites using immersion and air-coupled ultrasonic techniques. In: 9th European Conference on Non-destructive Testing, ECNDT, 2529 September 2006, Berlin, Germany, 2006. [25] Jones TS, Lindgren EA. Thermographic inspection of marine composite structures. International conference on thermal sensing and imaging diagnostic applications. SPIE; 1994. p. 1735. [26] Baidya KP, Ramakrishna S, Rahman M, Ritchie A. Quantitative radiographic analysis of fiber reinforced polymer composites. J Biomater Appl 2001;15(3):27989. [27] Prakash R. Non-destructive testing of composites. Composites 1980;11(4):21724. [28] Summerscales J. Non-destructive measurement of the moisture content in fibre reinforced plastics. Br J Nondestr Test 1994;36:6472. [29] Green Jr. RE. Nondestructive evaluation of thick-composite fatigue damage. Nondestructive evaluation of aging maritime applications. Oakland, CA, USA: SPIE; 1995. 68 June 1995. [30] Gu H. Behaviours of glass fibre/unsaturated polyester composites under seawater environment. Mater Des 2009;30:133740. [31] Veazie DR, Robinson KR, Shivakumar K. Effects of the marine environment on the interfacial fracture toughness of PVC core sandwich composites. Compos Part B 2004;35(461):466. [32] Han W, Chen S, Campbell J, Zhang X, Tang Y. Fracture toughness and wear properties of nano silica/epoxy composites under marine environment. Mater Chem Phy 2016;177:14755. [33] Meng M, Le H, Grove S, Rizvi MJ. Moisture effects on the bending fatigue of laminated composites. Comp Struct 2016;154:4960. [34] Afshar A, Liao H-T, Chiang F-P, Korach CS. Time-dependent changes in mechanical properties of carbon fibre vinyl ester composites exposed to marine environments. Compos Struct 2016;144:805. [35] Siriruk A, Penumadu D. Degradation in fatigue behaviour of carbon fibrevinyl ester based composites due to sea environment. Compos Part B 2014;61:948. [36] Afshar A, Alkhader M, Korach CS, Chiang F-P. Effect of long-term exposure to marine environments on the flexural properties of carbon fibre vinyl ester composites. Compos Struct 2015;126:727. [37] Xu LR, Krishnan A, Ning H, Vaidya U. A seawater tank approach to evaluating the dynamic failure and durability of E-glass/vinyl ester marine composites. Comp Part B 2012;43:24806. [38] https://www.azom.com/article.aspx?ArticleID 5 8155.
Natural fiber-reinforced polymer composites: application in marine environments
73
Further reading Monchalin J-P. Optical detection of ultrasound. IEEE Trans Ultrason Ferroelectr Freq 1986;33(5):48599. Scruby CB, Drain LE. Laser ultrasonics: techniques and applications. New York: Taylor & Francis Group; 1990.