- Email: [email protected]
Mechanical characterisation of hybrid composite laminates based on basalt fibres in combination with flax, hemp and glass fibres manufactured by vacuum infusion
Accepted Manuscript Technical report Mechanical Characterisation of Hybrid Composite Laminates Based On Basalt Fibres in Combination with Flax, Hemp and Glass Fibres Manufactured By Vacuum Infusion R. Petrucci, C. Santulli, D. Puglia, F. Sarasini, L. Torre, J.M. Kenny PII: DOI: Reference:
S0261-3069(13)00110-6 http://dx.doi.org/10.1016/j.matdes.2013.02.014 JMAD 5148
To appear in:
Materials and Design
Received Date: Accepted Date:
4 December 2012 6 February 2013
Please cite this article as: Petrucci, R., Santulli, C., Puglia, D., Sarasini, F., Torre, L., Kenny, J.M., Mechanical Characterisation of Hybrid Composite Laminates Based On Basalt Fibres in Combination with Flax, Hemp and Glass Fibres Manufactured By Vacuum Infusion, Materials and Design (2013), doi: http://dx.doi.org/10.1016/ j.matdes.2013.02.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
MECHANICAL CHARACTERISATION OF HYBRID COMPOSITE LAMINATES BASED ON BASALT FIBRES IN COMBINATION WITH FLAX, HEMP AND GLASS FIBRES MANUFACTURED BY VACUUM INFUSION R. Petrucci1, C. Santulli2*, D. Puglia1, F. Sarasini2, L. Torre1, J.M. Kenny1 1
Università di Perugia, Civil and Environmental Engineering Dept., Materials Science and Technology, Strada di Pentima 4, 05100 Terni 2 Sapienza Università di Roma, Dept. of Chemical, Materials and Environmental Engineering, via Eudossiana 18, 00184 Roma, Italy ABSTRACT This work concerns the production by vacuum infusion and the comparison of the properties of different hybrid composite laminates, based on basalt fibre composites as the inner core, and using also glass, flax and hemp fibre laminates to produce symmetrical configurations, all of them with a 21-23% fibre volume, in an epoxy resin. The laminates have been subjected to tensile, three-point flexural and interlaminar shear strength tests and their fracture surfaces have been characterised by scanning electron microscopy. The mechanical performance of all the hybrid laminates appears superior to pure hemp and flax fibre reinforced laminates and inferior to basalt fibre laminates. Among the hybrids, the best properties are offered by those obtained by adding glass and flax to basalt fibre reinforced laminates. Scanning electron microscopy (SEM) observation of hybrid laminates showed the diffuse presence of fibre pull-out in hemp and flax fibre reinforced layers and a general trend of brittle failure. Keywords: basalt; flax; glass; hemp; hybrid composites; vacuum infusion; mechanical properties; fracture morphology 1. Introduction Hybridization is a commonly used procedure to obtain properties, which are intermediate between the two originating materials. Dealing with polymer composites, hybridization may result in a compromise between mechanical properties and cost to meet specified design requirements, as one of the reinforcements is usually cheaper than the other one. A number of studies have been performed recently, which suggest that mechanical properties can be possibly tailored using hybridization based on glass or basalt fibre laminates and including other natural (aiming at a more sustainable material) [1-3] or synthetic fibres [4-5]. In particular, with respect to plant fibres, which equally show thermal and acoustic insulation properties, the higher specific weight of basalt fibres (around 2700 kg/m³) is widely compensated by their higher modulus, excellent heat resistance, good resistance to chemical attack and low water absorption [6]. This suggests that hybrid laminates, based on basalt fibres and plant fibres, and/or glass-plant fibre hybrid laminates, the latter being particularly studied when it comes to the need for sufficient impact resistance [7], may have some interest. This would possibly result in a more sustainable end-of-life scenario without substantially affecting the structural performance of the laminates. As a matter of fact, hybridization of basalt fibres has been attempted with ceramic fibres, to provide improved hot wear resistance to friction materials [8], with high tensile strength fibres, such as carbon [9-10] and aramid [11-12], and with glass fibres [6, 13]. In these cases, basalt provided an impact and environmental resistance superior to that provided by the corresponding hybrids with *
Corresponding author, telephone: 0039-06-44585408, e-mail: [email protected]
1
glass fibres, coupled with a substantial reduction in costs, with respect to carbon and aramid fibre composites. In the case of basalt/Nylon fibres hybrid laminates, low tensile modulus of Nylon is improved by adding basalt fibres, whilst Nylon provides conversely a higher impact resistance [4]. Also basalt hybridization with glass fibres has been attempted, which is based on the use of two fibres, which are chemically not very different: continuous basalt fibre has a not very different content in silica and alumina from glass fibres and also a comparable, if not superior, tensile strength [14]. A significant difference is their behaviour under corrosion: for basalt fibres, resistance to acids is much higher than that to alkalis, whilst for glass fibres resistance to acids is nearly the same as that to alkalis [15]. As regards stacking sequences in glass/basalt hybrids, a previous study suggested that a symmetrical configuration including the lower strength material (glass) as a core for the higher strength one (basalt) presents the most favourable degradation pattern [5]. Another study suggested that the presence of external layers of basalt fibres involved the greatest increase in flexural and tensile properties of glass fibre reinforced laminates with respect to other glass/basalt stacking sequences [13]. This is likely to depend on the fact that a hybrid configuration including basalt fibres as internal layers increases the brittleness of the composite. It is therefore worth investigating whether this is the case only on basalt/glass hybrids or it is a more general trend. Based on the above considerations, hybrids made using basalt fibres composites as the core laminates are produced, including for the first time three types of fibres in the same laminate, using a vacuum infusion technique. Three hybrid configurations were produced including, together with basalt fibres, glass/flax, glass/hemp and hemp/flax, and compared with the relevant composite laminates, including each of the above fibres. Their mechanical properties and their damage patterns were compared, in order to establish the most suitable solution for possible wider scale production. 2. Materials and methods 2.1 Composite manufacturing The resin system used was an EC360 (resin)/W160 (hardener) epoxy, provided by Elantas Camattini s.p.a. The reinforcements based on flax (surface density 300 g/m²), hemp (300 g/m²), and the basalt grid (240 g/m²), were all provided by Fidia Srl, while the glass mat (100 g/m²) has been provided by G. Angeloni Srl. All the composite panels have been produced by means of a vacuum infusion process, whose layout is given in Figure 1. For this purpose, for each configuration, a stack of dry reinforcement plies has been laminated over a glass mould. After the lamination stage, the layout has been completed with the flow media and the infusion network, and finally the mould has been sealed with the vacuum bag. The curing stage of the resin, after the infusion is concluded, has been carried out at room temperature, while the post curing took place in an oven in two sub-stages: at 60°C for three hours and subsequently at 80°C for four hours. The in-mould pressure measured during the infusion stages was equal to 20 mbar. Vacmobiles model 20/2 vacuum pump, provided by Vacmobiles Europe by Filter Technics has been used. Rectangular 260 mm x 450 mm sheets have been obtained. Subsequent cutting operations have been carried out with the aim to produce specimens suitable for mechanical characterization, in accordance to the related standards. Three laminates were based on hemp, flax and basalt fibres respectively, which were used for comparison with the three hybrids whose structure is schematized in Figure 2. It is worthwhile to point out that the surface density of the employed textiles has been precisely measured. In particular, the surface density of the flax textile was equal to 292 g/m2, while that of the hemp textile was 234 g/m2, and that of the basalt textile was 300 g/m2. All these reinforcements 2
have a balanced configuration on warp and weft fabrics. Finally the glass mat surface density was equal to 100 g/m2. The fibre volume fraction of each reinforcement type was calculated by the value of the whole laminate thickness in the case of the homogeneous systems. In the case of the hybrid ones, the thickness of each layer has been measured with the aid of an optical microscope and, consequently, the related fibre volume fraction been calculated. In both cases, for the thickness calculation, equation (1) has been used:
f
n d
(1)
where n is the number of layers of the same typology, is the corresponding surface density, d is the thickness of the layers of the same reinforcement typology and is the density of the fibres. Going more into detail, the following stacking sequences have been employed: Hemp, flax and basalt laminates have all been produced by stacking together 4 layers of biaxial textiles, according to a [0/90]2S lay-out. Fibre volume fraction was 20.16 (± 1.37)% for hemp; 24.82 (±0.83)% for flax; 28.23 (±0.85)% for basalt. The basalt based laminate also contains two plies of glass mat on the external surfaces, with volume fraction of 2.56 % (±0.09), with the only function to improve the laminate surface appearance. GFB laminate: total fibre volume fraction equal to 21.18 (±0.32)%, of which flax 11.72 (± 0.18)%, basalt 7.16 (±0.11)% and glass 2.30 (±0.04)%; GHB laminate: total fibre volume fraction 22.53 (±0.48)%, of which hemp 8.56 (±0.16)%, basalt 11.38 (±0.21)% and glass 2.59 (±0.05)%; FHB laminate: total fibre volume fraction 21.18 (±0.32)%, of which flax 9.11 (±0.20)%, hemp 7.85 (±0.12)% and basalt 5.57 (±0.05)%. For all hybrids, the fibre direction into each textile network is 0/90. 2.2 Mechanical testing Specimens cut from the above-mentioned sheets of planar dimensions 250x25 mm have been subjected to tensile test, according to the standard ASTM: D3039-08, using as a mechanical testing machine a dynamometer, INSTRON model 3382. A 100 kN load cell has been used and a testing speed of 5 mm/min has been applied to the specimens. Five samples for the main directions of each sheet have been tested (longitudinal and transverse, according respectively to the warp and weft direction of the textile). This has been done to take into account the possible defects present into the textile, although nominally balanced, to get a realistic measurement of the scattering in mechanical properties. In the analysis of the flexural and tensile properties all the data (longitudinal and transverse) have been considered together. The same procedure has been used also in the case of the flexural test. The dimensions were decided on the base of the panels’ thickness. Indeed, provided that the specimens’ width was 10 mm, the minimum length was 20 times the relevant thickness, allowing a span of 16 times the thickness itself. In this case, as a mechanical testing machine, a dynamometer, LLOYD model 30K, has been employed. As a reference standard, ASTM: D790-10 has been taken into account and a testing speed of 1.7 mm/min has been set. The tensile modulus been measured by fitting all the points of the stress-strain diagram between the strain point of 0.0025 and 0.0005 (mm/mm). The strain was measured by a contacting extensometer. The flexural modulus has been measured using equation (2):
3
E
L3m 4bd 3
(2)
where L is the span length, b and d are respectively the specimen width and thickness and m is the slope of the tangent to the initial straight-line portion of the load-deflection curve, N/mm of deflection itself. The interlaminar shear strength (ILSS) of each laminate configuration was evaluated in accordance with ASTM: D2344-00. The test fixture is shown in figure 3. Tests have been carried out at a testing speed of 1 mm/min and load as a function of the related strain has been measured and plotted. To this purpose, ILSS can be calculated by applying equation (3):
ILSS 0.75
PMax bh
(3)
where PMax is the maximum load, b and h are the measured specimen width and thickness, respectively. To this purpose, the specimens’ dimensions have been selected according to the following rules: -
Length = thickness x 6; Width = thickness x 2; Support span =thickness x 4;
The density of the specimens was evaluated by displacement in accordance with the standard ASTM: D792-08. 2.3 SEM characterisation The fracture surfaces of the specimens were investigated using both a scanning electron microscope (SEM) (Philips XL40) and a field emission (FE) SEM (Zeiss, Auriga). All specimens were sputter coated with gold prior to examination. 3. Results and discussion The results were analyzed especially in the view of comparing the three hybrids having all basalt fibre laminates as their core. The fabrication of hybrids with plant fibres can be recommended in that it brings to a significant weight reduction, as shown in Table 1. It can be noticed that the low areal weight of the glass mat used results in a slightly lower density for the GHB and GFB laminates than for the FHB. As expected, the basalt based composite showed the best mechanical performance over all the hybrids, which in turn performed better than laminates based on flax and hemp fibres. Comparing the three hybrids among them, it is significant to note that, as regards tensile strength results, reported in Table 2, the two hybrids including also glass fibre laminates (GFB and GHB) show superior properties than the FHB one. In terms of stiffness, the worst performance among hybrids is shown by GHB, as it can be noticed from data in Table 2 and 3. This result can be considered somehow surprising, in view of the higher basalt volume present in these hybrids. A previous study [16] suggested the addition of hemp to a basalt fibre composite in a phenol-phormaldehyde resin did improve the flexural properties. The deceptive results in this case are rather to be attributed to a lower quality interface with the epoxy matrix, which is more critical in the case of hemp than in the case of flax addition. In addition, as observable in Figures 4 and 5, the initial slope of the tensile and 4
flexural curves is lower for GHB than for FHB hybrids, while at higher strains the situation appears to be reversed. Flexural strength results (Table 3) also indicate a considerably better performance of the FHB hybrid with respect to the other two, while flexural modulus results substantially match tensile modulus ones. It can be therefore suggested that whenever a higher flexural strength with reduced weight is desired, the introduction of plant fibres in the hybrid laminate can be recommended. As regards interlaminar shear strength, a first observation concerns the fact that specimens have shown a failure mode typical of the combined presence of two different phenomena: pure shear mode followed by bending mode. This can also be observed by the fact that the ILSS curves, shown in Figure 6 for the single reinforcement based laminates and in Figure 7 for the hybrid ones, do not indicate a linear behaviour up to failure. This is a common occurrence in interlaminar shear strength tests by short beam shear (SBS), whose consequence is that usually only the linear part of the diagram is considered, as closer to pure shear mode [17]. The lowest performance, due possibly to an early onset of the bending mode, is obtained in GHB hybrids. This behaviour may indicate an higher proneness to delamination due to a scarce quality of the interface. ILSS results are summarised in Figure 8. In the case of “homogeneous” laminates, according to the experimental data, as expected, the best interlaminar shear strength is shown by the basalt based laminates, followed by the flax fibres based ones. The worst performance is shown by the hemp based materials. This is confirmed also in the case of the hybrids laminates, as the system containing basalt and flax reinforcement (GFB) performs better than the whole of the other materials tested, including basalt-based laminates. As for the other hybrids, GHB and FHB show an improvement by approximately 13% and 6% with respect to hemp-based laminates and flax-based laminates, respectively. This indicates that for GHB and FHB the increase in ILSS obtained with basalt introduction closely matches the respective increase in weight, while GFB appears obviously superior in this respect. SEM characterisation of flax reinforced laminates shows the brittle character of the fracture at a macroscopic level with significant presence of pull-out (Figure 9a), with weak interface and presence of fibrillation (Figure 9b and 9c). This is basically confirmed in the hemp fibre reinforced laminates (Figure 10), though the fibrillation appears less diffuse in this case. The macroscopically brittle character of fracture can be confirmed for the basalt/glass fibre reinforced laminates (Figure 11a), where a sufficient fibre/matrix adhesion can be observed for glass (Figure 11b), which is not the case for basalt fibres (Figure 11c). For hybrids including plant fibres, FHB hybrid laminates show brittle behaviour and tensile damage at hemp/flax fibres layers interface (Figure 12a) and the presence of extensive pull-out (Figure 12b). GHB hybrids show again brittle behaviour (Figure 13a), debonding (Figure 13b), glass/hemp delamination under flexural loading (Figure 13c), non optimal interface in hemp layers, as confirmed from ILSS results (Figure 13d). A similar brittle behaviour is also present in GFB hybrids (Figure 14a) with diffuse pull-out (Figure 14b). It is worthy to note that two types of interface exist in natural fibre reinforced composites, one between the fibre bundle and the matrix and the other between the cells of the natural fibres, the latter being also critical in that it may lead to interfibrillar failure and uncoiling of the helical fibrils [18]. In practice, fibrillation leads in composites to diffuse matrix cracking, which appears to be of more serious consequences for hemp, where the average dimension of the fibril are larger than those of flax fibre (compare Figure 9c with 10b). The first significant indication obtained from this study is that the best compromise between mechanical properties and composite weight appears to be obtained when adding glass and flax to basalt fibre reinforced laminates. Moreover, it is suggested that using basalt fibre laminates as the internal layers for hybrid composite laminates, such as reported already in [13] for glass/basalt ones, results in a brittle mode of failure also for plant fibre/basalt fibre hybrid composites. A more general 5
observation would involve the fact that, given the different structural characteristics between plant fibre composites and basalt fibre composites, the influence of stacking sequence is never negligible, as demonstrated in [19], where it was also indicated that tensile and flexural properties slightly increased with alternate layers of basalt and jute fibre composites. This suggests that more complex stacking sequences with intercalation of layers may produce even better results also on the kind of ternary hybrids based on basalt composites studied in this work. As a matter of fact, also the production of hybrid fabrics, such the ones which were realised in [5], though not easily feasible using plant and basalt fibres, would possibly result in tailoring the properties of the final composite to the structural requirements. The information obtained can be considered preliminary to further studies, involving impact and post-impact evaluation of these materials. In this sense, the above results may suggest that concerns about the possible sudden collapse of the basalt fibre reinforced core during impact or post-impact loading are justified, as once again was the case for glass-basalt hybrid composites [6]. Another recent work indicated also that E-glass/basalt hybrid laminates with intercalated configuration yields higher impact energy absorption and enhanced damage tolerance, while symmetrical laminates with E-glass fibre fabrics as core and basalt fibre fabrics as skins exhibit the most favourable flexural behaviour [20]. What observed in the present study indicates that a similar behaviour could be shown by hybrids including plant fibre and basalt fibre composites. The main open questions in this regard appear to be the influence of strength at the interface between different layers of plant fibre composites and, as a consequence, the effect of damage dissipation achievable through a plant fibre composite core, which was quite promising e.g., in glass/flax fibre hybrids [3]. 4. Conclusions The study of ternary hybrid laminates, including a basalt fibre core, proved interesting to suggest which combinations of the three reinforcements, glass fibres and two ligno-cellulosic fibres, hemp and flax, performed better in tensile, flexural and interlaminar shear strength tests (ILSS). It was expected that, in general terms, the performance of the hybrids would be mainly intermediate between that of basalt fibre composites and that of plant fibre (hemp, flax) composites. It was important to consider nonetheless that the weight penalty carried by basalt fibre composites with respect to the hybrids was always in the region of an apparent density higher by around 0.3 g/cm³. The indications provided suggest that the best performance among hybrids is globally shown by glass/flax/basalt hybrids (GFB), although with some not negligible differences. In particular, the measured increase of GFB hybrids with respect to glass/hemp/basalt (GHB) and flax/hemp hybrids (FHB) is of approximately 19% and 32% in terms of tensile strength, respectively, and of approximately 22% and 5% in terms of tensile modulus, respectively. The differences between the three hybrids are limited to a few percents as for flexural strength, while again for flexural modulus GFB is superior by 8% and 36% to FHB and GHB, respectively. However, the most impressive result is shown by GFB hybrids, when dealing with interlaminar shear stress, their performance being in this case even superior to basalt fibre laminates by approximately 23%. It is suggested that, in general terms, hybrid configurations including hemp fibres had a lower quality interface. It is also reported that all laminates show a brittle fracture during quasi-static tests, an observation which would be appropriate to verify further by performing dynamic tests, such as e.g., falling weight impact, in future work. Also, indications from this study are deemed valuable in preparation for the future manufacturing of basalt/hybrid laminates with bio-based matrices, which will pose further problems of matrix/fibre compatibility, introducing other factors of complexity. References [1] Nunna S, Ravi Chandra P, Shrivastava S Jalan AK. A review on mechanical behavior of natural fiber based hybrid composites. J Reinf Plast Compos 2012; 31: 759-769. 6
[2] Arbelaiz A, Fernández B, Cantero G, Llano-Ponte R., Valea A, and Mondragon I. Mechanical properties of flax fibre/polypropylene composites. Influence of fibre/matrix modification and glass fibre hybridization. Compos Part A-Appl S 2005; 36: 1637-1644. [3] Santulli C, Janssen M, Jeronimidis G Partial replacement of E-glass fibres with flax fibres in composites and effect on falling weight impact performance, J Mater Sci 2005; 40: 3581-3585. [4] Dehkordi MT, Nosraty H, Shokrieh MM, Minak G, Ghelli D. Low velocity impact properties of intraply hybrid composites based on basalt and nylon, woven fabrics. Mater Des 2010; 31: 3835–3844. [5] Majid Tehrani Dehkordi MT, Nosraty H, Shokrieh MM, Minak G, Ghelli D. The influence of hybridization on impact damage behavior and residual compression strength of intraply basalt/nylon hybrid composites. Mater Des 2013; 43: 283–290. [6] De Rosa IM, Marra F, Pulci G, Santulli C, Sarasini F, Tirillò J, Valente M. Post-impact mechanical characterisation of E-glass/basalt woven fabric interply hybrid laminates. Express Polym Lett 2011; 5: 449–459. [7] Santulli C, Review. Impact properties of glass/plant fibre hybrid laminates. J Mater Sci 2007; 42; 3699-3707. [8] Öztürk B, Aslan F, Öztürk B. Hot wear properties of ceramic and basalt fiber reinforced hybrid friction materials, Tribol Int 2007; 40: 37-48. [9] Artemenko SE, Kadykova YA. Polymer composite materials based on carbon, basalt, and glass fibres, Fibre Chem+ 2008; 40: 37-39. [10] Cao S, Wu Z, Wang X. Tensile properties of CFRP and hybrid FRP composites at elevated temperatures, J Compos Mater 2009; 43: 315-330. [11] Wang X, Hua B, Feng Y, Lianga F, Moa J, Xiong J, Qiu Y. Low velocity impact properties of 3D woven basalt/aramid hybrid composites, Compos Sci Technol 2008; 68: 444-450. [12] Yao L, Wang X, Liang F, Wuc R, Hua B, Feng Y. Qiu Y, Modeling and experimental verification of dielectric constants for three-dimensional woven composites, Compos Sci Technol 2008; 68: 1794–1799. [13] Fiore V, Di Bella G, Valenza A. Glass–basalt/epoxy hybrid composites for marine applications, Mater Des 2011; 32: 2091–2099 [14] Deak T, Czigány T. Chemical composition and mechanical properties of basalt and glass fibers: a comparison, Text Res J 2009; 79: 645-651. [15] Wei B, Cao H, Song S. Environmental resistance and mechanical performance of basalt and glass fibers, Mater Sci Eng A-Struct 2010; 527: 4708-4715. [16] Öztürk S. The effect of fibre content on the mechanical properties of hemp and basalt fibre reinforced phenol formaldehyde composites, J Mater Sci 2005; 40: 4585-4592. [17] Fan Z, Santare MH, Advani SG. Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with multi-walled carbon nanotubes Compos Part A –Appl S 2008; 39: 540–554. [18] Bismarck A, Aranberri-Askargorta I, Springer J, Lampke T, Wielage B, Stamboulis A, Shenderovich I, Limbach H-H, Surface characterization of flax, hemp and cellulose fibers; surface properties and the water uptake behavior, Polym Compos 2002; 23: 872–894. [19] Amuthakkannan P, Manikandan V, Jappes JTW, Uthayakumar M, Influence of stacking sequence on mechanical properties of basalt-jute fiber-reinforced polymer hybrid composites, J Polym Eng 2012; 32: 547–554. [20] Sarasini F, Tirillò J, Valente M, Valente T, Cioffi S, Iannace S, Sorrentino L, Effect of basalt fibre hybridization on the impact behaviour under low impact velocity of glass/basalt woven fabric/epoxy resin composites, Compos Part A-Appl S 2013; 47: 109–123.
7
FIGURE CAPTIONS Figure 1. Lay-out of the vacuum infusion system Figure 2. Layout of the hybrid composites based on glass, flax and basalt fibres (GFB) (a); glass, hemp and basalt fibres (GHB) (b); flax, hemp and basalt fibres (FHB) (c) Figure 3. Horizontal shear load diagram for flat laminates Figure 4. Typical tensile stress-strain diagrams Figure 5. Typical flexural stress-strain diagrams Figure 6. ILSS vs displacement diagram for the single reinforcement based laminates Figure 7. ILSS vs displacement diagram for the hybrid laminates Figure 8. ILSS values for each tested materials Figure 9 SEM images of the fracture surface of flax fibre reinforced laminates Figure 10 SEM images of the fracture surface of hemp fibre reinforced laminates Figure 11 SEM images of the fracture surface of basalt/glass fibre reinforced laminates Figure 12 SEM images of the fracture surface of FHB hybrid laminates Figure 13 SEM images of the fracture surface of GHB hybrid laminates Figure 14 SEM images of the fracture surface of GFB hybrid laminates TABLE CAPTIONS Table 1. Materials apparent density Table 2. Tensile properties of the laminates Table 3. Flexural properties of the laminates
8
Figure 1. Lay-out of the vacuum infusion system
Figure 2. Layout of the hybrid composites based on glass, flax and basalt fibres (GFB) (a); glass, hemp and basalt fibres (GHB) (b); flax, hemp and basalt fibres (FHB) (c)
Figure 3. Horizontal shear load diagram for flat laminates
9
Material
Apparent Density (g/cm3)
Basalt
1.59 0.04
Flax
1.20 0.04
Hemp
1.18 0.03
GFB
1.31 0.02
FHB
1.37 0.05
GHB
1.27 0.04
Table 1. Materials apparent density
Figure 4. Typical tensile stress-strain diagrams
10
Laminate
Tensile strength (MPa)
Strain at break
Young’s modulus (GPa)
Basalt (B)
267.54 31.83
(3.33 0.39)*10-2
15.86 1.10
Flax (F)
89.03 3.57
(3.45 0.11)*10-2
6.29 0.41
Hemp (H)
79.72 8.64
(2.68 0.19)*10-2
5.97 0.35
FHB
115.97 3.77
(3.30 0.25)*10-2
7.69 0.63
GHB
128.84 8.70
(3.50 0.24)*10-2
6.64 0.49
GFB
153.16 17.41
(3.03 0.15)*10-2
8.11 0.60
Table 2. Tensile properties of the laminates
Figure 5. Typical flexural stress-strain diagrams
Laminate
Flexural strength (MPa)
Strain at break
Young’s modulus (GPa)
Basalt (B)
249.36 29.86
(5.15 0.10)*10-2
10.26 0.58
Flax (F) Hemp (H)
119.97 4.62 99.18 14.08
(8.83 1.45)*10 (6.74 0.90)*10-2
5.32 0.56 5.35 0.74
-2
11
128.46 29.14 FHB
(5.44 1.40)*10-2
7.45 0.,67
GHB
126.22 13.63
(3.79 0.06)*10-2
5.90 0.42
GFB
137.95 19.85
(2.00 0.33)*10-2
8.02 0.68
Table 3. Flexural properties of the laminates
Figure 6. ILSS vs displacement diagram for the single reinforcement based laminates
Figure 7. ILSS vs displacement diagram for the hybrid laminates 12
Figure 8. ILSS values for each tested materials
13
Figure 9 SEM images of the fracture surface of flax fibre reinforced laminates
Figure 10 SEM images of the fracture surface of hemp fibre reinforced laminates
14
Figure 11 SEM images of the fracture surface of basalt/glass fibre reinforced laminates
Figure 12 SEM images of the fracture surface of FHB hybrid laminates
15
Figure 13 SEM images of the fracture surface of GHB hybrid laminates
Figure 14 SEM images of the fracture surface of GFB hybrid laminates
16
1. 2. 3. 4. 5.
For the first time, hybrid laminates with three different fibres were produced Concerns are confirmed on the brittleness of hybrid laminates with basalt fibre core An optimal configuration (FHB) for flexural properties was singled out Differences between tensile and flexural properties of hybrids were identified In general, the specific mechanical properties of the hybrids are quite high
S0261-3069(13)00110-6 http://dx.doi.org/10.1016/j.matdes.2013.02.014 JMAD 5148
To appear in:
Materials and Design
Received Date: Accepted Date:
4 December 2012 6 February 2013
Please cite this article as: Petrucci, R., Santulli, C., Puglia, D., Sarasini, F., Torre, L., Kenny, J.M., Mechanical Characterisation of Hybrid Composite Laminates Based On Basalt Fibres in Combination with Flax, Hemp and Glass Fibres Manufactured By Vacuum Infusion, Materials and Design (2013), doi: http://dx.doi.org/10.1016/ j.matdes.2013.02.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
MECHANICAL CHARACTERISATION OF HYBRID COMPOSITE LAMINATES BASED ON BASALT FIBRES IN COMBINATION WITH FLAX, HEMP AND GLASS FIBRES MANUFACTURED BY VACUUM INFUSION R. Petrucci1, C. Santulli2*, D. Puglia1, F. Sarasini2, L. Torre1, J.M. Kenny1 1
Università di Perugia, Civil and Environmental Engineering Dept., Materials Science and Technology, Strada di Pentima 4, 05100 Terni 2 Sapienza Università di Roma, Dept. of Chemical, Materials and Environmental Engineering, via Eudossiana 18, 00184 Roma, Italy ABSTRACT This work concerns the production by vacuum infusion and the comparison of the properties of different hybrid composite laminates, based on basalt fibre composites as the inner core, and using also glass, flax and hemp fibre laminates to produce symmetrical configurations, all of them with a 21-23% fibre volume, in an epoxy resin. The laminates have been subjected to tensile, three-point flexural and interlaminar shear strength tests and their fracture surfaces have been characterised by scanning electron microscopy. The mechanical performance of all the hybrid laminates appears superior to pure hemp and flax fibre reinforced laminates and inferior to basalt fibre laminates. Among the hybrids, the best properties are offered by those obtained by adding glass and flax to basalt fibre reinforced laminates. Scanning electron microscopy (SEM) observation of hybrid laminates showed the diffuse presence of fibre pull-out in hemp and flax fibre reinforced layers and a general trend of brittle failure. Keywords: basalt; flax; glass; hemp; hybrid composites; vacuum infusion; mechanical properties; fracture morphology 1. Introduction Hybridization is a commonly used procedure to obtain properties, which are intermediate between the two originating materials. Dealing with polymer composites, hybridization may result in a compromise between mechanical properties and cost to meet specified design requirements, as one of the reinforcements is usually cheaper than the other one. A number of studies have been performed recently, which suggest that mechanical properties can be possibly tailored using hybridization based on glass or basalt fibre laminates and including other natural (aiming at a more sustainable material) [1-3] or synthetic fibres [4-5]. In particular, with respect to plant fibres, which equally show thermal and acoustic insulation properties, the higher specific weight of basalt fibres (around 2700 kg/m³) is widely compensated by their higher modulus, excellent heat resistance, good resistance to chemical attack and low water absorption [6]. This suggests that hybrid laminates, based on basalt fibres and plant fibres, and/or glass-plant fibre hybrid laminates, the latter being particularly studied when it comes to the need for sufficient impact resistance [7], may have some interest. This would possibly result in a more sustainable end-of-life scenario without substantially affecting the structural performance of the laminates. As a matter of fact, hybridization of basalt fibres has been attempted with ceramic fibres, to provide improved hot wear resistance to friction materials [8], with high tensile strength fibres, such as carbon [9-10] and aramid [11-12], and with glass fibres [6, 13]. In these cases, basalt provided an impact and environmental resistance superior to that provided by the corresponding hybrids with *
Corresponding author, telephone: 0039-06-44585408, e-mail: [email protected]
1
glass fibres, coupled with a substantial reduction in costs, with respect to carbon and aramid fibre composites. In the case of basalt/Nylon fibres hybrid laminates, low tensile modulus of Nylon is improved by adding basalt fibres, whilst Nylon provides conversely a higher impact resistance [4]. Also basalt hybridization with glass fibres has been attempted, which is based on the use of two fibres, which are chemically not very different: continuous basalt fibre has a not very different content in silica and alumina from glass fibres and also a comparable, if not superior, tensile strength [14]. A significant difference is their behaviour under corrosion: for basalt fibres, resistance to acids is much higher than that to alkalis, whilst for glass fibres resistance to acids is nearly the same as that to alkalis [15]. As regards stacking sequences in glass/basalt hybrids, a previous study suggested that a symmetrical configuration including the lower strength material (glass) as a core for the higher strength one (basalt) presents the most favourable degradation pattern [5]. Another study suggested that the presence of external layers of basalt fibres involved the greatest increase in flexural and tensile properties of glass fibre reinforced laminates with respect to other glass/basalt stacking sequences [13]. This is likely to depend on the fact that a hybrid configuration including basalt fibres as internal layers increases the brittleness of the composite. It is therefore worth investigating whether this is the case only on basalt/glass hybrids or it is a more general trend. Based on the above considerations, hybrids made using basalt fibres composites as the core laminates are produced, including for the first time three types of fibres in the same laminate, using a vacuum infusion technique. Three hybrid configurations were produced including, together with basalt fibres, glass/flax, glass/hemp and hemp/flax, and compared with the relevant composite laminates, including each of the above fibres. Their mechanical properties and their damage patterns were compared, in order to establish the most suitable solution for possible wider scale production. 2. Materials and methods 2.1 Composite manufacturing The resin system used was an EC360 (resin)/W160 (hardener) epoxy, provided by Elantas Camattini s.p.a. The reinforcements based on flax (surface density 300 g/m²), hemp (300 g/m²), and the basalt grid (240 g/m²), were all provided by Fidia Srl, while the glass mat (100 g/m²) has been provided by G. Angeloni Srl. All the composite panels have been produced by means of a vacuum infusion process, whose layout is given in Figure 1. For this purpose, for each configuration, a stack of dry reinforcement plies has been laminated over a glass mould. After the lamination stage, the layout has been completed with the flow media and the infusion network, and finally the mould has been sealed with the vacuum bag. The curing stage of the resin, after the infusion is concluded, has been carried out at room temperature, while the post curing took place in an oven in two sub-stages: at 60°C for three hours and subsequently at 80°C for four hours. The in-mould pressure measured during the infusion stages was equal to 20 mbar. Vacmobiles model 20/2 vacuum pump, provided by Vacmobiles Europe by Filter Technics has been used. Rectangular 260 mm x 450 mm sheets have been obtained. Subsequent cutting operations have been carried out with the aim to produce specimens suitable for mechanical characterization, in accordance to the related standards. Three laminates were based on hemp, flax and basalt fibres respectively, which were used for comparison with the three hybrids whose structure is schematized in Figure 2. It is worthwhile to point out that the surface density of the employed textiles has been precisely measured. In particular, the surface density of the flax textile was equal to 292 g/m2, while that of the hemp textile was 234 g/m2, and that of the basalt textile was 300 g/m2. All these reinforcements 2
have a balanced configuration on warp and weft fabrics. Finally the glass mat surface density was equal to 100 g/m2. The fibre volume fraction of each reinforcement type was calculated by the value of the whole laminate thickness in the case of the homogeneous systems. In the case of the hybrid ones, the thickness of each layer has been measured with the aid of an optical microscope and, consequently, the related fibre volume fraction been calculated. In both cases, for the thickness calculation, equation (1) has been used:
f
n d
(1)
where n is the number of layers of the same typology, is the corresponding surface density, d is the thickness of the layers of the same reinforcement typology and is the density of the fibres. Going more into detail, the following stacking sequences have been employed: Hemp, flax and basalt laminates have all been produced by stacking together 4 layers of biaxial textiles, according to a [0/90]2S lay-out. Fibre volume fraction was 20.16 (± 1.37)% for hemp; 24.82 (±0.83)% for flax; 28.23 (±0.85)% for basalt. The basalt based laminate also contains two plies of glass mat on the external surfaces, with volume fraction of 2.56 % (±0.09), with the only function to improve the laminate surface appearance. GFB laminate: total fibre volume fraction equal to 21.18 (±0.32)%, of which flax 11.72 (± 0.18)%, basalt 7.16 (±0.11)% and glass 2.30 (±0.04)%; GHB laminate: total fibre volume fraction 22.53 (±0.48)%, of which hemp 8.56 (±0.16)%, basalt 11.38 (±0.21)% and glass 2.59 (±0.05)%; FHB laminate: total fibre volume fraction 21.18 (±0.32)%, of which flax 9.11 (±0.20)%, hemp 7.85 (±0.12)% and basalt 5.57 (±0.05)%. For all hybrids, the fibre direction into each textile network is 0/90. 2.2 Mechanical testing Specimens cut from the above-mentioned sheets of planar dimensions 250x25 mm have been subjected to tensile test, according to the standard ASTM: D3039-08, using as a mechanical testing machine a dynamometer, INSTRON model 3382. A 100 kN load cell has been used and a testing speed of 5 mm/min has been applied to the specimens. Five samples for the main directions of each sheet have been tested (longitudinal and transverse, according respectively to the warp and weft direction of the textile). This has been done to take into account the possible defects present into the textile, although nominally balanced, to get a realistic measurement of the scattering in mechanical properties. In the analysis of the flexural and tensile properties all the data (longitudinal and transverse) have been considered together. The same procedure has been used also in the case of the flexural test. The dimensions were decided on the base of the panels’ thickness. Indeed, provided that the specimens’ width was 10 mm, the minimum length was 20 times the relevant thickness, allowing a span of 16 times the thickness itself. In this case, as a mechanical testing machine, a dynamometer, LLOYD model 30K, has been employed. As a reference standard, ASTM: D790-10 has been taken into account and a testing speed of 1.7 mm/min has been set. The tensile modulus been measured by fitting all the points of the stress-strain diagram between the strain point of 0.0025 and 0.0005 (mm/mm). The strain was measured by a contacting extensometer. The flexural modulus has been measured using equation (2):
3
E
L3m 4bd 3
(2)
where L is the span length, b and d are respectively the specimen width and thickness and m is the slope of the tangent to the initial straight-line portion of the load-deflection curve, N/mm of deflection itself. The interlaminar shear strength (ILSS) of each laminate configuration was evaluated in accordance with ASTM: D2344-00. The test fixture is shown in figure 3. Tests have been carried out at a testing speed of 1 mm/min and load as a function of the related strain has been measured and plotted. To this purpose, ILSS can be calculated by applying equation (3):
ILSS 0.75
PMax bh
(3)
where PMax is the maximum load, b and h are the measured specimen width and thickness, respectively. To this purpose, the specimens’ dimensions have been selected according to the following rules: -
Length = thickness x 6; Width = thickness x 2; Support span =thickness x 4;
The density of the specimens was evaluated by displacement in accordance with the standard ASTM: D792-08. 2.3 SEM characterisation The fracture surfaces of the specimens were investigated using both a scanning electron microscope (SEM) (Philips XL40) and a field emission (FE) SEM (Zeiss, Auriga). All specimens were sputter coated with gold prior to examination. 3. Results and discussion The results were analyzed especially in the view of comparing the three hybrids having all basalt fibre laminates as their core. The fabrication of hybrids with plant fibres can be recommended in that it brings to a significant weight reduction, as shown in Table 1. It can be noticed that the low areal weight of the glass mat used results in a slightly lower density for the GHB and GFB laminates than for the FHB. As expected, the basalt based composite showed the best mechanical performance over all the hybrids, which in turn performed better than laminates based on flax and hemp fibres. Comparing the three hybrids among them, it is significant to note that, as regards tensile strength results, reported in Table 2, the two hybrids including also glass fibre laminates (GFB and GHB) show superior properties than the FHB one. In terms of stiffness, the worst performance among hybrids is shown by GHB, as it can be noticed from data in Table 2 and 3. This result can be considered somehow surprising, in view of the higher basalt volume present in these hybrids. A previous study [16] suggested the addition of hemp to a basalt fibre composite in a phenol-phormaldehyde resin did improve the flexural properties. The deceptive results in this case are rather to be attributed to a lower quality interface with the epoxy matrix, which is more critical in the case of hemp than in the case of flax addition. In addition, as observable in Figures 4 and 5, the initial slope of the tensile and 4
flexural curves is lower for GHB than for FHB hybrids, while at higher strains the situation appears to be reversed. Flexural strength results (Table 3) also indicate a considerably better performance of the FHB hybrid with respect to the other two, while flexural modulus results substantially match tensile modulus ones. It can be therefore suggested that whenever a higher flexural strength with reduced weight is desired, the introduction of plant fibres in the hybrid laminate can be recommended. As regards interlaminar shear strength, a first observation concerns the fact that specimens have shown a failure mode typical of the combined presence of two different phenomena: pure shear mode followed by bending mode. This can also be observed by the fact that the ILSS curves, shown in Figure 6 for the single reinforcement based laminates and in Figure 7 for the hybrid ones, do not indicate a linear behaviour up to failure. This is a common occurrence in interlaminar shear strength tests by short beam shear (SBS), whose consequence is that usually only the linear part of the diagram is considered, as closer to pure shear mode [17]. The lowest performance, due possibly to an early onset of the bending mode, is obtained in GHB hybrids. This behaviour may indicate an higher proneness to delamination due to a scarce quality of the interface. ILSS results are summarised in Figure 8. In the case of “homogeneous” laminates, according to the experimental data, as expected, the best interlaminar shear strength is shown by the basalt based laminates, followed by the flax fibres based ones. The worst performance is shown by the hemp based materials. This is confirmed also in the case of the hybrids laminates, as the system containing basalt and flax reinforcement (GFB) performs better than the whole of the other materials tested, including basalt-based laminates. As for the other hybrids, GHB and FHB show an improvement by approximately 13% and 6% with respect to hemp-based laminates and flax-based laminates, respectively. This indicates that for GHB and FHB the increase in ILSS obtained with basalt introduction closely matches the respective increase in weight, while GFB appears obviously superior in this respect. SEM characterisation of flax reinforced laminates shows the brittle character of the fracture at a macroscopic level with significant presence of pull-out (Figure 9a), with weak interface and presence of fibrillation (Figure 9b and 9c). This is basically confirmed in the hemp fibre reinforced laminates (Figure 10), though the fibrillation appears less diffuse in this case. The macroscopically brittle character of fracture can be confirmed for the basalt/glass fibre reinforced laminates (Figure 11a), where a sufficient fibre/matrix adhesion can be observed for glass (Figure 11b), which is not the case for basalt fibres (Figure 11c). For hybrids including plant fibres, FHB hybrid laminates show brittle behaviour and tensile damage at hemp/flax fibres layers interface (Figure 12a) and the presence of extensive pull-out (Figure 12b). GHB hybrids show again brittle behaviour (Figure 13a), debonding (Figure 13b), glass/hemp delamination under flexural loading (Figure 13c), non optimal interface in hemp layers, as confirmed from ILSS results (Figure 13d). A similar brittle behaviour is also present in GFB hybrids (Figure 14a) with diffuse pull-out (Figure 14b). It is worthy to note that two types of interface exist in natural fibre reinforced composites, one between the fibre bundle and the matrix and the other between the cells of the natural fibres, the latter being also critical in that it may lead to interfibrillar failure and uncoiling of the helical fibrils [18]. In practice, fibrillation leads in composites to diffuse matrix cracking, which appears to be of more serious consequences for hemp, where the average dimension of the fibril are larger than those of flax fibre (compare Figure 9c with 10b). The first significant indication obtained from this study is that the best compromise between mechanical properties and composite weight appears to be obtained when adding glass and flax to basalt fibre reinforced laminates. Moreover, it is suggested that using basalt fibre laminates as the internal layers for hybrid composite laminates, such as reported already in [13] for glass/basalt ones, results in a brittle mode of failure also for plant fibre/basalt fibre hybrid composites. A more general 5
observation would involve the fact that, given the different structural characteristics between plant fibre composites and basalt fibre composites, the influence of stacking sequence is never negligible, as demonstrated in [19], where it was also indicated that tensile and flexural properties slightly increased with alternate layers of basalt and jute fibre composites. This suggests that more complex stacking sequences with intercalation of layers may produce even better results also on the kind of ternary hybrids based on basalt composites studied in this work. As a matter of fact, also the production of hybrid fabrics, such the ones which were realised in [5], though not easily feasible using plant and basalt fibres, would possibly result in tailoring the properties of the final composite to the structural requirements. The information obtained can be considered preliminary to further studies, involving impact and post-impact evaluation of these materials. In this sense, the above results may suggest that concerns about the possible sudden collapse of the basalt fibre reinforced core during impact or post-impact loading are justified, as once again was the case for glass-basalt hybrid composites [6]. Another recent work indicated also that E-glass/basalt hybrid laminates with intercalated configuration yields higher impact energy absorption and enhanced damage tolerance, while symmetrical laminates with E-glass fibre fabrics as core and basalt fibre fabrics as skins exhibit the most favourable flexural behaviour [20]. What observed in the present study indicates that a similar behaviour could be shown by hybrids including plant fibre and basalt fibre composites. The main open questions in this regard appear to be the influence of strength at the interface between different layers of plant fibre composites and, as a consequence, the effect of damage dissipation achievable through a plant fibre composite core, which was quite promising e.g., in glass/flax fibre hybrids [3]. 4. Conclusions The study of ternary hybrid laminates, including a basalt fibre core, proved interesting to suggest which combinations of the three reinforcements, glass fibres and two ligno-cellulosic fibres, hemp and flax, performed better in tensile, flexural and interlaminar shear strength tests (ILSS). It was expected that, in general terms, the performance of the hybrids would be mainly intermediate between that of basalt fibre composites and that of plant fibre (hemp, flax) composites. It was important to consider nonetheless that the weight penalty carried by basalt fibre composites with respect to the hybrids was always in the region of an apparent density higher by around 0.3 g/cm³. The indications provided suggest that the best performance among hybrids is globally shown by glass/flax/basalt hybrids (GFB), although with some not negligible differences. In particular, the measured increase of GFB hybrids with respect to glass/hemp/basalt (GHB) and flax/hemp hybrids (FHB) is of approximately 19% and 32% in terms of tensile strength, respectively, and of approximately 22% and 5% in terms of tensile modulus, respectively. The differences between the three hybrids are limited to a few percents as for flexural strength, while again for flexural modulus GFB is superior by 8% and 36% to FHB and GHB, respectively. However, the most impressive result is shown by GFB hybrids, when dealing with interlaminar shear stress, their performance being in this case even superior to basalt fibre laminates by approximately 23%. It is suggested that, in general terms, hybrid configurations including hemp fibres had a lower quality interface. It is also reported that all laminates show a brittle fracture during quasi-static tests, an observation which would be appropriate to verify further by performing dynamic tests, such as e.g., falling weight impact, in future work. Also, indications from this study are deemed valuable in preparation for the future manufacturing of basalt/hybrid laminates with bio-based matrices, which will pose further problems of matrix/fibre compatibility, introducing other factors of complexity. References [1] Nunna S, Ravi Chandra P, Shrivastava S Jalan AK. A review on mechanical behavior of natural fiber based hybrid composites. J Reinf Plast Compos 2012; 31: 759-769. 6
[2] Arbelaiz A, Fernández B, Cantero G, Llano-Ponte R., Valea A, and Mondragon I. Mechanical properties of flax fibre/polypropylene composites. Influence of fibre/matrix modification and glass fibre hybridization. Compos Part A-Appl S 2005; 36: 1637-1644. [3] Santulli C, Janssen M, Jeronimidis G Partial replacement of E-glass fibres with flax fibres in composites and effect on falling weight impact performance, J Mater Sci 2005; 40: 3581-3585. [4] Dehkordi MT, Nosraty H, Shokrieh MM, Minak G, Ghelli D. Low velocity impact properties of intraply hybrid composites based on basalt and nylon, woven fabrics. Mater Des 2010; 31: 3835–3844. [5] Majid Tehrani Dehkordi MT, Nosraty H, Shokrieh MM, Minak G, Ghelli D. The influence of hybridization on impact damage behavior and residual compression strength of intraply basalt/nylon hybrid composites. Mater Des 2013; 43: 283–290. [6] De Rosa IM, Marra F, Pulci G, Santulli C, Sarasini F, Tirillò J, Valente M. Post-impact mechanical characterisation of E-glass/basalt woven fabric interply hybrid laminates. Express Polym Lett 2011; 5: 449–459. [7] Santulli C, Review. Impact properties of glass/plant fibre hybrid laminates. J Mater Sci 2007; 42; 3699-3707. [8] Öztürk B, Aslan F, Öztürk B. Hot wear properties of ceramic and basalt fiber reinforced hybrid friction materials, Tribol Int 2007; 40: 37-48. [9] Artemenko SE, Kadykova YA. Polymer composite materials based on carbon, basalt, and glass fibres, Fibre Chem+ 2008; 40: 37-39. [10] Cao S, Wu Z, Wang X. Tensile properties of CFRP and hybrid FRP composites at elevated temperatures, J Compos Mater 2009; 43: 315-330. [11] Wang X, Hua B, Feng Y, Lianga F, Moa J, Xiong J, Qiu Y. Low velocity impact properties of 3D woven basalt/aramid hybrid composites, Compos Sci Technol 2008; 68: 444-450. [12] Yao L, Wang X, Liang F, Wuc R, Hua B, Feng Y. Qiu Y, Modeling and experimental verification of dielectric constants for three-dimensional woven composites, Compos Sci Technol 2008; 68: 1794–1799. [13] Fiore V, Di Bella G, Valenza A. Glass–basalt/epoxy hybrid composites for marine applications, Mater Des 2011; 32: 2091–2099 [14] Deak T, Czigány T. Chemical composition and mechanical properties of basalt and glass fibers: a comparison, Text Res J 2009; 79: 645-651. [15] Wei B, Cao H, Song S. Environmental resistance and mechanical performance of basalt and glass fibers, Mater Sci Eng A-Struct 2010; 527: 4708-4715. [16] Öztürk S. The effect of fibre content on the mechanical properties of hemp and basalt fibre reinforced phenol formaldehyde composites, J Mater Sci 2005; 40: 4585-4592. [17] Fan Z, Santare MH, Advani SG. Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with multi-walled carbon nanotubes Compos Part A –Appl S 2008; 39: 540–554. [18] Bismarck A, Aranberri-Askargorta I, Springer J, Lampke T, Wielage B, Stamboulis A, Shenderovich I, Limbach H-H, Surface characterization of flax, hemp and cellulose fibers; surface properties and the water uptake behavior, Polym Compos 2002; 23: 872–894. [19] Amuthakkannan P, Manikandan V, Jappes JTW, Uthayakumar M, Influence of stacking sequence on mechanical properties of basalt-jute fiber-reinforced polymer hybrid composites, J Polym Eng 2012; 32: 547–554. [20] Sarasini F, Tirillò J, Valente M, Valente T, Cioffi S, Iannace S, Sorrentino L, Effect of basalt fibre hybridization on the impact behaviour under low impact velocity of glass/basalt woven fabric/epoxy resin composites, Compos Part A-Appl S 2013; 47: 109–123.
7
FIGURE CAPTIONS Figure 1. Lay-out of the vacuum infusion system Figure 2. Layout of the hybrid composites based on glass, flax and basalt fibres (GFB) (a); glass, hemp and basalt fibres (GHB) (b); flax, hemp and basalt fibres (FHB) (c) Figure 3. Horizontal shear load diagram for flat laminates Figure 4. Typical tensile stress-strain diagrams Figure 5. Typical flexural stress-strain diagrams Figure 6. ILSS vs displacement diagram for the single reinforcement based laminates Figure 7. ILSS vs displacement diagram for the hybrid laminates Figure 8. ILSS values for each tested materials Figure 9 SEM images of the fracture surface of flax fibre reinforced laminates Figure 10 SEM images of the fracture surface of hemp fibre reinforced laminates Figure 11 SEM images of the fracture surface of basalt/glass fibre reinforced laminates Figure 12 SEM images of the fracture surface of FHB hybrid laminates Figure 13 SEM images of the fracture surface of GHB hybrid laminates Figure 14 SEM images of the fracture surface of GFB hybrid laminates TABLE CAPTIONS Table 1. Materials apparent density Table 2. Tensile properties of the laminates Table 3. Flexural properties of the laminates
8
Figure 1. Lay-out of the vacuum infusion system
Figure 2. Layout of the hybrid composites based on glass, flax and basalt fibres (GFB) (a); glass, hemp and basalt fibres (GHB) (b); flax, hemp and basalt fibres (FHB) (c)
Figure 3. Horizontal shear load diagram for flat laminates
9
Material
Apparent Density (g/cm3)
Basalt
1.59 0.04
Flax
1.20 0.04
Hemp
1.18 0.03
GFB
1.31 0.02
FHB
1.37 0.05
GHB
1.27 0.04
Table 1. Materials apparent density
Figure 4. Typical tensile stress-strain diagrams
10
Laminate
Tensile strength (MPa)
Strain at break
Young’s modulus (GPa)
Basalt (B)
267.54 31.83
(3.33 0.39)*10-2
15.86 1.10
Flax (F)
89.03 3.57
(3.45 0.11)*10-2
6.29 0.41
Hemp (H)
79.72 8.64
(2.68 0.19)*10-2
5.97 0.35
FHB
115.97 3.77
(3.30 0.25)*10-2
7.69 0.63
GHB
128.84 8.70
(3.50 0.24)*10-2
6.64 0.49
GFB
153.16 17.41
(3.03 0.15)*10-2
8.11 0.60
Table 2. Tensile properties of the laminates
Figure 5. Typical flexural stress-strain diagrams
Laminate
Flexural strength (MPa)
Strain at break
Young’s modulus (GPa)
Basalt (B)
249.36 29.86
(5.15 0.10)*10-2
10.26 0.58
Flax (F) Hemp (H)
119.97 4.62 99.18 14.08
(8.83 1.45)*10 (6.74 0.90)*10-2
5.32 0.56 5.35 0.74
-2
11
128.46 29.14 FHB
(5.44 1.40)*10-2
7.45 0.,67
GHB
126.22 13.63
(3.79 0.06)*10-2
5.90 0.42
GFB
137.95 19.85
(2.00 0.33)*10-2
8.02 0.68
Table 3. Flexural properties of the laminates
Figure 6. ILSS vs displacement diagram for the single reinforcement based laminates
Figure 7. ILSS vs displacement diagram for the hybrid laminates 12
Figure 8. ILSS values for each tested materials
13
Figure 9 SEM images of the fracture surface of flax fibre reinforced laminates
Figure 10 SEM images of the fracture surface of hemp fibre reinforced laminates
14
Figure 11 SEM images of the fracture surface of basalt/glass fibre reinforced laminates
Figure 12 SEM images of the fracture surface of FHB hybrid laminates
15
Figure 13 SEM images of the fracture surface of GHB hybrid laminates
Figure 14 SEM images of the fracture surface of GFB hybrid laminates
16
1. 2. 3. 4. 5.
For the first time, hybrid laminates with three different fibres were produced Concerns are confirmed on the brittleness of hybrid laminates with basalt fibre core An optimal configuration (FHB) for flexural properties was singled out Differences between tensile and flexural properties of hybrids were identified In general, the specific mechanical properties of the hybrids are quite high