- Email: [email protected]
Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing Anil Kumar a,⇑, Surjit Angra b, A.K. Chanda c a
National Institute of Technology, Kurukshetra, India ME Department, NIT, Kurukshetra, India c MAE Department, G B Pant Government Engineering College, New Delhi, India b
a r t i c l e
i n f o
Article history: Received 29 July 2019 Received in revised form 11 October 2019 Accepted 20 November 2019 Available online xxxx Keywords: Composites Kevlar Honeycomb Mechanical properties Water absorption Test Soil degradation Test
a b s t r a c t This study presents the Experimental characterizations of composite sandwich structures needed to optimize structure design. We fabricated 2 composite sandwich structures; one is having a Kevlar Honeycomb Core of 3 mm thickness and another having a Kevlar Honeycomb Core of 5 mm thickness. Honeycomb sandwich panels had Carbon and Basalt fiber face sheets (2 layers of Carbon of 0.2 mm each and 1 layer of Basalt of 2.34 mm). The mechanical properties of the constituent materials were discovered experimentally using ASTM/ISO standards. After testing a comparison is made of the different properties achieved from the two different specimen having core thickness of 3 mm and 5 mm.by analysis it was observed that Tensile, Flexural and Impact strength increases with increase of core thickness but the hardness decreases. Also water absorption and acid corrosion test were done on two specimens and it was observed that the specimen having the higher thickness will absorb less water and surface destruction due to acid is almost the same in the two specimens. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Mechanical and Energy Technologies.
1. Introduction All composite materials consist of 2 or more materials and always contain an interface between these materials. A sandwich composite consists of honeycomb material having face sheet on the top and bottom sides. Composite materials may include aramid or Kevlar (very light), glass, Carbon (high strength) etc. Most matrix materials include Polymeric matrix’s (thermoplastic and thermosetting resins), Mineral matrix’s (silicon carbide, carbon), and metallic matrix’s (aluminum alloys, titanium alloys, and orientated eutectics). Composites allow for a weight reduction of 10–50% with equal or greater performance with a 10–20% decrease in material and comparatively less manufacturing cost. Composites have a good fatigue and corrosion resistance which leads to long term savings and a reduction in maintenance costs of the part.
Types of Composites The first way of classification is with respect to the matrix constituent-In this classification composite can be Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix Composites (CMCs). The second way of classification is with respect to the reinforcement form-This reinforcement can be fiber composites, laminar composites and particulate composites. Fiber Reinforced composites (FRP) can be define in two more way in which composite have discontinuous or continuous fibers. Methods of Composite Fabrication For creating polymeric composites, there are currently 3 different types of layups that are most commonly used in industry. 1. ‘‘Pre-Preg” layup Method- The most favored method is known as ‘‘Pre-preg” layup, which is a composite that has had the resin pre-impregnated into the composite when it is initially created. 2. ‘‘Wet-Layup” Method -The second method is known as the ‘‘wet-layup” involves taking dry fibers and ingraining resin by hand, before curing.
⇑ Corresponding author. E-mail address: [email protected] (A. Kumar). https://doi.org/10.1016/j.matpr.2019.11.242 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Mechanical and Energy Technologies.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
2
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
3. Resin Infusion or Vacuum Assisted Transfer-Molding System (VARTM) – This method uses a vacuum to pull resin across a composite part, whilst also infusing the fibers with the resin. Honeycomb sandwich panels were one of the outcomes of research into decreasing structural mass. Sandwich panel structures consist of two thin face sheets on the top and bottom of a shear resistant lightweight core. The relative separation of the stable face sheets result in high stiffness to weight ratios. Essentially the honeycomb was used as a shear web between two upper and lower skins. With the development of Epoxy resin, it was possible to bond aluminum skins to an aluminum honeycomb core, which occurred in 1954. Since then, much advancement has been made in honeycomb studies, with the most commonly used honeycomb for aircraft structures being Nomex Honeycomb [9]. Composite panels are designed to meet the application requirements. They have the same normal strengths that composites have, due to the face sheets being constructed from materials of high modulus of elasticity’s (when compared with the core) like fiber-resin mixtures, metal alloys and plastics. The cores have low elastic moduli that yield without failure in the high deflection regimes [8]. K. Kantha Ra et al. [1] constructed a sandwich, which consists of two thin facing layers separated by a thick core, offers various advantages for design of weight critical structure. Depending on the specific requirements of the structures, aluminum alloys, high tensile steels, titanium or composites are used as the material of facings skins. They theoretically made Strength Analysis on Honeycomb Sandwich Panels of different materials. Shan-shan Shi et al. [2] investigated the Interfacial bonding, essential to carbon-fiber and Al-honeycomb sandwich composites under bending and uni-axial compression. They observed that the adhesive joint, in-situ formed from resin and short Kevlar fibers at the interface effectively became a composite. The peak load and energy absorption of the sandwich composites, with and without the short Kevlar fiber interfacial toughening, were compared with predictions from analytical models. Uthirapathy Tamilarasana et al., [3] found the various properties such as flexural, tensile and impact value of fabricated Carbon fiber reinforced AL sandwich laminates. All the tests are carried out as per ASTM standard. Scanning Electron Microscope (SEM) analysis is carried out to investigate the structure of the sandwich laminates. Girish Gautam et al., [4] examines the tensile, flexural and impact strength of Kevlar 29 (K-29) fiber reinforced polymer composite. The composite samples used in this study were prepared by hand lay-up technique. The acquired results showed that developed Kevlar-29 fiber reinforced polymer composite has good tensile, flexural and impact strength.
K.K. Herbert Yeung et al. [5] choose Kevlar as a strenghting material in their study. In this study Kevlar is inserted with carbon fiber to make a composite. They found that this composite provide a very high compressive and tensile strength as compare to a carbon fiber and it was conclude that Kevlar have high compressive and tensile strength as compare to carbon fiber. Varun Panwar et al. [6] reviewed FEM updating and updating of composite sandwich related studies. They wanted to find the different techniques used in updating of the material’s parameter, the limitations involved with these techniques and the different assumptions while making the experiments. They found that the different studies on elimination of error from experimental model and FE model are available and the issues arrived from parameterization and regularization. R.T.Durai Prabhakaran et al. [7] were keen to know the behaviour of flax fibre layups and orientation affect of laminated composites in bending loading. They used different orientations (Unidirectional [00]2S, cross-ply [0/90]S, and angle-ply [+45/45]S ) to study flexural stresses and mid-span deflections. They used the Classical Beam Theory (CBT) are to obtain analytical solutions, and then compared the CBT based results with results finite element simulation results. They found good agreement in these two types of results. It was found that from this past data that carbon fiber, Basalt have properties (Basalt have great bonding and tensile strength, carbon fiber have compressive strength) which is used to produce composite to get desired properties. we can use these fiber together with a Honeycomb structure of Kevlar to produce a composite which can have very fine compressive, tensile strength, corrosive resistance and provide many improve property which can be used as a future material for purpose and also replace the metal used for these purpose. 2. Main objectives and scope of research Composite materials have a very long history. It was observed from the past data of composites that much research work has been done to get the desired properties of the composite. Composite is very interesting topic for the scholars from the last few decades. But not much has been found on Kevlar Honeycomb sandwich structures with carbon and basalt fiber as face plates. So we will try to find the effects on various properties of a Kevlar Honeycomb Composite structure by varying its core thickness. The main objective of this study is to analyse the effects on various properties of a composite structure, having a Kevlar Honeycomb core, by varying its core thickness. Fabrication and testing of sandwich honeycomb kevlar composite under various regimes of load are done to determine the strength of composite material under different regimes of load.
Fig. 1. Example of how honeycomb stiffens a structure without materially increasing its weight.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
3
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Design of Basalt fiber.
3. Composite fabrications We fabricated 2 composite structures having; one having a Kevlar Honeycomb Core of 3 mm thickness and another having a Kevlar Honeycomb Core of 5 mm thickness. The face sheets and the epoxy in both the structures will remain same and consists of Carbon and Basalt fibers (2 layers of Carbon of 0.2 mm each and 1 layer of Basalt of 2.34 mm) and in same sequence (Fig. 2).
Fiber type
Wrap Wrap
Woven pattern Linear density (10 mm) Size (mm) Area weight (g/m2)
Wrap Welt Thickness
6K 6K plain 4K 0.38 320
3.1. Manufacturing route and procedure Technical Data Sheet of Matrix used Basalt Fiber Fabric 320 GSM Plain (Table 1) Technical Datasheet – Carbon Woven Reinforcement Fabric 200 GSM – 2X2 Twill Woven Carbon Fabric (Table 2) Technical Datasheet – PK2 Kevlar N636 Para-Aramid Fiber Honeycomb Cell Sizes : 1/800 3/1600 Densities : 2.0 pcf 6.0 pcf Sheet ‘‘Ribbon” (L) : 48‘‘ typical Sheet ‘‘Transverse” (W) : 96‘‘ typical PK2 Kevlar honeycomb is specified as follows: Material – Cell Size – Density – Cell Configuration (Fig. 3) Curing of Epoxy with Hardener Mixing ratio 100: 18p.b.w Pot life at RT 1.5–2.5ours Curing at RT 16–24 h Post Curing at 70–80 °C 2 h (if required) in mold or conformer only to avoid warp edge. Properties:- (Table 3 and Fig. 4)
Table 2 Design of Carbon fiber and its properties. Fiber Properties Density Pgpcm3o Filament Diameter Pmmo Tensile Strength P MPa Tensile Modulus P GPa Elongation P%o Sizing
g58 7 345y –3y g55 Epoxy Compatible
4 Carbon Fibre Sheets 2 Basalt Fibre Sheets 1 Kevlar Honeycomb Sheet (3 mm/5mm) Step 2: Preparation of Epoxy Resin- Hardener Mixture Epoxy resin amounted to 300 ml is taken into a container. Hardener is added to this resin equal to 18% of quantity of resin (i.e. 0.18*300 = 54 ml). This mixture is continuously mixed for thorough lamination.
3.2. Steps used in fabrication of composite sandwich Step 3: Preparation of Mould/Work SurfaceHere we are using Wet Lay-up Method followed by VARTM Method for even spreading and mixing of the resin with the composite. Step 1: Cutting of Fibre Sheets With the help of special purpose scissors, we cut all the sheets in dimensions of 300 mm * 300 mm. Tolerance of 3–5 mm is taken on all the sides. So the overall dimension cut is 300 mm * 300 mm. Special care is being taken in cutting since the chances of damage of the fibres are high since the orientation of the fibrestructure is to be maintained. After the cutting process, we are now left with the following sheets (each of same dimensions) :
The work surface is thoroughly cleaned with a clean soft cloth. A release agent is applied on the surface to clear off the any minute debris left Then the surface is allowed to dry for a minute. Then with the help of a sealant tape, the work boundaries are made in such a way that a clearance of 200 min is provided on all sides. A layer of resin- hardener mixture (epoxy layer) is spread on the surface. Step 4: Layer Reinforcement onto the Surface First the Kevlar fibre is spread on the epoxy layer.
Fig. 2. Composite Structure Design.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
4
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 3. PK2 Kevlar honeycomb Specification.
Table 3 Properties of Epoxy with Hardener. HDT Flexural Strength Compressive strength Tensile strength Impact strength
Table 4 Load VS Extension for Tensile test. oC Psi Psi Psi lb/in
95 17,000 16,000 10,300 0.45
Load (N)
0 750 1500 2250 3000 3750 4296.22 4500 5250 6000 6750 7500 8250 9000 9546.78
EXTENSION (MM) Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
0 1.75 2 2.35 2.5 2.65 3 3.5 4 4.5 4.8 5.5 6 6.75 8.09
0 0.35 0.8 1.1 2.9 3 3.76 – – – – – – –
Fig. 4. Reinforcing the Kevlar with Epoxy Resin. Table 5 Results of Tensile test.
Fig. 5. Layer by Layer Enforcement.
S. N.
Parameters
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
1 2 3
Peak load (N) Extension (mm) Tensile Strength N/mm2
9546.78 8.09 69.0
4296.22 3.76 79.7
After this, we put sufficient resin; the whole reinforcement is lifted and turned upside down. Same process is repeated again and again by putting a layer of Basalt fibre and 2 layers of Carbon fibre. Step 5: Tape the Reinforcement-
With the application of brush, resin mixture is applied on the fibre, first horizontally and then vertically on the surface. Brush is dabbed on the surface so as to impregnate the surface entirely. A layer of Basalt fibre is spread on the Kevlar layer. The resin is applied with the brush in the same manner. Small pressure is applied by a roller tool to remove the air between the layers. subsequent layers of Carbon fibre are applied in the same manner on top of the Basalt layer.
After layering the fibre sheets one over the, masking tape is used to make sure that the reinforcement stays in place while the bagging material is added. Step 6: Cut and position the Peel Ply over the Reinforcement Several layers of peel ply are cut about the size of the working surface and subsequent plies are placed one over another.
Fig. 6. Standard Specimen ISO 527-2 for Tensile Test.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 7. Graph between load and extension for tensile testing for 2 specimens.
Each layer of ply is pressed by the roller after applying the resin over it so as to obtain better lamination over the contours and also remove the air between the layers. The plies are positioned with the help of masking tape.
The indicator is checked many times over the time to see that the pressure indicator reading is constant being brought down. Step 10: Remove the Pump and the Bagging film and all infusion mesh-
Step 7: Cut and position the Infusion Mesh The infusion mesh is cut about the area under the sealant tape. This is taped with the masking tape over the sealant area. Step 8: Cut the bagging film oversize of the sealant area The bagging film is cut bigger to allow for pleating so when vacuum is created, it does not stick or hinder with the reinforcement. This film is sealed with a layer of sealant tape applied with the film and then onto the previous sealant tape applied at the start. Step 9: Connect the pump with the hoses and connector to the bagging film The pump is connected to the mains supply. Connector is clamped on the bagging film and hoses connected to it and other end to the pump. Pump is switched on and it is allowed to run for 10 min. Careful monitoring is done to prevent any leakage from the bag.
The hose is connected from the connector and the pump. The bagging is removed film by removing the tapes. To get rid of the infusion mesh, masking tapes are removed. Step 11: Cure the reinforcement and remove the plies The reinforcement is allowed to cure overnight. Then the peel plies are removed from the reinforcement. Step 12: Trim the edges and clean the plate The edges are trimmed and the obtained composite plate is cleaned (Fig. 5).
4. Results and discussion The following tests have been performed to find the effects of varying thickness on different properties of the composite structure as per ISO/ASTM standard
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
6
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 6 Flexural test results. S. N.
Parameters
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
1 2 3
Peak load (N) Extension (mm) Flexural Strength N/mm2
369.87 11.490 48
6209.94 5.620 64
Fig. 8. Specimen for Flexural test.
1. 2. 3. 4. 5. 6.
Tensile Test Flexural Test Izod Impact Test Barcol Hardness Test Water Absorption Test Acid Corrosion Test
Table 7 Barcol hardness test results. Name of test
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
Barcol Hardness
90
72
4.1. Tensile Test (ISO 527-2002) To find the tensile strength of the newly developed composite structures, two specimens, one from each structure as per dimension of ISO 527–2 Point were prepared. UTM (Enkay, 20000 kg) was used for testing of the material (Fig. 6). RESULT – (Tables 4 and 5 and Fig. 7).
Table 8 Izod test result. Name of test
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
Izod Impact strength, Kj/m2
21.3
22.6
4.2. Flexural Test
4.3. Barcol Hardness (ASTM-D2583-1981)
Specimen use for flexural test was designed according to ISO (1172–1996) standard (Figs. 8 and 9, Table 6).
Hardness is a characteristic of a material, not a fundamental physical property. It is defined as the resistance to indentation,
Fig. 9. Graphs for Flexural Testing for 3 mm & 5 mm Core Thickness.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
7
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
(%) CHANGE IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 5.2%. (%) CHANGE IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 0.75%
Fig. 10. Specimen for water absorption test.
Table 9 Water absorption test result. S. No
Time (In Hours)
Weight (In gram) Specimen 1 (Core Thickness 3 mm)
Weight (In gram) Specimen 2 (Core Thickness 5 mm)
1 2 3 4 5 6 7
00 24 48 72 96 120 144
1.9200 2.0710 2.0300 2.0601 2.0301 2.0300 2.0201
2.8101 2.8112 2.8131 2.8203 2.8312 2.8312 2.8313
and it is determined by measuring the permanent depth of the indentation. Barcol Hardness Testing Machine was used to determine the Barcol Hardness of the specimens (Table 7).
In this work we find that the weight of the specimen is was varying continuously with time. Basalt and carbon fiber absorb water as the time passes but it is also noticed that the initial and final weight of the specimen have very small variation which can be neglected and our specimen can survive in humid environment for a long time (Fig. 11). 4.6 Acid corrosion test In the present work our aim to find out the survival of our composite in corrosive environment that help to predict the life of composite in different corrosive environment. A solution of 50% sulphuric acid was prepared. After this the specimen was dipped into the solution and leaved for the next measurement. This process was repeated continuously for next 6 days and readings were taken after every 24 h (Fig. 12 and Table 10). (%) REDUCTION IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1) --- 11.76%. (%) REDUCTION IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 13.51%.
4.4. Izod Test Impact load (NOTCHED) (ISO 180-2000) Impact value-1.07 (Somya Technocrates make machine was used) (Table 8). 4.5. Water absorption test Moisture absorption studies were performed according to the ASTM D570 standards. The initial weights of the samples were taken and then after the samples were immersed into Distilled water. After 24 h, the samples were taken out from the water and surface moisture was removed. Subsequently the samples were reweighed to the nearest of 0.001 mg. The samples were regularly weighed over the interval 24, 48, 72, 96,120, 144 h respectively. The percentage change in weight or the weight of water gained is estimated as:
Wt Wo 100 W% ¼ Wo where, Wt = weight of sample at time t; Wo = initial weight of the sample and; W = weight of water absorbed (Fig. 10 and Table 9)
Fig. 12. Specimen after Acid Corrosion test.
Table 10 Acid Corrosion Test. S. No
Time (In Hours)
Weight (In gram) Specimen 1 (Core Thickness 3 mm)
Weight (In gram) Specimen 2 (Core Thickness 5 mm)
1 2 3 4 5 6 7
00 24 48 72 96 120 144
1.87 1.81 1.79 1.75 1.72 1.70 1.65
3.84 3.80 3.78 3.72 3.61 3.51 3.32
Fig. 11. Time Vs Weight Graph for Water Absorption Test.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
8
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 13. Time Vs Weight Graph for Acid Test.
Fig. 14. Comparison of results of two specimens.
Table 11 Summary of Results. S. N.
Test Performed
1
Tensile Strength (N/mm2)
2
Flexural Strength (N/mm2)
3
Hardness test (Barcol)
4
Izod Impact Test(Izod Impact strength, Kj/m2) Water Absorption Test(% Increase in Weight)
5
6
Alkali Test (% Reduction in Weight)
Standard Used
Results
Conclusion
SPECIMEN 1
SPECIMEN 2
ISO: 5272002 ISO-11721996
69
79.7▲
48
64▲
ASTMD25831981 ISO-1802000 –
90
72.
21.3
22.6▲
5.2
0.75.
–
11.7
13.5▲
The tensile strength of the specimen increases as we increases the thickness of the core i.e. kevlar Honeycomb core. The Flexural strength of the specimen increases as we increases the thickness of the core i.e. kevlar Honeycomb core. So it was observed from these two tests that the tensile and flexural strength of the composite increases as we increases the thickness of the core. It was also observed that the hardness of the composite decreases if the honeycomb core thickness is increased. Impact strength of the two samples is almost the same and it was observed that the core thickness is having less impact on the impact strength value. The 2 specimens have very small variation in weight, which can be neglected if the specimen is considered at individual level, but if we will consider the variation in water absorption capacity due to increased thickness, it was observed that the water absorption will be less at increased core thickness. The 2 specimens are very sensitive to the corrosion environment and we have observed that there is continuous reduction in weight. It also has been observed that the surface of the specimen is damaged due to the corrosion and the reduction of weight in both the samples is almost the same. So we can say that it’s a surface phenomenon and independent on the thickness of the core.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
The present work shows that our specimen is very sensitive to corrosion environment and continuous reduction in weight. It also has been observed that the surface of the specimen is damaged due to the corrosion (Fig. 13). 5. Conclusions It was observed from the past data that not much work has been found on Kevlar Honeycomb sandwich structures with carbon and basalt fiber as face plates. So we will try to find the effects on various properties of a Kevlar Honeycomb Composite structure by varying its core thickness. The aim of present work is to find out the behavior of hybrid composite of Honeycomb Kevlar, Basalt, Carbon fiber, on various scales like tensile strength, Flexural strength, indentation loading etc. The effect of alkali treatment, soil degradation and water absorption on the strength of hybrid composite is compared and discussed in detail for individual cases. The work is focused to understand the overall mechanical and physical behavior of Composite structure in a real world conditions. The following conclusions are drawn from the analysis on the basis of experimental results: (Fig. 14 and Table 11). Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
9
References [1] K. Kantha Rao, K. Jayathirtha Rao, A.G. Sarwade, M. Sarath Chandra, International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 3, May-Jun 2012, pp. 365-374. [2] Shan-shan Shi, Zhi Sun, Xiao-zhi Hu, Hao-ran Chen, Carbon-fiber and aluminum-honeycomb sandwich composites with and without Kevlar-fiber interfacial toughening, Compos. A Appl. Sci. Manuf. 67 (2014) 102–110, https:// doi.org/10.1016/j.compositesa:2014.08.017. [3] Uthirapathy Tamilarasan, Loganathan Karunamoorthy, Kayaroganam Palanikumar, Mechanical Properties Evaluation of the Carbon Fibre Reinforced Aluminium Sandwich Composites, Mat. Res. 18 (5) (2015) 1029–1037, https:// doi.org/10.1590/1516-1439.017215. [4] Girish Gautam, Gavendra Norkey, Arun Kumar Pandey (2017), Mechanical Characterization of Kevlar-29 Fiber Reinforced Polymer Composite, ELK Asia Pacific Journals – 978-93-85537-06-6, ARIMPIE -2017. [5] K.K. Herbert Yeung, K.P. Rao, Mechanical Properties of Kevlar-49 Fibre Reinforced Thermoplastic Composites, Polym. Polym. Compos. 20 (5) (2012) 411–424. [6] ‘‘A Review on studies of Finite Element Model Updating and Updating of Composite Materials” Varun Panwar, Prashant Gupta, Ashok K Bagha, Nitin Chauhan, Materials Today: Proceedings ,Volume 5, Issue 14, Part 2, 2018, Pp 27912-27918 [7] ‘‘Flax/Epoxy Composite Beams - Simulation of Flexural Stresses” R.T.Durai Prabhakaran, Graham A Ormondroyd, Guan Zhongwei, Materials Today: Proceedings, Volume 8, Part 3, 2019, Pp 760-768. [8] Joshua M. Lister, ‘‘Study the Effects of Core Orientation and Different Face Thicknesses on Mechanical Behavior of Honeycomb Sandwich Structures Under Three Point Bending” A Thesis Presented to ‘The Faculty of California Polytechnic State University, San Luis Obispo’ February 2014. [9] S.B. Akiwate, V.D. Shinde, ‘‘Development of Honeycomb Sandwich Structure for Aeronautical Flooring Components” Journal of Advances in Science and Technology Vol. 13, Issue No. 01, (Special Issue) March-2017, ISSN 22309659. Pp 186-192.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing Anil Kumar a,⇑, Surjit Angra b, A.K. Chanda c a
National Institute of Technology, Kurukshetra, India ME Department, NIT, Kurukshetra, India c MAE Department, G B Pant Government Engineering College, New Delhi, India b
a r t i c l e
i n f o
Article history: Received 29 July 2019 Received in revised form 11 October 2019 Accepted 20 November 2019 Available online xxxx Keywords: Composites Kevlar Honeycomb Mechanical properties Water absorption Test Soil degradation Test
a b s t r a c t This study presents the Experimental characterizations of composite sandwich structures needed to optimize structure design. We fabricated 2 composite sandwich structures; one is having a Kevlar Honeycomb Core of 3 mm thickness and another having a Kevlar Honeycomb Core of 5 mm thickness. Honeycomb sandwich panels had Carbon and Basalt fiber face sheets (2 layers of Carbon of 0.2 mm each and 1 layer of Basalt of 2.34 mm). The mechanical properties of the constituent materials were discovered experimentally using ASTM/ISO standards. After testing a comparison is made of the different properties achieved from the two different specimen having core thickness of 3 mm and 5 mm.by analysis it was observed that Tensile, Flexural and Impact strength increases with increase of core thickness but the hardness decreases. Also water absorption and acid corrosion test were done on two specimens and it was observed that the specimen having the higher thickness will absorb less water and surface destruction due to acid is almost the same in the two specimens. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Mechanical and Energy Technologies.
1. Introduction All composite materials consist of 2 or more materials and always contain an interface between these materials. A sandwich composite consists of honeycomb material having face sheet on the top and bottom sides. Composite materials may include aramid or Kevlar (very light), glass, Carbon (high strength) etc. Most matrix materials include Polymeric matrix’s (thermoplastic and thermosetting resins), Mineral matrix’s (silicon carbide, carbon), and metallic matrix’s (aluminum alloys, titanium alloys, and orientated eutectics). Composites allow for a weight reduction of 10–50% with equal or greater performance with a 10–20% decrease in material and comparatively less manufacturing cost. Composites have a good fatigue and corrosion resistance which leads to long term savings and a reduction in maintenance costs of the part.
Types of Composites The first way of classification is with respect to the matrix constituent-In this classification composite can be Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix Composites (CMCs). The second way of classification is with respect to the reinforcement form-This reinforcement can be fiber composites, laminar composites and particulate composites. Fiber Reinforced composites (FRP) can be define in two more way in which composite have discontinuous or continuous fibers. Methods of Composite Fabrication For creating polymeric composites, there are currently 3 different types of layups that are most commonly used in industry. 1. ‘‘Pre-Preg” layup Method- The most favored method is known as ‘‘Pre-preg” layup, which is a composite that has had the resin pre-impregnated into the composite when it is initially created. 2. ‘‘Wet-Layup” Method -The second method is known as the ‘‘wet-layup” involves taking dry fibers and ingraining resin by hand, before curing.
⇑ Corresponding author. E-mail address: [email protected] (A. Kumar). https://doi.org/10.1016/j.matpr.2019.11.242 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Mechanical and Energy Technologies.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
2
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
3. Resin Infusion or Vacuum Assisted Transfer-Molding System (VARTM) – This method uses a vacuum to pull resin across a composite part, whilst also infusing the fibers with the resin. Honeycomb sandwich panels were one of the outcomes of research into decreasing structural mass. Sandwich panel structures consist of two thin face sheets on the top and bottom of a shear resistant lightweight core. The relative separation of the stable face sheets result in high stiffness to weight ratios. Essentially the honeycomb was used as a shear web between two upper and lower skins. With the development of Epoxy resin, it was possible to bond aluminum skins to an aluminum honeycomb core, which occurred in 1954. Since then, much advancement has been made in honeycomb studies, with the most commonly used honeycomb for aircraft structures being Nomex Honeycomb [9]. Composite panels are designed to meet the application requirements. They have the same normal strengths that composites have, due to the face sheets being constructed from materials of high modulus of elasticity’s (when compared with the core) like fiber-resin mixtures, metal alloys and plastics. The cores have low elastic moduli that yield without failure in the high deflection regimes [8]. K. Kantha Ra et al. [1] constructed a sandwich, which consists of two thin facing layers separated by a thick core, offers various advantages for design of weight critical structure. Depending on the specific requirements of the structures, aluminum alloys, high tensile steels, titanium or composites are used as the material of facings skins. They theoretically made Strength Analysis on Honeycomb Sandwich Panels of different materials. Shan-shan Shi et al. [2] investigated the Interfacial bonding, essential to carbon-fiber and Al-honeycomb sandwich composites under bending and uni-axial compression. They observed that the adhesive joint, in-situ formed from resin and short Kevlar fibers at the interface effectively became a composite. The peak load and energy absorption of the sandwich composites, with and without the short Kevlar fiber interfacial toughening, were compared with predictions from analytical models. Uthirapathy Tamilarasana et al., [3] found the various properties such as flexural, tensile and impact value of fabricated Carbon fiber reinforced AL sandwich laminates. All the tests are carried out as per ASTM standard. Scanning Electron Microscope (SEM) analysis is carried out to investigate the structure of the sandwich laminates. Girish Gautam et al., [4] examines the tensile, flexural and impact strength of Kevlar 29 (K-29) fiber reinforced polymer composite. The composite samples used in this study were prepared by hand lay-up technique. The acquired results showed that developed Kevlar-29 fiber reinforced polymer composite has good tensile, flexural and impact strength.
K.K. Herbert Yeung et al. [5] choose Kevlar as a strenghting material in their study. In this study Kevlar is inserted with carbon fiber to make a composite. They found that this composite provide a very high compressive and tensile strength as compare to a carbon fiber and it was conclude that Kevlar have high compressive and tensile strength as compare to carbon fiber. Varun Panwar et al. [6] reviewed FEM updating and updating of composite sandwich related studies. They wanted to find the different techniques used in updating of the material’s parameter, the limitations involved with these techniques and the different assumptions while making the experiments. They found that the different studies on elimination of error from experimental model and FE model are available and the issues arrived from parameterization and regularization. R.T.Durai Prabhakaran et al. [7] were keen to know the behaviour of flax fibre layups and orientation affect of laminated composites in bending loading. They used different orientations (Unidirectional [00]2S, cross-ply [0/90]S, and angle-ply [+45/45]S ) to study flexural stresses and mid-span deflections. They used the Classical Beam Theory (CBT) are to obtain analytical solutions, and then compared the CBT based results with results finite element simulation results. They found good agreement in these two types of results. It was found that from this past data that carbon fiber, Basalt have properties (Basalt have great bonding and tensile strength, carbon fiber have compressive strength) which is used to produce composite to get desired properties. we can use these fiber together with a Honeycomb structure of Kevlar to produce a composite which can have very fine compressive, tensile strength, corrosive resistance and provide many improve property which can be used as a future material for purpose and also replace the metal used for these purpose. 2. Main objectives and scope of research Composite materials have a very long history. It was observed from the past data of composites that much research work has been done to get the desired properties of the composite. Composite is very interesting topic for the scholars from the last few decades. But not much has been found on Kevlar Honeycomb sandwich structures with carbon and basalt fiber as face plates. So we will try to find the effects on various properties of a Kevlar Honeycomb Composite structure by varying its core thickness. The main objective of this study is to analyse the effects on various properties of a composite structure, having a Kevlar Honeycomb core, by varying its core thickness. Fabrication and testing of sandwich honeycomb kevlar composite under various regimes of load are done to determine the strength of composite material under different regimes of load.
Fig. 1. Example of how honeycomb stiffens a structure without materially increasing its weight.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
3
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Design of Basalt fiber.
3. Composite fabrications We fabricated 2 composite structures having; one having a Kevlar Honeycomb Core of 3 mm thickness and another having a Kevlar Honeycomb Core of 5 mm thickness. The face sheets and the epoxy in both the structures will remain same and consists of Carbon and Basalt fibers (2 layers of Carbon of 0.2 mm each and 1 layer of Basalt of 2.34 mm) and in same sequence (Fig. 2).
Fiber type
Wrap Wrap
Woven pattern Linear density (10 mm) Size (mm) Area weight (g/m2)
Wrap Welt Thickness
6K 6K plain 4K 0.38 320
3.1. Manufacturing route and procedure Technical Data Sheet of Matrix used Basalt Fiber Fabric 320 GSM Plain (Table 1) Technical Datasheet – Carbon Woven Reinforcement Fabric 200 GSM – 2X2 Twill Woven Carbon Fabric (Table 2) Technical Datasheet – PK2 Kevlar N636 Para-Aramid Fiber Honeycomb Cell Sizes : 1/800 3/1600 Densities : 2.0 pcf 6.0 pcf Sheet ‘‘Ribbon” (L) : 48‘‘ typical Sheet ‘‘Transverse” (W) : 96‘‘ typical PK2 Kevlar honeycomb is specified as follows: Material – Cell Size – Density – Cell Configuration (Fig. 3) Curing of Epoxy with Hardener Mixing ratio 100: 18p.b.w Pot life at RT 1.5–2.5ours Curing at RT 16–24 h Post Curing at 70–80 °C 2 h (if required) in mold or conformer only to avoid warp edge. Properties:- (Table 3 and Fig. 4)
Table 2 Design of Carbon fiber and its properties. Fiber Properties Density Pgpcm3o Filament Diameter Pmmo Tensile Strength P MPa Tensile Modulus P GPa Elongation P%o Sizing
g58 7 345y –3y g55 Epoxy Compatible
4 Carbon Fibre Sheets 2 Basalt Fibre Sheets 1 Kevlar Honeycomb Sheet (3 mm/5mm) Step 2: Preparation of Epoxy Resin- Hardener Mixture Epoxy resin amounted to 300 ml is taken into a container. Hardener is added to this resin equal to 18% of quantity of resin (i.e. 0.18*300 = 54 ml). This mixture is continuously mixed for thorough lamination.
3.2. Steps used in fabrication of composite sandwich Step 3: Preparation of Mould/Work SurfaceHere we are using Wet Lay-up Method followed by VARTM Method for even spreading and mixing of the resin with the composite. Step 1: Cutting of Fibre Sheets With the help of special purpose scissors, we cut all the sheets in dimensions of 300 mm * 300 mm. Tolerance of 3–5 mm is taken on all the sides. So the overall dimension cut is 300 mm * 300 mm. Special care is being taken in cutting since the chances of damage of the fibres are high since the orientation of the fibrestructure is to be maintained. After the cutting process, we are now left with the following sheets (each of same dimensions) :
The work surface is thoroughly cleaned with a clean soft cloth. A release agent is applied on the surface to clear off the any minute debris left Then the surface is allowed to dry for a minute. Then with the help of a sealant tape, the work boundaries are made in such a way that a clearance of 200 min is provided on all sides. A layer of resin- hardener mixture (epoxy layer) is spread on the surface. Step 4: Layer Reinforcement onto the Surface First the Kevlar fibre is spread on the epoxy layer.
Fig. 2. Composite Structure Design.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
4
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 3. PK2 Kevlar honeycomb Specification.
Table 3 Properties of Epoxy with Hardener. HDT Flexural Strength Compressive strength Tensile strength Impact strength
Table 4 Load VS Extension for Tensile test. oC Psi Psi Psi lb/in
95 17,000 16,000 10,300 0.45
Load (N)
0 750 1500 2250 3000 3750 4296.22 4500 5250 6000 6750 7500 8250 9000 9546.78
EXTENSION (MM) Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
0 1.75 2 2.35 2.5 2.65 3 3.5 4 4.5 4.8 5.5 6 6.75 8.09
0 0.35 0.8 1.1 2.9 3 3.76 – – – – – – –
Fig. 4. Reinforcing the Kevlar with Epoxy Resin. Table 5 Results of Tensile test.
Fig. 5. Layer by Layer Enforcement.
S. N.
Parameters
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
1 2 3
Peak load (N) Extension (mm) Tensile Strength N/mm2
9546.78 8.09 69.0
4296.22 3.76 79.7
After this, we put sufficient resin; the whole reinforcement is lifted and turned upside down. Same process is repeated again and again by putting a layer of Basalt fibre and 2 layers of Carbon fibre. Step 5: Tape the Reinforcement-
With the application of brush, resin mixture is applied on the fibre, first horizontally and then vertically on the surface. Brush is dabbed on the surface so as to impregnate the surface entirely. A layer of Basalt fibre is spread on the Kevlar layer. The resin is applied with the brush in the same manner. Small pressure is applied by a roller tool to remove the air between the layers. subsequent layers of Carbon fibre are applied in the same manner on top of the Basalt layer.
After layering the fibre sheets one over the, masking tape is used to make sure that the reinforcement stays in place while the bagging material is added. Step 6: Cut and position the Peel Ply over the Reinforcement Several layers of peel ply are cut about the size of the working surface and subsequent plies are placed one over another.
Fig. 6. Standard Specimen ISO 527-2 for Tensile Test.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 7. Graph between load and extension for tensile testing for 2 specimens.
Each layer of ply is pressed by the roller after applying the resin over it so as to obtain better lamination over the contours and also remove the air between the layers. The plies are positioned with the help of masking tape.
The indicator is checked many times over the time to see that the pressure indicator reading is constant being brought down. Step 10: Remove the Pump and the Bagging film and all infusion mesh-
Step 7: Cut and position the Infusion Mesh The infusion mesh is cut about the area under the sealant tape. This is taped with the masking tape over the sealant area. Step 8: Cut the bagging film oversize of the sealant area The bagging film is cut bigger to allow for pleating so when vacuum is created, it does not stick or hinder with the reinforcement. This film is sealed with a layer of sealant tape applied with the film and then onto the previous sealant tape applied at the start. Step 9: Connect the pump with the hoses and connector to the bagging film The pump is connected to the mains supply. Connector is clamped on the bagging film and hoses connected to it and other end to the pump. Pump is switched on and it is allowed to run for 10 min. Careful monitoring is done to prevent any leakage from the bag.
The hose is connected from the connector and the pump. The bagging is removed film by removing the tapes. To get rid of the infusion mesh, masking tapes are removed. Step 11: Cure the reinforcement and remove the plies The reinforcement is allowed to cure overnight. Then the peel plies are removed from the reinforcement. Step 12: Trim the edges and clean the plate The edges are trimmed and the obtained composite plate is cleaned (Fig. 5).
4. Results and discussion The following tests have been performed to find the effects of varying thickness on different properties of the composite structure as per ISO/ASTM standard
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
6
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 6 Flexural test results. S. N.
Parameters
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
1 2 3
Peak load (N) Extension (mm) Flexural Strength N/mm2
369.87 11.490 48
6209.94 5.620 64
Fig. 8. Specimen for Flexural test.
1. 2. 3. 4. 5. 6.
Tensile Test Flexural Test Izod Impact Test Barcol Hardness Test Water Absorption Test Acid Corrosion Test
Table 7 Barcol hardness test results. Name of test
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
Barcol Hardness
90
72
4.1. Tensile Test (ISO 527-2002) To find the tensile strength of the newly developed composite structures, two specimens, one from each structure as per dimension of ISO 527–2 Point were prepared. UTM (Enkay, 20000 kg) was used for testing of the material (Fig. 6). RESULT – (Tables 4 and 5 and Fig. 7).
Table 8 Izod test result. Name of test
Specimen 1 (Core Thickness 3 mm)
Specimen 2 (Core Thickness 5 mm)
Izod Impact strength, Kj/m2
21.3
22.6
4.2. Flexural Test
4.3. Barcol Hardness (ASTM-D2583-1981)
Specimen use for flexural test was designed according to ISO (1172–1996) standard (Figs. 8 and 9, Table 6).
Hardness is a characteristic of a material, not a fundamental physical property. It is defined as the resistance to indentation,
Fig. 9. Graphs for Flexural Testing for 3 mm & 5 mm Core Thickness.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
7
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
(%) CHANGE IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 5.2%. (%) CHANGE IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 0.75%
Fig. 10. Specimen for water absorption test.
Table 9 Water absorption test result. S. No
Time (In Hours)
Weight (In gram) Specimen 1 (Core Thickness 3 mm)
Weight (In gram) Specimen 2 (Core Thickness 5 mm)
1 2 3 4 5 6 7
00 24 48 72 96 120 144
1.9200 2.0710 2.0300 2.0601 2.0301 2.0300 2.0201
2.8101 2.8112 2.8131 2.8203 2.8312 2.8312 2.8313
and it is determined by measuring the permanent depth of the indentation. Barcol Hardness Testing Machine was used to determine the Barcol Hardness of the specimens (Table 7).
In this work we find that the weight of the specimen is was varying continuously with time. Basalt and carbon fiber absorb water as the time passes but it is also noticed that the initial and final weight of the specimen have very small variation which can be neglected and our specimen can survive in humid environment for a long time (Fig. 11). 4.6 Acid corrosion test In the present work our aim to find out the survival of our composite in corrosive environment that help to predict the life of composite in different corrosive environment. A solution of 50% sulphuric acid was prepared. After this the specimen was dipped into the solution and leaved for the next measurement. This process was repeated continuously for next 6 days and readings were taken after every 24 h (Fig. 12 and Table 10). (%) REDUCTION IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1) --- 11.76%. (%) REDUCTION IN WEIGHT AFTER 144 HOURS (FOR SPECIMEN 1)--- 13.51%.
4.4. Izod Test Impact load (NOTCHED) (ISO 180-2000) Impact value-1.07 (Somya Technocrates make machine was used) (Table 8). 4.5. Water absorption test Moisture absorption studies were performed according to the ASTM D570 standards. The initial weights of the samples were taken and then after the samples were immersed into Distilled water. After 24 h, the samples were taken out from the water and surface moisture was removed. Subsequently the samples were reweighed to the nearest of 0.001 mg. The samples were regularly weighed over the interval 24, 48, 72, 96,120, 144 h respectively. The percentage change in weight or the weight of water gained is estimated as:
Wt Wo 100 W% ¼ Wo where, Wt = weight of sample at time t; Wo = initial weight of the sample and; W = weight of water absorbed (Fig. 10 and Table 9)
Fig. 12. Specimen after Acid Corrosion test.
Table 10 Acid Corrosion Test. S. No
Time (In Hours)
Weight (In gram) Specimen 1 (Core Thickness 3 mm)
Weight (In gram) Specimen 2 (Core Thickness 5 mm)
1 2 3 4 5 6 7
00 24 48 72 96 120 144
1.87 1.81 1.79 1.75 1.72 1.70 1.65
3.84 3.80 3.78 3.72 3.61 3.51 3.32
Fig. 11. Time Vs Weight Graph for Water Absorption Test.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
8
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 13. Time Vs Weight Graph for Acid Test.
Fig. 14. Comparison of results of two specimens.
Table 11 Summary of Results. S. N.
Test Performed
1
Tensile Strength (N/mm2)
2
Flexural Strength (N/mm2)
3
Hardness test (Barcol)
4
Izod Impact Test(Izod Impact strength, Kj/m2) Water Absorption Test(% Increase in Weight)
5
6
Alkali Test (% Reduction in Weight)
Standard Used
Results
Conclusion
SPECIMEN 1
SPECIMEN 2
ISO: 5272002 ISO-11721996
69
79.7▲
48
64▲
ASTMD25831981 ISO-1802000 –
90
72.
21.3
22.6▲
5.2
0.75.
–
11.7
13.5▲
The tensile strength of the specimen increases as we increases the thickness of the core i.e. kevlar Honeycomb core. The Flexural strength of the specimen increases as we increases the thickness of the core i.e. kevlar Honeycomb core. So it was observed from these two tests that the tensile and flexural strength of the composite increases as we increases the thickness of the core. It was also observed that the hardness of the composite decreases if the honeycomb core thickness is increased. Impact strength of the two samples is almost the same and it was observed that the core thickness is having less impact on the impact strength value. The 2 specimens have very small variation in weight, which can be neglected if the specimen is considered at individual level, but if we will consider the variation in water absorption capacity due to increased thickness, it was observed that the water absorption will be less at increased core thickness. The 2 specimens are very sensitive to the corrosion environment and we have observed that there is continuous reduction in weight. It also has been observed that the surface of the specimen is damaged due to the corrosion and the reduction of weight in both the samples is almost the same. So we can say that it’s a surface phenomenon and independent on the thickness of the core.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242
A. Kumar et al. / Materials Today: Proceedings xxx (xxxx) xxx
The present work shows that our specimen is very sensitive to corrosion environment and continuous reduction in weight. It also has been observed that the surface of the specimen is damaged due to the corrosion (Fig. 13). 5. Conclusions It was observed from the past data that not much work has been found on Kevlar Honeycomb sandwich structures with carbon and basalt fiber as face plates. So we will try to find the effects on various properties of a Kevlar Honeycomb Composite structure by varying its core thickness. The aim of present work is to find out the behavior of hybrid composite of Honeycomb Kevlar, Basalt, Carbon fiber, on various scales like tensile strength, Flexural strength, indentation loading etc. The effect of alkali treatment, soil degradation and water absorption on the strength of hybrid composite is compared and discussed in detail for individual cases. The work is focused to understand the overall mechanical and physical behavior of Composite structure in a real world conditions. The following conclusions are drawn from the analysis on the basis of experimental results: (Fig. 14 and Table 11). Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
9
References [1] K. Kantha Rao, K. Jayathirtha Rao, A.G. Sarwade, M. Sarath Chandra, International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 3, May-Jun 2012, pp. 365-374. [2] Shan-shan Shi, Zhi Sun, Xiao-zhi Hu, Hao-ran Chen, Carbon-fiber and aluminum-honeycomb sandwich composites with and without Kevlar-fiber interfacial toughening, Compos. A Appl. Sci. Manuf. 67 (2014) 102–110, https:// doi.org/10.1016/j.compositesa:2014.08.017. [3] Uthirapathy Tamilarasan, Loganathan Karunamoorthy, Kayaroganam Palanikumar, Mechanical Properties Evaluation of the Carbon Fibre Reinforced Aluminium Sandwich Composites, Mat. Res. 18 (5) (2015) 1029–1037, https:// doi.org/10.1590/1516-1439.017215. [4] Girish Gautam, Gavendra Norkey, Arun Kumar Pandey (2017), Mechanical Characterization of Kevlar-29 Fiber Reinforced Polymer Composite, ELK Asia Pacific Journals – 978-93-85537-06-6, ARIMPIE -2017. [5] K.K. Herbert Yeung, K.P. Rao, Mechanical Properties of Kevlar-49 Fibre Reinforced Thermoplastic Composites, Polym. Polym. Compos. 20 (5) (2012) 411–424. [6] ‘‘A Review on studies of Finite Element Model Updating and Updating of Composite Materials” Varun Panwar, Prashant Gupta, Ashok K Bagha, Nitin Chauhan, Materials Today: Proceedings ,Volume 5, Issue 14, Part 2, 2018, Pp 27912-27918 [7] ‘‘Flax/Epoxy Composite Beams - Simulation of Flexural Stresses” R.T.Durai Prabhakaran, Graham A Ormondroyd, Guan Zhongwei, Materials Today: Proceedings, Volume 8, Part 3, 2019, Pp 760-768. [8] Joshua M. Lister, ‘‘Study the Effects of Core Orientation and Different Face Thicknesses on Mechanical Behavior of Honeycomb Sandwich Structures Under Three Point Bending” A Thesis Presented to ‘The Faculty of California Polytechnic State University, San Luis Obispo’ February 2014. [9] S.B. Akiwate, V.D. Shinde, ‘‘Development of Honeycomb Sandwich Structure for Aeronautical Flooring Components” Journal of Advances in Science and Technology Vol. 13, Issue No. 01, (Special Issue) March-2017, ISSN 22309659. Pp 186-192.
Please cite this article as: A. Kumar, S. Angra and A. K. Chanda, Analysis of the effects of varying core thicknesses of Kevlar Honeycomb sandwich structures under different regimes of testing, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.11.242