Effect of Fiber Orientation on Interlaminar Shear Strength of GFRP Composites

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1 Effect of Fiber Orientation on Interlaminar Shear Strength of GFRP Composites Mahesh Chandrashekhar Swamy 1, Parmeshwar Patil 2, Shivaji D. Chame 3, 1 Associate Prof., Dept. of Mechanical Engg., M.S.Bidve Engg. College, Latur (SRTMU, Nanded) 2 Asst. Prof., Dept. of Mechanical Engg., G.N.D. Engg. College, Bidar (VTU, Belgavi) 3 PG Student, M.E. Machine Design, M.S.Bidve Engg. College, Latur (SRTMU, Nanded) Abstract This paper examines the influence of fibre orientation on ILSS properties of laminated composites. The specimens were made from three different fiber orientations (i) Bi woven glass fibers (ii) Unidirectional glass fiber or 1D and (iii) Bi directional glass fiber or 2D with thicknesses of 2mm. These specimens are subjected to bending loads causing shear stress in the structures. The purpose of this work is to experimentally analyse the progressive failure process of laminated composites subjected to shear loads. Shear loading causes stresses in the laminated composites, which vary through the thickness and also depends on the orientation of fibres. The result shows that, for same thickness unidirectional glass/epoxy composite laminates have more shear strength over other types of laminates. Keywords: Laminate; Shear Strength; Short beam test; three point bending. Introduction Composite materials have growing demand for applications in different areas like aerospace, automotive, marine, transportation and bridges in civil engineering. Structural composite is a mixture of two or more constituents (or phases) fiber and matrix with different physical/chemical properties at the macroscopic or microscopic scale. Fibers are the principal load-carrying constituents while the surrounding matrix helps to keep them in desired location and orientation and also act as a load transfer medium between them. The designers are in search of materials which withstand the effect of all variety of loading conditions and at the same time at a very competitive price. The composites are complex material and their properties vary as the NCADOMS-2016 Special Issue 1 Page 94

2 constituents change in any of its parameters like fiber orientation, stacking sequence, fiber volume fraction or the matrix and the method of fabrication. Hence, in the present paper an effort is made to characterize the composites by designing the testing equipments, test procedures and more importantly careful conduction of tests. Mr. B.V.Babukiran and Dr.G.Harish in their Research paper [1] studied the influence of thickness on shear properties of laminated composites. The bending properties of composite materials are often characterized with simply supported beams under concentrated loads. The horizontal shear test with a short-beam specimen in three-point bending appears suitable as a general method of evaluation for the shear properties in fiber-reinforced composites because of its simplicity. In the experimental part of this work, the shear strength of glass fiber-epoxy, Graphite fiber- Epoxy & Carbon fiber epoxy laminated composite material were investigated with different thickness under three-point-bending test (Short beam Test).This paper examines the influence of thickness on ILSS properties of laminated composites. Many structures used in Automobile, Aerospace, Naval and other Transportation vehicle structural parts are subjected to various kinds of loads. These structures are further subjected to bending loads causing Shear stress in the structures. The purpose of this work is to experimentally analyze the progressive failure process of laminated composites subjected to shear loads, Shear loading causes stresses in the composites, which vary through the thickness. Mr. Prashant Turla et al [2] studied the inter laminar shear strength (ILSS) of glass and carbon fiber reinforced epoxy matrix hybrid composite and to know the influence of glass and carbon fibers individually on ILSS carbon fiber epoxy composite and glass fiber epoxy composite were also prepared and studied extensively. The results show that the ILSS of hybrid composite is significantly improved as compared to glass fiber reinforced composite / carbon fiber reinforced composite. E. Sideridis, G. A. Papadopoulos [3] studied shear and flexural properties in unidirectionalfiber-reinforced epoxy composites. In the experimental part of this work, the shear strength of unidirectional-glass-fiber reinforced epoxy resin composites was determined in different fiber NCADOMS-2016 Special Issue 1 Page 95

3 directions with the short-beam three-point-bending test. Also, the elastic constants and flexural properties of the same materials were determined from bending experiments carried out on specimens in the various directions from 0 to 90 fiber directions with high span thickness ratios. According to A. Agirregomezkorta et al [4] the inter laminar shear strengths of carbon fiber reinforced pcbt and epoxy matrix composites molded by VA-RTM have been characterized at quasi-static and low energy impact tests. pcbt composites show higher damaged volume but lower inter laminar shear strength, which could be a consequence of its lower tensile strength and higher void content. Inter laminar shear strength has found to be strain rate dependent for both composites. Relationship between voids and inter laminar shear strength of polymer matrix composites was investigated by Kenneth J. Bowles and Stephen Frimpong [5], Lewis Research Center, Cleveland, Ohio. The results of these tests were evaluated by using ultrasonic results, photomicrographs, statistical methods, theoretical relationships derived by other investigators, and comparison of the test data with the Integrated Composite Analyzer (ICAN) computer program developed at the Lewis Research Center for predicting composite ply properties. Jeevan Ealias et al [6] have worked on causes of de lamination in Composite structures. Composite s find many useful applications in the field of aerospace, civil infrastructure and construction. De-lamination is one of the major failure modes. Inter-laminar shear stresses are the source of failure, unique in composite structures. The presence of inter-laminar shear stress at the interface leads to de-lamination, if it exceeds beyond its strength and hence reduces the strength of structural component. Inter-laminar shear stress arises due to various reasons. All layers may have different properties depending upon the selection of fibers in lamina as well as its orientation. Inter-laminar shear stress is the out of plane stress z, xz and yz at the interface between layers in laminated composite structures. Inter-laminar shear stress would tend to delaminate at the interface. Classical laminate theory (CLT) assumed that components of all out of plane stress are zero. An appropriate evaluation of inter-laminar shear stress leads to an accurate prediction of failure mechanism which is a challenging task for researchers and NCADOMS-2016 Special Issue 1 Page 96

4 analysts. The study focuses for the determination of inter-laminar shear stress of composite structures. The most direct way to predict inter-laminar shear stress using solid element but is very computation intensive. Layered shell elements are used for relatively thin structures. Layered solid element is used for thick structures but it has its own limitations. A case study is carried out to compare afore mentioned three approaches. The solution for the interlaminar shear stress distribution in an adhesive layer within a bonded structure is highly complex. The objective of the present study is to characterize E- glass/epoxy laminates for interlaminar shear strength and to determine the effect of fiber orientations on interlaminar shear strength. Materials and Processing The material and their properties selected for the study are listed in table.1 given below: Properties Reinforcing material Matrix material Hardener E-glass fiber of 360GSM Bidirectional woven roving, 1D and 2D Epoxy Resin (LY556 [Araldite] Density 2.55 g/cm 3 Young s modulus 72 Gpa, Tensile strength 2.2 Gpa, Tensile Elongation 2.4 % Aspect (visual) clear, pale yellow liquid Viscosity at 25 C (ISO 9371B) [MPa s] Density at 25 C (ISO 1675) [g/cm 3 ] HY 951 [Aradur] At 20 0 C 1:1 in water Boiling point > 200 o C, Thermal decomposition > 200 o C, Flash point : C Density : 1 g/cm 3 Table.1 Materials and their properties The GFRP laminates are carefully fabricated by using hand lay-up technique of size 25cm X 25cm. The prepared laminates of E-glass/epoxy laminates are shown in Fig.1 NCADOMS-2016 Special Issue 1 Page 97

Bidirectional woven roving laminate 1D laminate 2D laminate (0-90 0 ) Fig.

specimens were prepared for ILSS as per ASTM standard D2344/2344M; calculations for specimen

Length of specimen = 6 x Thickness of laminate Specimen width B = 2 x Thickness of laminate

5 Bidirectional woven roving laminate 1D laminate 2D laminate ( ) Fig. 1: Fabricated laminates Preparation of samples for flexural test as per ASTM: D 790 The specimens were prepared for ILSS as per ASTM standard D2344/2344M; calculations for specimen size are as follows. The prepared specimens for ILSS are shown in figure 2. Length of specimen = 6 x Thickness of laminate Specimen width B = 2 x Thickness of laminate Specimens of unidirectional (1D&2D) fiber Bidirectional woven roving fiber with orientation NCADOMS-2016 Special Issue 1 Page 98

Fig. 2 Specimens for ILSS test Inter Laminar Shear Strength of Polymer Matrix Composites The inter-laminar shear strength (ILSS) is one of the most important parameters in determining the ability of

Inter laminar stresses are the source of failure mechanisms uniquely characteristic of composite materials; their existence is a major reason that laminated composites tend to delaminate near free

6 Fig. 2 Specimens for ILSS test Inter Laminar Shear Strength of Polymer Matrix Composites The inter-laminar shear strength (ILSS) is one of the most important parameters in determining the ability of a composite to resist de-lamination damage. There is much confusion about what inter laminar stresses are and how to calculate them using composites analysis. Inter laminar stresses are the source of failure mechanisms uniquely characteristic of composite materials; their existence is a major reason that laminated composites tend to delaminate near free edges, such as an edge of a plate or around a hole. However, there seems to be a lot of misunderstanding of how to define inter laminar stresses and how to predict them using finite element analysis. Referring to the figure 3 inter laminar stresses are the out-of-plane stresses z, xz, and yz, defined at the interfaces between layers in a laminated composite material. From the figure, it is clear that a tensile stress z along an interface would tend to separate the layers along NCADOMS-2016 Special Issue 1 Page 99

7 the interface, and the inter laminar shear stresses would tend to shear apart the interface in the corresponding directions. Fig.3. Inter laminar shear strength Short-Beam Strength is calculated by using equation 1.1 as follows: Ʈ= 3P/4bd Where, Ʈ- Interlaminar Shear Stress in MPa. P- Peak load in Newton. b- Width of the Specimen in mm, and d- Thickness of the Specimen in mm. RESULTS AND DISCUSSION Interlaminar shear strength test of bidirectional woven rovings, unirectional (1D) and 2D ( ) of glass/epoxy for 2mm thick laminates were conducted in Raghavendra Laboratory, Bangaluru as per ASTM standard D23344/2344M maintaining the span length of 30 mm on KUDALE Make, Horizontal Tensometer machine of serial no. PC2000/599/6. The value of peak load for each specimen is noted on the machine and the interlaminar shear strength is calculated using equation number 1.1. Inter laminar shear strengh (ILSS) properties evaluated for six identical specimes of bidirectional woven rovings, unirectional (1D) and 2D ( ) of glass/epoxy for 2mm thick laminates. The average values of ILSS for each type of specimen are presented in table 2. NCADOMS-2016 Special Issue 1 Page 100

SL. Specimen Specimen Type NO. thichness, mm ILSS, MPa 1 Bidirectional woven rovings 2 13.460 2 unirectional (1D) 2 32.733 3 2D (0-90 0 ) 2 20.

8 SL. Specimen Specimen Type NO. thichness, mm ILSS, MPa 1 Bidirectional woven rovings unirectional (1D) D ( ) Table 2 ILSS results of composite laminates The results shows that, the maximum value of shear shtrengh is for unidirectional (1D) laminates of MPa and the minimum value is MPa for bidirectional woven roving laminate. The ILSS for 2D ( ) is MPa. Comparison of Inter laminar Shear Strength The comparison results for Bidirectional woven roving, 1D and 2D glass fiber / epoxy laminate is shown using bar graph in figure 4. From the graph, it is observed that, the ILSS for unidirectional (1D) fiber specimen is maximum as compared to other type of specimens. Fig. 4 Comparison of ILSS of laminates of 2 mm thick specimen NCADOMS-2016 Special Issue 1 Page 101

9 CONCLUSIONS Based on the experimental results of ILSS of glass/epoxy composite laminates of different fiber orientation, the following conclusions are drawn. The orientation of fiber has significant effect on the interlaminar shear strength of composite laminates Among the three types of fiber orientations, the unidirectional (1D) glass epoxy laminates are found to have more interlaminar shear strength than others. The bidirectional woven roving s glass epoxy laminates have least strengths among the three types.. REFERENCES [1] B.V.BabuKiran, Dr. G.Harish Influence of Thickness on Shear Properties of Laminated Composites INTERNATIONAL JOURNAL OF RESEARCH IN AERONAUTICAL AND MECHANICAL ENGINEERING (IJRAME) volume2,issue1,january2014,pp 54-60,ISSN (ONLINE): [2] Prashanth Turla, S. Sampath Kumar, P. Harshitha Reddy, K.Chandra Shekar, Interlaminar Shear Strength of Carbon Fiber and Glass Fiber Reinforced Epoxy Matrix Hybrid Composite. IJREAT International Journal of Research in Engineering & Advanced Technology, Volume 2, Issue 2, Apr-May, 2014.ISSN: [3] E. Sideridis, G. A. Papadopoulos,"Short-Beam and Three-Point-Bending Tests for the Study of Shear and Flexural Properties in Unidirectional-Fiber-Reinforced Epoxy Composites 19 Dec DOI /app Published online in Wiley InterScience. [4] A. Agirregomezkorta, J. Zurbitu, G. Aretxaga, M. Sarrionandia, J. Aurrekoetxea STRAIN RATE EFFECT ON INTERLAMINAR SHEAR STRENGTH OF CARBON FIBRE REINFORCED pcbt AND EPOXY COMPOSITES. Mechanical and Industrial Production Department, Mondragon Unibertsitatea, Mondragon, Spain [5] Kenneth J. Bowles and Stephen Frimpong, Relationship Between Voids and Interlaminar Shear Strength of Polymer Matrix Composites NASA Technical Memorandum Lewis Research Center Cleveland, Ohio36th International SAMPE Symposium and Exhibition NCADOMS-2016 Special Issue 1 Page 102

10 sponsored by the Society for the Advancement of Materials and Process Engineering San Diego, California, April 15-18, 1991 [6] Jeevan Ealias, Lalmoni, Jenny John Mattam, Study of Inter-laminar Shear stress of composite structures, International Journal of Emerging Technology and Advanced Engineering, Volume 3, Issue 8, August 2013, ISSN [7] Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials, ASTM: D [8] Standard Test Methods for-short Beam Strength of Polymer Matrix Composite Materials and Their Laminates, ASTM: D 2344/D 2344M-00 (Reapproved 2006) NCADOMS-2016 Special Issue 1 Page 103

EFFECTS OF MATRIX TYPES AND LOADING SPEED ON THE FAILURE BEHAVIOUR OF FRP COMPOSITES

For consideration of award of prizes EFFECTS OF MATRIX TYPES AND LOADING SPEED ON THE FAILURE BEHAVIOUR OF FRP COMPOSITES B. Das *, Dr. S. K. Sahu #, Dr. B. C. Ray $ * M.Tech. Student, # Asst. Prof., Deptt.