9 In-Situ Observation of Damage Evolution in Quasi-Isotropic CFRP Laminates 71 Fig. 9.4 (a) The shear contour with vertical line crossing all the plies, and Shear strain along the vertical line for different stresses (b) 0/ 45/90/C45, (c) 0/ 45/C45/90 and (d) 0/90/C45/ 45 respectively 9.4.3 Interlaminar Shear Strain As the arrangement plies changes in the laminate the interlaminar shear strain developed at the interfaces also varies. As shown in the Fig. 9.4, the quantity of the shear strain across all the interfaces are plotted. The plots for each laminate shows that there is a similarity on the interfaces where there is a significant interlaminar shear for the (0/90/C45/ 45) and (0/ 45/C45/90) laminates. In both laminates the highest interlaminar shear occurred at the interface of the C45/ 45 plies and this result agrees with different numerical and analytical models [6, 13]. However, for the (0/ 45/90/C45) laminate, there is no a direct contact between the C45ı and 45ı plies. Instead, the 90ı ply is located between them, then the interlaminar shear strain due to the C45ı and 45ı plies also distorts the 90ı ply. In addition, the matrix cracks in the 90ı ply propagated to the interfaces of the neighboring plies. As it reaches the interfaces, the tip of these angled matrix cracks brings additional interlaminar strains which initiates delaminating crack across the interface. Therefore, in the (0/ 45/90/C45) laminate the highest shear strain localisation occurs at the interfaces of C45/90 and 90/ 45 plies. The magnitude of the interlaminar shear strain in each laminate are seen to vary for the same amount of applied stress. The shear strain recorded for the (0/ 45/90/C45) laminate is much higher than the other laminates. Relatively close results are obtained for the (0/90/C45/ 45) and (0/ 45/C45/90) laminates. The load transfere in laminate is through a shear lagg at the interface, thus the higher the strength and stiffness of the interface the better the load transfer between plies [14]. The amount of shear strain localisations are related with the stiffness and the quantity of shear load transferred through the interface. Regarding the stiffness, it is highly influenced by the shear property of the individual plies that make up the
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