A Study on the Effect of Thickness and Stacking Sequence on the Stiffness of Composite Laminates Under Quasi-Static Loading

The quasi-static loading characteristics of symmetric carbon fibre-reinforced epoxy matrix composites loaded to a peak of 2500 N and then unloaded were evaluated in terms of the characteristics of the response, bending stiffness and energy consumed for lay-up configuration in the families of [0/90/±45]s , [±45/0/90]s and [0/90/0/90]s. The test samples were manufactured measuring 100 x 150 (mm) and during testing they were held firmly with toggle clamps on the support fixture placed on the bed of an instrumented Tinius Olsen universal testing 25ST machine. The macro-mechanical behaviour of laminates with respect to quantities of the laminate extensional and bending stiffness matrices were compared in relation to the experimentally obtained normalized plate bending stiffness; also, the energy absorbed quantities related to the bending stiffness of the different categories of the laminates. The results obtained reveal that the ratios of the extensional stiffness to the bending stiffness elements of the matrices are relevant quantities affecting the load – displacement plot, energy absorbed and the bending stiffness. Also, the increase in the number of surface cross plies in composites is a good approach to increase resistance to major damage for composite structures.