RESPONSE OF THERMOPLASTIC AND THERMOSETTING COMPOSITES UNDER COMPRESSIVE LOADING - AN EXPERIMENTAL AND FINITE-ELEMENT STUDY

The influence of long-term moisture exposure and temperature on the co mpressive properties of T-300/epoxy (thermosetting) and APC-2 (thermop lastic) composites has been studied. Specimens of quasi-isotropic conf iguration [45-degrees/90-degrees/-45-degrees/0-degrees]s were designed on the basis of the Euler buckling criterion, and a temperature range of 23-100-degrees-C was considered for both dry as well as wet tests. Specimens for wet tests were soaked in distilled water for a period o f 360 days, and the effects of moisture absorption on the compressive properties and geometry of the specimens were investigated. The result s of the investigation indicated that the moisture absorption rate of T-300/epoxy was higher than that of APC-2. It was noticed that the geo metry of the specimen influenced the moisture absorption rate. The thi ck plate with a smaller surface area absorbed less moisture than the t hin plate with a larger surface area. The compressive strength and mod ulus of APC-2 were found to be comparatively higher than that of T-300 /epoxy both in dry and wet conditions. The effect of moisture at 100-d egrees-C was negligible for both materials. The modes of failure in bo th materials under compressive load were found to be delamination, int erlaminar shear and end brooming. Thick laminates of thermoplastic com posites (APC-2) were modeled with isoparametric layered shell elements to predict the responses of the dry laminate at various temperatures under compressive loading. A large-displacement finite element analysi s was performed by considering the geometric non-linearities in the co mposite structure. Multiple load steps with linear material behavior w ere used to model the load-displacement characteristics found in the e xperimental study. The compressive response with respect of displaceme nts, normal stresses and interlaminar shear stresses under three diffe rent temperatures is presented. The laminate response along the length as well as through the thickness is also presented, to analyze and un derstand the failure mechanisms under such loading. Experimental data were compared with the FEM results to test the accuracy of the finite element analysis (FEA) using the layered shell element under the assum ption of first-order shear-deformation theory. A reasonably good corre lation between FEA and experimental results was found.