Non-linear Behavior of Polymer Based Composite Laminates under Cyclic Thermal Shock and Its Effects on Residual Stresses
The residual stresses in composite laminates depend on several factors including the conditions of fabricating process, property of materials, direction and lay-ups of the layers. However the thermo-elastic behavior of composite is one of the most important parameters affecting the magnitude of residual stresses. The elastic properties and residual stresses do not remain constant under cyclic thermal loading and vary in a non-linear manner. The study of these non-linear variations of modulus and strength and their effects on residual stresses in laminates while experiencing thermal load cycles is the main goal of this paper. An experimental device is designed and manufactured conveniently to exert defned thermal load cycles with different temperatures and cycle time on composite laminates. Then orthotropic glass-epoxy composite laminates made by hand lay-up are tested under cyclic thermal loading. The elastic modulus and fracture strength of the samples are measured before and after experiencing defned number of thermal shocks. The residual stresses in composite laminates are calculated and compared based on the actual behavior of composite and by means of a modifed classical laminate theory. The results of this study demonstrate that the non-linear behavior of composites infuences the residual stresses signifcantly. In addition, if the sample becomes more brittle, the residual strains remain constant; while the elasticity modulus and residual stresses decrease.