Ply cracking and property degradations of symmetric balanced laminates under general in-plane loading

Abstract The authors have previously proposed a method of using a resistance curve to characterize transverse crack multiplication in balanced symmetric laminates. The method was based on the concept of a through-the-thickness inherent flaw and energy balance principle. In the present paper, this model is further extended to shear and general in-plane loading conditions. The corresponding mechanical property degradations due to transverse ply cracking are also investigated. The effective longitudinal modulus and Poisson's ratio depend not only on the crack density but also on the thermal residual and applied stresses. The reason is that the cracks do not close tightly even upon unloading due to the residual stress. Experimental results for the mechanical property degradations correlate well with the analysis except for the shear modulus. The nonlinear behavior of the shear modulus should be considered for better correlation.