Behavior of laminated composites under monotonically increasing random load

A model using stochastic function theory is proposed to predict the behavior of laminated composites under random loads. Random in-plane loading is defined as a Gaussian process. A numerical procedure for predicting damage evolution and its effect on deformation history of laminated composites is developed. The probabilities of failure of a mesovolume at ply level are used in reducing ply stiffness. The probability of mesovolume failure is calculated based on the theory of excursions of random process beyond the limits. Fiber breakage, matrix failure in transverse direction, as well as matrix or interface shear cracking, are taken into account. The results of a numerical study of the effects of loading speed and dispersion on damage evolution and final failure of a Kevlar/epoxy laminated composite are presented as an illustration. Cases of tension, shear, and complex in-plane loading of the laminate are analyzed for a vast range of loading speeds. The results indicate that the laminate strength and failure strain are higher at higher loading speeds. The analytical results are qualitatively compared with the available experimental observations.