Mechanisms and Structural Parameters Affecting the Interlaminar Stress Field in Laminates with Ply Drop-offs

Abstract

The mechanisms and structural parameters affecting the interlaminar stress field in laminates with ply drop-offs have been investigated to help better understand the effects of different parameters in such laminates. Based on equilibrium considerations, two fundamental mechanisms that give rise to interlaminar stresses have been identified: the termination effect, caused by the load transfer from the terminated ply group to the continuous ply groups; and the offset effect, caused by the redistribution of the load in the outer continuous ply groups through an offset in the through-thickness direction from the undropped region to the dropped region. The characteristics of the two mechanisms and the factors that affect the inter-laminar stress field caused by these mechanisms are described by considering two specific laminate configurations in which these mechanisms can be isolated. Factors of particular importance are the magnitudes of the far-field loads in the terminated and outer continuous ply groups, the offset distance, and the taper angle. Parametric studies of five factors are conducted via an analytical method for configurations under in-plane and bending loads to obtain general trends of the interlaminar stress field and a better understanding of the contributions of the two fundamental mechanisms. The structural parameters considered are the taper angle, the location of the terminated plies, the overall stiffness and layup sequence of the terminated ply group, and the number of terminated plies. The overall characteristics and trends of the interlaminar stresses can be explained easily in terms of the two fundamental mechanisms. The current study presents a clear view of the mechanisms giving rise to interlaminar stresses. Such a perception can be used to understand and anticipate interlaminar stress field trends in generic laminates with ply drop-offs in a simple and systematic manner. This can be particularly useful in preliminary design where these trends can be anticipated for the many configurations often under consideration, without performing actual analysis of these many potential configurations.