Interlaminar Stresses Due to In-Plane Gradient Stress Fields

Abstract

Interlaminar stresses that arise in composite laminates where gradients exist in in-plane stress fields are investigated. Two distinct mechanisms give rise to interlaminar stresses in generic problems, the presence of free edges and in-plane gradients. It is shown that the latter mechanism should be considered separately from the former and that interlaminar stresses from such in-plane gradients can be significant. A methodology to approximate these stresses through direct integration of the equilibrium equations is presented. The methodology involves the use of closed-form expressions of the in-plane stress field obtained by solving two-dimensional elasticity problems using homogenized material properties. As an example, the methodology is applied to the case of a laminate with a circular hole through which the importance of interlaminar stresses from in-plane gradients is demonstrated. The results show that the characteristics of the interlaminar stresses from in-plane gradients are very different from those of interlaminar stresses arising from free edges. Specifically, the parameters that affect the decay rates and magnitudes of the interlaminar stresses from the two mechanisms are found to be different. The current investigation provides new insights into interlaminar stress problems, in general, and offers a simple method for calculating the interlaminar stresses due to in-plane gradients.