Interlaminar Stresses at a Hole in a Composite Member Subjected to In-Plane Loading

Abstract

This paper presents results from a numerical and experimental study of interlaminar stresses and damage in a 28-ply graphite/epoxy composite member with a 6 mm cir cular hole subjected to in-plane loading. The free span length and width of the specimen investigated were both 24 mm. The numerical results of a three-dimensional finite element analysis show that high interlaminar stress gradients occur at the intersections of the ply interfaces and the free edge. The largest positive value of the interlaminar normal stress, which is about 0.3 times the mean in-plane compressive stress, occurs perpendicularly to the loading direction at the hole boundary between the second and third plies. The experimental part of this study concerned damage detection for structural members subjected to compression fatique loading. Tetrabromoethane (TBE)-enhanced X-Ray techniques combined with sectioning of the samples showed that the damage consisted of transverse matrix cracks in the 0° plies at a tangent to the hole boundary and delamination at the hole boundary perpendicular to the loading direction. The transverse matrix cracks are attributed to the high in-plane shear stresses which must balance the axial stress concentration. The observed delamination damage is located in regions with the highest calculated positive interlaminar normal stress.