Effect of Stacking Sequence and Lay-Up Angle on Free Edge Stresses Around a Hole in a Laminated Plate Under Tension

Abstract

One mode of failure in fiber reinforced laminated plates is delamination initiating at a free edge. Experimental results and theoretical stress investi gations found in the literature indicate that the interlaminar normal stress, σ _z, is a factor in this mode of failure. In this paper, the stress behavior around a circular hole in a laminated plate is investigated using a three- dimensional finite element stress analysis. First, computed results for the tangential strain distribution around a circular hole for a (0/±45/0) _s lamin ate under uniaxial loading are compared with laboratory data to provide a level of confidence in the analysis. Next, attention is focused on the inter laminar normal stress distribution around the free edge of the circular hole and the effects of changes in stacking sequence and lay-up angle. Initially, laminates with stacking sequences of (0/90) _s are analyzed. Graphite/epoxy laminates of the type (0₂/±θ/∓θ) _S, (±θ/∓θ/0 ₂) _S, (90₂/±θ/∓θ) ₂ , and (±θ/∓θ/90₂) _S where θ is 30° , 45°, and 60° are also considered. Each lamin ate is subjected to a uniaxial stress loading distant to a hole.