Interlaminar stresses in composite laminates with a circular hole

The purpose of this paper is to evaluate a recently developed analytical model by Ko & Lin which determines the interlaminar stress distributions around a circular hole in symmetric composite laminates under in-plane tensile loading. For this purpose, a three-dimensional finite-element (FE) analysis is performed and the stress distributions for symmetric cross-ply laminates are presented in three ways: through the thickness; along radial lines away from the hole; and around the hole. Because a mathematical interlaminar stress singularity is expected between the 0 degrees and 90 degrees plies at the hole, the computed normal stress sigma(z) and the shear stress tau(z0) are presented near but not at the hole edge. There is good qualitative agreement on tau(z0) but the FE results are considerably higher by a ratio of between 3 and 5 than those predicted by the Ko-Lin analysis. For sigma(z), again the FE values are considerably higher, but there is also poor qualitative agreement. The delamination initiation load and delamination location are predicted by using the FE and Ko-Lin stress results together with a quadratic failure criterion. (C) 1997 Elsevier Science Ltd.