Delamination initiation of laminates with pin-loaded holes

A finite element analysis is conducted to determine the three-dimensional stress field in a composite laminate with a pin-loaded hole. The accuracy of computation is established by comparison with the strain gauge measurements near and away from the hole boundary. An acoustic emission technique was used to determine the initial failure load as the specimen was subjected to a quasi-static loading rate. Specimens were examined between the load steps using radiography and micrography in order to detect delamination initiation. The delamination initiation site and the corresponding load level are predicted by applying the strain energy density criterion. The critical parameters were extracted from the experimental measurements and finite element analysis of a double cantilever beam specimen. The analysis predictions indicate that delaminations could initiate close to the free surface at the interface between layers with a fiber orientation of ±45° relative to the load direction. These predictions confirm the experimental observations.