A simple stress-based failure criterion for predicting unfolding failure

Abstract

Corners of highly curved composite laminates experience unfolding failure when they are loaded under opening bending moments. This work provides a comprehensive experimental test campaign and a detailed stress analysis to gain insight into the different failure mechanisms occurring in curved CFRP laminates made from three different thermoset materials. Two distinct failure mechanisms are observed: firstly, traditional unfolding failure, occurring in unidirectional curved composite laminates exhibiting pure interlaminar delamination associated to the maximum interlaminar stresses in the curved region and, secondly, induced unfolding failure occurring in multi-directional curved composite laminates, where the failure is assumed to be originated from intralaminar matrix cracks which, under the presence of high interlaminar stresses, further propagate as an interlaminar delamination. A simple stress-based failure criterion is proposed to predict the unfolding failure load which provides a fairly good agreement with the experimental results in all cases.