Delamination Onset and Growth Prediction of Advanced Composite Materials With a Fabrication Flaw

Abstract

The delamination failure mode is particularly significant in the damage tolerance design of advanced composite, since manufacturing flaws and in-service damage most often manifest themselves as interlaminar cracks. The primary goal of this paper is to evaluate the validity and accuracy of the developed cohesive interface model in predicting the fracture parameters at coupon and component level. To capture crack initiation and growth under mixed mode loading, a cohesive model based on a bi-linear constitutive material law is implemented in LSDYNA via a user-defined material model. The cohesive model parameters and the associated fracture toughness are determined for both primary and secondary bond coupons subjected to double cantilever beam and end notch flexure loading. An iterative solution procedure is used to determine the cohesive parameters by matching the failure load/displacement prediction with the observed test data. To explore the feasibility of using coupon level fracture parameters for fracture prediction at component level, the determined cohesive models are used to predict the critical failure load associated with delamination onset and growth of doubler specimens under axial and bending loads.