A combined modeling-experimental study of the crack opening displacement fracture criterion for characterization of stable crack growth under mixed mode I/II loading in thin sheet materials

Recent experimental studies have shown that a critical Crack Opening Displa cement (COD) has the potential to be a viable parameter for predicting the onset of crack growth in thin sheet 2024-T3 aluminum under combined tension (mode I) and in-plane shear (mode II) loading conditions. To assess the vi ability of using a critical COD criterion for prediction of crack growth in components experiencing mixed mode loading, the enclosed work presents a c omplete set of simulation studies and experimental measurements for crack g rowth under nominally mode I/II conditions. For the first time, finite elem ent crack growth simulations under mixed mode I/II conditions have been per formed for the Arcan test specimen using recently measured crack growth pat h information and the load-crack extension data for the mode I/II experimen ts. Simulation results indicate that the predicted COD is in excellent agre ement with measurements. Specifically, simulation results indicate that (a) the magnitude of COD during simulated crack growth is nearly constant for Delta a > 5 mm; (b) for Phi less than or equal to 60 degrees, the predicted COD is primarily perpendicular to the crack path (i.e., mode I in nature); (c) for Phi > 60 degrees, the predicted COD is primarily parallel to the c rack path (i.e., mode II in nature); (d) near the transitional angle betwee n mode I and mode II fracture, the COD components are more unstable during the crack growth process and (e) simulation predictions for the strain fiel ds are in quantitative agreement with measurement. Taken together, the resu lts from the combined simulation-experimentation program provides strong ju stification for the use of a COD-based fracture criterion to predict crack growth in thin-sheet materials. (C) 2000 Elsevier Science Ltd. All rights r eserved.