Stable crack growth and instability prediction in thin plates and cylinders

Many fracture applications require accurate prediction of the tearing resistance of thin metallic components. However, the three-dimensional (3D) nature of crack front advance is significant even in thin plates and requires special considerations for accurate predictions. An advanced fracture code, WARP3D, was used to model 3D effects and predict the large amounts of crack tearing preceding instability in flat plates and cylinders. In this work, the crack tearing resistance of thin plate aluminum alloy 2219-T87 fracture test specimens was measured experimentally. Finite element analysis (FEA) computations that modeled crack tunneling behavior were performed with WARP3D to determine a characteristic crack tip opening angle to match the observed tearing resistance behavior. Fracture predictions for the same thickness in a pressurized cylinder were then made using the calibrated values, and compared with results from tests and with uniform crack front FEA predictions. The experiments and calculations were performed for two thicknesses of material, the thinner one to verify the methodology, and a thicker one to predict critical crack length for the International Space Station modules.