Validation of the Two-Parameter Fracture Criterion using 3D finite-element analyses with the critical CTOA fracture criterion

A Two-Parameter Fracture Criterion (TPFC) was derived from Inglis' elastic-stress-concentration equation for an elliptical hole under remote uniform stress and Neuber's equation relating the plastic stress and strain concentration factors to the elastic stress-concentration factor at the maximum stress location. Elastic-plastic 3D finite-element analyses (FEA) employing the critical crack-tip-opening-angle (CTOA) fracture criterion was used to simulate fracture on thin-sheet middle-crack-tension, M(T), and compact, C(T), specimens made of 7249-T76511 aluminum alloy over a wide range in crack-length-to-width ratios to validate the TPFC. A critical CTOA (7.6°) and the fracture parameters (KF and m) were determined from M(T) test specimens, and these values were then used to predict the failure on C(T) specimens. The FEA predicted failure loads on C(T) specimens were within a few percent; whereas, the TPFC generally over predicted the failure loads (5-15%). The TPFC over prediction on the C(T) specimens is likely related to net-section stress (Sn) being greater than the yield stress of the material for all test data, while the M(T) specimens all had Sn less than the yield stress.