Prediction of Low Cycle Fatigue Crack Growth under Mixed-mode Loading Conditions Using Cohesive Zone Models

Abstract

Damage tolerant design is based on reliable fatigue crack growth methods for both high cycle and low cycle fatigue problems. While the Paris’ law can be applied for estimate crack growth life in quasi-elastic materials, elastic-plastic fatigue crack growth needs more accurate computational models. In the past decade numerous cohesive zone models were proposed and investigated for predicting elastic-plastic fatigue crack growth. However, most cohesive zone models were used to reproduce fatigue crack growth with vanishingly small scale yielding and failed to predict low cycle fatigue crack growth with the finite plastic zone. In the present work a new CCZM is introduced for the high fatigue crack growth rate and attempting to give a uniform description from cyclic fatigue crack growth to elastoplastic rupture in ductile materials. The damage accumulation equation in the cohesive model contains both monotonic damage as well as cyclic damage mechanism. Experimental verification was carried out in an austenitic stainless steel AISI 304 through fracture tests and fatigue crack growth tests of compact tension (CT) specimens under mode I and compact-tension shear (CTS) specimens under mixed mode loading conditions. Detailed finite element computations confirmed that the present cohesive zone model provides a uniform description for the whole fatigue crack growth regimes. The model parameters can be determined in the conventional CT specimens. The cohesive zone model has the potential to be applied for more complex structural failure analysis.