Modelling the influence of strain hardening and plastic constraint on crack closure of arbitrarily thick CCT-specimens

The triaxial stress constraint and the effective yield stress distribution in the plastic zone for strain hardening materials are studied, and then a modified strip-yield model is proposed to investigate the thickness effect of CCT specimens. Consequently, a plastic constraint factor α is defined and analysed in detail. The results show that the factor α can comprehensively account for the influence of thickness, crack length, loading level and hardening exponent. A simple expression for the plastic zone length and a fitting expression involving a are obtained. Application of the modified strip model to Newman's crack closure model, and comparison with FEM results, show that the model can account for the influence of thickness on crack closure.