Void growth model and stress modified critical strain model to predict ductile fracture in structural steels

Material tests and analyses are presented to investigate the accuracy of two micromechanics-based continuum criteria for predicting ductile crack initiation in low-carbon steels, which are representative of mild steels used in civil engineering construction. Referred to as the stress modified critical strain (SMCS) model and the void growth model (VGM), both criteria integrate plastic strains and triaxial stresses to predict crack initiation associated with the mechanisms of void initiation, growth and coalescence. The models are suitable for implementation through finite-element analyses to simulate fracture initiation in steel structures. Material tests and finite-element analyses of seven varieties of structural steels, including two new high-performance steels, are conducted to validate and calibrate the model parameters for practical structural engineering applications. Both models are shown to predict fracture accurately across the spectrum of steel samples and geometric configurations. However, application of the models to situations with high stress and strain gradients is shown to be quite sensitive to the characteristic length parameter of the models, which leads to large model variability in such cases. A strong empirical relationship between Charpy V-notch upper-shelf energy and the SMCS and VGM parameters is observed, which can be utilized to estimate the model parameters.