Investigation of Scaling Effects in Elastic-Plastic Ductile Fracture Using the Local Approach

This paper investigates the ability of a simple ductile local fracture model to predict the fracture initiation conditions for geometrically similar specimens of different sizes containing either sharp cracks or blunt notches. The material considered is the high strength, low hardening HY 130 steel. We simulated fracture tests on fatigue-precracked compact tension specimens and three-point bend bars containing blunt notches, using the local fracture model to control crack initiation in the finite element analyses. We compared the results of the simulations with experimental results. The comparison indicates that the model qualitatively predicts the right scaling effects for cracked specimens when a characteristic material length is adequately introduced. However, the model failed to predict the fracture initiation conditions and the scaling behavior of notched specimens. The discrepancy arises because the actual micromechanism leading to fracture initiation at the notch (void growth in a band of localized shear) is different from the mechanism underlying the model (quasi-isotropic void growth). Therefore, new or improved models capable of handling ductile failure by void growth under predominantly shear deformation must be developed to predict ductile fracture initiation conditions and scaling laws for generalized loading and geometric configurations.