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 o r blunt notches. The material considered is the high strength,low hard ening HY 130 steel. We simulated fracture tests on fatigue-precracked compact tension specimens and three-point bend bars containing blunt n otches, using the local fracture model to control crack initiation in the finite element analyses. We compared the results of the simulation s with experimental results. The comparison indicates that the model q ualitatively predicts the right scaling effects for cracked specimens when a characteristic material length is adequately introduced. Howeve r, the model failed to predict the fracture initiation conditions and the scaling behavior of notched specimens. The discrepancy arises beca use the actual micromechanism leading to fracture initiation at the no tch (void growth in a band of localized shear) is different from the m echanism underlying the model (quasi-isotropic void growth). Therefore , new or improved models capable of handling ductile failure by void g rowth under predominantly shear deformation must be developed to predi ct ductile fracture initiation conditions and scaling laws for general ized loading and geometric configurations.