A computational investigation of local material strength and toughness on crack growth

Abstract Computational simulation of stable crack growth is an important aspect of structural integrity prediction. Modern alloy strength and ductility increase local material fracture toughness but simultaneously complicate stable crack growth predictions. Material modeling, material parameter identification, fracture criterion and numerical crack growth algorithms are issues which must be addressed for robust crack growth prediction. In this investigation, a series of finite element simulations were undertaken to investigate two-dimensional mode I crack growth in a modified compact tension specimen geometry. Two different crack lengths were considered. HY-100 steel parameters, previously characterized for large strain deformation, were utilized. Additional material responses, based on the HY-100 nonlinear response but with different yield strengths and ductilities, were also considered to assess parametrically material effects on crack growth. A debonding algorithm was employed to produce crack growth by nodal release when local material conditions, satisfying a specified local fracture criterion, were met. Material fracture and crack growth were treated as dependent variables of the analysis, generating crack growth in discrete increments. The results of this parametric computational study demonstrated crack growth of up to 67% of the initial crack length over the total number of load increments allowed for each combination of geometry, material strength and material toughness. The current crack tip energy density histories exhibited piecewise smooth behavior, consistent with the changing crack tip position produced by discrete crack growth across finite elements. The relative loads and crack growth sustained by each specimen were observed to depend on the elastic stress and strain response of the material in addition to the local fracture toughness of the material.