Numerical modeling of ductile fracture initiation in structural steel

Abstract

Numerical modeling of ductile fracture initiation on a precracked geometry, taking into account the behaviour of simple uncracked material, has been done in the scope of micromechanical analysis. Numerical simulation has been applied in two steps: first, a tensile smooth cylindrical specimen and then, the standard CT specimen. Analysis was performed on a structural steel 22 NiMoCr 3 7, in the scope of ESIS TC8 Numerical Round Robin on Micromechanical Models, Phase II, Task A. The large strain (updated Lagrangian) finite element (FE) formulation was used to simulate expected level of strains. Material non-linearity was modeled by true stress-strain curve, employing Von Mises yield criterion with isotropic hardening. The results obtained in this way were in good agreement with the experimental results, in particular for the force-contraction relation. Using results for strains and stresses, obtained for the standard tensile specimen, further numerical analysis has been performed to evaluate critical void growth ratio (R/RO)c, as the maximum value of (R/RO), obtained according to the Rice-Tracey micromechanical model. The critical void growth ratio value was then used for the analysis of crack growth initiation in CT25 specimen, as the further step in the scope of numerical modeling of ductile fracture initiation. The criterion for crack growth initiation evaluation was the critical void growth ratio value, (R/RO)c, obtained for the smooth round specimen, compared with the void growth ratio value, obtained in the element ahead of crack tip. For the load level at which (R/RO)c has been reached, the corresponding J integral was evaluated and compared with the experimentally determined Ji value. Since these two values turned out to be in good agreement, it was concluded that the Rice-Tracey model can be applied for numerical simulation of ductile fracture initiation in the scope of the procedure employed here. .

U radu je dato numeričko modelisanje inicijalizacije daktilne frakture u strukturnom čeliku na geometriji pre loma uzimanjem u obzir ponašanje jednostavnog neslomljenog materijala uz pomoć mikromehaničke analize. Numerička simulacija bazirana je na metodi konačnih elemenata. Zaključuje se da Rice-Tracey model može da bude primenjen za numeričku simulaciju inicijalizacije daktilne frakture. .