Bifurcation analysis of fracture mode by simulated and experimental ductile fracture progress based on the proposed crack opening criterion

In the previous papers (Kobayashi, 2017a, Kobayashi, 2017b), the crack opening criterion was deduced from the proposed micro-crack evolution equation. To solve the discrepancies between the estimated and experimental strengths of ductile materials by considering the plastic/damage energy dissipation according to ASTM standard E1820-01, an improved version of the proposed crack opening criterion was proposed and successively applied to the ductile materials such as A533B steel, Al2024-T4 and SiAlon. With regard to the fracture progress, it is well known that the chaotic behavior of crack propagation seems to be caused by the bifurcation of the fracture mode. In this paper, the simulation of ductile fracture progress in notched FCC single crystal specimens characterized by different crystal orientations under the uniaxial tension is performed using the crystal plasticity finite element model (CPFE) to consider specifically the dependence of ductile fracture progress on the crystal orientation. The model was also integrated with a proposed micro-/macro-crack nucleation criteria deduced by two different stationary discontinuity bands characterized by the vanishing velocity condition. The simulated results were compared with the experimental ones. Both bifurcation mechanisms of the fracture mode of the simulated and experimental results were then studied using the proposed crack opening criterion based on the bifurcation structure characterized by two different stationary discontinuity bands. It can be concluded that the proposed crack opening criterion and its improved application including the proposed diagram contribute to study fracture physical mechanisms.