二軸応力下の低サイクル疲労における粒界形き裂の成長の解析

抄録

Cracking behavior in low cycle fatigue regime is affected by stress level and biaxiality, and also by material microstructure. More reasonable estimation for fatigue life requires an appropriate modeling of crack growth, including not only crack initiation and propagation, but also crack linking during the whole fatigue process. In the present study, the growth of fatigue cracks of the grain-boundary type under biaxial stresses was modeled to analyze cracking behavior and to evaluate fatigue life. In the modeling, deformed hexagonal elements with a double-slip system were employed as constituent grains in a polycrystalline material. An analytical procedure for crack growth was established as a competition between the coalescences among initiated and propagating cracks during a whole fatigue process and the propagation of a dominant crack as a single crack. The evaluation of fatigue life described by the size of the dominant crack was made based on the same procedure combined with a statistical analysis of the Monte Carlo type. Fatigue lives obtained for pure copper under several stress conditions were found to lie in the ranges of results simulated from fifty trials. Characteristics of intergranular cracking in the copper were very well-simulated using the present analytical procedure.