抄録
The porosity of die cast aluminum alloy significantly affects its fatigue strength. However, the stress intensity around macroscopic pores is occasionally mitigated by its large curvature, so the maximum pore is not always guaranteed to be of a fatigue crack origin. Moreover, die cast materials include a large number of pores, therefore there is a need to consider the interaction of pores as well as the size of each pore. For macroscopic pores, we have proposed a methodology to evaluate the effect of pores on the fatigue strength by means of the stress concentration factor. In this study, as the first step to evaluate the stress enhancement around internal clustered pores, an empirical formulation of the elastic stress concentration factor around dual-pore was obtained from the numerical results of the three-dimensional finite element linear elastic analysis. Two spherical pores of the same radius in the middle of a sufficiently large region were considered to eliminate the effects of the outer surface. Uniform tensile stress was applied to the boundary of the analysis domain, and the stress concentration factor was evaluated as the ratio of the maximum principal stress to the applied nominal stress. The inter-pore distance and loading angle were systematically changed, and the variation of stress concentration factor was obtained numerically. After the selection of suitable function form for stress concentration factor prediction, the optimum coefficients were determined by least-square fitting to the numerical results, and its validity and availability were discussed from a mechanical standpoint.
