Stress Intensity Factors for Semi-elliptic Surface Cracks in Compression Coil Springs Having Cylindrical Anisotropy

Abstract

This study has made 3D finite element analyses on the stress intensity factors for semi-elliptical surface cracks in compression coil springs having cylindrical anisotropy in order to clarify the effects of the anisotropy on the correction factors F_i (i=I, II and III) for the three modes of the stress intensity factors. The cylindrical anisotropy was modeled by the stiffness tensor composed of the same components as those of the orthotropic material plus the additional C₄₅ component that corresponds to out-of-plane shear component. The results revealed that the mode-I correction factor FI was dominant and of the order of 0.7-0.9 around the periphery of the cracks in the cylindrically anisotropic coil springs. As the C₄₅ value increased, the FI value decreased around the periphery of the cracks except for the vicinity of the wire surface. The absolute values of F_II and F_III increased locally beyond 1.