1994 年 43 巻 490 号 p. 772-778
The present paper deals with the multi-indentation model in which the residual stress can be easily estimated not only experimentally but also analytically to clarify the fundamental characteristics of residual stress of ground ceramics, the stress distribution, the contribution of hardness of the materials to the stress, and the effect of X-ray penetration depth on the stress measurement. In the experiments, Vickers multi-indentation was performed on the surface of ceramics and metal, and then the residual stress was measured with several characteristic X-rays. In the analysis, the residual stress distribution in the multi-indented surface layer was estimated by applying the Hill's solution for spherical-cavity expansion and the residual stress, which is equivalent to the stress measured by X-ray, was evaluated by taking the weighted average of the distribution into account. The residual stress based on the analysis was confirmed to coincide with those obtained from the experiments. The characteristics of the residual stress was discussed in detail based on the results of the elastic/plastic analysis. The main results obtained are as follows.
(1) The compressive residual stress in the multi-indented surface has a peak at the depth right beneath the bottom of indentation. Its magnitude can be estimated as k(b/L)2Hv: b=size of plastic zone multi-indented, L=indentation interval, Hv=Vickers hardness, k=constant (-0.69 for Si3N4, -0.35 for S15C).
(2) The compressive residual stress decreased linearly with increasing depth. The compression stress attained zero when the depth was about 80% of b.
(3) The residual stress of ceramics measured by X-ray is considerably smaller than the peak stress even if the characteristic X-ray with shallower penetration depth is used. This result shows that the effective penetration depth of X-ray is not sufficiently shallow in comparison with the depth where the compressive stress exists in ceramic materials.