2018 年 67 巻 3 号 p. 375-382
Shot peening, which imparts compressive residual stress, is a very effective means for improving the fatigue strength and is widely used for manufacturing process such as automobile industry and aircraft industry. In this study, with the aim of clarifying experimentally the microscopic residual stress distribution of a single dent by projecting a fine ceramic ball with a diameter of 3 mm onto an aluminum alloy material, and the existence of shear stress is clarified by triaxial stress analysis. Furthermore, the change of the residual stress distribution when multiple shots are given to the same position of single dent is also clarified. Obtained results are summarized as follows: (1) The central portion of the dent has a tensile residual stress in both radial and circumferential directions of the dent. A residual stress in the radial direction of the dent has a peak of compressive residual stress outside the dent mark, and a compressive residual stress is given up to an area up to about four times the dent diameter. On the other hand, a tensile residual stress is generated in the circumferential direction of the dent to the region of four times the dent diameter, and the peaks of the tensile residual stress are present on the central part of the dent and outer of the dent. (2) The macroscopic residual stress in the radial direction gradually changes to compressive stress in accordance with the number of shot projections, but does not change substantially in the circumferential direction. (3) As a result of triaxial stress analysis on a single dent, shear stress components σ12 and σ23 does not exist, but it became clear that shear stress σ13 is generated at the dent boundary.