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The effects of shot peening (SP) on the strength of partially stabilized zirconia (PSZ) were studied. The compressive residual stress, apparent fracture toughness (KC), and bending strength values of specimens subjected to SP were investigated. Results of X-ray diffraction analyses showed that SP introduced large compressive residual stress in specimens. As a result, the KC and bending strength values of specimens having semi-elliptical pre-cracks on their surfaces increased significantly. Shot-peened specimens having surface pre-cracks with lengths less than 140 µm exhibited strength comparable to that of smooth specimens, and fractured outside the pre-crack zone, indicating that the pre-cracks were rendered harmless by SP. Thus, the introduction of a compressive residual stress by SP is an effective technique for increasing the strength of PSZ.

Effect of shot peening (SP) on bending fatigue limit of high strength steel (SUP9A) containing a semielliptical surface slit was investigated. SP was conducted on the specimens containing a semi-elliptical surface slit with aspect ratio, a/c = 0.4, where a was the slit depth (a=0.1, 0.2 and 0.3mm), and c was the half of surface length of slit. Bending fatigue tests were carried out under stress ratio, R = 0. The result showed that the fatigue limit of the shot-peened specimens having the slit under 0.2 mm in depth was almost same as that of the shot-peened smooth specimens. Meanwhile, some of the specimens fractured from the surface other than the slit. Thus, the maximum depth of slit which could be rendered harmless by SP was 0.2 mm. The maximum depth of crack with various aspect ratios which can be rendered harmless by SP was predicted, assuming that the crack was arrested when apparent stress intensity factor at the slit tip was less than threshold stress intensity factor of the material. The estimated values were in good agreement with experimental values. According to the estimation method, the harmless crack assessment diagram was proposed.

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