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Purpose – The purpose of this paper is to investigate the effect of peening on the fatigue limit of steels for welded structure with a crack in the weld toe zone. Design/methodology/approach – An artificial semi-circular slit was created in the weld toe, and peening was conducted. Then, bending fatigue tests were carried out. Findings – First, owing to the shot peening, the maximum slit depths that can be rendered harmless were 1.0 and 1.2 mm in SUS316 and SM490, respectively. Second, during the fatigue test, the fracture of a peened specimen originated outside the slit, which indicated that peening eliminated the effect of the slit on the fatigue limit. Third, the fatigue limit of a slit specimen was improved by the enhanced residual stress distribution and the decreased stress concentration due to plastic deformation at the weld toe. Originality/value – There are very few studies about which a fatigue crack is rendered harmless by residual compressive stress, as a result the structures could be continued to use. Moreover, the study defining the concept about rendering crack harmless and systematic investigation was not able to be found.

PurposeThe purpose of this paper is to investigate the effect of shot peening (SP) on the fatigue limit of high‐tensile‐strength steel containing a crack in the stress concentration zone.Design/methodology/approachAn artificial semi‐circular slit was introduced into the bottom of notch, and SP was performed. Bending fatigue tests were then carried out.FindingsFirst, the fatigue limits of specimens containing a slit of 0.2 or 0.3 mm in depth were improved up to approximately twice their original values. Second, in the case of shot‐peened specimens with a crack of 0.2 mm in depth, the fractures occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to those of non‐slit specimens. Finally, the effect of stress concentration (Kt=1.9) on the slit size could be rendered harmless by SP was not found in the fatigue test.Originality/valueThere are very few examples of evaluations of the fatigue limit of materials containing crack‐like surface defects after SP has been performed in the stress concentration zone. The study elucidated the effect of SP on the fatigue limit in such materials, compared with that of a smooth zone.

Purpose -Zirconia ceramics exhibit high strength and fracture toughness. The purpose of this paper is to research a possibility of crack healing in zirconia ceramics. Design/methodology/approach -ZrO 2 /SiC composite ceramics are sintered and subjected to three-point bending. A surface crack of 100 mm in diameter is formed on each specimen. The cracks are healed and the specimens are tested under bending. Findings -The paper finds that ZrO 2 /SiC composite ceramic material had a high crack-healing ability at a considerably low temperature. For example, a crack of 100 mm in diameter is healed even at 6008C.Research limitations/implications -The paper provides a low temperature healing and a new mechanism of crack healing. Originality/value -The paper shows the healing temperature and the minimum time required to heal showed a good proportional relation on the Arrhenius plot at temperatures of 600-8008C. Moreover, the crack healing is caused by SiO 2 cristobalite produced during the healing.

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