| Summary: | 碩士 === 國立高雄應用科技大學 === 土木工程與防災科技研究所 === 94 === Cold expanded and ring indented methods were employed for crack-tip buildup of residual compressive stresses, strain hardening and plasticity-induced closure. This occurrence leads toward crack growth retardation.
The compact tension specimens of AISI 304 stainless steel were used in the fatigue test. In drilling and ring indented process, the method was that drilled（diameter=2㎜） through crack-tip, then various punches（diameter=5㎜、diameter=7㎜） and testing load（6kN、9kN） were employed. For the same punches, the increase in testing load gives rise to the retardation effect. Thus, crack initial life and total life were increased. For the same testing load, the smaller punch gives better in the retardation effect. Under the punch（diameter=5㎜） and testing load（6kN）, the total life is up to 571,031 cycles. However, the testing load（9kN） could make the crack more retarded because the crack was arrested after 1,100,029 cycles for it expanded 0.8㎜ from hole edge. In cold expanded（diameter=2.094㎜） and ring indented（punches of diameter=5㎜、diameter=7㎜, and testing load of 6kN、9kN） process, the crack growth behavior induced by this process were similar to that of drilling and ring indented process. The increase in testing load and the smaller punch give better rise in the retardation effect. Moreover, the effect of the process was better than that of drilling and ring indented process. For the punch（diameter=5㎜） and the testing load（6kN）, the crack did not grow for 1,500,591 cycles and therefore enhanced the retardation development.
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