철도 구조물용 맞대기 용접시편 가공에 의한 피로수명 영향 및 용접부 형상을 이용한 피로수명 예측 연구

초록

This study investigates the effects of the material properties and the fatigue behaviors in the SM490A material butt weld specimens due to the heat-treatment and the grinding. In the fatigue behavior, the heat-treatment affects the fatigue life. The S-N curves of both matrix specimen and butt weld specimen are reversed at some cycle by the existence or nonexistence of heat-treatment. The grinding on the bead makes the fatigue limit decrease in the all specimens. But the reinforcement removed, the fatigue limit increases at the high cycle. Also, this study investigates the fatigue life estimation by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by θ, ρ and h. The stress concentration factors Kt, are changed by each different θ, ρ and h from 1.395 to 2.863. Hence, the sensitivity of Kt is changed by each θ, ρ and h. As θ becomes lower and ρ and h become higher, Kt increases. The fatigue life can be estimated very closely for the AAY specimens without residual stress using only butt weld bead profiles. But, for the AAN specimens with residual stress, the fatigue life must be estimated by considering both the weld bead profiles and the residual stress data.

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