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Title |
Failure Behavior of 3-Inch Steel Pipe Elbows Under Variable Amplitude Cyclic Loading
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Authors |
김성완(Sung-Wan Kim) ; 전법규(Bub-Gyu Jeon) ; 박동욱(Dong-Uk Park) ; 정영수(Young-Soo Jeong) ; 장성진(Sung-Jin Chang) |
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DOI |
https://doi.org/10.11112/jksmi.2026.30.4.117 |
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Keywords |
Banon 지수; 대표 항복점; 강재 배관 엘보; 극한 파괴 상태 Banon index; Representative yield point; Steel pipe elbow; Ultimate failure state |
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Abstract |
This study investigated the failure behavior of steel pipe elbows subjected to variable amplitude loads and quantitatively evaluated their ultimate failure state, which was characterized by leakage due to fatigue cracking. To this end, representative carbon steel (A234 WPB) pipe elbows of a single specification (3-inch, Schedule 40) were subjected to in-plane constant and variable amplitude loading. Experimental results revealed that cross-sectional ovalization and the accumulation of plastic deformation under cyclic loading concentrated bending and membrane stresses at the crown of the elbow. This resulted in distinct failure behaviors, with clear differences observed in the time of failure and cumulative dissipated energy depending on whether the loading condition was bidirectional or unidirectional. To quantitatively express such damage accumulation and the ultimate failure state of the steel pipe elbows, a damage index was calculated using the Banon index. However, defining individual yield points is difficult under loading conditions where sufficient plastic deformation does not occur in the initial cycle. Therefore, in this study, a representative yield point was applied across all amplitude loading conditions to calculate the Banon index. The Banon index calculated using the representative yield point exhibited minimal error compared to that calculated using conventional individual yield points. Furthermore, it was confirmed that the Banon index fell within the ±2σ interval under all loading conditions. Consequently, this study confirmed that the Banon index calculated using a representative yield point can quantitatively evaluate the failure behavior and ultimate failure state of steel pipe elbows subjected to variable amplitude loads.
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