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스테인레스강 용접부의 피로균열 전파속도 예측에 관한 연구
이용복,정진성,박영근,김호경 한국공작기계학회 1998 한국생산제조학회지 Vol.7 No.3
Welding structure contains residual stress due to thermal-plastic strain during welding process, and its magnitude and distribution depend on welding conditions. Cracks initiate from various of the weldment, propagate and lead to final fracture. The crack initiation and propagation processes are affected by the magnitude and distribution. Therefore, the magnitude and distribution of weldment residual stress should be considered for safety design and service of welding structures. Also it is very important that more accurate assessment method of fatigue crack growth must take into account the redistributing the residual stress quantitatively, because the residual stress in weldment has characteristics of its redistribution with loading magnitude, number of cycles and fatigue crack propagation. In this study, fatigue crack behavior of STS-304 weldment was investigated during crack propagation into tensile residual stress region or compressive residual stress region. Crack growth rates were predicted and compared with experimental results.
李龍福 弘益大學校 科學技術硏究所 1994 科學技術硏究論文集 Vol.4 No.-
In this study, to evaluate the chraracteristics of fatigue crack propagation from the surface of material general structual rolled steel(ss41) was used, which was machined with surface pit shaped defects with different depths and radii. Surface fatigue crack characteristics considered crack closure effect could be well evaluated by experiments. The experimental results are summarized as follows: 1. The surface crack was varied to semicircular shape until a plate thickness ratio reachs 0.4 times and then become semi-elliptical shape. It could be expressed the fatigue crack shape by following equation. ?=1.0-0.67(?)+0.49(?)² 2. As the surface fatigue crack propargate, crack closure effect increases and has maximum value near crack depth with 0.5mm to 2mm and then decreases until it has bean constant value near crack depth ratio with 0.35 to 0.closure factor has 0.87 in the surface direction and 0.9 in the depth direction. 3. Considering the crack closure effect, it could be tacken crack closure ratio. ?=1.04 in both surface direction and depth direction and predicted characteristics of the surface fatigue crack correctly by using it.