용접부의 잔류응력이 피로파괴 거동에 미치는 영향

Abstract

본 연구에서는 LNG 선박의 극저온 Ball Tank 재료인 Al 5083-O Aluminium 합금의 접합부를 T1G용접하여 Crank이 인장잔류응력 부분인 용접선으로부터 저파할 때, 피로파괴거동에 대한 영향을 조사하였으며, 또한 Forman식에 의한 피로성장 속도의 예측치와 실험치를 비교하여 다음의 결과를 얻었다.

1.용접부의 피로균열 성장거동은 인장잔류응력 구간에서는 균역진전 속도가 빠르나, 압축응력 구간에서는 둔화되어 점차 모재와 일치함을 알 수 있다. 즉 피로피괴 결과에는 잔류응력이 그다지 영향을 주지 않는다.

2.용접부의 결함으로 발생된 피로균열 성장거동은 Forman식에 의한 예측이 가능함을 알게되었다.

3.인장잔류응력 구간에서의 실험치와 예측치(Region Ⅰ)의 불합치는 균열 초기의 인장잔류응력이 반복하중으로 다소 이완되었기때문으로 판단된다.

In the weldment of Al5083-O aluminlum alloy, The effect of fatigue crack propagation rate due to residual stress was investigated. The experimental values were compared with the predicted values by the Forman equation. The experimental results are as follows;

1.The crack propagation rate is hagh in the tensile stress region. However, it shows the almost same behavior of the base metal outside the residual stress region.

2.Forman equation is found to be very useful to Predict the fatigue crack growth rate of materials with the residual stress.

3.The difference between the experimental and predicted results in initial stage seems to be due to the relieved residual stress by the cyclic load.

In the weldment of Al5083-O aluminlum alloy, The effect of fatigue crack propagation rate due to residual stress was investigated. The experimental values were compared with the predicted values by the Forman equation. The experimental results are as follows;

1.The crack propagation rate is hagh in the tensile stress region. However, it shows the almost same behavior of the base metal outside the residual stress region.

2.Forman equation is found to be very useful to Predict the fatigue crack growth rate of materials with the residual stress.

3.The difference between the experimental and predicted results in initial stage seems to be due to the relieved residual stress by the cyclic load.