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70계열 알루미늄합금 용접부의 피로균열진전 거동과 피로수명 예측에 관한 연구
옹장우,김재훈,정근춘 忠南大學校 産業技術硏究所 1988 산업기술연구논문집 Vol.3 No.1
It has been important to determine life cycle and stress range for the each welded metal under high cycle load control test conditions. In this study, fatigue crack propagation rate for 7017, 7020, 7039 and 5083 alluminum welded alloy was compared with stress intensity factor range linear elastic fracture mechanics. Compact tension specimens were used and crack growth rate da/dN and stress intensity factor range ΔK were analyzed concerning to the R value of 0.1 and 0.3. In order to find out the value of ΔK, ΔK-inceasing test method was applied by the standard fatigue testing method describes in ASTM E647-81. From the result, the stable crack propagation region of 7017, 7020, 7039 and 5083 alluminum welded alloy was applicable to the Paris equation da/dN = C(ΔK)m (C and m are material constants). Constant m decreases and constant C increases with increasing of stress ratio R. Without dependence on materials, the fatigue life and the propagation rate increase, while the gradients of crack propagation rate decrease, whith increasing stress ratio. Fatigue life was observed roughly in the order of 7020 > 5083 > 7017 > 7039, independently on crack propagation direction and stress ratio. The fatigue life is longer when the crack propagation direction of specimen and welded bead are parallel to each other than transverse. The crack propagation rate and the gradient of it are larger in the case of parallel specimen than transverse. The minimum crack length of fatigue life can be estimated through the knowledge of maximum equivalent crack length obtained by using nondestructive test.
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