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고강도 알루미늄합금의 피로균열의 하한계 및 안정 전파거동
옹장우,진근찬,김종배,김재훈,하태수 대한기계학회 1988 대한기계학회논문집 Vol.12 No.2
본 연구에서는 항공기, 압력용기 및 지상운송차량 등에 고강도와 용접성이 요구되는 고강도 알류미늄합금 7017T651, 7020T651 및 5083 H115에 대해 균열진전 하한계특성 및 안정 균열진전 하한계특성에 미치는 영향을 고찰 하고자 한다. The threshold fatigue crack growth and the stable crack propagation behaviors were studied in 7017 T 651, 7020 T 651 and 5083 H 115 aluminum alloys. The threshold (.DELTA. K $_{th}$) fatigue crack growth can be expressed by the equation .DELTA. $K_{th}$) = .DELTA. $K_{tho}$(1-R)$^{r}$ , where R is stress ratio, .DELTA. $K_{tho}$ is .DELTA. K at R = 0 and r is material constant. The stable crack growth rate against stress intensity factor range .DELTA. K exhibits the trilinear form with two transitions and results of investigation on crack closure phenomena showed that the crack opening stress intensity factor $K_{op}$ is approximately equal to R $K_{max}$. + .DELTA. K $_{th}$.th/.
5083-H115 알루미늄 합금의 혼합 모우드 피로 균열성장 특성
옹장우,진근찬,이성근,김종배 대한기계학회 1989 대한기계학회논문집 Vol.13 No.3
본 연구에서는 혼합 모우드 균열문제의 연구를 위하여 .KAPPA.$_{II}$ /.KAPPA.S1I\ulcorner조절이 간편하고, 균열진전경로가 하중방향에 따른 균일전면의 자유표면의 영향을 균일하게 한 시험편(이하 RCM 또는 round compact mixed-mode 시험편이라 한다)을 고안하여 균열길이 및 하중작용 방향에 따른 .KAPPA.$_{I}$ 및 .KAPPA.S1II를 수치해석한 다음 일반화 하였다. 또 고강도와 용접성이 요구되는 항공기부품, 압력용기, 지상운송차량 등에 사용되고 있는 5083-H115 알루미늄 합금에 대해 혼합 모우드 균열진전 방향 및 피로균열 진전특성을 분석하고자 한다.다. For the mixed-mode crack problems the direction of crack growth, the crack path and the rational representation of fatigue crack growth rates should be studied to predict fatigue life and safety of structures. In this study, a round specimen which produce nearly identical effects in all loading directions is proposed to make an easy measurement of initial direction of crack growth. The mode I and mode II stress intensity factors of the specimen were calculated using finite element method, in which the square root singular stresses at the crack tip are modeled by means of four rectangular quarter-point eight-noded elements surrounding the crack tip. Experimental results for high strength aluminum alloy showed that the direction of mixed-mode crack growth agree well with maximum principal stress criterion as well as minimum strain energy density criterion, but not with maximum shear stress criterion. From data of fatigue crack growth rates using crack geometry projected on the line perpendicular to the loading direction it is easily established that mixed-mode fatigue crack growth in 5083-H115 aluminum alloy goes predominantly with mode I crack growth behaviors.
남수우,진근찬,신동혁 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.9
Primary creep tests were performed on commercially pure aluminum in the temperature range of 0.32 - 0.38 T_m. The activation energies were obtained by usual method using different specimens (Q_c) and the temperature cycling method (Q_(T.C.)). The relation of activation energy with effective stress, σ_e, has been analysed. The activation length, ℓ_c^*, obtained from Q_c is linearly proportional to the inverse of affective stress. But no such relationship is observed in ℓ_(T.C).^* obtained from Q_(T.C.). The Q_c seems to have better physical meaning compared to Q_(T.C).