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Mixed Mode Crack Initiation 에서의 Fracture Criterion 에 관한 연구 (Ⅰ)
최용식,구재민 成均館大學校 科學技術硏究所 1987 論文集 Vol.38 No.2
This paper has clarified that minimum strain energy density criterion (SED) is of use in the uniaxial tension, but not in the uniaxial compression concerning with the crack extension angle of the slit crack. The proposing concept of maximum Smin is solved with the problem of the Smin selection. This concept is that crack extends to the direction that sign (σ_θ)·Smin has a maximum value. Its result is very excellent. In the mixed mode crack propagation, σ_r seems to be an important factor, and it is clarified that Williams' stress solution neglecting non-singular terms isn't useful and Swedlow's modified solution with the transverse stress, σ_t is useful in the compression of slit cracks, and also Swedlow's of a friction coefficient has a good result.
최용식,구재민 成均館大學校 科學技術硏究所 1990 論文集 Vol.41 No.2
본 논문에서는 혼합모드의 예리한 노치형 균열에 대한 응력확대계수를 제안하였다. 이 응력확대 계수를 PMMA로 실험한, 일축인장과 압축인 경우에 적용시킨 결과 MTS와 연구자들이 제안하였던 MTSE가 잘 적용됨을 알 수 있었다. In this paper, the stress intensity factor of the sharp notch in the mixed mode is proposed. As this S.I.F. is applied to the experimental results of PMMA in the uniaxial tension and compression, we know that MTS and MTSE proposed by us are applied well.
혼합모드 피로문제에서의 최소 변형에너지 밀도기준의 적용
심규석,구재민 한국산업안전학회 2002 한국안전학회지 Vol.17 No.2
In this paper, the maximum minimum strain energy density criterion was applied to the mixed mode fatigue test of A5052 H34 alloy. In this study result, we can have seen that the authors stress intensity factor for the finite width specimen and method of determining testing load, based on the plastic zone size and the limited maximum stress intensity factor by ASTM STANDARD E-647-95, is useful.
최용식,구재민 成均館大學校 科學技術硏究所 1988 論文集 Vol.39 No.1
Choy and Koo proposed maximum togential strain energy density criterion (MTSE) as crack extension starts from the direction with the maximum tangential strain energy density factor. That result weli agreed with experimental results. In this study, We compared MTSE with other criteria under the biaxial and pure shear loading, Under the pure shear loading, MTSE agrees best with the experimental results,
Prediction of Residual Strength after Impact of CFRP Composite Structures
Koo, Jae-Mean,Choi, Jung-Hun,Seok, Chang-Sung Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.7
This study predicts the residual strength of composite structures with impact damage by using the characteristic length of the composite with the hole corresponding to the impact damage area. Since C shaped structure differs from that of the specimen, the shape factor was obtained from the concentration factor of the plate specimen and that of the structure by finite element analysis. The factor was applied to the prediction model for the residual strength of the CFRP composite plate specimen. Comparison between the experimental result and prediction result shows that the prediction method using the characteristic length can be applied to the prediction of the residual strength of CFRP composites after impact.
구재민(Jae-Mean Koo),석창성(Chang-Sung Seok),강민성(Min-Sung Kang),김대진(Dae-Jin Kim),이동훈(Dong-Hoon Lee),김문영(Mun-Young Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.4
가스터빈 블레이드는 터빈 가동 시 발생하는 고온화염으로부터 블레이드를 보호하고, 구조물의 표면 온도를 안전한 수준으로 낮추기 위하여 블레이드 표면에 열차폐 코팅(TBC; Thermal barrier coating)을 하여 사용하고 있다. 본 논문에서는 가스터빈 1단 블레이드에 적용되는 코팅 방식을 이용하여 코인형 시험편을 제작하였고 열화 온도 및 유지 시간의 변화에 따른 코팅 계면 산화물의 성장 거동을 분석하였다. 코팅 단면에 대하여 코팅 계면 산화물의 두께와 마이크로 비커스 경도를 측정하여 열화 특성을 평가 하였다. 또한 성분분석을 통하여 미세조직의 변화를 관찰함으로써 열차폐 코팅의 열적 열화특성을 평가하였다. The thermal barrier coating of a gas turbine blade was degraded by isothermal heating in a furnace and by varying the exposure time and temperature. Then, a micro-Vickers hardness test was conducted on the cross section of the bond coat and Ni-based superalloy substrate. Further, the thickness of TGO(Thermally Grown Oxide) was measured by using an image analyzer, and the changes in the microstructure and element contents in the coating were analyzed by using an optical microscope and by performing SEM-EDX analysis. No significant change was observed in the Vickers hardness of the bond coat when the coated specimen was degraded at a high temperature; delamination was observed between the top coat and the bond coat when the coating was degraded for 50 h at a temperature 1,151℃.
혼합 모드 파괴 기준에서의 T 응력의 영향에 관한 연구
구재민,최태주 한국산업안전학회 2000 한국안전학회지 Vol.15 No.2
Under the mixed mode loading, it has been known that the influence of non-singular terms in the stress fields is serious, because the critical distance, γ_o - the distance of nonlinear elastic region near the crack tip has no negligible value. In this paper, it has been studied on the influence of non-singular terms, T-stress, and the case of T=0, σcos²β, σcos(2β) and 0.05 σcos(2β), under uniaxial tension and compression. It has been seen that the T-stress of σcos(2β) has better than others as comparing to the experimental data.