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서창민,이정주,정은화,박희범 대한기계학회 1988 대한기계학회논문집 Vol.12 No.5
본 연구에서는 이 좁은 벤트내에 자료가 모이는 피로균열의 특성을 이용하여 표면피로균열의 성장거동을 파괴역학적으로 해석, 연구하여 균열의 성장특성과 $S-N_{f}$ 곡선의 추정을 마이크로 컴퓨터로 계산하였다. This paper deals with surface crack behavior and the fatigue life prediction of notched specimens using the relation between surface crack length, a, and the cycle ratio, $N/N_{f}$. From the $a-N\;/\;N_{f}$ curves, UC(the upper limit curve), LC(the lower limit curve) and MC(the middle limit curve) were assumed and utilized to predict the fatigue life and crack growth rate. The data computed from the three assumed curves were compared with the experimental data. It has been found that in the stable crack growth region ($N/N_{f}=0.3-0.8$) fatigue life can be predicted within 20% errors. Using the characteristics of $a-N\;/\;N_{f}$ curve, it is possible to predict the $da/dN-K_{max}$ curve, the $da/dN-{\Delta}K_{{\varepsilon}_t}$ curve, and the $S-N_{f}$ curve.
AE 法 에 의한 高强度鋼 ( SCM - 4 ) 의 應力腐식균열進展 의 檢出 에 관한 硏究
서창민,문용식 대한기계학회 1982 대한기계학회논문집 Vol.6 No.4
Acoustic emission (AE) of a high strength steel (SCM-4) was measured under stress corrosion cracking(SCC) test at a constant displacement in 3.5% artificial NaCl solution of 18.deg.C, 45.deg.C and 60.deg.C, respectively. The results are as follows; During the SCC test, AE is detected and AE count rate is approximately proportional to the crack growth rate. Even though crack is not propagated macroscopically, AE is detected. The crack growth rate of SCC and the AE count rate are higher for the solution of higher temperature, 45.deg.C and 60.deg.C, than for the solution of lower temperature, 18.deg.C. In the early stage of SCC, AE total counts mostly depend on crack growth. In the later stage, however, AE mostly depends on the film fracture and the dissolution of anode.
SUS 304鋼 의 常溫下 表面피勞균열 의 發생.成長 擧動 에 관한 硏究
서창민,김규남 대한기계학회 1984 대한기계학회논문집 Vol.8 No.3
본 연구에서는 SUS 304강의 상온하의 평골재 표면에 발생. 성장하는 미소표면 피로균열의 거동을 파괴역학적 관점과 수법으로 정량적으로 조사하려는 연구의 일환 이다. In-plane tension fatigue tests(R=0.1) were carried out to investigate the initiation and growth behaviors of very small surface fatigue cracks on smooth unnotched surfaces of type 304 stainless steel at room temperature. The present paper deals with the unification of two approaches to the analysis of fatigue: the one approach is based on fracture mechanics concept and the other on low-cycle fatigue concept. The results are;(1)Maximum crack length, 2 $a_{max}$, initiated at a very small surface scratch not exceeding 20 .mu.m which can exist on the surface after buffing. And the density of small surface crack is remarkably low compared to that of mild steel. (2) The growth rate, d(2a)/dN, of very small fatigue cracks can be represented by one straight line as a function of either stress intensity factor range, .DELTA. $K_{I}$ or cyclic total strain intensity factor range, .DELTA. $K_{\epsilon}$$_{I}$/, for various values of the nominal stress range.e.e.e.e.
장시간 사용된 1Cr-0.5Mo 강의 피로균열진전 특성
서창민,고영태,남승훈,장상엽 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.9
As the service time of power plant approaches its design life, the crack initiation and growth in boiler components becomes major concerns. Though there are many research effort for finding out the properties of used materials with the materials artificially aged by heat treatment, the obtained results are nothing but the estimated values to be verified. In this study, characteristics of the crack growth behavior for 1Cr-0.5Mo steel which was served for a boiler header for about 30 years were studied by performing fatigue crack growth tests at 538℃ and room temperature under triangular and trapezoidal wave-shapes. In order to evaluate hold time effect at elevated temperatures, the fatigue test with 10 second hold time (0.083Hz) was performed. From the experimental results, it was found that the increase of the fatigue test temperature had a significant effect on the increase of the rate of fatigue crack propagation. In the case of hold time testing, the oxidation layer formed at the crack wake was thicker than in the case without hold time.
서창민,김정규 대한기계학회 1984 大韓機械學會誌 Vol.24 No.4
"파면해석과 그 응용"이란 제목하의 4회에 걸친 강좌는 파면해석에 필요한아주 기본적인 사항에 관하여 서술하였다. 이것은 다음과 같은 의의에 있어서 필요할 것 같다. 즉 파괴로 인한 인명 및 재산피해를 막고 고가인 기기를 경제적으로 설치. 운영하기 위해서 문제시된 조건의 파괴는 파괴역학적인 취급에 의하여 정성적인 해석과 정량적인 데이터를 얻어 보다 체계화된 부재의 선택, 검사, 보수 및 건전성 평가에 사용되어야 할 것이다.되어야 할 것이다.
서창민,김정규 대한기계학회 1984 大韓機械學會誌 Vol.24 No.3
본고에서는 피로파괴에 관하여 크게 두가지로 나누어서 설명한다. 첫째 피로현상에 의하여 생기는 피로파면형태 및 전위조직에 관하여 설명하고 그 다음에는 피로균열의 생성기구에 관하여 피로균열의 각 단계별로 설명하고 파면의 특성에 관하여 파괴역학적인 수법도 사용하여 설명한다.
${Al_2}}O_3}-TiO_2$ 플라즈마 코팅된 유리의 입자충격에 의한 손상기구
서창민,이문환,홍대영,Suh, Chang-Min,Lee, Moon-Hwan,Hong, Dea-Yeong 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.3
A quantitative study of impact damage of ${Al_2}}O_3}-TiO_2$ plasma coated soda-lime glasses was carried out and compared with that of the uncoated smooth glass specimen. The shape of cracks by the impact of steel ball was observed by stereo-microscope and the decrease of the bending strength due to the impact of steel ball was measured through the 4-point bending test. At the low velocity, cone cracks were occurred. As the impact velocity increases, initial lateral cracks were propagated on the slanting surface of a cone crack, and radial cracks were generated at the crushed site. When the impact velocity of steel ball exceeds the critical velocity, the contact site of specimen was crushed due to plastic deformation and then radial and lateral cracks were largely grown. Crack length of coated specimens was smaller than that of uncoated smooth specimen due to the effect of coating layer on the substrate surface. According to impact velocity, the bending strength of coated specimens had no significant difference, compared with that of the uncoated smooth specimen. But this represents that the bending strength of coated specimens was increased, considering the effect of sand blasting damage which was performed to increase the adhesion force of coating layer.