${Al_2}}O_3}-TiO_2$ 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.

복수 표면피로균열의 성장합체거동과 시뮬레이션에 관한 연구

서창민,황남성,박명규 대한기계학회 1994 대한기계학회논문집 Vol.18 No.3

In this paper, fatigue tests were carried out to study the behavior of growth and coalescence of multi-surface cracks which were initiated at the semi-circular surface notches, and a simulation program was developed to predict their growth and coalescence behavior. By comparing the experimental result with those of the simulation based on SPC(surface point connection), ASME and BSI(British Standards Institution) conditions, we tried to enhance the reliance and integrity of structures. This shows that the simulation result has utility for fatigue life prediction.

작은 表面疲勞균열의 成長擧動에 關한 硏究

徐昌敏,李正州 경북대학교 공과대학 1984 工大硏究誌 Vol.13 No.-

In this paper, rotating bending fatigue tests have been carried out in three kinds of carbon steel specimen; an annealed low carbon steel, an annealed medium carbon steel, an annealed high carbon steel and quenched-tempered high carbon steel; with a small artificial defect that might exist in real structure. Fatigue crack lengths have been observed by a method of replication in order to investigate the growth behavior of fatigue crack in the view points of strength of matevials. The main results obtained are as follows: 1) The effect of a small surface defect upon the reduction of fatigue limit is considerably large, and the rate of fatigue limit reduction of surface defect with dlia 0.?? and depth 0.5mm is larger than the surface defect of 0.1mm. 2) When the growth rate of surface crack length (2 a) was investigated, growth rate of surface crack was not related with stress level and materials, and there exist the following relationships between da/dn and σ^n_a, ie surface crack length propagated from small surface crack can be expressed as da/dn = C.,σ^n_a.(a)

回轉굽힘에 의한 軟鋼橫孔노치材의 疲勞균렬進展速度

徐昌敏 慶北大學校 1977 論文集 Vol.24 No.-

This study attempts to clarify the behaviour of fatigue crack propagation through observation and study on the fatigue crack propagation rate and its application of stress intensity factor. These experimental and analytical approaches to the problem of the fatigue crack propagation suggest the following results; (1) The rate of fatigue crack propagation in the notched specimen under rotating bending may be expressed as a function of K, d(2a)/dN=CK^4 that has been proposed by paris et al. (2) The following equation is derived from this experiment on the fatigue crack propation rate, bending stress and crack length. d(2a)/dN=1.93×10^-12Δσ^1.5(Δσ√π(2a))^2.3 or d(2a)/dN=1.93×10^-12Δσ^4.3[π(2a)]^1.4 (3) On the crack initiation in the vicinity of the transverse hole, the slip band is generated and accumulated to the direction of maximum shearing stress as the bending stress level becomes low and it grows up to the micro-crack.

고온 피로균열 성장거동에 관한 파괴역학의 응용에 관한 연구

서창민,김영호 대한기계학회 1990 대한기계학회논문집 Vol.14 No.6

본 연구에서는 로터강(Cr-Mo-V 강)과 저탄소합금강(A517-F강)의 CT시험편을 대상으로 한 고온피로 시험결과를 토대로 차원해석법을 도입시켜 고온하의 균열성장률 을 유도한 다음 온도(T)와 응력확대계수범위(.DELTA.K,T)인 아레니우스 형태의 식을 유도하 였다.그리고 유도된 균열 성장 법칙을 파리스식과 비교 검토하여 본 연구에서 유도 된 이 균열성장법칙의 타당성을 검토하고자 한다. A general form of the mathematical function in the fatigue crack growth rate law for CT specimens was determined by means of the dimensional analysis at elevated temperatures. The experimental results can be rigorously described by the combination of rate theory and fracture mechanics. The rate theory approach extends the scope of fracture mechanics through the consideration of the temperature. The fatigue crack growth rates are represented by the Arrhenius type equation. This equation explains fairly well the experimental data for Cr-Mo-V rotor steel and A517-F steel in the comparatively wide temperature regions as affected with the temperature and the stress intensity factor range interaction.

고온하 304 스테인레스강의 작은 표면구열의 성장거동에 관한 연구

서창민,김영호 대한기계학회 1990 대한기계학회논문집 Vol.14 No.1

Rotating bending fatigue tests of an authentic steel 304 were performed at various temperatures such as room temperature, $538^{\circ}$ and $593^{\circ}C$. The plastic replica method was also applied in order to estimate the fatigue life on the basis of serial observation of small fatigue crack initiation and growth on the pit specimen surface. The fatigue crack growth behavior of 304 stainless steel was investigated within the frame work of elastic-plastic fracture mechanics within a narrow scatterband in spite of different stress levels at elevated temperature as at room temperature. The growth law of small surface crack is determined uniquely by the term. $\DELTA\sigma^{n}a$ where $\DELTA\sigma$ is the stress amplitude, a is the crack length, and n is a constant. It is found that the small crack growth behavior is basically equivalent to the S-$N_{f}$ relationship, where S and $N_{f}$ are stress and number of cycles to failure, and the fatigue life prediction is in good agreement with the experimental results. 본 연구에서는 고온기기의 구조용 부재로 널리 사용되고 있는 304스테인리스 강을 선택하여 상온, $538^{\circ}C$($1000^{\circ}$ F) 및 $593^{\circ}C$($1100^{\circ}C$ F) 고온하의 작은 표면노치 시험편 에서 발생한 표면 피로 균열의 성장거동을 레플리카법에 의하여 상세히 관찰측정하여 파괴역학적으로 해석 연구하고자 한다. 즉 피로균열의 성장특성을 ....$\DELTA\sigma^{n}$a의 매 개변수를 도입하여 정량적으로 평가하고, 수명예측을 실시하여 그 유용성을 비교검토 하였다. 또한 피로균열의 성장에 관한 실험결과 자료들을 PC를 이용하여 전산하고 도식화함으로써 파괴역학적 설계에 유용한 기초적 자료를 제시하고자 하였다.

HSS-Co와 SM55C 이종 마찰용접재의 피로강도에 관한 연구(1)

서창민,서덕영,이동재 대한기계학회 1995 대한기계학회논문집 Vol.19 No.4

This paper deals with the various mechanical properties and fatigue strength in the FRW1 (friction welded interface) of high speed steel (HSS-Co) to SM55C through the tensile test, hardness test and fatigue test. The data of FRW specimens are also compared with those of the base materials (HSS-Co and SM55C steel). Three kinds of specimens used in this study are the friction welded joints, HSS-Co and SM55C carbon steel with circumferential notch, saw notch and smooth, respectively. It is confirmed that the applied welding conditions are optimum methods in order to minimize the heat affected zone (HAZ) and hardness distribution at the HAZ. The fatigue strengths at N = 10$^{6}$ cycles of smooth, circumferential notch and saw notch specimens in the FRW joints are about 299.2 MPa, 123.8 MPa and 247.5 MPA, respectively. The fatigue strength of the friction welded joints is almost equal to that of the SM55C carbon steel in the optimum welding conditions. The fatigue cracks initiated at the welded zone are propagated along the side of SM55C steel.

高張力 鋼板과 亞鉛鍍金 鋼板間의 疲勞特性 II

서창민,강성수 대한기계학회 1989 대한기계학회논문집 Vol.13 No.2

본 연구에서는 편면도금 강판과 복합조직 고장력 강판간의 이종 용접재의 피로거동을 연구하고져 한다. 즉 유한요소법으로 응력분포를 조사하고 그 결과와 피로균열발생 위치를 비교 검토해 보고자 한다. The influence of monogalvanized layer to fatigue strength of two different mating metal specimens (HS*GA, HS*GAB) of high strength steels(HS) and of monogalvanized steel sheets(GA, GAB) were investigated under tensile-shear repeated load, and hardness test. Some of the results are; (1) The main cause of crack initiation and growth at high load range is plastic bending hinge. (2) In low load range, the cracks initiated near the nugget front where the hardness variation is steep.

고온형 금형에 봉화법을 응용하는 기술개발

서창민 경북대학교 공과대학 1998 산·학·연 공동기술개발 결과보고서 Vol.1998 No.-

PEID를 利用한 中型 프레스의 設備總合效率 向上에 關한 硏究

徐昌敏,李文煥,徐德榮 경북대학교 산업기술연구소 1993 産業技術硏究誌 Vol.21 No.-

In recent years a serious interruption loss often occurs at highly expensive developed equipment. To maximize the total equipment efficiency of the Midium-Press it is essential to reveal and improve the potential loss of equipment based on these 6 kinds of chronic loss. Further, the way to minimize the investment in equipment has been presented by applying the PEID(Program for Equipment Improvement & Development).