疲勞强度에 미치는 鹽水와 노치의 影響에 關한 硏究

表東根 弘益大學校 1987 弘大論叢 Vol.19 No.2

In order to study the differente of fatigue strength in different environments, comparative fatigue tests in the rotating bending were carried out in air and artifical sea water with cyclic rate 750cpm, using smooth bar specimens and Center holed specimens of SM45C and SM5OB steel. The following results were obtained. 1. The relations between the stress amplitude and the number of cycles to failure were found by the least square method as follow. ◁표 삽입▷(원문을 참조하세요) 2. In comparison with the air environment, the fatigue strength decrease about 72% in artificial sea water. The fatigue strength is higher the high cyclic rate than low cyclic rate condition. 4. The fatigue strength decreases with the stress concentration factor K_(t) increases. 5. For the stress concentration factor K-(t) is 2.02, N/N is about 39~54%. 6. For the high stress amplitude level, the final fracture surface located in the central part of specimens and large. But for the low stress amplitude level lo-cated in the circumference of the fracture surface and small. 7. By the macroscopic observation, environment was not effected at the fracture surface.

보강재의 형상이 평판의 고유진동수에 미치는 영향에 관한 연구

金泰玩,姜俊洙,表東根 弘益大學校 科學技術硏究所 1995 科學技術硏究論文集 Vol.6 No.-

An analysis is presented for the free vibration of a cantilever plate. For this papers, there are compared with the stiffener, I-shape and T-shape of the plate. The method is applied to cantilever plate with stiffened plate, I-shape and T-shape, and the natural frequencies and mode shapes of vibration are calculated numerically, given the results and confirmed experimentally.

A Statistical Study on Fatigue Life Distributions of SM 45C

표동근,박종우 대한기계학회 1990 대한기계학회 춘추학술대회 Vol.- No.-

알루미늄 7075-T6에 관한 랜덤하중이 작용할때의 피로강도

表東根 弘益大學校 科學技術硏究所 1994 科學技術硏究論文集 Vol.5 No.-

An investigation was made of cumulative fatigue damage of center holed specimens which subjected to programmed varying load in vending condition. The following conclusions were obtained through the constant stress amplitued experiment and the block loading experiment. 1. In constant loading test, fatigue life was affected by speed of revolution. From experimental data, Nf(100cpm)/Nf(3000cpm) equal to 0.31. 2. In case of Al7075-T6 with varying load, Modified Miner's Rule is not acceptable. 3. In case of Al7075-T6 with varying load, we need modified S-N curve method like Freudenthal-Heller's modified S-N curve method.

P 분포 블록하중에 의한 용접부의 누적피노 손상에관한 연구

표동근,안태환,신광철 대한용접접합학회 1991 대한용접·접합학회지 Vol.9 No.1

The most fatigue tests carried out under the either stress or strain control, but machines and structures had taken variable stress. This variable stress was treated as statistics based on p-type distributions. In this paper, the cumulative fatigue damage of SM45C round bar specimens having a center hole resulting from block loading with p-distributions in rotating bending conditions, is presented. The value of p was changed in the range from 0.25 to 1; 0.25, 0.5, 0.75, 1. The following conclusions were obtained through the constant stress amplitude experiments and the block loading experiments. (1) In constant loading test, fatigue life was affected by cyclic rate. From experimental data, N$_{f}$ (100cpm)/N$_{f}$(3000cpm)equal to 0.56. (2) In case of the cyclic rate 100cpm and 3000cpm, at the high stress amplitude level the crack propagation life N$_{*}$f is longer than the low stress amplitude level. (3) Miner's hypothesis may be valid for p=0.75 and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5, while the modified Miner's method agree with experimental data well for the case p=0.25.5.

P分布 Block荷重에 依한 累積疲勞損傷에 關한 硏究

表東根 弘益大學校 1988 弘大論叢 Vol.20 No.2

An investigation was made of cumulative fatigue damage of center holed specimens which subjected to programmed block fatigue loading with p-distribution in bending conditon. The value of p was changed in the range of 0.25 to 1(0.25, 0.5, 0.75, 1) and the fatigue life was defined on the criterion of fatigue life. The following conclusions were obtained through the constant stress amplitude experiment and the block loading experiment. (1) Miner's hypothesis may be valid for p=0.75, and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5. While the modified Miner method agree with experimental data well for the case p=0.25. (2) In constant loading test, fatigue life was affected by speed of revolution. From experimental data, N(100cpm)/N(3,000cpm) equal to 0.83. (3) For center holed specimen, the final fracture surface located in the central part of the specimen and became large according to increase of the stress amplitude.

랜덤하중에서의 균열전파속도 추정법에 관한 연구

표동근(D. K. Pyo),안태환(T. H. An) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.2

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history.<br/> The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper.<br/> The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm : A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height.<br/> It showed that the good agreement with between the experiment results and simulation of storm loads.<br/> So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

高强度鋼의 Cyclic-rate 變化에 따른 疲勞强度에 關한 硏究

表東根,李廷澤 弘益大學校 1990 弘大論叢 Vol.22 No.2

This study has been made inverstigation for the difference of fatigue strength under variable cyclic-rate, compared with three types cyclic-rate, 2,700cmp and 100cpm using smooth specimens(K?=1.025) and center holed specimens(K?=2.02) of SCM440 steel were obtained through fatigue tests in the rotating. The following conclusions were obtained 1. The difference of fatigue strength under variable cycle-rate is large more the low stress amplitude level than high stress amplitude level. 2. The fatigue strength decrease with concentration factor increase, but the difference is comparatively decrease more than the concentration factor is high level. 3. According to decrease of the cyclic-rate, the failure time take long time. 4. The form of the fatigue crack propagation showed to the straight line according to increase of the cyclic-rate, and for the stress amplitude level, the final fracture surface located in the central part of specimens and large, and the fracture surface showed to the striation and dimple by the microscopic observation.

P분포 블록하중에 의한 인공해수중의 부식피로강도특성에 관한 연구

표동근(Dong-Keun Pyo),고주석(Ju-Seok Ko) 한국해양공학회 1989 韓國海洋工學會誌 Vol.3 No.1

Rotating bending fatigue tests were carried out on notched specimens made of S45C carbon steel under constant stress amplitude and block loading. Each test was performed in air and in artificial sea water.<br/> The testing machine is an Ono-Type Rotating Bending Machine and the block loading tests were applied by Gassner Type.<br/> The value of p was changed in the range of 0.25 to 1.0(0.25, 0.5, 0.75 and 1.0) and the fatigue life was defined on the criterion of failure life.<br/> The following conclusions were obtained ;<br/> 1) Fatigue life was affected by speed of revolution in the constant load test and the fatigue strength is higher at the high cyclic rate than at the low cyclic rate condition at the same fatigue life. From experimental data [N?(1000cpm)/N?(3000cpm) equals 0.46.<br/> 2) Corrosion fatigue strength of S45C carbon steel were monotonously decreased with increasing number of cycles. The fatigue strength in A. S. W decreased 34% at 100cpm and 31% at 3000cpm compared with that in air.<br/> 3) When the cyclic rate is 100cpm, the initial fatigue crack appeared on 66% at 50㎏?/㎟ stress level and on 33% at 15㎏?/㎟. Also, the fatigue crack propagation is more rapidly in case of high stress than low stress.<br/> 4) The fatigue limit was obtained by the Staircase Method of fatigue limit tests under constant amplitude loads ; Se=12.37㎏?/㎟.<br/> 5) Miner's hypothesis may be valid for p=0.75, and the prediction of fatigue life by Haibach's method agrees with this experimental data well for the case p=0.5. While the modified Miner's method agrees with this experimental data well for the case p=0.25.

鎔接殘留應力이 應力比에 따라 疲勞龜裂傳播에 미치는 影響

表東根,李龍福,金鍾鉉,吳湞淵 弘益大學校 1989 弘大論叢 Vol.21 No.2

To examine the effects of the welding residual stress on Mode I fatigue crack propagation behavior, 3mm thickness SS41 steel plate was welded by an Auto-matic Submerged Arc Welding. Initial residual stress and relaxation residual stresses according to each stress ratio were measured. The fatigue crack propagation behavior from the region of compressive residual stress to region of tensile residual stress was analyzed. The results predicted by the Forman's equation using the superposition approach of the respective stress intensity factors for the initial residual stress and for the applied stress according to each stress ratio were compared with experimental data. The validity of the superposition approach was investigated. The conclusion are summerized as follows: 1. When the component is subjected to a constant amplitude cyclic tensile loading, the welding residual stress is reduced as stress ratio increase. 2. As the fatigue crack is propagation through the compressive residual stress field, it was found that the effects of welding compressive residual stress on fatigue crack growth in weldments, and the stress ratio decreases, become larger and delay the fatigue crack growth rate. 3. For negative values of the effective stress ratio, R? in the welding compressive residual stress field, the prediction of fatigue crack growth rate by the Forman's equation were found to be corresponded to experimental data for stress ratio R?0.3, as the effective stress ratio R? approached zero, when the stress ratio R>0.3 the prediction of the fatigue crack growth rate by Forman's equation were found to be impossible.