• 대한기계학회논문집
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• 제14권2호
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• pp.382-392
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• 1990

This study investigates the behavior of fatigue crack propagating between holes of holes filled with another materials. When holes of the holes filled with another materials are located symmetrically near a center crack, it is noted that the crack propagation rate is influenced by both the bonding force of the brazing part and the elastic modulus of another material. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes of the holes filled with another materials and it propagates to final fracture.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1097-1105
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• 1997

Because of the existence of stress interaction field made by other defects and propagating cracks, the structure may be weakened. Therefore in this study, the crack behavior in the interaction field made by two different cracks is studied experimentally. In the experiment, vertical distance between two cracks and applied stress are varied to make different stress interacted field. In addition, the effect of plastic zone is used to examine crack propagation path and rate. Three types of crack propagation in the interacted field were found, and crack propagating path and rate of two cracks were significantly changed according to different applied stress as each crack propagates. And the results are attributed to the effect of the size and shape of the plastic zone.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.786-789
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• 1997

Ti-6Al-4V has been used widely in biomedical field. But because of its toxicity, the ${\beta}$ stabilizing element, V, in Ti-6Al-4V has been replaced by Nb, Ta. Ti-10Ta-10Nb has been developed for biomedical applications. The fatigue crack propagation behavior of Ti-alloy(Ti-10Ta-10Nb) was investigated, in comparison with that of pure Ti. In order to better understand the fundamental fatigue behavior of Ti-10Ta-10Nb, rotating bending fatigue tests have been carried out. Ti-10Ta-10Nb has a better fatigue strength than pure Ti. In this paper, fatigue life has been predicted with Nisitani's equation of the fatigue crack propagation that can be established by measuring fatigue crack growth rates.

• 대한기계학회논문집
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• 제13권5호
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• pp.901-910
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• 1989

본 연구에서는 2상계 스테인리스강의 모재 및 용접부에 대하여 대기중의 피로시험과 인공해수중의 부식피로 시험을 모재부와 용접부의 .alpha.,.gamma.상의 상비율 변화에 따른 조직의 변화 및 용접잔유응력의 영향이 크랙전파에 미치는 영향을 검토하였다. 응력-스트레인의 히스테리스곡선에서 균열닫힘 거동을 실측하고 이들의 결과로 부터 유효응력확대계수와 균열전파속도와 관계를 정리하여 이들의 문제를 해석하였다.

• 한국해양공학회지
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• 제6권2호
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• pp.85-93
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• 1992

The only hardness of 2nd phase of martensite in dual phase steel which was composed of the martensite and ferrite was changed. Fatigue test was conducted by cantilever type of self-made rotated bending fatigue testing machine. The corrosion fatigue fracture behaviors of dual phase steel were investigated in 3% NaCl solution at $N_f$ = $1.5\times$$10^5$ $N_f$=1.0 $\times$ $10^6$ cycles. The fatigue strength was increased with increasing the hardness of 2nd phase. The size and number of corrsion pits were influenced by the 2nd phase hardness and pits remain constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of $\Delta$K and da/dn has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the higher the corrosion fatigue life becomes. Corrosion fatigue fracture behavior was effected by mechanics in case of $N_f$=1.5$\times$10$^5$$N_f$=1.5$\times$10$^6$ cycles.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.185-194
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• 1998

In this study, the rotary bending fatigue test was carried out with two kinds of material, S43C and S50C, using in the Front engine and Front drive wheels(F.F.) of vehicle. The one part of specimens was heated by high frequency induction method(about 1mm depth and $H_RC$ 56~60) and tested environment temperature were $-30^{\circ}C$, $+25^{\circ}C$ and $+80^{\circ}C$ in order to look over the influence of the heat treatment and the temperatures. In the experimented result at $+25^{\circ}C$ and $+80^{\circ}C$, the fatigue life of non-heated specimens were decreased about 35%, but that of heated specimens were decreased about only 5% at $+80^{\circ}C$ more than at $25^{\circ}C$. And in the experiment result at $-30^{\circ}C$ and $+25^{\circ}C$, the non-heated and heated specimens were about 110%, 120% higher fatigue life at $-30^{\circ}C$ than at the $+25^{\circ}C$ each other. On the other hand, the fatigue crack propagation rate of S50C was higher than that of S43C.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.759-764
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• 1997

In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

• 한국정밀공학회지
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• 제11권4호
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• pp.47-57
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• 1994

This study investigates the crack propagation behavior to examine the effect of welding residual stress by the superposition method. Especially, as the crack propagation behavior is affected by the applied stress and the stress ratio in compressive residual stress filed, it is studied for three cases as follows; (1) $K_{min}$is smaller than l $K_{r}$l, (2) $K_{min}$ is smaller than l $K_{r}$l in the later stage, (3) $K_{min}$is lager than l $K_{r}$l. The resuslts show that the superposition method is very useful in all the three cases of compressive residual stress field, but is inappropriate in predicting the crack propagation behavior in tensile residual stress field.field.field.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.186-192
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• 2002

The fatigue crack propagation characteristics were investigated on dissimilar friction weld of two kind of heat-resisting steels (STR3 and STR35) commonly used in valve materials for vehicles. A small circular artificial defect was machined to induce fatigue crack at bonded line, heat affected zone and base metal of the weld on the surface of the specimens. From the results of the experiment, the fatigue limits of the materials STR3 and STR35 were obtained to be 429.0MPa and 409.4MPa respectably. The STR35 base metal and 1.0mm HAZ specimens showed 190% and 82% higher fatigue life than STR3 base metal. And the fatigue life of 1.0mm HAZ specimen was shown 99% on STR3 and 29% on STR35 higher than that of their base metal. But the fatigue life of weld interface specimen was shown 18% on STR3 and 72% on STR35 lower than that of their base metal because of the weld interface separation.

• 한국해양공학회지
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• 제6권1호
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• pp.140-147
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• 1992

Corrsion fatigue test was performed under rotated bending in 3.5% NaCl aqueous solution having a temperature from 278.deg.K in order to investigate the effects of aqueous solution remperature on the corrosion fatigue fracture of raw material steel(SS41) and dual phase steel that was produced from SS41 by a series of heat treatment. Corrosion fatigue life decreases remarkably with increase in solution temperature or with decrease in stress level. The corrosion fatigue life and the crack propagation rate at 303.deg.K show the similar behaviors with those at 318.deg.K, which is assumed to be caused by concentration polarization phenamena. The number and the lengths of microcracks increase with increase in solution temperature, so they lead to the decrease in corrosion fatigue life.