• 대한토목학회논문집
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• 제32권4A호
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• pp.245-253
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• 2012

본 연구에서는 장대터널이나 지하차도 등에 시공되는 횡류식 환기시스템을 구성하는 내화패널이 부착된 프리캐스트 풍도슬래브의 구조성능을 평가하기 위해서 실물모형 구조실험을 수행하였다. 또한, 내화패널의 휨강도와 Pull-off test를 통하여 내화패널과 슬래브의 부착성능 등의 기초성능을 우선적으로 확인하였다. 실물모형시험은 내화패널과 프리캐스트 PSC 슬래브의 정적 휨성능과 차량의 통행 시 발생하는 표면압력 이상의 하중에 대한 동적피로부착성능을 평가하였다. 동적피로하중 시험에서 내화패널과 PSC 슬래브 사이의 탈락이나 손상은 발생하지 않았으며, 정적재하시험에서도 매우 안정적인 거동을 보였으며, 하부에 부착된 내화패널의 탈락은 발생하지 않았다. 따라서 시공 중이나 시공 후 외부하중에 의해 내화패널의 탈락은 발생하지 않을 것으로 판단된다.

• Journal of Welding and Joining
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• 제32권4호
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• pp.34-38
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• 2014

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

• 대한금속재료학회지
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• 제46권2호
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• pp.80-87
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• 2008

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than $1,000{\Omega}$. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

• 한국농공학회논문집
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• 제62권3호
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• pp.29-38
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• 2020

Since some warm-mix asphalt (WMA) concretes were known to show poorer rut resistance than the hot-mix asphalt (HMA) concretes, many studies were performed in efforts of improving its performance at high temperature. The reason is assumed to be due to the moisture remaining in aggregates dried at lower temperature. Therefore, not only the rut resistance, the crack resistance of WMA concrete was also in question. In this study, fatigue life of WMA concrete was evaluated in comparison with HMA using 3-point bending (3PB) beam test. The asphalt mixtures were prepared based on Korean mix-design guide using a 13 mm dense-graded aggregate and 6 binders; two HMA binders and four WMA binders. By 3PB fatigue test, normal (unmodified) and polymer-modified WMA concretes were evaluated in comparison with normal and polymer-modified HMA concretes at a low temperature (-5℃). The results showed that most of WMA concretes showed longer fatigue lives than HMA concretes, even though the same PG binders were used for HMA and WMA. This result indicates that the WMA concretes have stronger resistance against fatigue cracking than HMA at the low temperature, and this result is in contrast to the high-temperature performance test.

• 대한금속재료학회지
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• 제49권10호
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• pp.774-779
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• 2011

S-N fatigue behavior of cast 304 stainless steel was studied at 25, -50 and $-196^{\circ}C$ and at a stress ratio of -1 in uniaxial and bending loading condition. It was found that the resistance to S-N fatigue was greatly improved with decreasing testing temperature. The normalized S-N fatigue curves by tensile strength at three different testing temperatures matched each other, suggesting that tensile strength determines the S-N fatigue resistance of cast 304 stainless steel at low temperatures. The effects of different loading on the resistance to S-N fatigue of cast 304 stainless steel were quantified. The S-N fatigue curves at 25, -50 and $-196^{\circ}C$ were described by using Basquin's law the relationship between the S-N fatigue curve and the testing temperature was obtained by using a simple regression method.

• 한국정밀공학회지
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• 제26권8호
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• pp.142-147
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• 2009

Spinal fixation systems provide surgical versatility, but the complexity of their design reduces their strength and fatigue resistance. There is no published data on the mechanical properties of such screws. Screws were assembled according to a vertebrectomy model for destructive mechanical testing. A group of two assemblies was tested in static compression. One group was applied to surface a grit blasting method and another group was applied to surface a bead blasting method. Modes of failure, yield, and ultimate strength, yield stiffness, and cycles to failure were determined for six assembles. Static compression 2% offset yield load ranges was from 327 to 419N. Fatigue loads were determined two levels, 37.5% and 50% of the average load from static compression ultimate load. An assembly of bead blasting treatment only achieved 5 million cycles at 37.5% level in compression bending.

• 마이크로전자및패키징학회지
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• 제18권1호
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• pp.55-59
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• 2011

유연성 기판 상의 동박의 반복 굽힘 변형에 따른 절곡 빛 굴곡 신뢰성과 인장 특성과의 관계를 규명하기 위해 4종류의 동박 시편의 절곡 신뢰성 실험, 굴곡 선뢰성 실험과 인장 실험을 실시하였다. 절곡 신뢰성 실험은 동박에 5.3%의 굽힘 변형률을, 굴독 선뢰성 실험은 동박에 2.0%의 굽힘 변형률을 반복적으로 인가하면서 전기 저항 변화를 관찰하고 피로 수명을 평가하였다. 또한, 4가지 시편의 인장 실험을 통해 탄성 계수, 항복 강도, 연장 강도, 인성 등의 재료 물성을 구한 결과, 연성과 인성이 우수한 시편의 경우 절곡 및 굴곡 신뢰성이 크게 우수한 것으로 나타났다. 반면, 탄성 계수, 항복 강도의 경우 절곡 및 굴곡 신뢰성과 큰 연관성을 보이지 않았다. 이는 절곡 및 굴곡 변형에 의한 금속의 피로 파괴 거동은 재료의 파괴 인성과 밀접한 관계를 가지기 때문으로 판단된다.

• 한국가구학회지
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• 제26권4호
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• pp.392-397
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• 2015

This study was carried out to analyze the effects on mechanical properties of deteriorated wood member by outdoor condition. The surface color, mechanical properties and structural stability of traditional wooden structures, exposed in water and UV, could be changeable. For the purpose, accelerated weathering test based on outdoor condition was carried out. The weathering time levels were composed 0, 500, 1000, 1,500 and 2,000 hours and mechanical properties were evaluated on each specimen according to weathering time level. Bending properties were decreased on weathering but recovered after 1,000 hours. Fatigue and impact strength were decreased to 1,000 hours and did not changed since then. Abrasion resistance was minimized in 1,000 hours. This results could be utilized for effectively stability management of traditional wooden structures and members.

• Journal of Advanced Marine Engineering and Technology
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• 제15권1호
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• pp.51-58
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• 1991

Corrosion fatigue test was performed by the use of plane bending fatigue tester in marine environment having various specific resistance from 25(natural sea water) to 5000.ohm.cm. It is in order to investigate the effects of marine environmental factor on the corrosion fatigue fracture of SS41 steel. The main results obtained are as follows; 1. The aspect ratio(b/a) of corner crack growing in natural sea water is lower than that in air. 2. The surface crack growth rate(da/dN) in marine environment is faster than that in air and da/dN delaies with the specific resistance increased. 3. The experimental constant m of paris rule [da/dN=C(${\delta}$K)$^m$] decrease with the specific resistance decreased and the effect of corrosion in proportion to the specific resistance is more sensitive than that of stress intensity factor range(${\delta}$K) under region II. 4. The accelerative factor(${\alpha}$) in marine environment is about 1.1-2.7 and .alpha. is increase under the low region of stress intensity factor range(${\delta}$K). 5. The electrode potential($E_0$) gets less noble potential with the specific resistance decreased.

• Applied Microscopy
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• 제43권2호
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• pp.81-87
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• 2013

The influence of carbide formation on mechanical properties has been investigated in carburized steels. Through controlled diffusion and precipitation processes, the morphologies of carbides could be changed and then fine, networked, and spherical shapes at carburized layers were obtained. These morphological changes affected tensile and bending fatigue properties of the steel. The fine and the spherical carbides acted as resistance sites against crack propagation, which improved the mechanical properties. However, the networked carbides deteriorated the properties because the cracks propagated along the boundaries of them. These results indicate that the morphological control of carbides is one of important keys to improve the mechanical properties.