• 동력기계공학회지
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• 제9권4호
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• pp.137-142
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• 2005

The effects of temperature and initial crack length on impact fracture behavior of side plate material of 35 ton class FRP ship, which are composed by glass fiber and unsaturated polyester resin, were investigated. Impact fracture toughness of GF/PE composites displayed maximum value when the temperature of specimen is room temperature and $50^{\circ}C$, and with decrease in temperature of specimen, impact fracture toughness decreased. Impact fracture energy of GF/EP composites decreased with increase in initial crack length of specimen, and this value decreased rapidly when the temperature of specimen is lowest, $-25^{\circ}C$,. It is believed that sensitivity of notch on impact fracture energy were increased with decrease in temperature of specimen. As the GF/EP composites exposed in low temperature, impact fracture toughness of composites decreased gradually owing to the decrease of interface bonding strength caused by difference of thermal expansion coefficient between the glass fiber/polyester resin. Further, decrease of interface bonding strength of composites with decrease in specimen temperature was ascertained by SEM photograph of impact fracture surface.

• Journal of Welding and Joining
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• 제16권2호
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• pp.93-99
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• 1998

The effects of welding conditions of gas metal arc welding on the elements loss of solid wire, oxygen content and impact toughness of weld metals were studied. Deoxidizing elements loss was increased with increase of arc voltage in both short-circuit transfer mode and globular transfer mode. It is believed that increase of arc voltage results in increase of reaction time between elements in the droplet and surrounding gas at the end of wire and in the arc column. Based on the thermodynamic equilibrium model, the oxygen content of weld metal can be predicted with the content of silicon and manganese as following : [%O] = $K([%Si][%Mn])^{-0.25}$, K = -15518/T+6.01. The equilibrium temperature was dependent on shielding gas, and it was 187$0^{\circ}C$ for $CO_2$ gas and 180$0^{\circ}C$ for 20%$CO_2$-80%Ar gas. The oxygen content of weld metal which shows maximum impact toughness was varied with deoxidizing alloy system of wires, 0.041 wt% for Si-Mn type wire and 0.026 wt% for Si-Mn-Ti type wire.

• Journal of Welding and Joining
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• 제24권1호
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• pp.64-70
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• 2006

570MPa grade weldable steels were gas metal arc welded with various heat inputs and interpass temperatures using flux cored wires. Effects of heat input and interpass temperature on the strength and impact toughness of weld metal were investigated in terms of microstructural change, recovery of alloying elements, and the amount of reheated weld metal. Increase of heat input and interpass temperature resulted in decrease of weld metal strength. This is because of the small amount of acicular ferrite, large columnar size and low recovery of alloying elements such as manganese and silicon. In addition to the microstructural change, weld metal toughness was also influenced by the deposition sequence. It increased with an increase of the amount of reheated weld metal.

• 한국재료학회지
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• 제25권8호
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• pp.417-422
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• 2015

In this study, low-carbon hypoeutectoid steels with different ferrite-pearlite microstructures were fabricated by varying transformation temperature. The microstructural factors such as pearlite fraction and interlamellar spacing, and cementite thickness were quantitatively measured and then Charpy impact tests conducted on the specimens in order to investigate the correlation of the microstructural factors with impact toughness and ductile-brittle transition temperature. The microstructural analysis results showed that the pearlite interlamellar spacing and cementite thickness decreases while the pearlite fraction increases as the transformation temperature decreases. Although the specimens with higher pearlite fractions have low absorbed energy, on the other hand, the absorbed energy is higher in room temperature than in low temperature. The upper-shelf energy slightly increases with decreasing the pearlite interlamellar spacing. However, the ductile-brittle transition temperature is hardly affected by the pearlite interlamellar spacing because there is an optimum interlamellar spacing dependent on lamellar ferrite and cementite thickness and because the increase in pearlite fraction and the decrease in interlamellar spacing with decreasing transformation temperature have a contradictory role on absorbed energy.

• 한국소음진동공학회논문집
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• 제14권7호
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• pp.551-560
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• 2004

A method how to determine the shock response spectrum from the FRF of the statistical energy analysis( SEA ) is presented here. The system of 3 different Plates connected by bolt joints is selected simulating missile structural sections Joined together. First, the SEA model was rendered by SEA parameters which were determined from experimental SEA method. Then, the mobility power was input to the SEA model and we can verify the validity of the model in the medium to high frequency range checking the reproduction of output average velocity. And, the shock induced shock response spectrum(SRS) was obtained using SEA FRF and arbitrarily chosen experimental FRF. We have compared the thus obtained SRS with actually measured SRS and they were relatively in good agreement. In this paper, we used the measured SEA FRF and therefore we have got the SRS well agreed with actually measured SHS even in the low frequency range. If the SEA FRF of well verified SEA model is used, the good result will come out in SEA effective frequency range which is more important at SRS.

• 대한금속재료학회지
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• 제56권11호
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• pp.796-804
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• 2018

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

• 열처리공학회지
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• 제32권4호
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• pp.161-167
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• 2019

Impact toughness and fracture behavior were studied in five kinds of non-heat treating steels containing bainite; standard(0.25C-1.5Mn-0.5Cr-0.2Mo-0.15V), high V(0.3V), Ni(0.5Mn-2Ni), W(0.4W instead of Mo), and high C-Ni(0.35C-0.5Mn-2Ni) steels. The good hardness and impact toughness balance was exhibited in the $1100^{\circ}C$-rolled condition, while the impact toughness was deteriorated due to coarse grained microstructure in the $1200^{\circ}C$-rolled condition. The impact toughness decreased with increasing the hardness in all steels studied. The fracture behavior was also basically identical, that is, the fracture area was divided into 3 zones; shear and fibrous zone, fracture transition zone with ductile dimples and cleavage cracks, where the cracks initiate and grow to critical size, unstable cleavage fracture propagation zone. The energy absorbed for the critical crack formation through the plastic deformation inside the plastic zone in front of the notch root contributed to a mostly significant portion of the total impact energy.

• 화약ㆍ발파
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• 제39권2호
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• pp.1-14
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• 2021

최근에는 GPGPU(General-Purpose computing on Graphics Processing Units)와 같은 고성능 연산장치의 보급과 함께 국방, 우주항공분야에서 암질재료에 대한 충격실험을 대신할 수 있는 3차원 동적해석기법의 개발이 활발하게 진행되고 있다. 그러나 높은 충격하중을 수반하는 암 발파 또는 소형미사일 등의 지중 관통과 같은 과정을 실험적으로 관찰하거나 계측하는 것은 암질재료의 비 균질성 및 불투명성 때문에 어려움이 있었다. 본 연구에서는 고속충돌에 의한 암석의 파괴 거동을 모사하기 위하여 3차원 동적 파괴 과정 해석 기법 (3D-DFPA)를 개발하였으며, 연산속도를 향상시키기 위하여 순차해석(explicity analysis) 및 접촉요소검색(Searching algolitm of contact elements)에 GPGPU연산이 가능한 알고리듬을 적용하였다. 제안된 동적파괴과정해석 기법에 대한 검증을 위해 Straight Notched Disk Bending (SNDB) 석회암시료에 대한 동적파괴인성시험을 모사하였고, 충격응력파의 전파과정, 암석-충격봉 경계면에서 반사 및 전달과정, 암석 시료의 파괴과정을 비교분석하여, 개발된 해석기법에 대한 검증을 수행하였다.

• 콘크리트학회논문집
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• 제14권3호
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• pp.283-290
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• 2002

일반적으로 불포화 폴리에스테르 모르타르 및 콘크리트는 강도가 우수하고 내약품성이 좋지만, 취성적이어서, 내충격성이 요구되는 용도로는 사용하기 어렵다. 그러므로, 본 연구에서는 재생골재와 불포화 폴리에스테르 액상수지를 사용한 바닥마감재를 개발하기 위해 불포화 폴리에스테르 모르타르의 취성을 개선시켜보고자 하였다. 불포화 폴리에스테르 모르타르의 취성을 개선하기 위한 재료로 폴리우레탄 액상고무를 사용하였으며, 폴리올의 분자량과 폴리우레탄 액상고무의 치환율에 따른 모르타르의 특성을 검토했다. 실험결과, 폴리우레탄 액상고무의 사용에 따라 불포화 폴리에스테르 모르타르의 점도가 증가하였고, 경화수축은 감소하였다. 그리고, 모르타르내에 생성된 고무입자에 의해 압축강도 및 휨강도는 다소 저하하였지만, 내충격성이 향상되고, 휨파괴시험결과에서 파괴하중이후에도 급격한 파괴를 보이지 않는 결과를 얻을 수 있었다. 따라서, 본 연구의 결과는 폴리올의 분자량 2000, 3000인 폴리우레탄 액상고무를 불포화 폴리에스테르 모르타르에 사용하여 취성의 개선효과를 얻을 수 있다는 것을 제시하고 있다.

• 월간당뇨
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• 통권209호
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• pp.19-24
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• 2007

당뇨병에 성기능장애가 많다는 것은 옛날부터 알려져 있지만 실제로는 그릇된 지식과 선입관에 의해 과장되게 잘못알고 있는 경우가 많다. 당뇨병이라고 모두 발기부전 환자는 아닌 것이며 정상 건강인보다 조금 높은 빈도를 보이는 것뿐이다. 식사요법과 운동요법으로 혈당조절을 잘하고 합병증을 예방하면 정상인과 다름없는 성생활을 할 수 있으며 인슐린 치료를 계속하면서 주의 깊게 혈당을 조절하고 합병증을 예방하면 60세 이후까지도 정상적인 성생활이 가능하다. 정상인도 노쇠하면 자연현상으로 언젠가는 모두 발기부전이 되므로 당뇨병환자만이 발기부전이 오는 것은 아니므로 미리 겁내고 불안해할 필요는 없는 것이다. 당뇨병환자중에는 선입관에 의해 당뇨라는 진단을 받고 정신적 충격과 그릇된 지식으로 심인성 발기부전에 빠지는 사람이 상당히 많다. 그러므로 당뇨병환자는 정상인보다 더 많은 노력을 하며 합병증의 병발을 미연에 방지하는 것이 가장 중요하다.