• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.183-186
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• 2000

The high temperature deformation behavior of spray-formed Al-19wt%Si-1.87wt%Mg-0.085wt.%Fe alloy was studied by torsion testing in the strain rate range of 0.001-1 sec-1 and in the temperature range of 300-500 $^{\circ}C$. The relationship between stress temperature and strain rate is expressed using the Power law. the behavior of dynamic recrystallization is showed in 300-35$0^{\circ}C$, 1-0.1sec-1 and the behavior of dynamic recovery is showed in 450-50$0^{\circ}C$, 0.01-0.001sec-1 The size of Si particles is mall when the temperature is low and the strain rate is high. The strain rate sensitivity(m) and the apparent activation energy(Q) indicate the dependence on strain rate and temperature for flow stress respectively. The hot ductility is high when m is high and Q is low. The maps of strain rate sensitivity and apparent activation energy suggest the optimum processing conditions.

• 한국구조물진단유지관리공학회 논문집
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• 제23권1호
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• pp.54-62
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• 2019

본 논문에서는 압축파괴에너지를 이용하여 고강도 구속콘크리트에 대한 응력-변형률 모델을 제안하였다. 참고문헌[5]에서 저자가 실시한 압축실험에는 변형률 게이지를 부착한 아크릴 막대를 실험체의 중앙부에 매립하여 압축부재의 국부 변형률 측정을 시도하였다. 이 아크릴 막대를 이용한 국부 변형률 측정은 매우 효과적인 것으로 나타났다. 압축파괴영역길이는 아크릴 막대로부터 측정된 국부 변형률 분포에 기초하여 정의되었다. 구체적으로, 구속콘크리트의 국소파괴영역길이는 압축강도 발현시의 변형률 ${\varepsilon}_{cc}$의 2배 이상 변형률이 증가하는 영역으로 정의하였다. 또한, 동일한 횡구속압을 받는 압축부재에 흡수된 에너지양은 부재의 형상이나 크기에 관계없이 일정하다는 가정에서 압축 파괴에너지를 도입한 구속콘크리트의 응력-변형률 관계를 제안하였다. 본 연구에서 제안된 모델은 본 연구의 실험결과뿐만 아니라 타 연구자들의 실험결과를 대체적으로 잘 예측하는 것으로 나타났다.

• 콘크리트학회논문집
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• 제27권4호
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• pp.363-375
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• 2015

본 연구에서는 탄성변형 에너지를 이용하는 충격실험장치인 변형에너지 충격시험장치(SEFIM)의 변형률 속도를 증가시키기 위하여, 탄성변형 에너지가 저장되는 에너지 프레임의 직경 및 재질을 다르게 하여 그 영향을 조사하였다. 현재 강재를 에너지 프레임의 재질로 사용한 SEFIM의 발현 가능한 변형률 속도범위는 10-40 /sec까지이지만, 에너지 프레임의 재질과 직경을 다르게 하여 충격 시 변형률 속도가 72 /sec까지 증가되었다. 충격실험에 사용된 HPFRCCs는 장섬유 1%와 단섬유 1%를 함께 초고강도 콘크리트에 혼입하였다. 정적 변형률 속도에서 뿐만 아니라, 네 가지 종류의 에너지 프레임을 사용한 높은 변형률 속도(14-72 /sec)에서도 변형경화 거동을 나타내었다. 에너지 프레임의 직경을 기존의 35 mm에서 25 mm로 작게 변경함에 따라서 변형률 속도가 증가하였으며, 에너지 프레임 재질을 강재, 알루미늄 그리고 티타늄으로 변경함에 따라, 강재보다 높은 탄성파 속도를 가지고 많은 크기의 탄성변형 에너지를 저장할 수 있는 티타늄 합금을 사용한 경우 더욱 높은 변형률 속도(72 /sec)를 생성하였다. 알루미늄 재질의 에너지 프레임의 경우 충격실험 시 작용되었던 응력으로 인해 탄성영역을 벗어나 소성변형을 일으켜 파단되어 본래 가지고 있던 성질을 발현하지 못하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.132-137
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• 2004

In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via [mite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions. which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress.strain curve with an average error less than 3%.

• Journal of Welding and Joining
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• 제10권1호
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• pp.43-51
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• 1992

The plastic zone formed around a notch tip is important in analyzing the fracture toughness of structures and particularly weld cracks existed in the weld HAZ (heat affected zone) which produces local plastic deformation at the crack tip. Therefore, in order to analyze the fracture toughness in weld HAZ, it is necessary to investigate the new fracture toughness parameter $K_{c}$ $^{*}$ and critical plastic strain energy $W_{p}$ $^{c}$ according to the shape and size of the plastic zone. 1) If the temperature corresponding to $K_{c}$ $^{*}$=130kg-m $m^{-3}$ 2/ is determined, transition temperature $T_{tr}$ the magnitude of plastic zone size, and heat input change depending on the fracture toughness. The blunted amounts of the parent and weld HAZ show mild linear variation until .delta.=0.4mm and then increase very steeply there after. 2) The relation between the plastic strain energy( $W^{p}$ ) and transition temperature( $T_{*}$tr) in parent metal is more sensitive than that of weld HAZ. However, the plastic strain energy depends on the transition temperature, and thus the yield stress, .sigma.$_{ys}$ becomes an important parameter for plastic strain energy. 3) The critical plastic strain energy( $W_{p}$ $^{c}$ ) absorbed by the plastic zone at the notch tip indicated in case of parent metal: 60J/mm, in case of heat input(20KJ/cm): 75J/mm, in case of heat input(30KJ/cm); 50J/mmJ/mm.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2002년도 제9회 학술 발표회 프로그램과 논문초록
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• pp.30-30
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• 2002

The native forms of common globular proteins are in their most stable state but the native forms of plasma serpins (serine protease inhibitors) show high-energy state interactions. The high-energy state strain of a ${\alpha}$$_1$-antitrypsin, a prototype serpin, is distributed throughout the whole molecule, but the strain that regulates the function directly appears to be localized in the region where the reactive site loop is inserted during complex formation with a target protease.(omitted)

• Geomechanics and Engineering
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• 제7권4호
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• pp.335-353
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• 2014

The softening hyperelastic model based on the strain energy limitation is of clear concepts and simple forms to describe the failure of materials. In this study, a linear and a nonlinear softening hyperelastic model are proposed to characterize the deformation and the failure in granular materials by introducing a softening function into the shear part of the strain energy. A method to determine material parameters introduced in the models is suggested. Based on the proposed models the numerical examples focus on bearing capacity and strain localization of granular materials. Compared with Volokh softening hyperelasticity and classical Mohr-Coulomb plasticity, our proposed models are able to capture the typical characters of granular materials such as the strain softening and the critical state. In addition, the issue of mesh dependency of the proposed models is investigated.

• 펄프종이기술
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• 제39권3호
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• pp.24-29
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• 2007

The stress and strain properties of KOCC were modified to improve the performance of KOCC as a packaging raw material. The refining consistency, refining degree, blending conditions and the grammage of handsheet were varied. The stress-strain properties, tensile energy absorption were measured. The refining improved significantly the stress and strain properties of paper, especially at lower refining consistency. The increase of grammage also contributed to the improvement in the stress and strain of paper. It was also found that the refining, blending and grammage contributed to the increase of tensile energy absorption. However, it is strongly recommended to apply the combination of refining consistency, refining degree and mechanical treatment(blending).

• Coupled systems mechanics
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• 제8권5호
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• pp.377-391
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• 2019

The present paper is focused on analyzing the delamination of inhomogeneous multilayered rods of circular cross-section loaded in torsion. The rods are made of concentric longitudinal layers of individual thickness and material properties. A delamination crack is located arbitrary between layers. Thus, the internal and external crack arms have circular and ring-shaped cross-sections, respectively. The layers exhibit continuous material inhomogeneity in radial direction. Besides, the material has non-linear elastic behavior. The delamination is analyzed in terms of the strain energy release rate. General solution to the strain energy release rate is derived by considering the energy balance. The solution is applied to analyze the delamination of cantilever rod. For verification, the strain energy release rate is derived also by considering the complementary strain energy.

• Geomechanics and Engineering
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• 제29권2호
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• pp.99-111
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• 2022

Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.