• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.516-517
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• 2007

Because forest fire can give a serious damage to overhead conductors, the thorough understanding about sag behavior of burned conductor is very important in maintaining the transmission line safely. Therefore, a systematic investigation was carried out by heating method. As the heating temperature increases, drastic change of tensile strength of Al wire due to the softening of Al wire occurred. When Al wire is exposed to the flame(about $800^{\circ}C$) during only 13 seconds, the remained tensile strength of Al wire showed under 90%. and then sag of overhead conductor become deteriorated. The detailed results will be given in the text.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.534-535
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• 2007

Because forest fire can give a serious damage to overhead conductors, the thorough understanding about aging behavior of burned conductor is very important in maintaining the transmission line safely. Therefore, a systematic investigation was carried out by heating method. As the heating temperature increases, drastic change of tensile strength of Al wire due to the softening of Al wire occurred. When Al wire is exposed to the flame(about $800^{\circ}C$) during only 13 seconds, the remained tensile strength of Al wire showed under 90%. The detailed results will be given in the text.

• Journal of Mechanical Science and Technology
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• 제19권7호
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• pp.1441-1448
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• 2005

Fine grained AZ31 and AZ61 magnesium alloys produced by equal channel angular pressing (ECAP) were tested for investigating tensile and fatigue properties, including microstructure, monotonic tensile flow, fatigue life and crack growth rate. For the two alloys, the yield stress of the ECAPed sample was lower than that of the unECAPed (=as received) sample, because of the fact that the softening effect due to texture anisotropy overwhelmed the strengthening effect due to grain refinement. Grain refinement of the AZ31 and AZ61 alloys through ECAP was found not to be significantly effective in increasing fatigue strength.

• Computers and Concrete
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• 제17권6호
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• pp.703-721
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• 2016

A novel approach to modeling concrete behavior at the stage of its maturing is presented in this paper. This approach assumes that at any point in the structure, concrete is composed of a set of layers that are activated in time layer by layer, based on amount of released heat that is produced during process of the concrete's maturing. This allows one to assume that each newly created layer has nominal stiffness moduli and tensile/compressive strengths. Hence introduction of explicit stiffness moduli and tensile/compressive strength dependencies on time, or equivalent time state parameter, is not needed. Analysis of plain concrete (PC) and reinforced concrete (RC) structures, especially massive ones, subjected to any kind of straining in their early stage of existence, mostly due to external loads but especially by thermal loading and shrinkage, is the goal of the approach. In this article a simple elasto-plastic softening model with creep is used for each layer and a general layered model behavior is illustrated on one-dimensional (1D) examples.

• Journal of Welding and Joining
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• 제27권2호
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• pp.69-75
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• 2009

The effects of welding speed were investigated on penetration characteristics, defects and mechanical properties including formability test in Nd:YAG laser welded 1000MPa grade DP steels. A shielding gas was not used and bead-on-plate welding was performed with various welding speeds at 3.5kW laser power. Defects of surface and inner beads were not observed in all welding speeds. As the welding speed increased, the weld cross-section varied from the trapezoid having wider bottom bead, through X type, finally to V type in partial penetration range of welding speeds. The characteristic of hardness distribution was also investigated. The center of HAZ had maximum hardness, followed by a slight decrease of hardness as approaching to FZ. Significant softening occurred at the HAZ near BM. Regardless of the welding speed, the weld showed approximately the same hardness distribution. In the perpendicular tensile test with respect to the weld direction, all specimens were fractured at the softening zone. In the parallel tensile test to the weld direction, the first crack occurred at weld center and then propagated into the weld. Good formability over 80% was taken for all welding conditions.

• 한국의류학회지
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• 제14권4호
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• pp.262-273
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• 1990

The purpose of this study is to investigate the softening effect of cellulase-treated cotton fabric and the damage on the fabric which is accompanied by the treatemnt. Cotton fabric is treated with cellulase under various concentrations and time, and the weight loss, hand values (by KES), surface characteristics, moisture regain, tensile strength, copper number and intrinsic viscosity of the treated samples and untreated samples have been compared. The results are as follows: 1. The weight loss of cotton fabric increased as the concentration of cellulase and the treating time increased. 2. The enzyme treatment had little effect on the stiffness of the treated samples but anti- drape stiffness decreased for the treated samples. Fullness and softness of the treated samples increased and crispness decreased with the lowest level reaching after two hours of the treatment for all concentrations. Scrooping feeling of the treated samples increased and flexibility with soft feeling increased as the treating time and the concentration of cellulase increased. 3. Moisture regain of the samples decreased as the treating time and the concentration of the enzyme increased and the treated fabric showed cracks on the fiber surface, and much surface fibers on the fabric have been removed after the treatment. 4. Tensile strength of the samples decreased as the treating time and as the concentration of cellulase increased, and the copper number increased while the intrinsic viscosity decreased as the treating time increased, but cellulase concentration had a little effect.

• 대한토목학회논문집
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• 제7권2호
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• pp.69-77
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• 1987

철근 콘크리트 구조물의 재료적 비선형 해석을 위해 유한요소법을 적용하였다. 2 축응력 상태에서의 콘크리트 거동은 인장균열과 균열사이의 인장증강효과(tension stiffening effect) 그리고 최대압축 강도를 넘어서의 변형연화(strain-softening) 효과를 고려하는 비선형 구성 방정식으로 나타냈다. 콘크리트를 직교성 (orthotropic) 재료로 가정함으로써 비선형 탄성체로 간주하고, 등가일축변형도 개념을 사용한 등가 일축 응력-변형도(equivalent uniaxial stress-strain) 관계식으로 모형화하고, 철근 보강재는 Bauschinger 효과를 갖는 탄소성 변형 경화재료(elasto-plastic strain-hardening material)로 모형화 했다. 평면 응력 상태에서 철근콘크리트 보의 모형화는 각 절점에 2 개의 자유도를 갖는 사각형요소로 모형화하여 적용 시쳤으며, 이로부터 구한 유한요소해석의 결과치를 실험결과치의 중앙처짐, 응력, 변형율 그리고 균열성장과정에 대하여 비교 검토 하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.868-880
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• 2020

One of the main concerns in the structural integrity of offshore pipelines is mechanical damage from external loads. Pipelines are exposed to fatigue failure in welded joints due to geometric discontinuity. In addition, fatigue loads such as currents, waves, and platform motions may cause significant plastic deformation and fracture or leakage within a relatively low-cycle regime. The 2007 ASME Div. 2 Code adopts the master S―N curve for the fatigue evaluation of welded joints based on the mesh-insensitive structural stress. An extension to the master S―N curve was introduced to evaluate the low-cycle fatigue strength. This structural strain method uses the tensile properties of the material. However, the monotonic tensile properties have limitations in describing the material behavior above the elastic range because most engineering materials exhibit hardening or softening behavior under cyclic loads. The goal of this study is to extend the cyclic stress-strain behavior to the structural strain method. To this end, structural strain-based procedure was established while considering the cyclic stress-strain behavior and compared to the structural strain method with monotonic tensile properties. Finally, the improved prediction method was validated using fatigue test data from full-scale girth-welded pipes.

• Geomechanics and Engineering
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• 제29권6호
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• pp.627-643
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• 2022

Water-rock interactions have a significant influence on the mechanical behavior of rocks. In this study, uniaxial compression and tension tests on different water-treated sandstone samples were conducted. Acoustic emission (AE) monitoring and micro-pore structure detection were carried out. Water-rock interactions and their effects on rock mechanical behavior were discussed. The results indicate that water content significantly weakens rock mechanical strength. The sensitivity of the mechanical parameters to water treatment, from high to low, are Poisson ratio (𝜇), uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), elastic modulus (E), and peak strain (𝜀). After water treatment, AE activities and the shear crack percentage are reduced, the angles between macro fractures and loading direction are minimized, the dynamic phenomenon during loading is weakened, and the failure mode changes from a mixed tensile-shear type to a tensile one. Due to the softening, lubrication, and water wedge effects in water-rock interactions, water content increases pore size, promotes crack development, and weakens micro-pore structures. Further damage of rocks in fractured and caved zones due to the water-rock interactions leads to an extra load on the adjoining coal and rock masses, which will increase the risk of dynamic disasters.

• 콘크리트학회논문집
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• 제13권5호
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• pp.491-498
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• 2001

본 연구에서는 강우와 같은 열 충격으로 보수체의 손상(표면 균열, 경계면 파괴)을 유발하는 표면 인장 응력과 기층과 보수층 경계면의 연직 인장 응력 및 진단 응력이 해석적으로 조사되었다. 응력 계산 시에는 사용 재료의 비선형 응력-변형률 곡선이 사용되었고, 특히 변형률 경화, 변형률 연화 특성이 고려되었다. 응력 계산은 보수층의 두께와 보수 재료를 변수로 하여 강우 강도별로 조사되었다. 강우 초기의 보수체의 온도는 하절기에 55$^{\circ}C$까지 가열됐다고 가정하였고, 강우 온도는 1$0^{\circ}C$로 결정하였다. 강우 빈도 1년 1회, 강우 지속 시간 10분, 60분의 강우 하중으로 응력을 계산한 결과, 보수체 표면에서는 실제 균열은 발생치 않고, 단지 변형률 연화 단계의 가상 균열만 형성되었다. 한편 경계면에서는 부착 전단 파괴는 발생치 않았으며, 연직 인장 파괴를 유발하는 음력이 일정한 강우 강도 및 보수 재료에서 보수층의 두께(do)가 클수록 증가하는 것으로 나타나, 경계면의 연직 인장 응력이 보수체의 안전성에 주요한 변수임을 알 수 있었다. 따라서 강우시 경계면의 파괴 예방을 위해 보수 재료의 성질 및 보수층의 두께를 결정할 수 있는 연직 인장 음력의 예측식을 제안하였다.