• Structural Engineering and Mechanics
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• 제50권1호
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• pp.89-103
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• 2014

According to experimental studies made so far, design formula of shear characteristics suggested by ISO 22762 and JEAG 4614, representative design code for Lead Rubber Bearing(LRB) shows dependence caused by changes in compressive stress. Especially, in the case of atypical special structure, such as a nuclear power structure, placement of seismic isolation bearing is more limited compared to that of existing structures and design compressive stress is various in sizes. As a result, there is a difference between design factor and real behavior with regards to shear characteristics of base isolation device, depending on compressive stress. In this study, a full-scale low hardness device of LRB, representative base isolation device was manufactured, analyzed, and then evaluated through an experiment on shear characteristics related to various compressive stresses. With design compressive stress of the full-scale LRB (13MPa) being a basis, changes in shear characteristics were analyzed for compressive stress of 5 MPa, 10 MPa, 13 MPa, 15 MPa, and 20 MPa based on characteristics test specified by ISO 22762:2010 and based on the test result, a regression analysis was made to offer an empirical formula. With application of proposed design formula which reflected the existing design formula and empirical formula, trend of horizontal characteristics was analyzed.

• 터널과지하공간
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• 제6권2호
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• pp.101-121
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• 1996

The thermomechanical characteristics of rocks such as temperature dependency of strength and deformation were experimentally investigated using Iksan granite, Cheonan tonalite and Chung-ju dolomite for proper design and stability analysis of underground structures subjected to temperature changes. For the temperature below critical threshold temperature $T_c$, the variation of uniaxial compressive strength, Young's modulus, Brazilian tensile strength and cohesion with temperature were slightly different for each rock type, but these mechanical properties decreased at the temperatures above $T_c$ by the effect of thermal cracking. Tensile strength was most affected by $T_c$, and uniaxial compressive strength was least affected by $T_c$. To the temperature of 20$0^{\circ}C$ with the confining prressure to 150 kg/$\textrm{cm}^2$, failure limit on principal stress plane and failure envelope on $\sigma$-$\tau$ plane of Iksan granite were continuously lowered with increasing temperature but those of Cheonan tonalite and Chung-ju dolomite showed different characteristics depending on minor principal stress on principal stress plane and normal stress on $\sigma$-$\tau$ plane. The reason for this appeared to be the effect of rock characteristics and confining pressure. Young's modulus was also temperature and pressure dependent, but the variation of Young's modulus was about 10%, which was small compared to the variation of compressive strength. In general, Young's modulus increased with increasing confining pressure and increased or decreased with increasing temperature to 20$0^{\circ}C$ depending on the rock type.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.101-104
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• 2003

Influences of transverse compressive stress on the critical current ( $I_{c}$) in AgMg and AgMn alloy sheathed Bi-2223 tapes were investigated at 77 K and 0 T. The $I_{c}$ degradation behavior depending on sample specifications was discussed in viewpoints of n-value and damage morphology. As a result, Bi-2223 tapes showed a significant drop in $I_{c}$ for stresses greater than 50MPa. The AgMg sheathed Bi-2223 tapes representing higher $I_{c}$ showed a lower $\sigma$$_{irr}$ and a significant $I_{c}$ degradation with increase in compressive stress. There existed a voltage tap separation dependency of the $I_{c}$ degradation behavior caused by the transverse compressive stress.sive stress.s.

• 한국세라믹학회지
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• 제50권1호
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• pp.82-86
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• 2013

A poled lead zirconate titanate (PZT) cube specimen is subjected to impulse-type compressive stress with increasing magnitude in parallel to the poling direction at four room and high temperatures. During the ferroelastic domain switching induced by the compressive stress, electric displacement in the poling direction and longitudinal and transverse strains are measured. Using the measured responses, linear material properties, namely, the piezoelectric and elastic compliance coefficients, are evaluated by a graphical method, and the effects of stress and temperature are analyzed. Finally, the dependency of the evaluated linear material properties on relative remnant polarization is analyzed and discussed.

• 대한전자공학회논문지SD
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• 제45권4호
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• pp.57-63
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• 2008

본 논문에서는 Contact Etch Stop Layer (CESL)인 nitride film의 mechanical stress에 의해 인가되는 channel stress가 소자 특성에 미치는 영향에 대해 분석하였다. 잘 알려진 바와 같이 NMOS는 tensile stress와 PMOS에서는 compressive stress가 인가되었을 경우 drain current가 증가하였으며 그 원인을 체계적으로 분석하였다. NMOS의 경우 tensile stress가 인가됨으로써 back scattering ratio ($\tau_{sat}$)의 감소와 thermal injection velocity ($V_{inj}$)의 증가로 인해 mobility가 개선됨을 확인하였다. 또한 $\tau_{sat}$, 의 감소는 온도에 따른 mobility의 감소율이 작고, 그에 따른 mean free path ($\lambda_O$)의 감소율이 작기 때문인 것으로 확인되었다. 한편 PMOS의 compressive stress 경우에는 tensile stress에 비해 온도에 따른 mobility의 감소율이 크기 때문에 channel back scattering 현상은 심해지지만 source에서의 $V_{inj}$가 큰 폭으로 증가함으로써 mobility가 개선됨을 확인 할 수 있었다. 따라서 CES-Layer에 의해 인가된 channel stress에 따른 소자 특성의 변화는 inversion layer에서의 channel back scattering 현상과 source에서의 thermal injection velocity에 매우 의존함을 알 수 있다.

• 대한기계학회논문집A
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• 제27권1호
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• pp.200-207
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• 2003

In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities of shot balls on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are being commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage II and the threshold stress intensity factor range Δ$K_{th}$ in stage I. Also the material constant C and the crack propagation index m in the formula of paris law da/dN= C $({\Delta}K^m)$ were suggested in this work to estimate the dependency on the shot velocity.

• 한국지반공학회논문집
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• 제21권7호
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• pp.73-80
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• 2005

도로기초에서 입상재료의 응력의존 특성을 반영하면 응력의존 탄성계수와 응력 의존 포와송 비 모두를 동시에 고려할 수 있다. 이 방식은 기존 연속체 역학에 기초한 해석 방식과는 달리 층모형 내에서 인장력의 발생 대신 압축력의 구현이 가능하여 재료의 강성과 연성에 대한 거동을 동시에 반영하여 입상재료층의 변형 예측에 많은 영향을 주고 있다 따라서 본 논문에서는 도로기초를 대상으로 제안된 응력의존 및 변형 모형을 대상으로 유한요소법에 의한 도로기초 층변형 예측 알고리즘을 제안하였고 층변형 예측시 응력의존의 고려에 따른 영향을 분석하였다.

• KCI Concrete Journal
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• 제13권1호
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• pp.53-60
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• 2001

Tests of cylindrical concrete specimens under lateral confining pressure of up to 5,000 psi were conducted for two different axial loading cases: monotonic compression and monotonic tension. The purpose of this experimental investigation is to provide stress-strain characteristics of plain concrete in triaxial stress conditions. Lateral confining pressure levels, loading rates, and strength of concrete specimens are varied as parameters. The loading rates are $34.75$\times$10^{-5}$ in/in/sec for fast, $\times$$6.95x10^{-5}$ in/in/sec for normal. and $0.579$\times$10^{-5}$ in/in/sec for slow loading cases. The concrete specimens used in the experiment have compressive strength of 3,500 psi and 6,500 psi, respectively. Findings of this experiment include dependency of the stress-strain behavior of concrete on the above parameters under two different types of loading conditions. The parametric study includes a series of 106 triaxial tests.

• 대한기계학회논문집A
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• 제32권8호
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• pp.642-653
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• 2008

In this paper, we propose a 3-D finite element (FE) analysis model with combined physical behavior and kinematical impact factors for evaluation of residual stress in multi-impact shot peening. The FE model considers both physical behavior of material and characteristics of kinematical impact. The physical parameters include elastic-plastic FE modeling of shot ball, material damping coefficient, dynamic friction coefficient. The kinematical parameters include impact velocity and diameter of shot ball. Multi-impact FE model consists of 3-D symmetry-cell. We can describe a certain repeated area of peened specimen under equibiaxial residual stress by the cell. With the cell model, we investigate the FE peening coverage, dependency on the impact sequence, effect of repeated cycle. The proposed FE model provides converged and unique solution of surface stress, maximum compressive residual stress and deformation depth at four impact positions. Further, in contrast to the rigid and elastic shots, plastically deformable shot produces residual stresses closer to experimental solutions by X-ray diffraction. Consequently, it is confirmed that the FE model with peening factors and plastic shot is valid for multi-shot peening analyses.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.274-275
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• 2005

The tensile strain dependency of critical current in YBCO coated conductors was examined at 77K and in the self magnetic field. A commercially available YBCO sample with Cu stabilizer layer was supplied. There existed a peak in the relation between the Ie and tensile strain, and the reversible variation of $I_c$ with applied tensile strain was found. In the neutral axis Ni alloy RABiTS-$Y_2O_3$/YSZ/$CeO_2$ buffered YBCO tape, the $I_c$ recovered reversibly until the applied strain reached to about 0.5%, representing that a significant residual compressive strain induced during cooling to 77 K influenced the axial strain tolerance of YBCO conductors. To investigate the strain and stress influence on the $I_c$, the stress-strain characteristics of YBCO conductors measured at 77 K were discussed.