• Structural Engineering and Mechanics
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• 제7권2호
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• pp.225-240
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• 1999

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

• 소성∙가공
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• 제6권2호
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• pp.102-109
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• 1997

The multistage deformation and stress relaxation were carried out to investigate the strain induced precipitation by torsion tests in the range of 1000~80$0^{\circ}C$, 0.05~5/sec for V-microalloyed steel. The starting temperature and time for the initiation of precipitation were determined by stress relaxation tests. The distribution of precipitates increased, as the strain rate increased and the mean size of precipitates was found to be about 10~30nm. The precipitation starting time$(P_s)$ decreased with increasing strain rate and the amount of pre-strain. The effect of deformation conditions on the no-recrystallization temperature$(T_nr)$ was also determined in the multistage deformation. $T_nr$ Tnr decreased with increasing the strain and strain rate. In the controlled rolling simulation, grain refinement and precipitation hardening effects could be achieved by the alternative large pass strain at the latter half pass stage under the condition of low temperature and high strain rate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 춘계학술대회 논문집
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• pp.159-162
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• 2002

In this paper the stress-strain curves of bearing steels at hot working conditions are obtained by compression test with a computer controlled servo-hydraulic Gleeble 3800 testing machine and elongations and reductions of area of the bearing steels are obtained by tensile test with a computer controlled servo-hydraulic Gleeble 1500 testing machine. These tests have been focused to obtain the flow stress data and optimal hot forging conditions under various conditions of strain rates and temperatures. The strain rate sensitivity exponent and reduction of area of the materials are evaluated. Experimental results are resented for various conditions of temperatures and strain rates.

• Structural Engineering and Mechanics
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• 제55권5호
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• pp.913-929
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• 2015

The ratcheting and strain cyclic behaviour of joined conical-cylindrical shells under uniaxial strain controlled, uniaxial and multiaxial stress controlled cyclic loading are investigated in the paper. The elasto-plastic deformation of the structure is simulated using Chaboche non-linear kinematic hardening model in finite element package ANSYS 13.0. The stress-strain response near the joint of conical and cylindrical shell portions is discussed in detail. The effects of strain amplitude, mean stress, stress amplitude and temperature on ratcheting are investigated. Under strain symmetric cycling, the stress amplitude increases with the increase in imposed strain amplitude. Under imposed uniaxial/multiaxial stress cycling, ratcheting strain increases with the increasing mean/amplitude values of stress and temperature. The abrupt change in geometry at the joint results in local plastic deformation inducing large strain variations in the vicinity of the joint. The forcing frequency corresponding to peak axial ratcheting strain amplitude is significantly smaller than the frequency of first linear elastic axial vibration mode. The strains predicted from quasi static analysis are significantly smaller as compared to the peak strains from dynamic analysis.

• 한국정밀공학회지
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• 제4권1호
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• pp.53-64
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• 1987

Low Cycle fatigue data through stress controlled and strain controlled tests at room temperature were obtained for solution treated and thermally aged 304 stainless steel. All the tests were conducted with the greguency, 1Hz of stress controlled and the strain rate, 40%/min of strain controlled. The aged specimen had the longer fatigue life at the lower stresses than at the higher stresses. It is shown that the fatigue limit of the aged specimen was a little higher than that of the solution treated specimen. It is considered to be due to the presence of carbide precipitates at grain boundary which depressed the crack propagation. The aged specimen showed the larger alternating stress and the more rapid cyclic work harding than the solution treated specimen. Bauschinger effect of the aged specimen was not pronounced than that of the solution treated specimen.

• 소성∙가공
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• 제14권1호
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• pp.65-70
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• 2005

A phase mixture model was employed to simulate the deformation behaviour of metallic materials covering a wide grain size range from micrometer to nanometer scale. In this model a polycrystalline material is treated as a mixture of two phases: grain interior phase whose plastic deformation is governed by dislocation and diffusion mechanisms and grain boundary 'phase' whose plastic flow is controlled by a boundary diffusion mechanism. The main target of this study was the effect of grain size on stress and its strain rate sensitivity as well as on the strain hardening. Conventional Hall-Petch behaviour in coarse grained materials at high strain rates governed by the dislocation glide mechanism was shown to be replaced with inverse Hall-Petch behaviour in ultrafine grained materials at low strain rates, when both phases deform predominantly by diffusion controlled mechanisms. The model predictions are illustrated by examples from literature.

• Korea-Australia Rheology Journal
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• 제16권4호
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• pp.213-218
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• 2004

Linear high-density polyethylene (PE) was controlled to induce strain-hardening behavior by introducing a small amount of second component with an anisotropic structure. In order to form an anisotropic structure in the PE matrix, the polymer was extruded through a twin-screw extruder, and the structure was controlled by varying the extrusion conditions. Depending on conditions, the second component formed a film, thread and droplet structure. If the second component was kept rigid, the morphology evolution could be delayed and the second component could maintain its film or thread structure without further relaxation. In par­ticular, the second component of the thread structure made a physical network and gave rise to remarkable strain hardening behavior under high extension. This study suggests a new method that induces strain hard­ening behavior by introducing a physically networked second component into the linear polymer melt. This result is anticipated to improve the processibility of linear polymers especially when extensional flow is dominant, and to contribute to our understanding of strain hardening behavior.

• 한국지진공학회논문집
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• 제28권1호
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• pp.33-39
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• 2024

Understanding the behavior of soil under cyclic loading conditions is essential for assessing its response to seismic events and potential liquefaction. This study investigates the effect of non-plastic fines content (FC) on excess pore pressure generation in medium-density sand-silt mixtures subjected to strain-controlled cyclic direct simple shear (CDSS) tests. The investigation is conducted by analyzing excess pore pressure (EPP) ratios and the number of cycles to liquefaction (Ncyc-liq) under varying shear strain levels and FC values. The study uses Jumunjin sand and silica silt with FC values ranging from 0% to 40% and shear strain levels of 0.1%, 0.2%, 0.5%, and 1.0%. The findings indicate that the EPP ratio increases rapidly during loading cycles, with higher shear strain levels generating more EPP and requiring fewer cycles to reach liquefaction. At 1.0% and 0.5% shear strain levels, FC has a limited effect on Ncyc-liq. However, at a lower shear strain level of 0.2%, increasing FC from 0 to 10% reduces Ncyc-liq from 42 to 27, and as FC increases further, Ncyc-liq also increases. In summary, this study provides valuable insights into the behavior of soil under cyclic loading conditions. It highlights the significance of shear strain levels and FC values in excess pore pressure generation and liquefaction susceptibility.

• Journal of Welding and Joining
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• 제12권1호
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• pp.73-79
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• 1994

Low cycle fatigue test was performed by companion specimens method to compare the properties of cyclic strain for the weldments of controlled rolling steel CR60 and welding structural steel SM58Q. And the result does not showed any difference of low cycle fatigue life between weldments. Especially, the values of coefficient of cyclic plastic strain $C_{p}$ and exponent of cyclic plastic strain $K_{p}$ of heat affected zones of CR60 steel and SM58Q steel were same. And $C_{p}$ and $K_{p}$ of CR60 steel were equal to the values of weld it means a good combination between the base metal, the heat affected zone and the weld of CR60 steel.eel.eel.

• 전산구조공학
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• 제10권4호
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• pp.229-238
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• 1997

본 논문에서는 반복하중에 의해 손상을 입은 아스팔트 콘크리트의 점탄성 구성모델에 대한 역학적 접근방법을 제시하였다. 모의변수로 나타낸 탄성-점탄성 일치원리는 아스팔트 콘크리트의 점탄성과 시간의존 손상의 증가를 별도로 평가하도록 적용되었다. 선형-점탄성 파괴역학에 사용되고 있는 미소균열의 증가법칙이 물체내 손상증가를 나타내는데 성공적으로 사용되었다. 응력과 모의변형도로 나타나는 구성방정식은 먼저 변형도조절에 대해 세워졌으며, 응력과 모의변형도를 모의응력과 변형도로 간단하게 대체함으로써 응력조절 구성방정식으로 변형되었다. 모의응력으로 나타낸 변형된 구성방정식은 응력조절모드에서 파괴에 이르는 아스팔트 콘크리트의 모든 역학적 거동을 충분히 예측하고 있다.