• Geomechanics and Engineering
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• v.31 no.1
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• pp.87-97
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• 2022

The excessive settlement and deformation of disintegrated carbonaceous mudstone (DCM) embankments under dynamic loading have long been problems for engineers and technicians. In this work, the characteristics and mechanism of the plastic deformation of DCM under different degrees of compaction, water contents and confining pressures were studied by static triaxial, dynamic triaxial and scanning electron microscopy testing. The research results show that the axial stress increases with increasing confining pressure and degree of compaction and decreases with increasing water content when DCM failure. The axial strain at failure of the DCM decreases with increasing confining pressure and degree of compaction and increases with increasing water content. Under cyclic dynamic stress, the change in the axial stress level of the DCM can be divided into four stages: the stable stage, transition stage, safety reserve stage and unstable stage, respectively. The effects of compaction, water content and confining pressure on the critical axial stress level which means shakedown of the DCM are similar. However, an increase in confining pressure reduces the effects of compaction and water content on the critical axial stress level. The main deformation of DCM is fatigue cracking. Based on the allowable critical axial stress, a method for embankment deformation control was proposed. This method can determine the degree of compaction and fill range of the embankment fill material according to the equilibrium moisture content of the DCM embankment.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.11
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• pp.158-165
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• 2003

A specific experimental method, the Split Hopkinson pressure bar (SHPB) technique has been widely used to determine the dynamic material properties under the impact compressive loading conditions with strain rate of the order of 10$^3$/s∼l0$^4$/s. In this paper, dynamic deformation behaviors of rubber materials widely used for the isolation of vibration from structure under varying dynamic loading are determined by using plastic SHPB technique. A transition point to scope with the dynamic deformation behavior of rubber-like material is defined in this paper and used to characterize the specifics of the dynamic deformation of rubber materials.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.96-100
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• 2003

In the tensile loading of sheet metals made from polycrystalline aluminum alloys, a single deformation band appears inclined to the elongation axis in the early stage of plastic deformation, and symmetric double bands are observed in the later stage. This character of the localized deformation bands has been analyzed by a perturbation method. Macroscopic slip modes composed of slip planes and slip directions were assumed to describe the tensile and shear strains. Along time integration path, the value of the perturbation growth parameter was checked to find at which angle to the elongation axis the localized deformation bands are generated. It was shown that the mode of the localized deformation is related to asymmetry of material property.

• Steel and Composite Structures
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• v.32 no.2
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• pp.157-171
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• 2019

In this research, the dynamic instability region (DIR) of the sandwich nano-beams are investigated based on nonlocal strain gradient elasticity theory (NSGET) and various higher order shear deformation beam theories (HSDBTs). The sandwich piezoelectric nano-beam is including a homogenous core and face-sheets reinforced with functionally graded (FG) carbon nanotubes (CNTs). In present study, three patterns of CNTs are employed in order to reinforce the top and bottom face-sheets of the beam. In addition, different higher-order shear deformation beam theories such as trigonometric shear deformation beam theory (TSDBT), exponential shear deformation beam theory (ESDBT), hyperbolic shear deformation beam theory (HSDBT), and Aydogdu shear deformation beam theory (ASDBT) are considered to extract the governing equations for different boundary conditions. The beam is subjected to thermal and electrical loads while is resting on Visco-Pasternak foundation. Hamilton principle is used to derive the governing equations of motion based on various shear deformation theories. In order to analysis of the dynamic instability behaviors, the linear governing equations of motion are solved using differential quadrature method (DQM). After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various shear deformation theories, nonlocal parameter, strain gradient parameter, the volume fraction of the CNTs, various distributions of the CNTs, different boundary conditions, dimensionless geometric parameters, Visco-Pasternak foundation parameters, applied voltage and temperature change on the dynamic instability characteristics of sandwich piezoelectric nano-beam.

• Transactions of Materials Processing
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• v.10 no.1
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• pp.42-52
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• 2001

The static softening mechanisms of 304 stainless steel were studied by hot torsion test. The interrupted deformation tests were performed In the range of 900~$1100^{\circ}C$ and 5.0$\times$$10^{-2}$- 5.0$\times$$10^0$/sec. The metadynamic recrystallization (MDRX) could be distinguished from the static recrystallization (SRX). Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. To the exact prediction of MDRX, the MDRX parameter, which could be simultaneously estimated by the interpass time and Zener-Hollomon parameter, was developed. The time lot 50% MDRX, $t_{0.5} was modeled using the deformation parameters : $t_{0.5} = 1.33\times10^{-11}$ $\.\varepsilon^{-0.41}$ D exp(230.3kJ/mol/RT) and the predicted value was very correspondent with the measurement. It was found that the static parameters such as interpass time can control the dynamic states in the several successive deformation process.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.2
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• pp.132-143
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• 2003

Viscoelastic components for vibration isolation or shock absorption in automobiles, machines and buildings are often subject to a high level of static deformation. From the dynamic design point of view, it is requisite to predict dynamic complex stiffness of viscoelastic components accurately and efficiently. To this end, a systematic procedure for complex modulus measurement of the viscoelastic material under large static deformation is often required in the industrial fields. In this paper, dynamic test conditions and procedures for the viscoelastic material under small oscillatory load superimposed on large static deformation are discussed. Various standard test methods are investigated in order to select an adequate test methodology. The influence of fixed boundary condition in the compression tests upon complex stiffness are investigated and an effective correction technique is proposed. Then the uniaxial tension and compression tests are performed and its results are compared with analysis results from conventional constitutive models.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.3
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• pp.1-6
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• 1991

In this study, intermediate thermo-mechanical treated Al-2.0 wt%Li, and Al-2.0 wt%Li-1.2 wt%Cu-1.0 wt%Mg-0.12 wt%Zr alloys were tested in tension at $10^{\circ}C$ and elevated temperature(100, 200 and $300^{\circ}C$). The results are follows : The tensile strength of Al-Li-Cu-Mg-Zr alloy is the highest but the elongation of Al-Li alloy is the highest(106%) among the all alloys in tension at $300^{\circ}C$. The Portervin-LeChartlier effect is showed in AI-Li-Cu-Mg-Zr alloy at 10 and $100^{\circ}C$, because of tangled dislocation by Mg and Cu. In the true stress-strain curves of all alloy, the peaks of stress at $300^{\circ}C$ are showed at the strain less than 0.1. In the binary alloy, the dynamic restoration process at 200 and $300^{\circ}C$ is nearly similar to dynamic recovery type. The hot deformation stress is decreased with increase of dynamic recovery degree, but the elongation is increased. When the strain the strain rate are constant, the temperature dependence of hot deformation stress is increased with increase of deformation temperature. The elongation and degree of dynamic recovery are decreased with increase of hot deformation activation energy, but the deformation stresses slightly increased.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.5
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• pp.209-215
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• 2016

In this study, the effect of Nb contents and processing parameters on dynamic recrystallization behaviour of 0.15C-0.2Si-0.5Mn low-carbon steels was investigated. Three kinds of steel specimens with different Nb contents were fabricated and then high-temperature compressive deformation test was conducted by varying reheating temperature (RT), deformation temperature (DT), and strain rate (SR). The Nb2 and Nb4 specimens containing Nb had smaller prior austenite grain size than the Nb0 specimens, presumably due to pinning effect by the formation of carbides and carbonitrides precipitates at austenite grain boundaries. The high-temperature compressive deformation test results showed that dynamic recrystallization behavior was suppressed in the specimens containing Nb as the strain rate increased and deformation temperature decreased because of pinning effect by precipitates, grain boundary dragging effects by solute atoms, although the compressive stress increased with increasing strain rate and decreasing deformation temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.849-853
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• 2002

A specific experimental method, the split Hopkinson pressure bar (SHPB) technique has been widely used to determine the dynamic material properties under the impact compressive loading conditions with strain-rate of the order of 103/s~104/s. In this paper, dynamic deformation behaviors of rubber materials widely used for the isolation of vibration from varying structures under dynamic loading are determined using a Split Hopkinson Pressure Bar technique.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.1014-1019
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• 2003

A dynamic modeling method for beams undergoing overall rigid body motion is presented in this paper. Two special deformation variables are introduced to represent the stretching and the curvature and are approximated by the assumed mode method. Geometric constraint equations that relate the two special deformation variables and the cartesian deformation variables are incorporated into the modeling method. By using the special deformation variables, all natural as well as geometric boundary conditions can be satisfied. It is shown that the geometric nonlinear effects of stretching and curvature play important roles to accurately predict the dynamic response when overall rigid body motion is involved.