• Transactions of Materials Processing
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• v.18 no.6
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• pp.448-452
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• 2009

Superplastic deformation behavior and texture evolution after equal channel angular pressing (ECAP) of Zn-0.3Wt%Al alloy were investigated in this study. ECAP was conducted at temperatures from $60^{\circ}C$ to $160^{\circ}C$ on the plate type specimens of 5 mm thickness and 20 mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED, which is called shear texture. Tensile tests were carried out at $100^{\circ}C$ for ECAPed specimens under the strain rate of 0.0002/s. After ECAP of the Zn-0.3Wt%Al alloy, elongation was dramatically increased up to 500% at $100^{\circ}C$. The effect of ECAP on the anisotropy in the superplastic deformation behavior was negligible.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.309-312
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• 2007

Deformation behavior of $Zr_{55}Cu_{30}Al_{10}Ni_5$(at. %) bulk metallic glass(BMG) fabricated by suction casting method has been investigated at elevated temperatures in this study. The BMG was first verified to have an amorphous structure with the analysis of X-ray diffraction(XRD) and differential scanning calorimetry(DSC) data. A series of compression tests has consequently been performed in the region of supercooled liquid temperature to investigate the behavior of high temperature deformation. A transition from Newtonian to non-Newtonian flow appeared to take place depending upon both the strain rate and test temperature. A processing map based on a dynamic materials model has been constructed to estimate a feasible forming condition for this BMG alloy.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.928-929
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• 2006

Tensile stress-strain and dynamic acoustic resonance tests were performed on Fe-C-Ni-Cu-Mo high-strength steels, characterized by a heterogeneous matrix microstructure and the prevalence of open porosity. All materials display the first yielding phenomenon and, successively, a continuous yielding behavior. This flow behavior can be described by the Ludwigson equation and developes through three stages: the onset of localized plastic deformation at the pore edges; the evolution of plastic deformation at the pore necks (where the austenitic Ni-rich phase is predominant); the spreading of plastic deformation in the interior of the matrix. The analytical modeling of the strain hardening behavior made it possible to obtain the boundaries between the different deformation stages.

• Korean Journal of Materials Research
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• v.20 no.1
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• pp.7-11
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• 2010

Yttria stabilized zirconia (Y-CSZ) single crystals show plastic deformation at high temperatures by activating dislocations. The effect of strain rate on the plastic behavior of this crystal was studied. As increasing strain rate from $\varepsilon=1.04\times10^{-5} sec^{-1}$ to $2.08\times10^{-5} sec^{-1}$ the yield drop was suppressed and resulted in higher Young's modulus and yield stress. Dislocation structures of the strained crystals were analyzed using a transmission electron microscope to elucidate the plastic behavior of these crystals. In the early stage of plastic deformation, dislocation dipoles and prismatic dislocation loops were formed in both samples. However, dislocation density was increased by increasing strain rate. Strong sessile dislocations were observed in the sample with higher strain rate, which may cause the higher work hardening.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.955-963
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• 2008

There are lots of tunnel intervals in the KTX II stage construction line for the linearity of railway line passing mountain region. In order to use the rocks from tunnel excavations, railway subgrades are constructed with crushed rock-soil mixtures. In this study, plain strain test using large scale box was conducted in order to analyze the characteristics of deformation behavior of railway subgrades composed of crushed rock-soil mixtures. The effects of variation of degree of saturation, stress level of applied loadings, and number of loading cycles on the resilient and permanent deformation behavior were analyzed. The results show that degree of saturation have a great effect on the deformation behavior of crushed rock-soil mixtures. The axial strain ranges between $0.1{\sim}0.8%$ with variation of degree of saturation, in assumption that deviatoric stress applied on the subgrade by high-speed train load is 55kPa.

• Korean Journal of Materials Research
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• v.23 no.7
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• pp.373-378
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• 2013

In order to clarify the effect of C/Ti atom ratios(${\chi}$) on the deformation behavior of $TiC_{\chi}$ at high temperature, single crystals having a wide range of ${\chi}$, from 0.56 to 0.96, were deformed by compression test in a temperature range of 1183~2273 K and in a strain rate range of $1.9{\times}10^{-4}{\sim}5.9{\times}10^{-3}s^{-1}$. Before testing, $TiC_{\chi}$ single crystals were grown by the FZ method in a He atmosphere of 0.3MPa. The concentrations of combined carbon were determined by chemical analysis and the lattice parameters by the X-ray powder diffraction technique. It was found that the high temperature deformation behavior observed is the ${\chi}$-less dependent type, including the work softening phenomenon, the critical resolved shear stress, the transition temperature where the deformation mechanism changes, the stress exponent of strain rate and activation energy for deformation. The shape of stress-strain curves of $TiC_{0.96}$, $TiC_{0.85}$ and $TiC_{0.56}$ is seen to be less dependent on ${\chi}$, the work hardening rate after the softening is slightly higher in $TiC_{0.96}$ than in $TiC_{0.85}$ and $TiC_{0.56}$. As ${\chi}$ decreases the work softening becomes less evident and the transition temperature where the work softening disappears, shifts to a lower temperature. The ${\tau}_c$ decreases monotonously with decreasing ${\chi}$ in a range of ${\chi}$ from 0.86 to 0.96. The transition temperature where the deformation mechanism changes shifts to a lower temperature as ${\chi}$ decreases. The activation energy for deformation in the low temperature region also decreased monotonously as ${\chi}$ decreased. The deformation in this temperature region is thought to be governed by the Peierls mechanism.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.4
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• pp.26-33
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• 2002

One characteristic of Fine-Blanking is that the size and the direction of stress and strain are very complex in the plastic flow according to the condition of blanking. Especially, they are affected by the clearance of punch and die, by the force of blanking holder and by the force of counter punch. The purpose of this research is to how the deformation behavior in shear zone more clearly, based on Green & Cauch's large deformation theory. The deformation behavior and cracks were investigated in each step of shear, according to punch penetration increase, the use of V-indenter ring and the hardness of materials. This research found that the transforming behavior was the same as pure discretion and the cracks could be prevented when hardness is low.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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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.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1407-1412
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• 2003

In MEMS devices, packaging induced stress or stress induced structure deformation become increasing concerns since it directly affects the performance of the device. In this paper, deformation behavior of MEMS gyroscope package subjected to temparature change is investigated using high-sensitivity $Moir{\acute{e}}$ interferometry. Using the real-time $Moir{\acute{e}}$ setup, fringe patterns are recorded and analyzed at several temperatures. Temperature dependent analyses of warpages and extensions/contractions of the package are presented. Linear elastic behavior is documented in the temperature region of room temperature to $125^{\circ}C$. Analysis of the package reveals that global bending occurs due to the mismatch of thermal expansion coefficient between the chip, the molding compond and the PCB.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.595-600
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• 2011

This paper investigates the effect of strain rate on the anisotropic deformation behavior of advanced high strength steel sheets. Uniaxial tensile tests were carried out on TRIP590 and DP780 steel sheets at strain rates ranging from 0.001/sec to 100/sec to determine yield stresses and r-values at various loading angles from the reference rolling direction. R-values were determined by the digital image correlation technique. Hill48 and Yld2000-2d yield functions were tested for their capability to describe the plastic deformation anisotropy of the materials. Initial yield loci were constructed using the Yld2000-2d yield function, which adequately described the anisotropic behavior of the materials. The shape of the initial yield loci was found to change with different strain rate, and the anisotropic behavior decreased with increasing strain rate.