• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.719-720
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• 2012

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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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.

• 소성∙가공
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• 제18권6호
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• pp.453-457
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• 2009

In this paper, plastic deformation behaviors of ESW105 and SCM435 steels are revealed by simulations and experiments. ESW105 is the special pre-heat-treated steel characterized by high initial yield strength and negligible strain-hardening behavior. The flow stresses of the two steels for large stain are calculated from tensile tests. Axial and lateral compressions of cylindrical bars are tested and simulated and the deformed shapes are compared to characterize the plastic deformation behaviors of the two materials. A forward extrusion process of a cylindrical bar is also simulated to reveal the difference. It has been shown that there are pretty much difference in plastic flow between ESW105 and SCM435 which causes from the difference in strain-hardening capability, implying that the experience-oriented design rules for common commercial materials may lead to failure in process design when the new material of ESW105 is applied without consideration of its plastic deformation behavior.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.48-51
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• 2009

In this paper, plastic deformation behaviors of ESW105 and SCM435 steels are revealed by simulations and experiments. ESW105 is the special pre-heat-treated steel characterized by high initial yield strength and negligible strain-hardening behavior. The flow stresses of the two steels for large stain are calculated from tensile tests. Axial and lateral compressions of cylindrical bars are tested and simulated and the deformed shapes are compared to characterize the plastic deformation behaviors of the two materials. A forward extrusion process of a cylindrical bar is also simulated to reveal the difference. It has been shown that there are pretty much difference in plastic flow between ESW105 and SCM435 which causes from the difference in strain-hardening capability, implying that the experience-oriented design rules for common commercial materials may lead to failure in process design when the new material of ESW105 is applied without consideration of its plastic deformation behavior.

• 소성∙가공
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• 제14권4호
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• pp.327-337
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• 2005

In the present work, the two back stress kinematic hardening models are proposed by combining Armstrong-Frederick, Phillips and Ziegler's hardening rules. Simple combination of hardening rules using simple rule of mixtures results in various evolutions of the kinematic hardening parameter. Using the combined hardening models the ultimate back stress fur the present models is also derived. The stress rate is co-rotated with respect to the spin of substructure due to the assumption of kinematic hardening rule in finite deformation regime. The work piece under consideration is assumed to consist of the elastic and the rigid plastic deformation zone. Then, the J2 deformation theory is facilitated to characterize the plastic deformation behavior under various loading conditions. The plastic deformation localization behaviors strongly depend on the constitutive description namely back stress evolution and its hardening parameters. Then, the analysis for Swift's effects under the fixed boundaries in axial directions is carried out using simple shear deformation.

• 소성∙가공
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• 제15권5호
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• pp.382-386
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• 2006

Preform design is an effective means of achieving the homogeneous deformation of workpiece materials and decreased load in metal forming. However, this approach has not been applied to equal channel angula. pressing (ECAP). In this paper, plastic deformation behavior of workpieces having four different preform shapes during ECAP was investigated using finite element analyses. The results indicated that a preform design of the workpiece head has a beneficial effect on homogeneous deformation, reducing the maximum pressing load at the initial stage and eliminating folding defects at strain concentration points.

• Journal of Welding and Joining
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• 제21권3호
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• pp.68-77
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• 2003

It is important to understand the characteristics of material strength and fracture under the dynamic loading like as earthquakes to assure the integrity of welded structures. The characteristics of dynamic strength and fracture in structural steels and their welded joints should be evaluated based on the effects of the strain rate and the service temperature. It is difficult to predict or measure temperature rise history with the corresponding stress-strain behavior. In particular, material behaviors beyond the uniform elongation can not be precisely evaluated, though the behavior at large strain region after the maximum loading point is much important for the evaluation of fracture. In this paper, the coupling phenomena of temperature and stress-strain fields under the dynamic loading was simulated by using the finite element method. The modified rate-temperature parameter was defined by accounting for the effect of temperature rise under the dynamic deformation, and it was applied to the fully-coupled analysis between heat conduction and thermal elastic-plastic behavior. Temperature rise and stress-strain behavior including complicated phenomena were studies after the maximum loading point in structural steels and their undermatched joints and compared with the measured values.

• Journal of Magnetics
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• 제16권3호
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• pp.294-299
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• 2011

Nd-Fe-B high performance magnets were prepared by die-upset forging. The effects of the deformation parameters on magnetic properties and flow stress were studied. Deformation temperatures in the range of $600{\sim}900^{\circ}C$ enable to achieve an effective anisotropy and temperature $800^{\circ}C$ proves to be suitable for deformation of Nd-Fe-B magnets. The amount of c-axis alignment along the press direction seems to depend on the amount of deformation and a saturation behavior is shown at deformation ratio of 75%. Magnetic properties are also related to strain rate, and maximum energy product is attained at an optimum strain rate of ${\varphi}=1{\times}10^{-2}s^{-1}$. By analyzing the relationship of stress and strain at different deformation temperature during die-upset forging process, deformation behavior of Nd-Fe-B magnets was studied and parameters for describing plastic deformation were obtained. Nd-rich boundary liquid phase, which is additionally decreasing the flow stress during deformation, is supposed to play the role of diffusion path and enhance the diffusion rate.

• 소성∙가공
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• 제18권6호
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• pp.500-507
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• 2009

Tensile deformation behavior with different strain rate was investigated. $Zr_{56.2}Ti_{13.8}Nb_{5.0}Cu_{6.9}Ni_{5.6}Be_{12.5}$(bulk metallic glass alloy possessed crystal phase which was called $\beta$-phase of dendrite shape, mean size of $20{\sim}30{\mu}m$ and occupied 25% of the total volume) was used in this study. Maximum tensile strength was obtained as 1.74GPa at strain rate $10^2s^{-1}$ and minimum strength was found to be 1.6GPa at $10^{-1}s^{-1}$. And then, maximum plastic deformation occurred at the strain rate of $5{\times}10^{-2}s^{-1}$ and represented 1.75%, though minimum plastic deformation showed 0%. In the specific range of strain rate, relatively higher plastic deformation and lower ultimate tensile strength were found with lots of shear bands. The fractographical observation after tensile test indicated that vein like pattern on the fracture surface was well developed especially in the above range of strain rate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.353-354
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• 2009

Tensile deformation behavior with different strain rate was investigated. $Zr_{56.2}Ti_{13.8}Nb_{5.0}Cu_{6.9}Ni_{5.6}Be_{12.5}$ (bulk metallic glass alloy possessed crystal phase which was called $\beta$-phase of dendrite shape, mean size of $20{\sim}30{\mu}m$ and occupied 25% of the total volume) was used in this study. Maximum tensile strength was obtained as 1.74Gpa at strain rate of $10^2/s$ and minimum strength was found to be 1.6GPa at $10^{-1}/s$. And then, maximum plastic deformation occurred at the strain rate of $5{\times}10^{-2}/s$ and represented 1.75%, though minimum plastic deformation showed 0%. In the specific range of strain rate, relatively higher plastic deformation and lower ultimate tensile strength were found with lots of shear bands. The fractographical observation after tensile test indicated that vein like pattern on the fracture surface was well developed especially in the above range of strain rate.