• Korean Journal of Materials Research
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• v.16 no.1
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• pp.68-74
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• 2006

2024 Al alloys were severely deformed by equal channel angular pressing(ECAP) to obtain an ultrafine grain structure. The more deformation amount increased, the more grain size decreased. Most of the grain structure were changed from elongated to equiaxed shape with increasing pass number. The morphology of S' phases was also changed from rod-type to spherical type. The grain size of 6 passed specimen was 100 to 200 nm, and the size of S' phases was about 10 nm in the microstructure. XRD measurements have revealed that the texture formed by plastic deformation disappeared in the 6 passed specimen. SP test results described that the start of crack propagation occurred at the transition zone between plastic bending and membrane stretching because of small elongation. The maximum strength of ECA pressed specimen increased 1.9 GPa to 2.9 GPa with increasing pass number.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.978-979
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• 2006

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders with least grain growth. ECAP (Equal channel angular pressing) was used for the powder consolidation. We investigated the consolidation, plastic deformation and microstructure evolution behavior of the metallic powders during ECAP using an experimental method. It was found that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process of gas atomized Al-Si powders.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.88-96
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• 1999

The effects of root gap on welding residual stress and deformation are dealt with the multi-pass weldment with three kinds(0, 6, 30mm) of root gap by F.E.M common code, and then compared with experiment data. In this analysis, an 100% ramp heat input model was used to avoid numerical convergence problem due to an instantaneous increase in temperature near the fusion zone, and the effect of a moving arc in a two dimensional plane was also included. During the analysis, a small time increment was applied in a period with instantaneous temperature fluctuation while a large time increment was used in the rest period. The residual stress is distributed as symmetric types and maximum value is also equivalent when the weldment with 0mm and 6mm root gap is welded. In the case of 30mm root gap welding, the distribution of the residual stress extends over a wide range as asymmetric types due to the built-up weld, and most of the residual stress is biased in the side of a built-up weld part. In case of 0mm gap welding and 6mm gap welding, a little angular distortion occurs, but the level of deformation is small. When the weldment with 30mm root gap is welded, the angular deformation of the asymmetric types, however, occurs larger than the other specimens. The experimental and the analytic results show good coincidence and indicate that the welding residual stress and deformation distribution of 30 mm root gap specimen may be asymmetric and the amplitude is larger than those of root gap specimen under standard.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.739-746
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• 2004

The plastic deformation behavior of an aluminum alloy containing a particle and porosities was investigated at room temperature during equal channel angular pressing (ECAP). Finite element analysis by using ABAQUS shows that ECAP is a useful tool for eliminating residual porosity in the specimen, and more effective under friction condition. The simulation, however, shows considerably low density distributions for matrix near a particle at which many defects may occur during severe deformation. Finite element results of effective strains and deformed shapes for matrix with a particle were compared with theoretical calculations under simple shear stress. Also, based on the distribution of the maximum principal stress in the specimen, Weibull fracture probability was obtained for particle sizes and particle-coating layer materials. The probability was useful to predict the trend of more susceptible failure of a brittle coating layer than a particle without an interphase in metal matrix composites.

• Transactions of Materials Processing
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• v.15 no.6 s.87
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• pp.441-444
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• 2006

The deformation behavior of copper during equal channel angular pressing(ECAP) was calculated using a three-dimensional version of a constitutive model based on the dislocation density evolution. Finite element simulations of the variation of the dislocation density and the dislocation cell size with the number of ECAP passes are reported. The calculated stress, strain and cell size are compared with the experimental data for Cu deformed by ECAP in a modified Route C regime. The results of FEM analysis were found to be in good agreement with the experiments. After a rapid initial decrease down to about 200nm in the first ECAP pass, the average cell size was found to change little with further passes. Similarly, the strength increased steeply after the first pass, but tended to saturate with further pressings. The FEM simulations also showed strain non-uniformities and the dependence of the resulting strength on the location within the workpiece.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.427-430
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• 2008

The influence of subsequent annealing treatment on the dynamic deformation and the fracture behavior of submicrocrystalline Al-4.4%Mg alloy is investigated in this study. After inducing an effective strain of 8 via equal-channel angular pressing at $200^{\circ}C$, most of the grains are considerably reduced to nearly equiaxed grains of $0.3{\mu}m$ in size. With an increment of various subsequent heat treatments for 1 hour, resultant microstructures are found to be fairly stable at temperatures up to $200^{\circ}C$, suggesting that static recovery will be dominantly operative, whereas grain growth is pronounced above $250^{\circ}C$. The results of tensile tests show that yield and ultimate tensile strength decrease, but elongation-to-failure and strain hardening rate increase with an increase in annealing temperatures. The dynamic deformation and the fracture behavior retrieved with a series of torsional tests are explored with respect to annealed microstructures. Such mechanical response is analyzed in relation to resultant microstructure and fracture mode.

• Korean Journal of Metals and Materials
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• v.46 no.9
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• pp.563-571
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• 2008

The influence of annealing treatment on dynamic deformation behavior of ultra-fine grained aluminum alloys was investigated in this study. After equal-channel angular pressing at $200^{\circ}C$, most of the grains were considerably reduced to nearly equiaxed grains of $0.3{\mu}m$ in size. With an increment of various annealing treatments for 1 hour, resultant microstructures were found to be fairly stable at temperatures up to $200^{\circ}C$, suggesting that static recovery would be dominantly operative, whereas grain growth was pronounced above $250^{\circ}C$. The tensile test results showed that yield and ultimate tensile strengths decreased, but elongation-to-failure and strain hardening rate increased with increasing annealing temperature. The dynamic deformation behavior retrieved with a series of torsional tests was explored with respect to annealed microstructures. Such mechanical response was analyzed in relation to resultant microstructure and fracture mode.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.547-556
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• 2001

This study presents new method in which to derive the constraint coefficient from the quantity of angular deformation by welding measured by varying the shape of welded joints and the magnitude of constraints by varying the shape of welded joints and the magnitude of constraints by experiment and from the result analyzed by elastic FEM method and then to decide equivalent load with it The numerical analysis results by this new method verified the validity by agreeing with the experimental result on specimen. In addition These results are applicable to the prediction of the quantity of welding deformation for large structures regardless of the size and the shape While in the effects of the constraints based on the shape of welded joints in the case of Butt welding when the constraint coefficients are not considered the deformed quantity is produced larger than one by the experiment and consequently is largely affected by the constraints But in the case of Fillet welding the deformed quantity is seldom affected regardless of considering the constraint coefficients or not.

• Journal of Korean Neurosurgical Society
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• v.65 no.2
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• pp.173-179
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• 2022

Disabilities can emerge due to traumatic spinal fractures. In terms of sacrococcygeal spine, because of its unique anatomic structure with minimal movement, the possibility for it to have a disability is relatively low. In Korea, unlike most disability criteria, private insurance companies acknowledge angular deformities caused by vertebral fractures as disabilities according to their degree, so there were several cases where patients required compensation, arguing angular deformity caused by sacrococcygeal fracture, which in some cases led to legal conflicts. Except the Act Welfare of Persons with Disabilities which recognizes only severe angular deformity affecting internal organs as disability and the industrial accident disability evaluation which does not recognize coccygeal fracture as disability but rarely recognizes sacral vertebra deformity equivalent to compressive deformation, there is little or no case where angular deformity is recognized as disability. Given the impairment evaluation standards in social insurance, McBride system, American Medical Association (AMA) guides, and newly proposed standards by the Korean Academy of Medical Sciences (KAMS), the most contentious point in the general terms and conditions of private insurance is spinal deformity. To overcome controversy over disability evaluation, the private insurance sector is now applying criteria for axial skeleton to sacrococcygeal vertebrae through revision of standards. Under these circumstances, it is fair to recognize sacrococcygeal fracture as impairment in terms of the pelvis only when the fracture leaves serious deformity and neurological symptoms with clear relevancy. Though it may not be easy to develop accurate disability evaluation standards, improvement is necessary to remove any irrationalities and make the standards as objective as possible.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.46-51
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• 2016

The TMCP steel has expanded in the marine structure during manufacturing process because of its excellent weld-ability and impact toughness. In the case of merchant ships, coverage of TMCP steel has been used widely on over DH36 Classifications material. The line heating process is applied to the outer surface of the steel plate for the shipbuilding. In this study, We compared between TMCP and normalizing steel for shipbuilding by analyzing some basic data through performing the natural cooling after the line heating. The experimental results show the angular misalignment changes in line heating. Heated surface of normalizing steel material expanded to $-0.3^{\circ}$ and reduced to $+0.2^{\circ}$ after cooling. And during cooling at $194^{\circ}C$ for 1,500 seconds, Angular Misalignment began from - direction to + direction, passed the critical point to the default at 2,200 seconds and did not take place any more at $103^{\circ}C$ after the 2,700 seconds. Angular Misalignment results of TMCP steels and Normalizing steel material show same angular misalignment lasted 1,200 seconds, TMCP steel has given more expansion and contraction angle which is $0.2^{\circ}$ than that of the Normalizing steel. Length difference between expansion and contraction is about 0.3 mm.