• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.233-235
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• 2007

Finite element analysis was conducted for cold roller leveler to verify numerical model of roller leveler developed by POSTECH. On-line model of roller leveler was developed to predict rapid and precise roll intermesh of roller leveler in thick plate mill. The cold roller leveler in thick plate mill was analyzed using MARC & MENTAT and the results are compared with the results of numerical model of roller leveler calculated by POSTECH.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.04a
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• pp.93-96
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• 2009

The high grade thick plate is in great demand in the ship building industry and the construction industry. The main problems to produce the high grade plate are residual stress and flatness of plate. In the previous research, Finite Element Analysis(FEA) was conducted for cold roller leveler to understand the behaviors of cold roller leveler under different conditions of thickness, intermesh, and yield stress. In this study, a numerical model of roller leveler is developed and the calculated results of this model are compared with the FEA results to show the validity of the numerical model. The optimal leveling conditions to improve flatness of plate are suggested using this numerical model.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.497-502
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• 2004

The shape of cold rolled steel sheets is defined as the degree of flatness, and the flatter, the better. Because undesirable strip shapes of cold rolled steel sheets can affect not only visible problem but also automatic working process in customer's lines, the requirement of the customers is more and more stringent. So we usually used the tension leveler to make high quality of strip flatness. For the improvement of the quality of strip flatness, this report developed three- dimensional FEM (Finite Element Method) simulation model, and analysis about the strain and stress distribution of strip in the tension leveling process. The numerical study can be summarized as follows. (1) If we pass the edge wave material (steepness: $1.0\%$) that the stress-difference between the strip center and the edge is 5.2kgf through tension leveler. the stress-difference is decreased 0.45kgf and the steepness is improved to $0.29\%$. (2) If the Intermesh is increased from 6mm to 7mm, the steepness is improved from $0.294\%$ to $0.268\%$. (3) If the initial steepness is decreased form $1.0\%$ to $0.75\%$, the final steepness is improved from $0.294\%$ to $0.263\%$. We know that more increased intermesh and lower initial steepness make the final steepness improved.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.74-79
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• 2004

The shape of cold rolled steel sheets is the degree of flatness, and the flatter, the better. Because undesirable strip shapes of cold rolled steel sheets can affect not only visible problem but also automatic working process in customer's lines, the requirement of the customers is more and more stringent. So we usually used the tension leveler to make high quality of strip flatness. For the improvement of the quality of strip flatness, this report developed three-dimensional FEM (Finite Element Method) simulation model, and analysis about the strain and stress distribution of strip in the tension leveling process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.112-115
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• 2007

In order to investigate the residual stress evolution during the leveling process of hot rolled high strength coils for cold forming, the in-plane residual stress of plate sampled at SPM, rough leveler and finish leveler were measured by cutting method. Residual stress was localized near the edge of plate. As the thickness of plate was increased, the region with residual stress was expanded. The gradient of residual stress within plate was reduced during the leveling process. But the residual stress itself was not removed at the ranges of tested conditions. From the measured residual stress distribution within the plate, camber of plate cut to small width was predicted exactly within error range of experiment.

• Transactions of Materials Processing
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• v.17 no.2
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• pp.107-112
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• 2008

In order to investigate the residual stress evolution during the leveling process of hot rolled high strength coils for cold forming, the in-plane residual stress of plate sampled at SPM, rough leveler and finish leveler were measured by cutting method. Residual stress was localized near the edge of plate. As the thickness of plate was increased, the size of residual stress region was expanded. The gradient of residual stress within the plate was reduced during the leveling process. But the residual stress itself was not removed completely within the ranges of tested conditions. The exact camber of cut plate was able to be predicted by the measurement of residual stress distribution after leveling of the plate.

• Journal of the Korea Society of Computer and Information
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• v.22 no.3
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• pp.1-8
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• 2017

In this paper, we propose a new hybrid wear leveling technique for NAND Flash memory, called Time-Aware Wear Leveling (TAWL). Our proposal prolongs the lifetime of NAND Flash memory by using dynamic wear leveling technique which considers the wear level of hot blocks as well as static wear leveling technique which considers the wear level of the whole blocks. TAWL also reduces the overhead of garbage collection by separating hot data and cold data using update frequency rate. We showed that TAWL enhanced the lifetime of NAND flash memory up to 220% compared with previous wear leveling techniques and our technique also reduced the number of copy operations of garbage collections by separating hot and cold data up to 45%.