• Transactions of the Korean Society of Mechanical Engineers A
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• 제35권8호
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• pp.889-897
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• 2011

In this work, we investigated the theoretical forming limit models for Zircaloy-4 and Zirlo used for spacer grid of nuclear fuel rods. Tensile and anisotropy tests were performed to obtain stress-strain curves and anisotropic coefficients. The experimental forming limit diagrams (FLD) for two materials were obtained by dome stretching tests following NUMISHEET 96. Theoretical FLD depends on FL models and yield criteria. To obtain the right hand side (RHS) of FLD, we applied the FL models (Swift's diffuse necking, M-K theory, S-R vertex theory) to Zircaloy-4 and Zirlo sheets. Hill's local necking theory was adopted for the left hand side (LHS) of FLD. To consider the anisotropy of sheets, the yield criteria of Hill and Hosford were applied. Comparing the predicted curves with the experimental data, we found that the RHS of FLD for Zircaloy-4 can be described by the Swift model (with the Hill's criterion), while the LHS of the FLD can be explained by Hill model. The FLD for Zirlo can be explained by the S-R model and the Hosford's criterion (a = 8).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.194-197
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• 2007

The dome stretching and tension test have been made to obtain a forming limit curve(FLC) for the copper alloy which is used for manufacturing the regenerative cooling chamber. For experimental survey of the forming limit curve, we have used in-plane tension specimen to obtain tension-compression strain state and also out of plane specimen to obtain tension-tension strain state through dome stretching test. All specimens are divided into longitudinal and radial direction specimens by the manufacturing method. The test results shows that in tension-tension region, copper alloy possesses a maximum major strain of 62.3% and maximum minor strain of 58.6%. In the tension-compression region, maximum major strain is 60.5% and maximum minor strain is 25.8%.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제36권2호
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• pp.179-186
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• 2012

In the automobile industry, reducing the weight is the most important objective for reducing air pollution and improving the fuel efficiency. For this reason, the application of aluminum sheets is increasing. When the sheets are applied to the automobile, using inappropriate variables for the material, product design, and press processing can generate tearing, wrinkling, and spring-back problems, which are the main types of failure in the manufacturing process. Therefore, it is necessary to reduce these failures by harmonizing the many variables and strictly managing the processes. In this research, we study the theoretical plasticity instability of Al5454 and obtain the forming limit diagram (FLD) using MATLAB. Moreover, we compare the theoretical FLD with an experimental FLD obtained from a stretching test.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제17권3호
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• pp.380-388
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• 2016

Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However, compared with automotive steels and aluminum alloys, there has not been much research on the plastic deformation characteristics and press formability of CP Ti sheet. In this study, the mechanical properties of CP Ti sheet are clarified in relation to press formability, including anisotropic properties and the stress-strain relation. The flow curve of the true stress-true strain relation is fitted well by the Kim-Tuan hardening equation rather than the Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet was experimentally evaluated as a criterion for press formability by punch stretching tests. Analytical predictions were also made via Hora's modified maximum force criterion. The predicted FLC with the Kim-Tuan hardening model and an appropriate yield function shows good correlation with the experimental results of the punch stretching test.

• Transactions of Materials Processing
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• 제6권4호
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• pp.300-310
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• 1997

A finite element inverse method is introduced for direct prediction of blank shapes, strain distributions, and reliable intermediate shapes from desired final shapes in axisymmetric multi-step deep drawing processes. This mothod enables the determination of process disign. The approach deals with the Hencky's deformation theory. Hill's second order yield criterion, simplified boundary conditions, and minimization of plastic work with constraints. The algorithm developed is applied to motor case forming, and cylindrical cup drawing with the large limit drawing ratio so that it confirms its validity by demonstrating resonably accurate numerical results of each problem. Numerical examples reveal the reason of difficulties in motor case forming with corresponding limit diagrams.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제38권1호
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• pp.65-70
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• 2014

This paper introduces a preform design method for a ring rolling process with an outer step. Underfilling is one of the general defects of the profile ring rolling process. It occurs when the deformation amount is small or step depth of the profiled region is large. To prevent underfilling, increasing the deformation amount or using a preform of size similar to that of the final product are required. Furthermore, the filling limit equation is suggested based on the shape factor and deformation ratio for preventing defects in the products. The filling limit equation has been derived through finite element analyses and production tests for four different cases. For verifying the suggested method, realsized profile rolling tests were performed, and test results were compared with the predictions of the equation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.281-281
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• 2007

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.222-225
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• 1997

This paper describes experimental investigation on the forming limit for mash-seam welded sheets. The uniaxial tensile test was conducted to evaluate the mechanical properties of weld bead. Experimental forming limit diagrams were investigated for the different thicknesses and properties of welded sheets.

• Transactions of the Korean Society of Mechanical Engineers
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• 제12권5호
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• pp.935-943
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• 1988

The forming limit diagram is assessed as a means of estimating the forming characteristics of sheet metal and is usually determined experimentally. The strain rates used in the determination are likely to be low. However, often in practice, the strain rates are much higher, so if forming limit diagram is determined at low rates, it may not be appropriate. This paper reconsiders the forming limit diagram for mild steel and aluminum sheet up to variation in strain rate from 10$^{-2}$ sec to 20/sec where its forming has been carried out under oil pressure using a hydraulic bulge test with circular and elliptical dies. To obtain higher strain rate, an impact bulge test had been employed with the same die sets as those used for a hydraulic bulge test. The results obtained are as follows: (1) As the strain rate increases, the fracture pressure increases and the polar height at fracture decreases. (2) Experiment has shown that, in the positive quadrant of the forming limit diagram, the diagram is lowered with increasing strain rate and the effect of strain rate changes according to strain paths and materials..

• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 2004년도 춘계학술대회 논문요약집
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• pp.59-59
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• 2004

최근의 전자통신 및 정밀의료 부품들은 제품의 경량화 및 집적화로 인해 크기는 작으면서도 많은 기능이 요구되어지는 다기능ㆍ소형화 추세에 있다. 따라서, 부품들은 복잡한 형상에 초고기능과 초정밀도가 요구되어 고강도의 재료와 MEMS 및 Nano-technology로 성형ㆍ가공된다. 이러한 방법은 고비용을 요하며 실용화에 많은 문제점을 내포하고 있다. 반면에 이러한 부품들을 생산단가가 저렴한 전통적인 소성가공기술로 생산할 경우에는 부품의 강도 및 정밀도에 한계를 갖게 된다.(중략)