• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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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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• v.35 no.8
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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).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.939-945
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• 2009

The dome stretching tests and tension tests have been performed to obtain a forming limit curve(FLC) for the copper alloy which is used for manufacturing the regenerative cooling thrust chamber. For experimental investigation of the forming limit curve, we have used in-plane tension specimen to obtain tension-compression strain state as well as out-of-plane specimen to obtain tension-tension strain state through dome stretching test. All specimens were divided into longitudinal and transverse directions according to the orientation of test specimen. The test results showed that in the tension-tension region, copper alloy revealed a maximum major strain of 62.3% and a maximum minor strain of 58.6%. In the tension-compression region, the maximum major strain and the maximum minor strain were measured to be 60.5% and 25.8%, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.725-726
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• 2012

• Journal of Navigation and Port Research
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• v.36 no.3
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• pp.181-187
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• 2012

Highly plastic clays in their normally consolidated states are not always linear but are concave downwards. Thus their compression index deceases with the increase of consolidation pressure. The $e-{\log}{\sigma}_{\upsilon}{\prime}$ curves of plastic or non-plastic silty clays are not linear but are convex upwards. In this paper, consolidation tests were conducted with several undisturbed field soils of Korea south coast and their $e-{\log}{\sigma}_{\upsilon}{\prime}$ plots are not always linear. In case of using Butterfield's method(liquid limit 50~100%), ${\ln}{\upsilon}-{\ln}{\sigma}_{\upsilon}{\prime}$ plots are linear. But some undisturbed samples which have void ratio over 2.24, liquid limit over 100% and plasticity index over 60% are not linear. In results of consolidation tests with remolded samples which contain silt(fly ash) contents of 90% has compression index increasing with the increase in consolidation pressure.

• Composites Research
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• v.13 no.2
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• pp.81-90
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• 2000

For automotive applications, a sandwich sheet which was made of a 5182 aluminum alloy (AA5182) sheet and a polypropylene (PP) sheet, AA5182/PP/AA5182, has been developed. In order to evaluate its formability, the forming limit diagrams (FLD) of the 5182 aluminum alloy sheet with 0.2mm thickness and the sandwich sheet with 1.2mm thickness have been obtained based on the modified Marciniak-Kuczynski (M-K) theory. To account for the anisotropy of the sheet, Hill's 1948 yield function has been applied. The FLD of the sandwich sheet was predicted to be better than that of the AA5182 sheet, which was well confirmed by experiments.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.1-10
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• 2005

This study proposes a fatigue reliability evaluation procedure for steel-composite high-speed railway bridge based on dynamic analysis and investigates the effectiveness of Tuned Mass Damper(TMD) in terms of the extension of fatigue life of the bridge. For the fatigue reliability evaluation, the limit state is determined using S-N curve and linear fatigue-damage accumulation. Dynamic analyses are peformed repeatedly to consider the uncertainties of train-velocity and damping ratio of the bridge. The distribution of random variables related to fatigue damage for the intended service life is then statistically estimated from analytical results. Finally, the fatigue reliability indices are obtained by means of the Advanced First-Order Second-Moment (AFOSM) method. Through numerical simulation of a steel-composite bridge of 40m span, the effectiveness of TMD on fatigue life of the bridge is examined and the results are presented.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.386-389
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• 2008

Forming limit diagram is created by graphical illustration indicating major and minor strain. In order to provide the criterion for forming safety, FLC(forming limit curve) need to be fitted to the diagram. However, the standard method for the strain measurement and FLC plotting are not fixed yet, which results in inconvenience in digitalized analysis. In this study, new construction method for FLC was suggested in order to minimize operator dependency. For this purpose, major and minor strain were measured automatically and analyzed. Then, a second order equation is adopted to fit the FLC. Optimized by response surface method was performed to ensure particular characteristics of the FLC.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.952-956
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• 1997

This paper describes the method that can expand the forming limit of T type forging products used in aircraft and automotive forged products. The forming limitis determined by the ratio of web thickness to rib width in T type and the reduction in height of workpiece and especially depends on the ratio of web thickness to rib width. For this method, the geometric condition that consists of triangle type was introduced and FEM simulations and model exoeriments were carried out and compared with each other. The objective of this paper is to give the method not only that sink mark and folding phenomenon are eliminated but also that the forming limit and the structural strength of rib and web is increased.

• Transactions of Materials Processing
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• v.22 no.6
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• pp.328-333
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• 2013

The current study aims to determine the limit strains more accurately and reasonably when producing a forming limit curve (FLC) from experiments. The international standard ISO 12004-2 in its recent version (2008) states that the limit major strain should be determined by using the best-fit inverse second-order parabola through the experimental strain distribution. However, in cases where fracture does not occur at the center of the specimen, due to insufficient lubrication, the inverse parabola does not give a realistic fit because of its intrinsic symmetry in shape. In this study it is demonstrated that an inverse quartic function can give a much better fit than an inverse parabola in almost all FLC test samples showing asymmetric strain distributions. Using a quartic fit creates more reliable FLCs.