• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.529-535
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• 2013

A new thin sandwich panel composed of an aluminum expanded metal core adhesively jointed with stainless steel face sheets is introduced, and its mechanical behavior under three-point bending is investigated. The strength and stiffness are analyzed theoretically, and the press-formability and strength enhancement are evaluated experimentally. The specimens with the specific configurations exhibit face yielding well before face-core separation, which means that the sandwich panel can be formed by a press without failure. The measured load levels corresponding to the face yielding and the face-core separation agree fairly well with the theoretical estimations. For a given weight, the sandwich panel is superior to a solid panel in terms of strength, stiffness, and press-formability.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.921-926
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• 2015

Embossed aluminum sheets were been used in heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement. However, there are many restrictions because of high rate of wrinkle occurrence on press working. We have performed the tensile and bending tests for embossed sheets to clarity its mechanical properties and springback characteristics. Embossed aluminum sheets showed a different flow stress after plastic yielding due to flattening the embossed cone shape. Above all, yield stress of parallel embossed specimen decreases while its diagonal one increases and the decrease of young's modulus in the embossed sheets contributes to the increase of springback amount.

• 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.

• 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).

• Transactions of Materials Processing
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• v.13 no.1
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• pp.15-20
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• 2004

In order to evaluate spring-back behavior in automotive sheet forming processes, a panel shape idealized as a double S-rail has been investigated. After spring-back has been predicted for double S-rails using the finite element analysis, results has been compared with experimental measurements for three automotive sheets. To account for hardening behavior such as the Bauschinger and transient effects in addition to anisotropic behavior, the combined isotropic-kinematic hardening law based on the Chaboche type model and a recently developed non-quadratic anisotropic yield function have been utilized, respectively.

• Transactions of Materials Processing
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• v.25 no.4
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• pp.275-282
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• 2016

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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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.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.79-88
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• 1990

Welded joint often contains soft or softened regions such as the HAZ of TMCP steel welded with high heat input. In this study, the equivalent yield strength of plate structure containing softened region was predicted by FEM analysis, and its incremental behavior was explained with the results of the analysis. The calculated results of yield strength indicated the following for the plate structures. 1) As the softened region starts to yield, shear stress begins to build up along the boundary between base metal and softened region. This results in multi-axial stress condition which gives restraint on the softened region. 2) Restraint effect has a significant influence on the distribution of the shear stress, the nominal stress, and the strain. 3) The yielding behavior of softened region becomes the same as that of base metal when both ratios of length to width and thickness to width of softened region are larger than 30 and 13 respectively.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.369-376
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• 2011

A non-quadratic anisotropic strain rate potential was introduced as a conjugate potential of the yield stress potential Yld2000-2d to describe anisotropic behavior of sheet metals, in particular, aluminum alloy sheets under plane stress state. This strain-rate potential takes into account the anisotropic yield stresses and R-values measured along the directions measured at 0, 45 and 90 degrees from the rolling direction, as well as the balanced biaxial yield stress and strain-rate ratio. The convexity of the strain-rate potential was completely proven. The strain-rate potential was applied for two anisotropic aluminum alloy sheets, AA6022-T4 and AA2090-T3. The results verified that the strain rate potential properly described the anisotropic behavior of aluminum alloy sheets and was closely conjugate of Yld2000-2d under the plane stress state.

• Journal of the Korea Convergence Society
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• v.13 no.4
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• pp.287-292
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• 2022

In this paper, the stochastic distribution of the springback amount is investigated for the stamping process of a U-channel shaped-product with ultra-high strength steel. Using the reliability-based design optimization technique (RBDO), stochastic distribution of process parameters is considered in the analysis including material properties and process variation. Quantification of the springback scatters is carried out with the statistical analysis method according to the material strength. It is found that the scattering amount of springback decreases while the amount of springback increases as the tensile strength of the blank material increases, which is investigated by analyzing the strain and stress distribution of the punch and die shoulder. It is noted that the proposed scheme is capable of predicting and responding to the unavoidable scattering of springback in the sheet metal forming process.