On the inverse identification of Lankford coefficients using geometrical changes under quasi-biaxial loading

Graeser, Matthias; Lenzen, Matthias; Merklein, Marion

doi:10.1007/s12289-019-01498-z

Cited by 5 publications

(3 citation statements)

References 11 publications

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“…The resulting parameters for Equation (1) are A = 88.2, B = 9460.673 and C = 0.526. Due to the occurrence of inhomogeneous strain in the cross section of the upsetting specimen as discussed in [15], a higher compression level would lead to barreling of the specimen. Inhomogeneities in the strain and thus also in the resulting hardness distribution are the consequence.…”

Section: Functional Relationship Between Plastic Strain and Increase ...mentioning

confidence: 99%

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Lenzen

Kraus

Merklein

2022

KEM

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Many sheet materials do not exhibit constant properties over the sheet thickness. On the one hand, this can be caused by a rolling process with a pass reduction of 1-2%, the so-called skin pass rolling. This is mainly used for deep drawing steel grades to eliminate the pronounced yield strength of the base material. Another possibility is abrasive blasting or shot peening of sheet metal. This causes plastic deformation of the sheet surface and material strengthening. The grading can be used to locally strengthen components or locally adapt the roughness. Since many production processes today are designed numerically, the mapping of such a grading is necessary but currently not implemented in FE code. Aim of this research is, to correlate the material hardness to a plastic pre-strain with a newly developed characterization method. For this purpose, graded material properties are generated by means of abrasive blasting as an example process. The resulitng locally varying work hardening over the sheet thickness is further integrated in finite element analysis by the assignment of a starting condition of a 2d-shell element formulation. With this approach, it is possible to map the graded material properties easily in FE simulations with a very good accuracy.

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Section: Functional Relationship Between Plastic Strain and Increase ...mentioning

confidence: 99%

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Lenzen

Kraus

Merklein

2022

KEM

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“…Another possibility for determining the anisotropy at high strain values is an inverse numerical calculation of a layer compression test. With this test, Graser et al 15 were able to determine the r -values at diagonal and transversal direction. For this purpose, the ovality of the upsetting specimen has been used as the target value and the r -values as optimization parameters.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the evolution of the Lankford coefficient in uniaxial tensile tests and validation with grain structure analysis

Lenzen

Merklein

2022

Proceedings of the Institution of Mechanical Engineers, Part B:

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Modern materials mostly exhibit a low formability or a complex material behavior. For example, the common mild steel DC06 exhibits a strain state dependency in the yield stress and a strain dependency of the Lankford coefficients. Thus it is necessary to characterize the material properties from the onset of plastic deformation up to fracture. For example in the uniaxial tensile test, the flow stress and the r-values can be determined. According to the standards, the characterization is only applicable up to uniform elongation. In the case of DC06, the uniform elongation is with 24% comparatively low in contrast to the ultimate elongation with 60%. Research has proven, that the true stress can be characterized up to high strain in the uniaxial tensile test. For the strain dependent Lankford coefficient, this validation is missing. The aim in this investigation is the analysis of the strain dependent anisotropy up to high strain levels in uniaxial tensile tests and the validation. This is done with a comparison of optically measured r-values with the grain structure evolution of the pre stretched parts. These results prove the applicability of the standardized evaluation of Lankford coefficients out of DIC data above the uniform elongation.

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“…Additionally, in-plane torsion tests [32] offer the possibility to obtain a proper flow curve. Finally, the inverse Lankford coefficients determination might be a feasible concept [33].…”

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Characterization of High-Strength Packaging Steels: Obtaining Material Data for Precise Finite Element Process Modelling

Knieps

Liebscher

Moldovan

et al. 2020

Metals

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The steadily increasing demand for downgauging to reduce costs in packaging steel applications requires the development of high-strength packaging steel grades to meet strength requirements. At the same time, the demand for a simulative, computer-aided layout of industrial forming processes is growing to reduce costs in tool constructions for downgauging manners. As part of this work, different high-strength packaging steels were characterized for use in a finite element based process layout and validated using application-oriented experiments. Due to a low hardening rate and the occurrence of Lüders bands, high-strength packaging steels show a low amount of elongation in tensile tests, while for other stress states higher degrees of deformation are possible. Thus, common extrapolation methods fail to reproduce the flow curve of high-strength packaging steels. Therefore, a new approach to extrapolate the flow curve of high-strength packaging steels is presented using the tensile test and bulge test data together with a combined Swift–Voce hardening law. Furthermore, it is shown that the use of complex anisotropic yield locus models such as Yld2000-2d is necessary for high-strength packaging steels in order to be able to precisely simulate application-oriented loads in between plane strain and biaxial tension in validation experiments. Finally, the benefit of a material selection process for packaging steel applications guided by finite element simulations based on precisely characterized material behaviour is demonstrated.

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On the inverse identification of Lankford coefficients using geometrical changes under quasi-biaxial loading

Cited by 5 publications

References 11 publications

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Analysis of the evolution of the Lankford coefficient in uniaxial tensile tests and validation with grain structure analysis

Characterization of High-Strength Packaging Steels: Obtaining Material Data for Precise Finite Element Process Modelling

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