A New Proposal for a Method to Measure Orthogonal R-Value Using a Single Tensile Test with Three-Dimensional Digital Image Correlation

• Published in: Experimental mechanics 2022-07, Vol.62 (6), p.999-1006
• Main Authors: Gu, G. H., Kim, Y., Kwon, H., Ahn, S. Y., Seo, M. H., Ahn, K., Kim, H. S.
• Format: Article
• Language: English
• Subjects: Accuracy; Alloys; Aluminum base alloys; Anisotropy; Biomedical Engineering and Bioengineering; Characterization and Evaluation of Materials; Coefficients; Control; Digital imaging; Dynamical Systems; Engineering; Finite element method; Isotropic material; Lasers; Low carbon steels; Magnesium base alloys; Mechanical properties; Metal sheets; Optical Devices; Optics; Photonics; Plastic deformation; Research Paper; Rolling direction; Solid Mechanics; Strain; Tensile tests; Titanium base alloys; TWIP steels; Vibration
• ISSN: 0014-4851; 1741-2765
• DOI: 10.1007/s11340-022-00857-3

Background The r-value, also called the Lankford coefficient or plastic strain ratio, is an essential factor that evaluates the mechanical anisotropy and sheet formability of materials and also an essential mechanical parameter for the finite element method simulations of anisotropic materials. In order to estimate this significant property of sheet metal, it is necessary to perform multiple tensile tests in three directions: rolling direction, 45° from the rolling direction, and transverse (90°) direction. Objective In this study, a new digital-image-correlation-aided method was devised to obtain the r-values along the loading direction ( r 0 ) and also orthogonal to the loading direction ( r 90 ) using a single tensile test. Methods The anisotropic properties of the materials were investigated by introducing the coefficients for width and thickness reduction. The equation applicable to isotropic materials was modified by adding the factors describing the anisotropy. The unknown coefficients of modified formulae were defined using the premise that there is no volume change during plastic deformation of the materials. Results The predicted r 90 -values of various alloys, such as DP steel, TWIP steel, low carbon steel, Mg alloy, Ti alloy, and Al alloy, were in good agreement with those measured from the single tensile tests. Conclusions This good agreement suggests that the method proposed in this study can help determine the mechanical anisotropy of materials with far less time and effort than the conventional method for estimating orthogonal r-values.