Large Strain and Small-Scale Biaxial Testing of Sheet Metals


Seymen Y., GÜLER B. , EFE M.

EXPERIMENTAL MECHANICS, vol.56, no.9, pp.1519-1530, 2016 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 56 Issue: 9
  • Publication Date: 2016
  • Doi Number: 10.1007/s11340-016-0185-7
  • Title of Journal : EXPERIMENTAL MECHANICS
  • Page Numbers: pp.1519-1530
  • Keywords: Biaxial tension, In-situ testing, Cruciform, Forming, DIC, Aluminum, FORMING LIMIT DIAGRAM, DIGITAL IMAGE CORRELATION, CRUCIFORM SPECIMEN, MAGNESIUM ALLOY, TENSILE TEST, DEFORMATION, ALUMINUM, PREDICTION, IDENTIFICATION, TEMPERATURE

Abstract

Small-scale and multi-axial testing of sheet metals, particularly of lightweight alloys and advanced steels are becoming important as these materials exhibit forming behavior sensitive to their unique microstructural features and strain paths. As an alternative to large-scale standard tests, in this paper we introduce a novel biaxial tensile test apparatus utilizing miniature cruciform samples. The compact and portable apparatus includes a custom-built optical microscope and high-resolution digital image correlation (DIC) equipment for in-plane and in-situ strain measurements at the microstructure scale. The small strain and premature fracture problems common to the cruciform tests are solved by optimizing the sample design and by meticulously controlling the manufacturing steps and surface finish. Strain analyses reveal a key mechanism responsible for large strains and fracture at the center. This mechanism suppresses the local neck formation and allows uniform deformation under equibiaxial conditions until fracture. When normalized with the strain hardening exponent of the sample material (Al 6061-T6), the effective strain value before fracture, , surpass the reported values for similar materials tested by cruciform and standard methods.