A Method for Direct Measurement of Multiaxial Stress-Strain Curves in Sheet Metal

Abstract

A method has been developed that allows measurement of stress-strain curves for sheet metal being deformed in multiaxial tension. The strain state is imposed using a modification of the Marciniak in-plane biaxial stretching test. Resulting stresses are measured using a modified Xray diffraction (XRD) residual stress measurement system. This system is flexible enough to allow spatial mapping of in-plane stress and measurement of stresses at specific locations of interest on the sample, such as developing localizations. Results are presented correlating measurements on a thin strip of AA5182 with data from standard uniaxial tension test. Also presented are experimentally determined curves for this material in balanced biaxial tension in both the rolling and transverse directions.

Multi-Axial Deformation Setup for Microscopic Testing of Sheet Metal to Fracture

“…As a result of the absence of contact a true in-plane deformation occurs and inhomogeneous material deformation is not artificially enforced. Accordingly, this test is perfectly suitable for characterizing microstructural mechanisms and, therefore, regained a lot of interest recently [18][19][20][21]. Furthermore, the Marciniak tests can be carried out safely in SEM since there is no influence on the working principles of electron microscopy.…”

Intergranular Strain Evolution During Biaxial Loading: A Multiscale FE-FFT Approach

“…The incoming beam, having a cross section of 3.8 9 3.8 mm 2 , is incident at the center of the circular gauge area. The detector and samples are oriented such that the diffraction vector g lies along direction 1 of cruciform sample and along the DB loading direction.…”

“…These complex strain paths, coupled with elastic/plastic anisotropy of polycrystals, result in heterogeneous distributions of intergranular strains, governing macroscopic response such as yield strength, work hardening, etc. Although biaxial testing is increasingly used to study macroscopic behavior of materials, [1][2][3] limited research efforts have been directed toward understanding the underlying microstructure and intergranular strain evolution. [4][5][6] In-situ neutron and synchrotron x-ray diffraction are well established techniques to study internal stress and microstructure evolution.…”

Crystallographic texture evolution in 1008 steel sheet during multi-axial tensile strain paths

“…Samples for non-uniaxial stain paths were loaded in a custom testing machine [26] using a sample geometry developed by Raghavan [27]. A clamp hold down force of -450 kN (force control) and a ram rate of 0.1 mm sec was applied resulting in a nominal strain rate of 0.2 strain sec .…”