Large strain compression testing of ductile materials at quasi-static and dynamic strain rates

Seth Skube, Purdue University

Abstract

The compression test, where a right cylindrical sample is axially compressed between two rigid platens, is a convenient test to obtain large strain behavior of ductile materials. However, friction between the sample and platens causes sample barreling, invalidating flow stress data. Samples with concentric end-grooves cut into their faces, to retain lubricant, were used to obtain valid quasi-static flow stress data for 5083-H116 Aluminum, to true strains approaching 1.1. Samples were cut from the material in two orientations to account for material anisotropy. Homogeneous sample deformations were observed. The samples' deformations were numerically modeled using finite element modeling techniques. The end-grooved sample's stress distribution was largely uniform, with the exception of stress concentrations near the end-grooves. The standard sample's stress distribution was highly non-uniform for relatively small plastic strain, but increased in uniformity with strain. Sample deformations local to the end-grooves were observed to be a function of strain hardening exponent, and FEM simulations were used to determine sample end-groove geometries for materials with strain hardening exponents 0 < n < 1. The end-grooved sample's use was expanded to high strain rate experiments, using a split Hopkinson pressure bar. Valid, high strain rate, 5083-H116 Aluminum flow stress data was obtained to true strains approaching 0.7, for the two sample material orientations. High-speed photographs of the sample's deformation were captured, and deformations similar to the quasi-static experiments observed.

Degree

M.S.A.A.

Advisors

Chen, Purdue University.

Subject Area

Aerospace engineering

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