Distinguishing inertia effects from the intrinsic mechanical behavior of soft materials at high strain rates by Kolsky bar experiments

Erik E Nishida, Purdue University

Abstract

Soft material characterization in the dynamic regime is needed for constitutive models to support numerical simulations for shock mitigation and characterization, blasts effects due to explosions, and vibration isolation. However, both the experimental techniques and dynamic properties of soft materials are scarce. A main reason for the lack of dynamic characterization methods and accurate material models are the complications associated with the soft materials that are not as significant with stronger materials, one of which is radial inertia effects. Many researchers have derived equations to describe the extra inertia-induced stress in the specimens used in Kolsky bar experiments. A recent derivation by Warren and Forrestal under the conditions of dynamic equilibrium and constant strain rate, describes the distribution of the extra inertia stress in the specimen. In this study, a Kolsky bar modified for soft material characterization was used to experimentally verify the inertia stress predicted by Warren and Forrestal. By experimentation, the extra radial inertia-induced stress due to strain, strain rate, and strain acceleration have been quantified. From a compressive stress-strain curve at a reference strain rate, Warren and Forrestal’s derivation was used to predict the stress-strain curves at strain rates both below and above the reference rate. The predictions agreed well with experimental results, which validates the derivation. The extra inertial stress can thus be subtracted from experimentally obtained stress-strain curves to reveal the intrinsic mechanical response of the soft specimen without inertia effects.

Degree

M.S.A.A.

Advisors

Chen, Purdue University.

Subject Area

Aerospace engineering|Materials science

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