Apparatus for Measuring Strength in Biaxial Compression

TL;DR

This paper introduces a new apparatus for measuring the biaxial compressive strength of ductile materials using the compression of thin spherical shells, addressing limitations of uniaxial testing methods.

Contribution

The paper proposes a novel experimental setup to measure biaxial compressive strength, including both quasistatic and dynamic tests, using detonating gas mixtures around spherical shells.

Findings

Potential to accurately measure biaxial strength in ductile materials.

Addresses limitations of uniaxial compression tests.

Introduces a method for dynamic strength measurement.

Abstract

Most measurements of compressive strength of ductile materials have involved Hopkinson-Kolsky bars or Taylor anvils placing samples in uniaxial compression. In these geometries strain is limited by the tendency of the sample to petal, in analogy to necking in uniaxial tension. Estimation of strength for any other form of the stress tensor requires assuming a shape for the yield surface; because data exist only for uniaxial compression these assumptions are untested. In an imploding spherical shell compression is biaxial, the plastic strain may not be small and the material behavior may be nonlinear as a result of work hardening and heating by plastic work. We propose to measure the strengths of materials in biaxial compression,both quasistatically and dynamically, using the compression of thin spherical shells. We suggest surrounding the shell with an annulus filled with a mixture of H$_2$ and Cl$_2$ gases whose volumetric detonation is initiated by a flash of blue and near-ultraviolet light. Less promising approaches are described in appendices.