Introduction

In many dynamic events, such as punch forming, metal cutting, and vehicle collision, the metallic components are susceptible to dynamic impact loading, in which case the maximum strain rate of the order of 10⁴ s⁻¹ can be achieved. During this extreme loading condition, the strength of the material can be significantly higher than that under quasi-static loading conditions. The shear mechanical properties of metallic materials, such as yield strength, flow stress and failure strain are essential information for analysis of shear failure of components, and are also the basic data for construction of constitutive relations. The shear mechanical properties of many metallic materials depend also on strain rate as properties under uniaxial load. Therefore, to determine the shear mechanical properties of metallic materials at high strain rates by torsion test is also of great importance for engineering design, structural optimization, processing and evaluation of metallic structures. For additional information see

— ISO 26203‑1 , and
— ISO 26203‑2 .

The split Hopkinson (Kolsky) bar is one of the major test methods for measurement of mechanical properties of materials at high strain rates (≥10² s⁻¹). It is designed on the base of two assumptions, namely

a) one-dimensional elastic wave propagation in elastic bars, and
b) uniform distribution of stress–strain along the length of the short test piece.

The fundamental principle is as follows: a small test piece is sandwiched between two long elastic bars, which are used as loading and measuring devices by means of elastic stress wave propagation. On the one hand, the propagating waves on elastic bars load dynamically the test piece; on the other hand the force and displacement measurements of test piece can be calculated by measuring the elastic strain of the bars through gauges attached to the bars. The torsional split Hopkinson bar apparatus, one kind of split Hopkinson bar techniques, can provide solutions for dynamic torsional testing problems and is widely used to obtain accurate stress-strain curves at around 10³ s⁻¹.

This document provides test method for the torsional split Hopkinson bar apparatus.

BS ISO 23838:2022

Metallic materials. High strain rate torsion test at room temperature

Current

Published:

31 Aug 2022