ISO 23838:2022

INTERNATIONAL ISO
STANDARD 23838
First edition
2022-06
Metallic materials — High strain rate
torsion test at room temperature
Matériaux métalliques — Essai de torsion à haute vitesse de
déformation à température ambiante
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and designations . 2
5 Principle . 4
6 Apparatus . 5
6.1 Apparatus components . 5
6.2 Loading device . 6
6.3 Bar components . 6
6.4 Data acquisition and recording system . 7
7 Test piece . 7
7.1 Dimensions of test piece . 7
7.2 Measurement of test piece dimensions . 9
8 Procedure .9
8.1 Calibration of the apparatus . 9
8.2 Recording the temperature of the test environment . 10
8.3 Checking the bar alignment . 10
8.4 Mounting test piece . 10
8.5 Loading . 11
8.6 Measuring and recording . 11
9 Data processing .11
9.1 Strain on bars . 11
9.2 Waveform processing . 11
9.2.1 Determination of waveform baseline . 11
9.2.2 Determination of starting points of waves . 11
9.2.3 Synchronization of waves .12
9.2.4 Determination of loading duration of stress wave .12
9.3 Engineering plastic shear strain rate .12
9.4 Engineering plastic shear strain.12
9.5 Engineering plastic shear stress .12
9.6 Engineering plastic shear stress-shear strain curve .12
9.7 Average engineering plastic shear strain rate .12
9.8 Test example . 13
10 Evaluation of test result .13
11 Test report .13
Annex A (informative) Torsional split Hopkinson bar .14
Annex B (informative) Data acquisition and recording system .28
Annex C (informative) Method for determining the starting points of waves .31
Annex D (informative) Example of torsional split Hopkinson bar method .32
Bibliography .36
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 2, Ductility testing
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
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
4 −1
order of 10 s 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
2 −1
properties of materials at high strain rates (≥10 s ). 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
3 −1
widely used to obtain accurate stress-strain curves at around 10 s .
This document provides test method for the torsional split Hopkinson bar apparatus.
v
INTERNATIONAL STANDARD ISO 23838:2022(E)
Metallic materials — High strain rate torsion test at room
temperature
1 Scope
This document specifies terms and definitions, symbols and designations, principle, apparatus, test
piece, procedure, data processing, evaluation of test result, test report and other contents for the
torsion test at high strain rates for metallic materials by using torsional split Hopkinson bar (TSHB).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
stress wave
strain wave
propagation of disturbance of stress (or strain) in a medium
Note 1 to entry: When a localized mechanical disturbance is applied suddenly into a deformable solid medium,
the disturbance results in the variations of particle velocity, and also the variations of stress and strain states
...