ISO 18338:2021

INTERNATIONAL ISO
STANDARD 18338
Second edition
2021-12
Metallic materials — Torsion test at
room temperature
Matériaux métalliques — Essai de torsion à température ambiante
Reference number
© ISO 2021
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and designations . 3
5 Principle of test . 4
6 Test piece . 4
6.1 Shape and dimensions of test pieces . 4
6.1.1 Cylinder test pieces . 4
6.1.2 Tube test pieces . 5
6.1.3 Preparation of test pieces . 6
7 Determination of original cross-sectional dimensions. 6
7.1 Cylinder test pieces. 6
7.2 Tube test pieces . 6
8 Accuracy of the testing apparatus . .6
8.1 Testing machine . . 6
8.2 Troptometer . 7
9 Conditions of testing .7
10 Determination of the properties .8
10.1 Calculations of shear stress and shear strain . 8
10.2 Determination of the slope of linear portion of shear stress-shear strain curve . 8
10.3 Torsional proof strength, plastic torsion . 9
10.4 Upper torsional yield strength and the lower torsional yield strength . 10
10.5 Determination of torsional strength. 11
10.6 Determination of maximum plastic shear strain .12
11 Test report .12
Annex A (informative) Determination of the reference proof strength, plastic torsion and
reference torsional strength .13
Bibliography .17
iii
Foreword
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The committee responsible for this document is ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 2, Ductility testing.
This second edition cancels and replaces the first edition (ISO 18338:2015), of which it constitutes a
minor revision. The changes are as follows:
— the duplicated part of Formula (A.4) has been deleted;
— minor editorial changes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 18338:2021(E)
Metallic materials — Torsion test at room temperature
1 Scope
This document specifies the method for torsion test at room temperature of metallic materials. The
tests are conducted at room temperature to determine torsional properties.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 377, Steel and steel products — Location and preparation of samples and test pieces for mechanical
testing
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ASTM E2624, Standard Practice for Torque Calibration of Testing Machines and Devices
DIN 51309, Materials testing machines — Calibration of static torque measuring devices
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology 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
troptometer gauge length
L
e
length of the parallel reduced section of the test piece for measurement of angle of twist by means of a
troptometer
3.2
torque
T
moment of couple that generates or tends to generate rotation or torsion
3.3
maximum torque
T
m
for materials displaying discontinuous yielding, highest torque that the test piece withstands during
the test after the yielding period, or for materials displaying no discontinuous yielding, highest torque
that the test piece withstands during the test
3.4
angle of twist
ϕ
angle of relative rotation measured between two planes normal to the test-piece’s longitudinal axial
over the gauge length
Note 1 to entry: See Figure 1.
3.5
shear angle
ψ
angle due to shearing displacement at surface of test piece along the gauge length
Note 1 to entry: See Figure 1.
3.6
shear stress
τ
any moment during the test, torque, T , divided by the original polar section modulus, W
p
3.7
shearing displacement
ΔL
arc length swept out by the cylinder or major tube radius moving through the angle of twist, also being
equivalent to the gauge length sweeping through the shear angle
Note 1 to entry: See Figure 1.
3.8
shear strain
γ
based on the gauge length, the increase of the shearing displacement, ΔL, at any moment during the
test, expressed as a percentage of the gauge length L , or is equal to the tangent of the shear angle, ψ
e
3.9
slope
m
G
slope of the linear, elastic portion of the shear stress-shear strain curve
3.10
torsional proof strength, plastic torsion
τ
p
shear stress at which the plastic component of shear strain, due to torsion at the test piece outer surface,
is equal to a specified percentage
Note 1 to entry: A suffix is added to the subscript to indicate the prescribed percentage, e.g. τ .
p0,35
3.11
torsional yield strength
when the metallic material exhibits a yield phenomenon, shear stress corresponding to the point
reached during the torsion test at which plastic deformation occurs without any increase in the torque
3.11.1
upper torsional yield strength
τ
e,H
maximum value of shear stress prior to the first decrease in torque when the discontinuous yielding
occurs
3.11.2
lower torsional yield strength
τ
e,L
lowest value of shear stress during discontinuous yielding, ignoring any initial transient effects
3.12
torsional strength
τ
m
shear stress corresponding to the maximum torque, T
m
3.13
maximum plastic shear strain
γ
max
maximum plastic shear strain component at the outer surface when total separation of the test piece
occurs
3.14
reference torsional proof strength, plastic torsion
τ
r,p
shear stress at the outer surface of a test piece, calculated according to Nadai’s expression, when cross-
section of the test piece is in partly plastic torsion and attained the proof plastic shear strain
Note 1 to entry: A suffix is added to the subscript to indicate the prescribed percentage, e.g. τ .
r,p0,35
3.15
reference torsional strength
τ
r,m
maximum shear stress is calculated according to the Nadai’s expression for fractured test piece
Figure 1 — Basic symbols for torsion test
4 Symbols and designations
Symbols and corresponding designations are given in Table 1 and Figure 1 or elsewhere in this
document where they appear.
Table 1 — Symbols and designations
Symbol Designation Unit
Test piece
d original external diameter of a tube or a cylinder test piece parallel length portion mm
d original internal diameter of the parallel length of a tube test piece mm
i
L parallel length mm
c
L troptometer gauge length mm
e
L total length of the test piece mm
t
W original polar section modulus [see Formulae (2) and (3)] mm
p
Torque
T Torque N·mm
Angle of twist – shearing displacement
ϕ angle of twist rad
Ψ shear angle rad
ΔL shearing displacement mm
Shear stress – shear strain
a
τ shear stress MPa
Δτ increment in shear stress MPa
γ shear strain %
Δγ Increment in shear strain %
γ specified plastic shear strain %
p
γ maximum plastic shear strain %
max
Yield strength – proof strength – torsional strength
b
m slope of elastic portion of the shear stress-shear strain curve MPa
G
τ upper torsional yield strength MPa
e,H
τ lower torsional yield strength MPa
e,L
τ torsional proof strength, plastic torsion MPa
p
τ torsional strength MPa
m
τ reference torsional proof strength, plastic torsion MPa
r,p
τ reference torsional strength MPa
r,m
a −2
1 MPa = 1 Nmm .
b
In the elastic portion of the shear stress-shear strain curve, the value of slope may not necessarily represent the shear modulus of
elasticity. The value can closely agree with the value of shear modulus of elasticity if optimal conditions (high resolution of troptometer,
high accuracy of torque measuring system,
...