ISO/TS 19096

Metallic materials — Instrumented indentation test for hardness and materials parameters — Evaluation of stress change using indentation force differences

Matériaux métalliques — Essai d'indentation instrumenté pour les paramètres de dureté et de matériaux — Évaluation de la variation de contrainte en utilisant les différences de force d'indentation

General Information

• Status: Not Published
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: ISO/TC 164/SC 3 - Hardness testing
• Drafting Committee: ISO/TC 164/SC 3/WG 4 - Revision of ISO 14577 - Metallic materials - Instrumented indentation test for hardness and materials parameters
• Current Stage: 6000 - International Standard under publication
• Completion Date: 18-Jul-2023

Standards Content (Sample)

© ISO 20##– All rights reserved
ISO/FD TS 19096:2023 (E)
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ISO/TC 164/SC 3/WG 4
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Secretariat: DIN
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Metallic materials — Instrumented indentation test for hardness and materials parameters —
Evaluation of stress change using indentation force differences
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ISO/FD TS 19096:2023(E)
© ISO 20XX

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part
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mechanical, including photocopying, or posting on the internet or an intranet, without prior written
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© ISO 20##– All rights reserved
ISO/FD TS 19096:2023 (E)
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© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no
part of this publication may be reproduced or utilized otherwise in any form or by any means,
electronic or mechanical, including photocopying, or posting on the internet or an intranet, without
prior written permission. Permission can be requested from either ISO at the address below or
ISO’s member body in the country of the requester.
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ISO/TS 19096:2023(E) Formatted: Font: Bold
Contents       Page Formatted: Font: 13 pt
Formatted: Font: 13 pt
Foreword . iv
Introduction. v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and designations . 2
5 Principle . 3
5.1 Shift of force/indentation depth curve by stress change . 3
5.2 Derivation of stress change from force difference . 3
6 Testing machine . 4
7 Test piece . 4
8 Procedure . 5
9 Calculation of stress change . 7
9.1 Force and projected area calculation at each state . 7
9.2 Force difference . 8
9.3 Projected area . 8
9.4 Calculation of average stress change . 8
10 Uncertainty of the results . 9
11 Test report . 10
Annex A (normative) Procedure for hardness uniformity verification . 11
Annex B (normative) Combining with stress relief method . 14
Annex C (informative) Determination of stress change ratio using Knoop indenter . 17
Annex D (informative) Verification of instrumented indentation test residual stress
measurement method by bending specimen . 20
Annex E (informative) Comparison with hole-drilling and saw-cutting methods . 23
Bibliography . 32

Foreword . iv
ii © ISO 2023 – All rights reserved

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ISO/FD TS 19096:2023 (E) Formatted: Font color: Auto
Formatted: Font color: Auto
Introduction. v
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Foreword . iv
Introduction. v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and designations . 2
5 Principle . 3
6 Testing machine . 4
7 Test piece . 4
8 Procedure. 4
9 Calculation of stress change . 6
10 Uncertainty of the results . 8
11 Test report . 9
Annex A . 10
Annex B . 11
Annex C . 13
Annex D . 15
Annex E . 17
Bibliography . 21



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ISO/TS 19096:2023(E) Formatted: Font: Bold
Formatted: Font color: Auto
Foreword
Formatted: Foreword Title, Don't adjust space between Latin
and Asian text, Don't adjust space between Asian text and
ISO (the International Organization for Standardization) is a worldwide federation of national standards
numbers
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of
patents. ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had received notice of
patents which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available
at  www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or
all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html. Formatted: English (United Kingdom)
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Formatted: Font color: Auto, English (United Kingdom)
Subcommittee SC 3, Hardness testing.
Formatted: Font: Cambria, Font color: Auto, English (United
Kingdom)
Any feedback or questions on this document should be directed to the user’s national standards body. A
Formatted: Font color: Auto, English (United Kingdom)
complete listing of these bodies can be found at
Formatted: Font: Cambria, Font color: Auto, English (United
www.iso.org/members.htmlwww.iso.org/members.html.
Kingdom)
Formatted: Font color: Auto, English (United Kingdom)

Formatted: English (United Kingdom)
Formatted: English (United Kingdom)


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ISO/FD TS 19096:2023 (E) Formatted: Font color: Auto
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Introduction
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Residual stress is defined as the “locked-in” stress that exists in materials and structures independent of
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the presence of any external loads. The mechanisms that create residual stress are diverse and include
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non-uniform plastic deformation, surface modification and thermal gradients.
Asian text, Don't adjust space between Asian text and
numbers
Numerous techniques have been developed for evaluating residual stress, each with their own merits and
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drawbacks. Physical methods such as X-ray diffraction (XRD) and neutron diffraction are non-destructive
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tests based on measuring lattice parameters, and thus they are restricted to crystalline materials; in
between Asian text and numbers
addition, they are sensitive to microstructure and to the test environment.
On the other hand, destructive methods such as hole drilling and sectioning method let us quantify the
residual stress mechanically and require no reference sample. However, these methods cannot avoid
destruction of the sample and require a strain gauge attachment. Then the observed change in strain must
be converted to the stress.
The results of these methods for determining residual stress can differ because the residual stress sensing
depth and area in each method are different. The hole-drilling measures the amount of strain relaxation
caused by the removal of the hole material. The spatial resolution of the method is approximately the size
of the hole (typically 2mm2 mm diameter). In case of XRD, the smaller size of irradiated area requires a
longer measurement time. The indentation method requires less precise surface preparation than XRD
because it obtains a direct response from the material, and strain gauges are unnecessary. It takes less
than 30 seconds s to measure one point and has high in-field applicability. This document, using a semi-
destructive method for measuring stress change, makes it unnecessary to machine samples from in-
service components or manufactured products exhibiting internal or external stress changes.
Residual stress is not a material property but a state of stress. In general, it has been observed that when
a material is subject to stress change, its indentation curve is shifted upward or downward compared to
the initial indentation curve, because the stress change makes indentation easier (relatively tensile) and
Field Code Changed
more difficult (relatively compressive). In a constant depth test (fixed ℎ ): h ): an increase in
𝑚𝑚𝑚𝑚𝑚𝑚 max
compressive stress squeezes the material around the indenter and hence a greater load is needed to reach
to the same indentation depth than in the initial stress state. On the other hand, an increase in tensile
stress releases the material and a smaller load is necessary to keep the same indentation depth than in
Field Code Changed
the initial stress state. In fact, a smaller load/larger load is required at constant ℎ h from initial
𝑚𝑚𝑚𝑚𝑚𝑚 max
surface. It seems as if an imaginary (virtual) force works in the same/opposite direction as/to the
indenting direction.
To quantify the effect of stress on indentation behaviorbehaviour, the deviatoric stress concept along the
indenting direction is proposed in this document. The method for calculation of the average stress change
is given in Clause 8. The described procedure can be applied only when the observed change in force- Formatted: cite_sec
displacement curves is a result of stress change. The proposed method measures the near-surface stress
Formatted: cite_sec
change in the direction parallel to the test surface.
Field Code Changed
Similarly, in a constant load test (fixed 𝐿𝐿 ): L ): compressive stress change makes indentation
𝑚𝑚𝑚𝑚𝑚𝑚 max
difficult and hence the indentation depth becomes shallow. Tensile stress change makes indentation easy
and the indentation depth becomes deeper. Thus, in the elastic modulus approach, the sign (mode) of
Field Code Changed
stress change can be determined by using this constant-load test as is similar to the above constant-depth
Formatted: cite_app
(ℎ )( h ) test in this proposal.
𝑚𝑚𝑚𝑚𝑚𝑚
max
Formatted: cite_app
Formatted: cite_app
The material for the reference and target states should be selected so as to maintain identical chemical
composition with relatively little change of mechanical properties to the target material. This test method Formatted: cite_app
is limited to examinations that conform to the conditions given in Annex A. Annex A provides a
Formatted: Font color: Auto
procedure to achieve satisfactory results by sorting out locally hardening test points. The test point
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showing the largest deviation is reasonably considered as being from a locally severely changed region.
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ISO/TS 19096:2023(E) Formatted: Font: Bold
The test point showing the greatest deviation from the average value should be screened out and this
process be repeated with remaining test points until the criterion is met. Nevertheless, it is recommended
to carefully control the factors between the target and reference states, such as chemical composition,
grain size, dislocation density and texture, which can cause errors in measurements.  Formatted: Font color: Auto
If the condition given in Annex A is not satisfied, destructive stress relief methods by electrical discharge Formatted: cite_app
machining or focused ion beam can be combined to obtain the reference state (stress-free state) without
Formatted: cite_app
changing material properties following Annex B. The stress change from this document can be converted
Formatted: cite_app
to the residual stress of the target state by considering the stress value of the reference state measured
Formatted: cite_app
by other methods, such as X-ray diffraction and hole-drilling method.
This document proposes a method to measure the average stress change between reference and target
states. Residual stress caused by non-uniform plastic forming and heat treatment usually shows stress
components of the same sign in the region requiring stress evaluation. Therefore, there is high demand
for the proposed method in many fields. Additionally, if the user wants to resolve stress components,
Annex C in the draft can be utilized. The average stress change measured by this method is change of half Formatted: cite_app
the first invariant of stress tensor because the stress normal to the test surface is zero. In other words,
Formatted: cite_app
the average normal stress change is always constant, even if the coordinate system is rotated on the
surface.
The method proposed in the draft has been applied and verified for many different materials and
conditions, and extensive evidence shows that it is both reasonable and useful, as shown in Annex D and Formatted: cite_app
E. The purpose of this item is to measure the stress change between reference and target states. As
Formatted: cite_app
proposed in this draft, the relative stress change can be quantitatively determined and whether the stress
Formatted: cite_app
change involved is tensile (indentation curve down) or compressive (indentation curve up) compared to
the reference (initial) state. Thus, if the state of initial stress is known, it is possible to determine the
magnitude and sign of the altered stress state as well.
Some materials show the sensitivity of indentation force to residual stress, which results the force
difference greater in a tensile stress state than a compressive stress state, although the difference is in
general not large. Even for materials showing different sensitivity of peak load in compressive vs. tensile
stress, the load difference is a monotone function of stress change, so that the region of maximum stress
can be identified. Furthermore, for many materials, the load difference sensitivity does not significantly
violate the fundamental concept.
This document has been prepared to provide useful guidelines on how to extract a two-dimensional Formatted: Font color: Auto
representation of the entire 3D residual stress state by means of local size-controllable indentations over
the component surface. The testing surface may be indented in one-dimensional or two-dimensional
indentation arrays for a more reliable evaluation of the entire bulk residual stress state. The stress state
detected by the proposed methodology provides accurate measurement of the plane stress residual
stress state from the near-surface region in the component. Formatted: Font color: Auto

vi © ISO 2023 – All rights reserved

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TECHNICAL SPECIFICATION ISO/TS 19096:2023(E)

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Metallic materials — Instrumented indentation test for hardness and materials parameters —
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Evaluation of stress change using indentation force differences
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single, No page break before
1 1 Scope Formatted: Font: 11 pt, Not Bold
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This document specifies the method of instrumented indentation test for evaluation of stress change Don't adjust space between Asian text and numbers
between reference and target states using indentation force differences.
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This document primarily applies to measuring the stress change in a specific location and the stress
difference between different locations.
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2 2 Normative references Don't adjust space between Asian text and numbers
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The following documents, in whole or in part, are normatively referenced in this document and are
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indispensable for its application. For dated references, only the edition cited applies. For undated
space between Latin and Asian text, Don't adjust space
between Asian text and numbers
references, the latest edition of the referenced document (including any amendments) applies.
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ISO 14577--1:2015, Metallic materials — Instrumented indentation test for hardness and materials
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parameters –— Part 1: Test method
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ISO 14577--2:2015, Metallic materials — Instrumented indentation test for hardness and materials
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parameters –— Part 2: Verification and calibration of testing machines
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ISO 14577-3:2015, Metallic materials — Instrumented indentation test for hardness and materials
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parameters – Part 3: Calibration of reference blocks
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ISO/IEC Guide 98--3:2008, Uncertainty of measurement –— Part 3: Guide to the expression of
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uncertainty in measurement (GUM:1995)
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ISO/DTS 19096:2023(E) Formatted: Font: Bold
3 3 Terms and definitions Formatted: Don't adjust space between Latin and Asian text,
Don't adjust space between Asian text and numbers
No terms and definitions are definedlisted in this document. Formatted: Font color: Auto
Formatted: Body Text
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
Formatted: Font: Times New Roman, 12 pt, English (United
States)
— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
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4 4 Symbols and designations
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space between paragraphs of the same style, Line spacing:
For the purpose of this technical specificationdocument, the symbols and designations in Table 1 shall
single, No bullets or numbering, Don't keep with next
be appliedapply.
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Table 1 — Symbols and designations
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Symbol Designation Unit
States)
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2 .
A Average projected area of reference and target states mm
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2
A Projected area of reference state mm
r
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2
At Projected area of target state mm
Formatted
...
Force difference from target curve to reference curve at maximum indentation
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 19096
ISO/TC 164/SC 3
Metallic materials — Instrumented
Secretariat: DIN
indentation test for hardness and
Voting begins on:
2023-05-22 materials parameters — Evaluation of
stress change using indentation force
Voting terminates on:
2023-07-17
differences
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 19096:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 1 ----------------------
ISO/DTS 19096:2023(E)
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 19096
ISO/TC 164/SC 3
Metallic materials — Instrumented
Secretariat: DIN
indentation test for hardness and
Voting begins on:
materials parameters — Evaluation of
stress change using indentation force
Voting terminates on:
differences
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/DTS 19096:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 2 ----------------------
ISO/DTS 19096:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and designations . 1
5 Principle . 2
5.1 Shift of force/indentation depth curve by stress change . 2
5.2 Derivation of stress change from force difference . 3
6 Testing machine.3
7 Test piece . 3
8 Procedure .4
9 Calculation of stress change . 5
9.1 Force and projected area calculation at each state . 5
9.2 Force difference . 6
9.3 Projected area . 6
9.4 Calculation of average stress change . 6
10 Uncertainty of the results . 6
11 Test report . 7
Annex A (normative) Procedure for hardness uniformity verification . 8
Annex B (normative) Combining with stress relief method . 9
Annex C (informative) Determination of stress change ratio using Knoop indenter .11
Annex D (informative) Verification of instrumented indentation test residual stress
measurement method by bending specimen.13
Annex E (informative) Comparison with hole-drilling and saw-cutting methods .15
Bibliography .19
iii
© ISO 2023 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/DTS 19096:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of
patents. ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had received notice of
patents which may be required to implement this document. However, implementers are cautioned
that this may not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent
rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals,
Subcommittee SC 3, Hardness testing.
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
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ISO/DTS 19096:2023(E)
Introduction
Residual stress is defined as the “locked-in” stress that exists in materials and structures independent
of the presence of any external loads. The mechanisms that create residual stress are diverse and
include non-uniform plastic deformation, surface modification and thermal gradients.
Numerous techniques have been developed for evaluating residual stress, each with their own merits
and drawbacks. Physical methods such as X-ray diffraction (XRD) and neutron diffraction are non-
destructive tests based on measuring lattice parameters, and thus they are restricted to crystalline
materials; in addition, they are sensitive to microstructure and to the test environment.
On the other hand, destructive methods such as hole drilling and sectioning method let us quantify the
residual stress mechanically and require no reference sample. However, these methods cannot avoid
destruction of the sample and require a strain gauge attachment. Then the observed change in strain
must be converted to the stress.
The results of these methods for determining residual stress can differ because the residual stress
sensing depth and area in each method are different. The hole­drilling measures the amount of
strain relaxation caused by the removal of the hole material. The spatial resolution of the method
is approximately the size of the hole (typically 2 mm diameter). In case of XRD, the smaller size of
irradiated area requires a longer measurement time. The indentation method requires less precise
surface preparation than XRD because it obtains a direct response from the material, and strain gauges
are unnecessary. It takes less than 30 s to measure one point and has high in-field applicability. This
document, using a semi-destructive method for measuring stress change, makes it unnecessary to
machine samples from in-service components or manufactured products exhibiting internal or external
stress changes.
Residual stress is not a material property but a state of stress. In general, it has been observed that
when a material is subject to stress change, its indentation curve is shifted upward or downward
compared to the initial indentation curve, because the stress change makes indentation easier
(relatively tensile) and more difficult (relatively compressive). In a constant depth test (fixed h ): an
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increase in compressive stress squeezes the material around the indenter and hence a greater load is
needed to reach to the same indentation depth than in the initial stress state. On the other hand, an
increase in tensile stress releases the material and a smaller load is necessary to keep the same
indentation depth than in the initial stress state. In fact, a smaller load/larger load is required at
constant h from initial surface. It seems as if an imaginary (virtual) force works in the same/
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opposite direction as/to the indenting direction.
To quantify the effect of stress on indentation behaviour, the deviatoric stress concept along the
indenting direction is proposed in this document. The method for calculation of the average stress
change is given in Clause 8. The described procedure can be applied only when the observed change
in force­displacement curves is a result of stress change. The proposed method measures the near­
surface stress change in the direction parallel to the test surface.
Similarly, in a constant load test (fixed L ): compressive stress change makes indentation difficult
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and hence the indentation depth becomes shallow. Tensile stress change makes indentation easy and
the indentation depth becomes deeper. Thus, in the elastic modulus approach, the sign (mode) of stress
change can be determined by using this constant-load test as is similar to the above constant-depth (
h ) test in this proposal.
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The material for the reference and target states should be selected so as to maintain identical chemical
composition with relatively little change of mechanical properties to the target material. This test
method is limited to examinations that conform to the conditions given in Annex A. Annex A provides
a procedure to achieve satisfactory results by sorting out locally hardening test points. The test point
showing the largest deviation is reasonably considered as being from a locally severely changed
region. The test point showing the greatest deviation from the average value should be screened out
and this process be repeated with remaining test points until the criterion is met. Nevertheless, it is
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ISO/DTS 19096:2023(E)
recommended to carefully control the factors between the target and reference states, such as chemical
composition, grain size, dislocation density and texture, which can cause errors in measurements.
If the condition given in Annex A is not satisfied, destructive stress relief methods by electrical
discharge machining or focused ion beam can be combined to obtain the reference state (stress­free
state) without changing material properties following Annex B. The stress change from this document
can be converted to the residual stress of the target state by considering the stress value of the reference
state measured by other methods, such as X-ray diffraction and hole-drilling method.
This document proposes a method to measure the average stress change between reference and target
states. Residual stress caused by non-uniform plastic forming and heat treatment usually shows stress
components of the same sign in the region requiring stress evaluation. Therefore, there is high demand
for the proposed method in many fields. Additionally, if the user wants to resolve stress components,
Annex C in the draft can be utilized. The average stress change measured by this method is change of
half the first invariant of stress tensor because the stress normal to the test surface is zero. In other
words, the average normal stress change is always constant, even if the coordinate system is rotated on
the surface.
The method proposed in the draft has been applied and verified for many different materials and
conditions, and extensive evidence shows that it is both reasonable and useful, as shown in Annex D
and E. The purpose of this item is to measure the stress change between reference and target states.
As proposed in this draft, the relative stress change can be quantitatively determined and whether
the stress change involved is tensile (indentation curve down) or compressive (indentation curve up)
compared to the reference (initial) state. Thus, if the state of initial stress is known, it is possible to
determine the magnitude and sign of the altered stress state as well.
Some materials show the sensitivity of indentation force to residual stress, which results the force
difference greater in a tensile stress state than a compressive stress state, although the difference
is in general not large. Even for materials showing different sensitivity of peak load in compressive
vs. tensile stress, the load difference is a monotone function of stress change, so that the region of
maximum stress can be identified. Furthermore, for many materials, the load difference sensitivity
does not significantly violate the fundamental concept.
This document has been prepared to provide useful guidelines on how to extract a two-dimensional
representation of the entire 3D residual stress state by means of local size-controllable indentations
over the component surface. The testing surface may be indented in one-dimensional or two-
dimensional indentation arrays for a more reliable evaluation of the entire bulk residual stress state.
The stress state detected by the proposed methodology provides accurate measurement of the plane
stress residual stress state from the near­surface region in the component.
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TECHNICAL SPECIFICATION ISO/DTS 19096:2023(E)
Metallic materials — Instrumented indentation test for
hardness and materials parameters — Evaluation of stress
change using indentation force differences
1 Scope
This document specifies the method of instrumented indentation test for evaluation of stress change
between reference and target states using indentation force differences.
This document primarily applies to measuring the stress change in a specific location and the stress
difference between different locations.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 14577­1:2015, Metallic materials — Instrumented indentation test for hardness and materials
parameters — Part 1: Test method
ISO 14577­2:2015, Metallic materials — Instrumented indentation test for hardness and materials
parameters — Part 2: Verification and calibration of testing machines
ISO/IEC Guide 98­3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Symbols and designations
For the purpose of this document, the symbols and designations in Table 1 apply.
Table 1 — Symbols and designations
Symbol Designation Unit
2
A Average projected area of reference and target states mm
2
A Projected area of reference state mm
r
2
A Projected area of target state mm
t
∆F Force difference from target curve to reference curve at maximum indentation displacement N
F Maximum test force N
max
F Maximum test force on reference state N
r
F Maximum test force on target state N
t
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ISO/DTS 19096:2023(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Designation Unit
h Indentation depth mm
h Maximum indentation depth (should be the same for target and reference state) mm
max
p Ratio of stress changes along one direction to that along the normal direction ­
r Reference state (used as subscript) ­
t Target state (used as subscript) ­
Δσ
Average stress change of surface stress change components. MPa
avg
Stress change from reference state to target state along a direction perpendicular to in­
Δσ MPa
denting direction
Δ′σ Shear deviatoric stress component of stress change from reference state to target state MPa
Δ′σ z component of shear deviatoric stress of stress change from reference state to target state MPa
z
5 Principle
5.1 Shift of force/indentation depth curve by stress change
The stress change in the same material between two different states creates a shift in the force/
indentation depth curve (see Figure 1). A stress increase to be in a relatively tensile state makes
indentation easier because the material around the indenter is relaxed. Thus, the indentation force
required to reach a given depth in a relatively tensile stress state is lower than that in the initial stress
state. In a relatively compressive stress state, the reverse is true. Therefore, the stress change can be
evaluated by measuring the indentation force difference at maximum indentation depth ( FF− )(=ΔF
rt
) between the reference and target states.
Key
X indentation depth
Y force
A tensile stress
B compressive stress
1 compressive
2 reference
3 tensile
Figure 1 — Change in morphology and force/indentation depth curve with stress change
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ISO/DTS 19096:2023(E)
5.2 Derivation of stress change from force difference
The stress change in one direction can be expressed asΔσ ; the stress normal to Δσ on the surface can
be expressed as pΔσ (p is the stress ratio). Since the stress change normal to the surface (along the
indentation test direction) is taken as zero, only surface biaxial stresses affect the shape of the force/
indentation depth curve. The biaxial stress change can be divided into a hydrostatic stress term and a
shear deviatoric stress term. The only shear deviatoric stress component (Δ′σ ) applied along the
indentation test direction (z), Δ′σ , can influence the force/indentation depth curve when the
z
indentation test is performed along the z direction. Δ′σ can be related to the force difference as in
z
Formula (5.1). This formula reflects the fact that the shear deviatoric stress along the indentation test
direction is directly related to the indentation stress change (indentation force difference divided by
[1],[2]
projected area) :
1+p FF−
() ()
rt
Δ′σσ= Δ = (5.1)
z
3 A
From Formula (5.1), the stress change; Δσ can be expressed as in Formula (5.2), and the other stress
normal to Δσ can be determined as pΔσ :
FF−
3 ()
rt
Δσ = (5.2)
()1+p A
6 Testing machine
6.1 The testing machine shall have the capability of applying predetermined test forces or
displacements within the required scope and shall fulfil the requirements of ISO 14577-2.
6.2 The testing machine shall have the capability of measuring and reporting applied force,
indentation displacement and time throughout the testing cycle.
6.3 The testing machine shall have the capability of compensating for the machine compliance (see
ISO 14577-1:2015 Annex C and ISO 14577-2:2015, 4.5).
6.4 A self-similar sharp indenter (e.g. Vickers pyramid and Berkovich pyramid) following
ISO 14577­1:2015, Clause 4, should be used for the measurement.
6.5 The testing machine shall operate at a temperature within the permissible range specified in
ISO 14577-1:2015 7.1 and shall maintain its calibration within the limits specified in ISO 14577-2:2015,
Clause 4.
6.6 The testing machine shall be calibrated following the procedures detailed in ISO 14577­2:2015,
Annex D and the use of a reference block (see ISO 14577-3) that shall be isotropic and homogeneous.
The repeatability of the testing machine shall be below 3,3 % of the coefficient of variation by using a
reference block with maximum permissible coefficient of variation below 3 %.
7 Test piece
7.1 The test piece shall fulfil the requirements of ISO 14577-1:2015, Clause 6.
7.2 The preparation of the test piece shall be carried out in such a way that any alteration of the
surface hardness and/or residual stress is minimized.
7.3 The thickness of the test piece shall be known or measured and its tolerance shall be specified.
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ISO/DTS 19096:2023(E)
8 Procedure
8.1 The test shall be in controlled conditions that fulfil the requirements of ISO 14577-1:2015,
Clause 7.
8.2 To measure a stress change in the same material, the force/indentation depth curve obtained
in the target state (target force/indentation depth curve) and that obtained in the reference state
(reference force/indentation depth curve) at the same maximum displacement are required (see
Figure 1). The flow chart showing the overall test procedure is seen in Figure 2.
8.3 Each state includes a minimum of six force/indentation depth curves. The procedure requires
a minimum of six indents which requires different sized array depending on the size of indents. The
stress comparison is with the stress average over this array size.
8.4 It is important that the test results are not affected by the presence of an interface, free surface
or by any plastic deformation introduced by a previous indentation in a series. The effect of any of these
depends on the indenter geometry and the materials properties of the test piece. Indentations shall be
at least three times their indentation diameter away from interfaces or free surfaces and the minimum
distance between indentations shall be at least five times the largest indentation diameter.
The indentation diameter is the in­plane diameter at the surface of the test piece of the circular
impression of an indent created by a conical indenter. For non-circular impressions, the indentation
diameter is the diameter of the smallest circle capable of enclosing the indentation. Occasional cracking
can occur at the corners of the indentation. When this occurs, the indentation curve with crack shall be
excluded from the calculation of stress change. If sufficient data are not obtained due to cracking, the
maximum displacement shall be lowered and the material shall be retested.
The minimum distances specified are best applicable to ceramic materials and metals such as iron and
its alloys. For other materials, it is recommended that separations of at least 10 indentation diameters
be used.
If in doubt, it is recommended that the values from the first indentation are compared with those from
subsequent indentations in a series. If there is a significant difference, the indentations can be too close
and the distance should be increased. A factor of two increases in separation is suggested.
It can be desirable to measure thin coatings in cross­section (e.g. to avoid problems due to surface
roughness). In this case, there cannot be enough coating thickness to meet the minimum spacing
requirements as specified above. Smaller spacing can be used if there is experimental evidence that this
does not significantly influence the force/indentation depth/time data sets with respect to correctly
spaced indentations on similar test pieces with thicker coatings. Note that the currently proposed
method assumes that there is no component of stress in the out of plane direction and cannot calculate
the stress for this situation.
8.5 The obtained data set shall conform to the criterion in Annex A.
Annex B shall be applied, if the criterion in Annex A is not satisfied or if there is no appropriate location
to be chosen as test region for the reference state.
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ISO/DTS 19096:2023(E)
8.7 The indented projected area shall be observed directly by suitable means.
Figure 2 — Flow chart for selection of test procedure to measure stress change
9 Calculation of stress change
9.1 Force and projected area calculation at each state
The force and projected area in each state can be calculated with the data set satisfying Annex A as in
the following formulas:
n
F
r , i
∑
i=1
F = (9.1)
r
n
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ISO/DTS 19096:2023(E)
n
F
∑ t , i
i=1
F = (9.2)
t
n
n
A
r , i
∑
i=1
A = (9.3)
r
n
n
A
∑ t , i
i=1
A = (9.4)
t
n
9.2 Force difference
From the obtained target force/indentation depth curves and reference force/indentation depth curves,
the force difference between two state is calculated by subtracting average maximum force of target
state from average maximum force of reference state (see Figure 1) as in following formula:
ΔFF=− F (9.5)
rt
9.3 Projected area
The area for the reference and target states will be averaged to calculate stress change as given in
Formula (9.6).
AA+
rt
A= (9.6)
2
NOTE If the reference sample is in a stress­free state, A can be used directly as A in Formula (9.6).
r
9.4 Calculation of average stress change
The calculation of average stress change is expressed by Formula (9.7) using Formula (5.2).
ΔΔσσ+p FF− ΔF
() 3() 3()
rt
Δσ = = = (9.7)
avg
2 2 A 2 A
The determination of stress change ratio (p) using a Knoop indenter is described in Annex C.
10 Uncertainty of the results
A complete evaluation of the uncertainty shall be carried out in
...