ISO 25218

• Abstract:

  This International Standard specifies test specimens and procedures for fatigue testing at ambient conditions, under repeated tensile loading, generating cross-tension loading to the bonded plates of carbon fibre reinforced plastics (CFRPs) to metal assemblies. The specimen undergoes cyclically stress, comprising an alternating stress on a static stress which represents the mean stress. This allows for estimating the safety condition regarding the fatigue resistance of joints. The method is intended for testing bonded plates used in bonding CFRPs to metal assemblies.

• Status: Not Published
• ICS: 77.140.50 - Flat steel products and semi-products
• ICS: 83.120 - Reinforced plastics
• Technical Committee: ISO/TC 61/SC 13 - Composites and reinforcement fibres
• Drafting Committee: ISO/TC 61/SC 13/WG 7 - Composites and metal assemblies
• Current Stage: 6000 - International Standard under publication
• Start Date: 22-Sep-2026
• Completion Date: 26-Sep-2026

Overview

ISO 25218 is an international standard for carbon fibre reinforced plastics (CFRPs) and metal assemblies. It specifies a test method for cross-tension fatigue properties of bonded plates used in CFRP-to-metal joints.

This standard is intended for fatigue testing at ambient conditions under repeated tensile loading that produces cross-tension loading on bonded plates. By applying cyclic stress with a mean stress component and an alternating stress component, the method supports evaluation of fatigue resistance, joint durability, and the overall safety condition of bonded assemblies.

ISO 25218 is especially relevant where adhesive-bonded CFRP and metal joints are used in engineering applications that require reliable long-term performance.

Key Topics

The standard covers the practical framework needed to test cross-tension fatigue behavior, including:

• Test specimens and geometry

  • Uses specimen configurations aligned with the referenced cross-tension strength method
  • Includes Type A and Type B specimen approaches
  • Focuses on bonded plates made with adhesive or other specified bonding methods

• Testing conditions

  • Fatigue testing is performed under ambient conditions
  • The specimen is subjected to repeated tensile loading
  • Test frequency is typically controlled within a defined operating range
  • Care is taken to avoid excessive heating during testing

• Measurement and interpretation

  • Supports construction of S-N curves
  • Uses stress amplitude, mean stress, stress ratio, and fatigue life as key values
  • Helps estimate fatigue limit and endurance behavior

• Reporting requirements

  • Includes specimen dimensions, bonded area, failure mode, and fatigue results
  • Records static cross-tension strength values and relevant test conditions
  • Requires clear documentation of the bonding process and materials used

For users working with composites testing, adhesive joints, and CFRP-metal fatigue performance, ISO 25218 provides a structured and repeatable method.

Applications

ISO 25218 is useful in sectors where lightweight composite structures are joined to metal components and fatigue reliability is critical. Common application areas include:

• Aerospace engineering

  • Qualification of bonded CFRP-metal assemblies
  • Support for type certification and design verification
  • Evaluation of maintenance, repair, and overhaul activities

• Advanced manufacturing

  • Performance assessment of adhesive-bonded composite structures
  • Quality control for bonded plates and hybrid material joints

• Engineering validation

  • Comparison of joint durability under cyclic loading
  • Estimation of resistance to fatigue-related degradation

The standard is valuable for teams assessing CFRP bonding reliability, cross-tension fatigue strength, and structural joint safety.

Related Standards

ISO 25218 is closely connected with other ISO standards used in composite and adhesive testing, including:

• ISO 24360 - Determination of the cross tension strength of CFRP and metal assemblies
• ISO 7500-1 - Calibration and verification of static uniaxial testing machines
• ISO 9513 - Calibration of extensometer systems for uniaxial testing
• ISO 10365 - Designation of main failure patterns for adhesives
• ISO 13003 - Fatigue properties of fibre-reinforced plastics under cyclic loading
• ISO 9664 - Fatigue properties of structural adhesives in tensile shear

Together, these standards support a broader framework for composite fatigue testing, adhesive joint evaluation, and materials conformity assessment.

FINAL DRAFT
International
Standard
ISO/FDIS 25218
ISO/TC 61/SC 13
Composites and reinforcements
Secretariat: JISC
fibres — Carbon fibre reinforced
Voting begins on:
plastics(CFRPs) and metal
2026-07-27
assemblies — Test method for
Voting terminates on:
cross-tension fatigue properties
2026-09-21
Composites et fibres de renfort — Assemblages de plastiques
renforcés de fibres de carbone (CFRP) et de métal — Méthode
d'essai pour les propriétés de fatigue en traction transversale
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
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
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.
Reference number
ISO/FDIS 25218:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 25218:2026(en)
International
Standard
ISO/FDIS 25218
ISO/TC 61/SC 13
Composites and reinforcements
Secretariat: JISC
fibres — Carbon fibre reinforced
Voting begins on:
plastics(CFRPs) and metal
assemblies — Test method for
Voting terminates on:
cross-tension fatigue properties
Composites et fibres de renfort — Assemblages de plastiques
renforcés de fibres de carbone (CFRP) et de métal — Méthode
d'essai pour les propriétés de fatigue en traction transversale
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.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 25218:2026(en) © ISO 2026

ii
ISO/FDIS 25218:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Test specimen . 3
5 Apparatus . 5
6  Test procedure . 6
6.1 General conditions .6
6.2 Construction of S-N curve .6
7  Test report . 9
Annex A (informative)  Cross tension fatigue test for an adhesive-bonded plate of carbon fibre
reinforced plastic (CFRP) to aluminium .10
Bibliography . 14

iii
ISO/FDIS 25218:2026(en)
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 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/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). 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 not received notice of (a)
patent(s) 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 61, Plastics, Subcommittee SC 13, Composites
and reinforcement fibres.
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
ISO/FDIS 25218:2026(en)
Introduction
This document specifies a method for determining the cross tensional fatigue properties of the bonded
plates of carbon fibre reinforced plastics (CFRPs) to metal assemblies, with a standard specimen loaded
in cross tension and under specified conditions of preparation, conditioning and testing. This method is
intended for testing only those bonded plates used in bonding carbon fibre reinforced plastics (CFRPs) to
metal assemblies.
The potential benefits to the users of CFRP-metal assemblies of assessing the cross tensional fatigue
properties of the bonded plates of carbon fibre reinforced plastics (CFRPs) to metal assemblies based on this
document are:
a) expanding CFRP applications to the fields of the combinations with metallic components;
b) the detection or the prevention of physical properties loss - such as ion migration and time-related
degradation in sealant film, injected calking layer and glass fibre reinforced plastics (GFRPs) layer;
c) demonstrating the conformity to specified conditions for type certification requirements in the
engineering such as aircraft developments;
d) evaluating the procedures for maintenance, repair and overhaul (MRO) in the engineering operations
such of CFRP aircrafts.
It is not the intent of this document to imply the need for:
— omitting relevant field tests for CFRP related engineering;
— generally specifying the dimensions of test specimen to represent CFRPs related bonded or fastened
structures;
— superimposing test results for specific applications of the parameters that exceed the range of this
document.
v
FINAL DRAFT International Standard ISO/FDIS 25218:2026(en)
Composites and reinforcements fibres — Carbon fibre
reinforced plastics(CFRPs) and metal assemblies — Test
method for cross-tension fatigue properties
IMPORTANT — Persons using this document should be familiar with normal laboratory practice, if
applicable. This document does not purport to address all of the safety problems, if any, associated
with its use. It is the responsibility of the user to establish appropriate safety and health practices
and to ensure compliance with any regulatory conditions.
SAFETY STATEMENT — It is recognized that some of the materials permitted in this document
might have a negative environmental impact. As technological advances lead to more acceptable
alternatives for such materials, they will be eliminated to the greatest extent possible. At the end of
the test, care should be taken to dispose of all waste in an appropriate manner.
1 Scope
This document specifies test specimens and procedures for fatigue testing at ambient conditions, under
repeated tensile loading, generating cross-tension loading to the bonded plates of carbon fibre reinforced
plastics (CFRPs) to metal assemblies.
This document applies to bonded plates used in bonding CFRPs to metal assemblies with adhesive or other
specified methods.
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 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ISO 10365, Adhesives — Designation of main failure patterns
ISO 24360, Composites and reinforcements fibres — Carbon fibre reinforced plastics (CFRPs) and metal
assemblies — Determination of the cross tension strength
3  Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10365 and the following 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
cross tension fatigue test
fatigue test that applies a repeated tensile load to the cross-tension test specimen mounted between the
jaws of the fatigue-testing machine

ISO/FDIS 25218:2026(en)
3.2
stress
σ
stress determined by dividing the tensile force by the bonded surface area
Note 1 to entry: Expressed in megapascal (MPa).
3.3
static cross-tension strength
σ
R
average static stress at rupture as determined by ISO 24360
Note 1 to entry: Expressed in megapascal (MPa).
3.4
maximum stress
σ
max
greatest algebraic value reached at regular intervals by the stress
Note 1 to entry: Expressed in megapascal (MPa).
3.5
minimum stress
σ
mim
smallest algebraic value reached at regular intervals by the stress
Note 1 to entry: Expressed in megapascal (MPa).
3.6
mean stress
σ
m
algebraic mean of the maximum and minimum stresses, expressed as σ = (σ + σ )/2
m min max
Note 1 to entry: Expressed in megapascal (MPa).
3.7
stress amplitude
σ
a
alternating stress equal to half the algebraic difference between the maximum and minimum stresses
Note 1 to entry: Expressed in megapascal (MPa).
3.8
stress ratio
R
algebraic ratio of the
...

ISO/FDIS 25218:2025(en)
ISO/TC 61/SC 13/WG 7
Secretariat: JISC
Date: 2026-6-807-13
Composites and reinforcements fibres -- — Carbon fibre reinforced
plastics(CFRPs) and metal assemblies –— Test method for cross-
tension fatigue properties
Composites et fibres de renfort — Assemblages de plastiques renforcés de fibres de carbone (CFRP) et de métal
— Méthode d'essai pour les propriétés de fatigue en traction transversale
FDIS stage
ISO/FDIS 25218:2026(en)
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/FDIS 25218:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test specimen . 3
5 Apparatus . 8
6 Test procedure . 9
6.1 General conditions . 9
6.2 Construction of S-N curve . 9
7 Test report . 13
Annex A (informative) Cross tension fatigue test for an adhesive-bonded plate of carbon fibre
reinforced plastic (CFRP) to aluminium . 15
Bibliography . 21

iii
ISO/FDIS 25218:2026(en)
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
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/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). 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 not received notice of (a) patent(s)
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 61, Plastics, Subcommittee SC 13, Composites
and reinforcement fibres.
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
ISO/FDIS 25218:2026(en)
Introduction
This document specifies a method for determining the cross tensional fatigue properties of the bonded plates
of carbon fibre reinforced plastics (CFRPs) to metal assemblies, with a standard specimen loaded in cross
tension and under specified conditions of preparation, conditioning and testing. This method is intended for
testing only those bonded plates used in bonding carbon fibre reinforced plastics (CFRPs) to metal assemblies.
The potential benefits to the users of CFRP-metal assemblies of assessing the cross tensional fatigue properties
of the bonded plates of carbon fibre reinforced plastics (CFRPs) to metal assemblies based on this document
are:
a) a) expanding CFRP applications to the fields of the combinations with metallic components;
b) b) the detection or the prevention of physical properties loss - such as ion migration and time-
related degradation in sealant film, injected calking layer and glass fibre reinforced plastics (GFRPs) layer;
c) c) demonstrating the conformity to specified conditions for type certification requirements in the
engineering such as aircraft developments;
d) d) evaluating the procedures for maintenance, repair and overhaul (MRO) in the engineering
operations such of CFRP aircrafts.
It is not the intent of this document to imply the need for:
— — omitting relevant field tests for CFRP related engineering;
— — generally specifying the dimensions of test specimen to represent CFRPs related bonded or fastened
structures;
— — superimposing test results for specific applications of the parameters that exceed the range of this
document;.
v
ISO/FDIS 25218:2026(en)
Composites and reinforcements fibres -- — Carbon fibre reinforced
plastics(CFRPs) and metal assemblies –— Test method for cross-
tension fatigue properties
IMPORTANT — Persons using this document should be familiar with normal laboratory practice, if
applicable. This document does not purport to address all of the safety problems, if any, associated
with its use. It is the responsibility of the user to establish appropriate safety and health practices and
to ensure compliance with any regulatory conditions.
SAFETY STATEMENT — It is recognized that some of the materials permitted in this document might
have a negative environmental impact. As technological advances lead to more acceptable alternatives
for such materials, they will be eliminated to the greatest extent possible. At the end of the test, care
should be taken to dispose of all waste in an appropriate manner.
1 Scope
This document specifies test specimens and procedures for fatigue testing at ambient conditions, under
repeated tensile loading, generating cross-tension loading to the bonded plates of carbon fibre reinforced
plastics (CFRPs) to metal assemblies.
This document applies to bonded plates used in bonding CFRPs to metal assemblies with adhesive or other
specified methods.
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 7500-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Calibration and verification of the force-measuring system
ISO 9513, Metallic materials — Calibration of extensometer systems used in uniaxial testing
ISO 10365, Adhesives — Designation of main failure patterns
ISO 24360, Composites and reinforcements fibres — Carbon fibre reinforced plastics (CFRPs) and metal
assemblies — Determination of the cross tension strength
ISO 10365, Adhesives — Designation of main failure patterns
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10365 and the following 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/
ISO/FDIS 25218:2026(en)
3.1 3.1
cross tension fatigue test
fatigue test that applies a repeated tensile load to the cross-tension test specimen mounted between the jaws
of the fatigue-testing machine
3.2 3.2
stress
σ
stress determined by dividing the tensile force by the bonded surface area
Note 1 to entry: Expressed in megapascal (MPa).
3.3 3.3
static cross-tension strength
σ
R
average static stress at rupture as determined by ISO 24360
Note 1 to entry: Expressed in megapascal (MPa).
3.4 3.4
maximum stress
σ
max
greatest algebraic value reached at regular intervals by the stress
Note 1 to entry: Expressed in megapascal (MPa).
3.5 3.5
minimum stress
σ
mim
smallest algebraic value reached at regular intervals by the stress
Note 1 to entry: Expressed in megapascal (MPa).
3.6 3.6
mean stress
σ
m
algebraic mean of the maximum and minimum stresses, expressed as σ = (σ + σ )/2
m min max
Note 1 to entry: Expressed in megapascal (MPa).
3.7 3.7
stress amplitude
σ
a
alternating stress equal to half the algebraic difference between the maximum and minimum stresses
Note 1 to entry: Expressed in megapascal (MPa).
3.8 3.8
stress ratio
R
algebraic ratio of the minimum stress to the maximum stress in one cycle
Note 1 to entry: Expressed as R = σmin / σmax. R shall be positive and 0 ISO/FDIS 25218:2026(en)
3.9 3.9
S-N curve
curve constructed by plotting the stress amplitude (σ) as ordinated and the fatigue life (N ) as abscissa
f
Note 1 to entry: It is normal practice to use logarithmic axes.
3.10 3.10
fatigue limit
σ
τ
maximum stress at which the test specimen can endure a specific number of test cycles (N) without failure
expressed as σ = σ + σ
τ m a
Note 1 to entry: Expressed in megapascal (MPa).
3.11 3.11
fatigue life
N
f
number of cycles that can be applied before failure occurs at a given stress
4 Test specimen
The size and the geometry of the specimen are same as defined by ISO 24360.
The test specimen is composed of two rectangular coupons as shown in Figure 1Figure 1.
The bonding shall be covered in the lapped area of each coupon in the test specimen.
One method is to bond two rectangular coupons to be a Type A cross specimen.
The other method is by cutting an adhered sheet of CFRP (thickness: 4 mm) and metal (thickness: 4 mm)
laminate in size of 260 mm × 150 mm into a cross shaped specimen. Then, notches are introduced in the
specimens as shown in Figure 3Figure 3. The notch of the laminate shall go as far as the adhesive line and care
shall be taken that the ply is cut completely, to be cross specimen Type B.
ISO/FDIS 25218:2026(en)
Dimensions in millimetres
Type A Type B
Figure 1 — Test specimens for cross tension test
------
...