ISO 25218

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)
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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

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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
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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
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 13, Composites
and reinforcement fibres.
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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;.
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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
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