EN ISO 14126:2023

SLOVENSKI STANDARD
01-december-2023
Z vlakni ojačeni polimerni kompoziti - Ugotavljanje tlačnih lastnosti v ravnini
laminiranja (ISO 14126:2023)
Fibre-reinforced plastic composites - Determination of compressive properties in the in-
plane direction (ISO 14126:2023)
Faserverstärkte Kunststoffe - Bestimmung der Druckeigenschaften in der Laminatebene
(ISO 14126:2023)
Composites plastiques renforcés de fibres - Détermination des caractéristiques en
compression dans le plan (ISO 14126:2023)
Ta slovenski standard je istoveten z: EN ISO 14126:2023
ICS:
83.120 Ojačani polimeri Reinforced plastics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 14126
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2023
EUROPÄISCHE NORM
ICS 83.120 Supersedes EN ISO 14126:1999, EN ISO
14126:1999/AC:2002
English Version
Fibre-reinforced plastic composites - Determination of
compressive properties in the in-plane direction (ISO
14126:2023)
Composites plastiques renforcés de fibres - Faserverstärkte Kunststoffe - Bestimmung der
Détermination des caractéristiques en compression Druckeigenschaften in der Laminatebene (ISO
dans le plan (ISO 14126:2023) 14126:2023)
This European Standard was approved by CEN on 5 October 2023.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 14126:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 14126:2023) has been prepared by Technical Committee ISO/TC 61 "Plastics"
in collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by SIS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by April 2024, and conflicting national standards shall be
withdrawn at the latest by April 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 14126:1999, EN ISO 14126:1999/AC:2002.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 14126:2023 has been approved by CEN as EN ISO 14126:2023 without any modification.

INTERNATIONAL ISO
STANDARD 14126
Second edition
2023-10
Fibre-reinforced plastic composites —
Determination of compressive
properties in the in-plane direction
Composites plastiques renforcés de fibres — Détermination des
caractéristiques en compression dans le plan
Reference number
ISO 14126:2023(E)
ISO 14126:2023(E)
© 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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 14126:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 3
5 Apparatus . 4
5.1 Test machine . 4
5.1.1 General . 4
5.1.2 Speed of testing . 4
5.1.3 Load measurement . 4
5.2 Strain measurement . 4
5.3 Micrometer . 5
5.4 Loading fixtures . 5
5.4.1 General . 5
5.4.2 Method 1: Shear loading . 5
5.4.3 Method 2: Combined loading . 7
6 Test specimens . 8
6.1 Shape and dimensions . 8
6.1.1 Type A specimen . 8
6.1.2 Type B specimen . 9
6.2 Preparation . 10
6.2.1 General . 10
6.2.2 End-tab material . 10
6.2.3 Application of end tabs to specimens . 10
6.2.4 Machining the specimens . 10
6.3 Checking specimen quality . . 10
6.4 Anisotropy . 11
7 Number of test specimens .11
8 Conditioning .11
9 Procedures .11
10 Expression of results .13
10.1 Compressive strength calculation . 13
10.2 Compressive modulus calculation. 13
10.3 Compressive failure strain calculation . 14
10.4 Statistical parameters. 14
10.5 Significant figures. 14
11 Precision .14
12 Test report .15
Annex A (normative) Alignment of specimen and loading train .16
Annex B (normative) Specimen preparation .17
Annex C (informative) Compression fixtures for method 1 .19
Annex D (informative) Compression fixtures for method 2 .21
Annex E (informative) Euler buckling criteria .25
Annex F (informative) Predicted tab length .26
iii
ISO 14126:2023(E)
Annex G (informative) Recommendations for strain and bending measurements using
digital image correlation (DIC) .27
Bibliography .30
iv
ISO 14126:2023(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 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 Technical Committee ISO/TC 61, Plastics,
Subcommittee SC 13, Composites and reinforcement fibres, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 249, Plastics, in accordance with
the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 14126:1999), which has been technically
revised.
The main changes are as follows:
— a new normative Annex A, alignment of specimen and loading train, has been added and subsequent
annexes have been renumbered;
— Annex B, specimen preparation, is now normative to emphasise the importance of producing good
quality specimens;
— two new informative Annexes F and G have been added.
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.
v
ISO 14126:2023(E)
Introduction
[1]
This document, originally published in 1999, was based on ISO 8515 with the scope extended from
glass-fibre reinforcement to include all fibre-reinforced plastic composites, such as composites based
[2]
on carbon and aramid fibres. Other source documents consulted included ASTM D 3410 , SACMA
[3] [4] [5] [6] [7]
SRM1 , prEN 2850 , CRAG 400 , DIN 65380 and JIS K7076 . Several different types of anti-
buckling fixtures/loading jigs, different materials and different specimen sizes are covered by these
source documents, although all are parallel-sided coupons. New or modified geometry support jigs are
[8]
still being developed, for example in JIS K7018
.
This document harmonizes and rationalizes the current situation by:
a) concentrating on the quality of the test by limiting the maximum bending strain allowable (i.e.
10 % between 10 % and 90 % of the maximum load, as recommended by ASTM), so that an axial-
load case can be assumed;
b) standardizing on two related specimen designs, one principally for aerospace type unidirectional
pre-impregnated materials (i.e. Type A) and one for other materials/formats (i.e. Types B1/B2).
The chosen specimen design can be used with different loading fixtures;
c) defining acceptable failure criteria (e.g. avoiding within grip failures);
d) including an equation for determining the specimen minimum thickness to avoid Euler buckling
[2]
proposed by ASTM for harmonization purposes (taken from ASTM D 3410 in a modified form);
e) allowing any design of support/loading fixture to be used that meets the above bending
requirements, using different principles of loading (i.e. essentially shear and combined loading);
f) ensuring that the test specimen and loading/support fixture are well aligned (see Annex A);
g) concentrating on the quality of specimen preparation (see Annex B);
h) including guidance on the use of digital image correlation (DIC) for strain and bending
measurements (see Annex G);
NOTE 1 Compression properties measured in the through-thickness direction (direction 3 in Figure 1) are
[9]
covered by ISO 20975-1 .
NOTE 2 Compression properties of rigid plastics having only unaligned short (<7,5 mm) fibres or no fibre
[10]
content [rather than long (>7,5 mm) discontinuous or continuous fibres] is covered by ISO 604 .
vi
INTERNATIONAL STANDARD ISO 14126:2023(E)
Fibre-reinforced plastic composites — Determination of
compressive properties in the in-plane direction
1 Scope
1.1 This document specifies methods for determining the compressive properties, in directions
parallel to the plane of lamination, of fibre-reinforced plastic composites, based on thermosetting or
thermoplastic matrices. The compressive properties are of interest for specifications and quality-
control purposes. The test specimens are machined from a flat test plate, or from suitable finished or
semi-finished products.
1.2 Two loading methods and two types of specimen are described.
The loading methods are:
— Method 1: provides shear loading of the specimen (gauge length unsupported)
— Method 2: provides combined loading of the specimen (gauge length unsupported)
NOTE For tabbed specimens loaded using method 2, load is transferred through a combination of end-
loading and shear-loading through the tabs.
The specimen designs are:
— Type A specimen: rectangular cross-section, fixed thickness, end-tabbed (mainly for aerospace
style preimpregnates (~ 0,125 mm ply thickness)
— Type B specimen: rectangular cross-section, range of thicknesses, untabbed or end-tabbed, two
specimen sizes are available (B1 and B2).
The Type A specimen is used for unidirectionally or biaxially reinforced materials tested in the
fibre direction, where the fibres are normally either aligned continuous or aligned long (>7,5 mm)
discontinuous. The Type B1 and B2 specimens are used for multi-directional aligned; mat, fabric and
other multi-directionally reinforced materials where the fibre structure is more complex and/or
coarser.
1.3 This document gives criteria for checking that the combination of test method and specimen
design result in valid failures. It is noted that alternative test method/specimen combinations will not
necessarily give the same result.
1.4 The methods specify required dimensions for the specimen. Tests carried out on specimens of
other dimensions, or on specimens that are prepared under different conditions, can produce results
that are not comparable. Other factors, such as the speed of testing, the support fixture used and the
conditioning of the specimens, can influence the results.
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 291, Plastics — Standard atmospheres for conditioning and testing
ISO 1268 (all parts), Fibre-reinforced plastics — Methods of producing test plate
ISO 14126:2023(E)
ISO 2602, Statistical interpretation of test results — Estimation of the mean — Confidence interval
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 23788, Metallic materials — Verification of the alignment of fatigue testing machines
ASTM E 1012, Standard practice for verification of testing frame and specimen alignment under tensile and
compressive axial force application
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
compressive stress
σ
c
compressive force experienced by the test specimen, at a particular time, divided by the initial cross-
sectional area of the parallel-sided portion of the specimen
Note 1 to entry: It is expressed in megapascals.
3.2
compressive strength
compressive failure stress
σ
cM
maximum compressive stress (3.1) sustained by the specimen
Note 1 to entry: It is expressed in megapascals.
3.3
compressive strain
Ɛ
c
decrease in length per unit length of the original gauge length
Note 1 to entry: It is expressed as a dimensionless ratio or in percent.
3.4
compressive failure strain
Ɛ
cM
longitudinal compressive strain at the compressive failure stress
Note 1 to entry: It is expressed as a dimensionless ratio or in percent.
3.5
modulus of elasticity in compression
chord modulus
E
c
stress difference (σ" minus σ') divided by the corresponding strain difference (Ɛ" (= 0,002 5) minus Ɛ'
(= 0,000 5))
Note 1 to entry: It is expressed in megapascals.
Note 2 to entry: See 10.2.
ISO 14126:2023(E)
3.6
specimen coordinate axes
1, 2, 3
orthogonal coordinate axes for material with the fibres preferentially aligned in one direction within a
planar laminate.
Note 1 to entry: See Figure 1. The directions, in the plane of the laminate, parallel to the fibre axes is specified
as the "1"-direction and the direction perpendicular to the fibre axes the "2"-direction. For other materials, the
"1"-direction is normally specified in terms of a feature associated with the production process, such as the
long or warp direction for a continuous-sheet or fabric process. The "2"-direction is again perpendicular, in the
plane, to the "1" direction. The direction perpendicular to the plane is the “3” direction. Results for specimens
cut parallel to the "1"-direction are identified by the subscript "11" (e.g. E ). Similarly, results for specimens cut
c11
parallel to the "2"-direction are identified by the subscript "22" (e.g. E ).
c22
Note 2 to entry: The "1"-direction is also referred to as the 0° or longitudinal direction, and the "2"-direction as
the 90° or transverse direction. More generally, the X, Y and Z (through-thickness) coordinate system for any
material can be equated to the "1"-, "2"- and "3"-directions.
Figure 1 — Unidirectionally reinforced composite plate element showing symmetry axes
3.7
gauge length
L
initial distance between the gauge marks on the central part of the test specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.8
thickness
h
smaller initial dimension of the rectangular cross-section in the central part of a test specimen
Note 1 to entry: It is expressed in millimetres (mm).
3.9
width
b
larger initial dimension of the rectangular cross-section in the central part of a test specimen
Note 1 to entry: It is expressed in millimetres (mm).
4 Principle
An axial force is applied to the unsupported gauge length of a rectangular specimen held in an anti-
buckling loading/support fixture, while the applied load and strain in this gauge length area are
monitored. The test method concentrates on the quality of the axial deformation experienced by the
specimen. Any loading fixture can be used, provided specimen failure occurs below a 10 % bending
ISO 14126:2023(E)
strain in the specimen (between 10 % and 90 % of the maximum load); and fails in the prescribed
manner and location.
The compressive load is applied to the specimen:
— by shear loading through end tabs (Method 1);
— by a combined loading mode through direct specimen end loading and shear loading though the
support fixture using a tabbed specimen (Method 2).
NOTE 1 The test results obtained by these methods using different specimen designs/sizes and different
loading fixtures are not necessarily comparable.
[4]
NOTE 2 End-loading is not covered by this document as the fixture in Method B of EN 2850 for end-loading
[11]
(c.f. modified ASTM D695 ) is not suitable for the standard Type A or B specimens. End loading is, in many
cases, a sufficient and simple method for determination of compressive modulus but is very limited for ultimate
strength determination.
NOTE 3 Each of these methods shows specific advantages and disadvantages. For example, shear loading is
not adapted for very thick laminates, because it causes strain distributions over the laminate thickness caused
by shear strains and the tabs can shear off at high forces. Combined loading overcomes several of the problems
described before and can also be used for higher laminate thicknesses. The disadvantage is the need for
supplementary machining of the specimen ends to ensure parallelism and squareness tolerances are met when
using end-tabbed specimens.
5 Apparatus
5.1 Test machine
5.1.1 General
The test machine shall be in accordance with ISO 7500-1 and ISO 9513, and meet the specifications
given in 5.1.2 to 5.1.3. The test machine should be kept in good condition and worn parts (e.g. threads,
grip faces) replaced. The test machine, gauge specimen and loading/support fixture alignment on the
machine axis shall be checked regularly or after any part of the loading train is moved/reassembled
using the procedures given in Annex A.
5.1.2 Speed of testing
The test machine shall be capable of maintaining the required speed of testing (see 9.5).
5.1.3 Load measurement
The force measurement system shall conform with class 1 as specified in ISO 7500-1 (i.e. error for
indicated load shall not exceed ±1 % of the true value). Suitable data recording equipment (data-loggers)
shall be used to record the load values throughout the tests.
5.2 Strain measurement
Strain shall be determined by means of strain gauges, mechanical extensometers, or optical
extensometers, [including digital image correlation (DIC)] meeting the requirement that the error for
the indicated strain shall not exceed ±1 % (see ISO 9513). Strain shall be measured on both faces of the
specimens to determine the degree of bending or on the sides (narrow face) of specimens if using DIC
(see Annex G). Strain gauge elements for type A and B1 specimens shall be less than 3 mm in length. B2
specimens will accommodate longer strain gauges (e.g. ≥10 mm).
ISO 14126:2023(E)
The gauges, the surface preparation and the bonding agents used shall be chosen to give acceptable
performance with the material being tested, and suitable continuous strain recording equipment (data-
logger/computer) shall be used.
NOTE Full-field strain measurements, as obtained by DIC, provide evidence for the “repeat structure” of the
[12]
reinforcement and therefore informs the choice of strain gauge length (i.e. larger gauge length than the size of
any repeated “reinforcement structure” which causes local non-uniformity of the strain field).
5.3 Micrometer
A micrometer, caliper or equivalent, reading to less than or equal to 0,01 mm shall be used to determine
the thickness h and width b of the test specimen.
For thickness measurements, callipers shall have faces appropriate to the surface being measured (i.e.
flat face for flat, cut or polished surfaces and hemisphere face for other surfaces) of ~6 mm diameter in
both cases.
5.4 Loading fixtures
5.4.1 General
Support/loading fixtures appropriate to the loading method chosen shall be used. The fixture shall load
the specimen so that the requirement on allowable specimen bending given in 9.8 is met. The main
requirement of the fixture design for all loading methods is the alignment (initial and throughout
the test) of the loading train and of the specimen when loaded in the fixture are maintained, so that
buckling is avoided. Procedures for obtaining satisfactory alignment of the loading train are given in
Annex A. The fixture used shall be fully identified and described in the test report.
5.4.2 Method 1: Shear loading
The load is applied to the specimen by shear through the faces of the specimen end tabs. The load is
applied through flat wedge or vee action grips, as shown diagrammatically in Figure 2 a). Aligned
hydraulic grips in aligned test machines are also acceptable. A schematic diagram of a compression
fixture for shear loading is given in Figure 3.
[2]
NOTE A Method 1 fixture in common use is shown in Annex C (i.e. ASTM D 3410: method B (known as
ITTRI that uses flat “back” wedge grips). An early design of this loading method known as Celanese (using cone-
[2]
shaped “back” wedge grips) is no longer included in ASTM D3410 .
ISO 14126:2023(E)
a) Method 1 b) Method 2
Shear loading Combined loading
Key
1 specimen
2 end tabs
3 shear loading
4 end loading
Figure 2 — Schematic of load condition for the alternative methods
ISO 14126:2023(E)
Key
1 upper housing block
2 locking screws
3 specimen
4 lower housing block
Figure 3 — Schematic diagram of compression test specimen and fixture for method 1
5.4.3 Method 2: Combined loading
Loading is by direct end loading of the specimen and by shear loading through the tab at the same time
resulting in a combined loading configuration, as shown diagrammatically in Figure 2 b). A schematic
diagram of a compression fixture for combined loading is given in Figure 4. Combined loading is also
obtained when a supporting or anti-buckling fixture involves clamping of the specimen, although the
exact loading path through the jig into the specimen gauge length is unclear. In addition, compression
loading of the specimen will increase the transverse load on the bolted clamps and similar constructions
due to Poisson’s expansion of the specimen.
NOTE Method 2 fixtures in common use are shown in Annex D.
ISO 14126:2023(E)
Key
1 specimen, untabbed (or tabbed — see insert)
2 support blocks
3 specimen
4 locking screws
5 tabs
6 end-loading plate
7 moveable face plate
Figure 4 — Schematic diagram of compression test fixture for method 2
6 Test specimens
6.1 Shape and dimensions
6.1.1 Type A specimen
The specimen shall be straight-sided and of rectangular cross-section, with the dimensions given in
Table 1 (see also Figure 5). Type A specimens are preferred for laminates constructed from ~0,125 mm
thick 0° laminae (e.g. unidirectional aerospace grade prepreg) and loaded in the 1 (axial) direction. For
these unidirectionally reinforced materials, the test specimen shall be extracted with its axis within
0,5° of the mean fibre axis of the test plate.
ISO 14126:2023(E)
Key
1 tabs
2 specimen
NOTE Dimensions are given in Table 1.
Figure 5 — Type A and B tabbed specimen designs
6.1.2 Type B specimen
The specimen shall be straight-sided and of rectangular cross-section, with the dimensions given in
Table 1. End tabs shall be used, if necessary, to avoid failure at the loaded ends of the specimen by
distributing the applied load over the larger area of the specimen and end tabs.
Type B1 specimens are suitable for material constructed with heavier weight laminae (n.b 16 layers
recommended, as used in Type A specimens with 16 layers of 0,125 mm thickness prepreg),
Type B2 specimens are suitable for “coarser” or structured fabrics [e.g. NCF (non-crimped fabrics)],
multi-directional layups and 3D fabrics.
Table 1 — Specimen dimensions
Dimensions, Symbol Type A Type B1 specimen Type B2 specimen
mm specimen
Overall length (minimum) l 110 110 125
Thickness h 2 ± 0,2 2 ± 0,2 to 10 ± 0,2 ≥ 4 ± 0,2
Width b 10 ± 0,5 10 ± 0,5 25 ± 0,5
Distance between end tabs L 10 10 25
Length of end tabs (minimum) l 50 50 50
t
(if required) (if required)
Thickness of end tabs d 1 0,5 to 2 0,5 to 2
t
(thickness variation allowed = 2 %) (if required) (if required)
NOTE Requirements for parallelism of specimen and end tabs are given in 6.2.4. Requirements for specimen
quality are given in 6.3.
ISO 14126:2023(E)
6.2 Preparation
6.2.1 General
A flat test plate shall be prepared using the appropriate fabrication route in accordance with the
relevant part of the ISO 1268 series or another specified and agreed procedure. Specimens cut from
finished parts (e.g. for quality control during manufacture or on delivery) shall be taken from flat areas
of uniform thickness.
6.2.2 End-tab material
The ends of the specimen shall be reinforced, if necessary, with end tabs made preferably from a 0°/90°
cross-ply or fabric laminate made from glass-fibre/resin with the fibre axes set at ±45° to the specimen
axis. The tab thickness shall be between 0,5 mm and 2 mm, with a tab angle of 90° (i.e. not tapered). If
tab failure occurs under high end loads, the fibre axes in the tab shall be set at 0°/90° to the specimen
axis.
Alternatives, such as tabs made from the material under test, mechanically fastened tabs, unbonded
tabs or friction materials (emery paper, grit paper or fine-finish grip faces), shall be shown, before use, to
[13]
give at least equal strength values (see 10.4) and no greater coefficient of variation (see ISO 3534-1 )
than the recommended tab material.
When the test is carried out on untabbed specimens, the "distance between tabs" shall be taken as, and
set at, the distance between the tabs of a corresponding tabbed specimen.
NOTE 1 Further guidance is available on grip face textures and tabbing intermediates (e.g. grit/sandpaper) in
[14] [15]
ISO 527-4:2023, Annex C and ISO 527-5 .
NOTE 2 Formula (F.1) in Annex F is given to predict the minimum end tab length as a function of tab (adhesive)
shear strength and expected specimen failure load.
6.2.3 Application of end tabs to specimens
The end tabs shall be bonded to the specimen as shown in Annex B. It is critical to the test result that
both the tab thickness and adhesive bond-line thickness shall be of constant thickness, so that the
specimen maintains a balanced symmetry (i.e. less than 5 % variation in adhesive bond thickness).
NOTE This tabbing procedure can be used for individual specimens or groups of specimens.
6.2.4 Machining the specimens
For Method 1: Machine the tab surfaces as necessary to ensure the tabs are symmetrical about the
specimen centreline and parallel to each other. The ends of the two tabs either side of the specimen
should be within 0,05 mm of each other at the edges of the gauge length.
For Method 2: Machine the end faces of each specimen so that they are parallel to each other and
perpendicular to the longitudinal axis of the specimen. The allowed deviation from parallel of the
areas of the end-loading plates in contact with the specimen ends is 0,1 % of the initial full length of
the specimen, i.e. the distance between the end-loading plates. Tabs, if used, shall be prepared as for
Method 1 and meet the above length measurement criteria.
[16]
NOTE Additional guidance on specimen preparation is given in Annex F and in ISO 2818 .
6.3 Checking specimen quality
The specimens, both when untabbed and tabbed, shall be free of twist and shall have symmetrical
pairs of parallel surfaces. The surfaces and edges shall be free from scratches, pits, sink marks and
flash. The specimens shall be checked for conformity with these requirements by visual observation
against straight edges, squares and flat plates, and by measuring with micrometre callipers. Specimens
ISO 14126:2023(E)
showing measurable or observable departure from one or more of these requirements shall be rejected
or machined to the correct size and shape before testing.
NOTE The quality of the prepared specimen has a major effect on the successful outcome of the test.
6.4 Anisotropy
The properties of fibre-reinforced plastic composites frequently vary with direction in the plane of the
sheet (anisotropy). For this reason, it is recommended that two groups of test specimens be prepared
with their major axes parallel and perpendicular, respectively, to the direction of some feature which is
inferred from a knowledge of the structure of the material or its method of manufacture (see 3.6).
NOTE Examples of tests required to be undertaken at different orientations (i.e. 0° and 90°) in the test plate
[17] [18]
are given in ISO 10350-2 and ISO 20144 .
7 Number of test specimens
7.1 At least five test specimens shall be tested in each direction of test, as required. As a minimum, 5
specimens shall be tested in the 1 direction.
The number of measurements may be more than five if greater precision of the mean value and standard
deviation are required. It is possible to calculate the number of successful tests needed in an individual
direction by means of the confidence interval (95 % probability, see ISO 2602).
7.2 The results from test specimens that rupture inside the grip end blocks or end tabs shall be
discarded and new specimens tested in their place. Replacement specimens shall also be used if bending
of the specimen exceeds the maximum value permitted in 9.8.
NOTE This test method can result in failures at the edge of the loading fixture or end tab rather than in
the middle of the gauge length. These failures are acceptable, but their occurrence can be minimized by using a
different type of loading fixture, tab, etc.
7.3 With batches of specimens greater than five, tests can be conducted without making two strain
measurements provided that:
a) the first five specimens are shown to fail at a bending strain less than the value given in 9.8 using
back-to-back strain measurements;
b) there is no change in the test conditions (i.e. batch, specimen type, test conditions, operator, test
equipment, etc.);
c) the tests are conducted over a short time period without disrupting the fixture alignment. In such
cases, the modulus, if required, can be obtained from a single strain measurement. The change in
procedure shall be noted in the test report [see Clause 12, p)].
8 Conditioning
Condition the test specimens as specified in the International Standard for the material tested. In the
absence of this information, select the most appropriate set of conditions from ISO 291, unless otherwise
agreed upon by the interested parties, e.g. when testing at an elevated or reduced temperature.
9 Procedures
9.1 Conduct the test in the atmosphere specified in the International Standard for the material tested.
In the absence of this information, select the most appropriate set of conditions from ISO 291, unless
otherwise agreed upon by the interested parties (e.g. when testing at elevated or low temperatures).
ISO 14126:2023(E)
9.2 Measure the width b of each tes
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