Test method for the evaluation of the adhesive properties of fibre reinforced polymer composite joints

This document provides a test method for the determination of the adhesive properties in joints of continuous fibre reinforced polymer matrix composite structures using the Lap Strap specimen.
The evaluation includes the optional concurrent use of the non-destructive technique of the Electrical Resistance Change Method (ERCM) and/or Acoustic Emission (AE) for the monitoring of the debonding of the lap from the strap optionally. The ERCM NDE technique has a limited application only on carbon fibre composites due to the inherent electrical conductivity of the carbon fibres.
This test applies to composites manufactured with continuous carbon fibres (woven or unidirectional) and thermoset or thermoplastic matrices, with quasi-isotropic lamination. This methodology can be used on repairable or self-healing composites in order to estimate the repair or healing efficiency respectively.
Safety aspects about manufacturing and mechanical testing of the composites are excluded.

Prüfverfahren zur Bewertung der Hafteigenschaften von faserverstärkten Polymerverbundverbindungen

Preskusna metoda za ovrednotenje adhezijskih lastnosti kompozitnih spojev iz polimerov, ojačenih z vlakni

General Information

Status
Published
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
08-Jun-2022
Completion Date
08-Jun-2022

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SLOVENSKI STANDARD
SIST CWA 17896:2022
01-september-2022
Preskusna metoda za ovrednotenje adhezijskih lastnosti kompozitnih spojev iz
polimerov, ojačenih z vlakni

Test method for the evaluation of the adhesive properties of fibre reinforced polymer

composite joints
Prüfverfahren zur Bewertung der Hafteigenschaften von faserverstärkten
Polymerverbundverbindungen
Ta slovenski standard je istoveten z: CWA 17896:2022
ICS:
83.120 Ojačani polimeri Reinforced plastics
83.180 Lepila Adhesives
SIST CWA 17896:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST CWA 17896:2022
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SIST CWA 17896:2022
CEN
CWA 17896
WORKSHOP
June 2022
AGREEMENT
ICS 83.120; 83.180
English version
Test method for the evaluation of the adhesive properties
of fibre reinforced polymer composite joints

This CEN Workshop Agreement has been drafted and approved by a Workshop of representatives of interested parties, the

constitution of which is indicated in the foreword of this Workshop Agreement.

The formal process followed by the Workshop in the development of this Workshop Agreement has been endorsed by the

National Members of CEN but neither the National Members of CEN nor the CEN-CENELEC Management Centre can be held

accountable for the technical content of this CEN Workshop Agreement or possible conflicts with standards or legislation.

This CEN Workshop Agreement can in no way be held as being an official standard developed by CEN and its Members.

This CEN Workshop Agreement is publicly available as a reference document from the CEN Members National Standard Bodies.

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, Turkey 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

© 2022 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No.:CWA 17896:2022 E
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SIST CWA 17896:2022
CWA 17896:2022 (E)
Contents Page

Foreword .......................................................................................................................................................................... 3

Introduction .................................................................................................................................................................... 5

1 Scope .................................................................................................................................................................... 6

2 Normative references .................................................................................................................................... 6

3 Terms, definitions, symbols and abbreviated terms .......................................................................... 6

3.1 Terms and definitions ................................................................................................................................... 6

3.2 Symbols and abbreviated terms ................................................................................................................ 7

4 Significance and Use ....................................................................................................................................... 8

5 Lap Strap Geometry ........................................................................................................................................ 8

5.1 Sampling ............................................................................................................................................................. 8

5.2 Laminate Configuration ................................................................................................................................ 8

5.3 Specimen Dimensions ................................................................................................................................... 8

5.4 Specimen preparation ................................................................................................................................... 9

5.4.1 Surface preparation ....................................................................................................................................... 9

5.4.2 Joint procedure of the measured bonding area ................................................................................... 9

5.5 Conditioning ................................................................................................................................................... 10

5.6 Repairable or self-healing composites ................................................................................................. 10

6 Mechanical testing ....................................................................................................................................... 11

6.1 Testing machine ........................................................................................................................................... 11

6.2 Grips .................................................................................................................................................................. 11

6.3 Placement of the specimen ....................................................................................................................... 11

6.4 Testing process ............................................................................................................................................. 12

7 Non-destructive evaluation (NDE) ......................................................................................................... 12

8 Calculation ...................................................................................................................................................... 13

8.1 Maximum strength (MPa) ......................................................................................................................... 13

8.2 Strain ................................................................................................................................................................ 14

8.3 Stiffness ............................................................................................................................................................ 14

8.4 Knockdown effect ......................................................................................................................................... 15

8.5 Repair efficiency ........................................................................................................................................... 15

9 Test report ...................................................................................................................................................... 15

Bibliography ................................................................................................................................................................. 17

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SIST CWA 17896:2022
CWA 17896:2022 (E)
Foreword

This CEN Workshop Agreement (CWA 17896:2022)has been developed in accordance with the CEN-

CENELEC Guide 29 “CEN/CENELEC Workshop Agreements – A rapid prototyping to standardization” and

with the relevant provisions of CEN/CENELEC Internal Regulations - Part 2. It was approved by a

Workshop of representatives of interested parties on 2022-04-06, the constitution of which was

supported by CEN following the public call for participation made on 2021-07-26. However, this CEN

Workshop Agreement does not necessarily include all relevant stakeholders.

The final text of this CEN Workshop Agreement was provided to CEN for publication on 2022-05-20.

Results incorporated in this CWA received funding from the European Union’s Horizon 2020 research

and innovation programme under grant agreement No 769274 (AIRPOXY project).

The following organizations and individuals developed and approved this CEN Workshop Agreement:

• Nerea Markaide – Chairperson, FUNDACIÓN CIDETEC (Spain)
• Esther Bermejo – Secretary, UNE (Spain)
• Alkiviadis Paipetis – CWA Leader, University of Ioannina (Greece)
• Georgios Foteinidis, University of Ioannina (Greece)
• Kyriaki Tsirka, University of Ioannina (Greece)
• Maria Kosarli, University of Ioannina (Greece)
• Nektaria-Marianthi Barkoula, University of Ioannina (Greece)
• Conor Kelly, ÉireComposites Teoroanta (Ireland)
• Alain Leroy, COEXPAIR S.A. (Belgium)
• Juan Pedro Berro Ramirez, Altair Engineering France (France)
• Alaitz Ruiz de Luzuriaga, FUNDACIÓN CIDETEC (Spain)
• Stefan Weidmann, Leibniz-Institut für Verbundwekstoffe GmbH-IVW (Germany)
• Stephan Becker, Leibniz-Institut für Verbundwekstoffe GmbH-IVW (Germany)
• Mª Eugenia Rodríguez, FUNDACIÓ EURECAT (Spain)
• Vincent Gayraud, FUNDACIÓ EURECAT (Spain)
• Diego Calderón, IDEC – Ingeniería y Desarrollos en Composites, S.L. (Spain)
• Rakel Gonzalez, IDEC – Ingeniería y Desarrollos en Composites, S.L. (Spain)

• Guillaume Messin, IPC-Centre Technique Industriel de la Plasturgie et des Composites (France)

• Mathieu Lions, IPC-Centre Technique Industriel de la Plasturgie et des Composites (France)

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SIST CWA 17896:2022
CWA 17896:2022 (E)
• Rafael Luterbacher, GMA Group (Germany)
• Dimitrios Bekas, MEGA PLAST Industrial-Exporting S.A. (Greece)
• Markus Wolfahrt, Polymer Competence Center Leoben (Austria)
• Robert Perrin, DGA Aeronautical Systems (France)
• Pierre Barbier, Hexcel Composites (France)
• Daniel Ng, ASD-STAN Aerospace

Attention is drawn to the possibility that some elements of this document may be subject to patent rights.

CEN-CENELEC policy on patent rights is described in CEN-CENELEC Guide 8 “Guidelines for

Implementation of the Common IPR Policy on Patent”. CEN shall not be held responsible for identifying

any or all such patent rights.

Although the Workshop parties have made every effort to ensure the reliability and accuracy of technical

and non-technical descriptions, the Workshop is not able to guarantee, explicitly or implicitly, the

correctness of this document. Anyone who applies this CEN Workshop Agreement shall be aware that

neither the Workshop, nor CEN, can be held liable for damages or losses of any kind whatsoever. The use

of this CEN Workshop Agreement does not relieve users of their responsibility for their own actions, and

they apply this document at their own risk. The CEN Workshop Agreement should not be construed as

legal advice authoritatively endorsed by CEN/CENELEC.
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SIST CWA 17896:2022
CWA 17896:2022 (E)
Introduction

Advanced fibre reinforced polymer composites, due to their lightweight, are used in aeronautics,

aerospace, automotive, and naval activities (e.g., aircraft fuselage, wind turbines, gears, chassis, etc.).

Skin-stiffened or “stringer run-outs” structures are used mostly in aerospace and are very sensitive to

local damages. Usually, the stringer tends to debond from the skin, and then the delamination may further

propagate in the skin. The mechanical characterization of these specimens is both time-consuming and

material intensive.

This document describes a modified test method used in a European project to characterize delamination

at the tip of the flange and to understand ‘stringer run-out’ experienced in the manufacture of composite

large panel, typically greater than 0,5 m in any in-plane direction. The method employed a simplified joint

configuration via a lap-strap geometry. The results of the work showed that the simplified lap-strap

specimens showed the same damage mechanisms as the stringer run-out.

Firstly, the lap debonds from the strap and then the delamination may further propagate interplay in the

strap. It should be mentioned that failure in the lap -strap geometry is manifested in a mixed-mode. At

the early stages of the test, the adhesive layer between lap and strap fails in mode II, followed by mode I

failure at higher stress levels. This test method could also be used to evaluate the healing or repair

efficiency at self-healing or repairable composites or their knockdown effect (see 5.6).

Non-destructive Evaluation (NDE) techniques, for example Acoustic Emission, can be optionally applied

to the Lap Strap specimen with the mechanical testing. NDE techniques include Electrical Resistance

Change Method (ERCM) and Acoustic Emission (AE). These techniques could provide information about

the failure of the geometry and, additionally, information about the damage that was induced before

failure. They are strongly suggested in cases of poor mechanical properties of the adhesive.

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SIST CWA 17896:2022
CWA 17896:2022 (E)
1 Scope

This document provides a test method for the determination of the adhesive properties in joints of

continuous fibre reinforced polymer matrix composite structures using the Lap Strap specimen.

The evaluation includes the optional concurrent use of the non-destructive technique of the Electrical

Resistance Change Method (ERCM) and/or Acoustic Emission (AE) for the monitoring of the debonding

of the lap from the strap optionally. The ERCM NDE technique has a limited application only on carbon

fibre composites due to the inherent electrical conductivity of the carbon fibres.

This test applies to composites manufactured with continuous carbon fibres (woven or unidirectional)

and thermoset or thermoplastic matrices, with quasi-isotropic lamination. This methodology can be used

on repairable or self-healing composites in order to estimate the repair or healing efficiency respectively.

Safety aspects about manufacturing and mechanical testing of the composites are excluded.

2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the following terms, definitions, symbols and abbreviated terms apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
non-destructive evaluation
NDE

process or procedure for determining the quality or characteristics of a material, part or assembly

without permanently altering the subject or its properties
[SOURCE: ISO 21648:2008, 2.1.29]
3.1.2
on-line monitoring
any inspection activity carried out concurrent with the mechanical testing
3.1.3
knockdown effect

the change of the initial mechanical properties of a composite material after the incorporation of a self-

healing or a self-repairing system
3.1.4
balanced laminate

continuous fibre-reinforced laminate that each +θ° (angle) lamina is balanced by a -θ° (angle) lamina in

regard to a reference axis
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SIST CWA 17896:2022
CWA 17896:2022 (E)
3.1.5
symmetric laminate

continuous fibre-reinforced laminate that each ply above the mid-plane is identically the same in terms

of position and orientation with one below the mid-plane
3.2 Symbols and abbreviated terms
AE Acoustic Emission
b measured specimen width
Ε apparent stiffness
ERCM Electrical Resistance Change Method
max
value of the load at the drop-off point
g measured grip-to-grip distance
h measured lap thickness
l extension
NDE Non-Destructive Evaluation
R Initial value of the resistance
ΔR The final value of the resistance minus the initial value of the resistance
ε lap strap strain
θ° angle
Initial
lap strap strength from a initial composite
max
Modified
lap strap strength from a modified composite
max
max lap strap strength at the drop off point
Reference
lap strap strength from a reference composite
max
Repaired
lap strap strength from a repaired composite
max
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SIST CWA 17896:2022
CWA 17896:2022 (E)
4 Significance and Use

The most common failure mode of stiffened composite panels is the debonding between the skin and the

stringer. The proposed test method provides the mechanical strength of the lap strap specimen that

simulates the mechanical and failure behaviour of a stiffened panel and reduces consum

...

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