National foreword

This British Standard is the UK implementation of ISO 19927:2018.

The UK participation in its preparation was entrusted to Technical Committee PRI/42, Fibre reinforced thermosetting plastics and prepregs.

A list of organizations represented on this committee can be obtained on request to its secretary.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 August 2018.

Foreword

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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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Introduction

Interlaminar shear (ILS) properties of load-bearing composite laminates are important for structural design, stress analysis and numerical modelling, material development and selection, component manufacture as well as for repair of delaminated structural components. A number of test methods have been developed for the determination of shear properties of composite laminates and several have been standardized, including short beam strength (SBS) [ASTM D2344, ISO 14130, EN 23771 and EN 2563¹⁾], V-notched beam (known also as Iosipescu shear), ASTM D5379, V-notched rail (ASTM D7078) and notched tension (ASTM D3846, BS 4994) or notched compression (BS 6464).

SBS methods are very popular due to their simplicity in specimen preparation, test operation and cost-effectiveness, though they are used to determine only an apparent ILS strength for QA purposes rather than for use in design. However, a loaded SBS specimen does not have a pure ILS region within its gauge section so it often fails in a number of modes, dependent on, amongst others, type of composite materials, lay-up and specimen thickness. Unacceptable SBS failure modes include flexural failure, local crushing (under central loading roller) and plastic deformation and roller-induced through-thickness shear band.

The DBS method is based on loading a composite beam on double support spans (i.e. between 5 loading points), which generates a stress state that minimises axial bending stresses while promoting interlaminar shear stresses. In DBS tests delamination occurred consistently within one of the pure ILS regions in the specimens, for a range of laminated composite materials or lay-ups.

Comparisons with the SBS ILS strength results indicated that the DBS ILS strengths were 20 % to >30 % higher. In addition, a value of the interlaminar shear modulus can be obtained, providing values of E₁₁, E₂₂, G₁₂ and ν₁₂ are known or measured separately for the material under test.

1 Scope

This document specifies a procedure for determining the interlaminar strength, and modulus, by double beam shear (DBS) tests of fibre-reinforced plastic composites.

The method is suitable for use with glass or carbon fibre-reinforced plastic composites with thermoset matrices, providing an acceptable interlaminar failure is obtained.

This document only applies to laminate with a symmetrical and balanced lay‐up as it avoids bending/twisting or bending/extension coupling deformations (see 6.2). The preferred lay-up is unidirectional, with fibres aligned along the specimen (axial) length.

The suitability of the test for specific lay-ups, matrices and fibres (e.g. natural) are assessed by trial tests to ensure the correct delamination failures are obtained.

2 Normative references

3 Terms and definitions

3.5 Specimen coordinate axes

4 Principle

5 Apparatus

5.1 Test machine

5.2

5.3

5.4 Displacement measurement

6 Test specimens

6.1 Shape and dimensions

6.2 Preparation of specimens

6.3 Checking the test specimens

7 Number of test specimens

8 Conditioning

9 Procedure

9.1 Test conditions

9.2 Specimen dimensions

9.3 Testing speed

9.4 Data collection

9.5 Failure mode acceptance

9.6 Critical load

9.7 Slope of load-displacement curve

10 Calculation and expression of results

10.1 Interlaminar shear strength

10.2 Interlaminar shear modulus

11 Precision

12 Test report

Bibliography

BS ISO 19927:2018

Fibre-reinforced plastic composites. Determination of interlaminar strength and modulus by double beam shear test

Current, Under Review

Published:

31 Aug 2018