ISO 19350:2025

Recycled carbon fibre - Determination of tensile strength distribution and interfacial shear strength of single filament embedded in matrix polymer

This document specifies methods for the simultaneous measurement of the fibre tensile strength distribution, and the fibre resin interfacial shear strength of recycled carbon fibres using the modified fragmentation test.

Fibre de carbone recyclée — Détermination de la distribution de la résistance à la traction et de la résistance au cisaillement interfacial d'un filament unique noyé dans une matrice polymère

General Information

• Status: Published
• Publication Date: 06-Jan-2025
• ICS: 59.100.20 - Carbon materials
• Technical Committee: ISO/TC 61/SC 13 - Composites and reinforcement fibres
• Drafting Committee: ISO/TC 61/SC 13 - Composites and reinforcement fibres
• Current Stage: 6060 - International Standard published
• Start Date: 07-Jan-2025
• Due Date: 30-Aug-2025
• Completion Date: 07-Jan-2025

Overview

ISO 19350:2025 specifies a laboratory method for evaluating recycled carbon fibre performance by simultaneously measuring the tensile strength distribution of single filaments and the interfacial shear strength between a recycled carbon fibre and a polymer matrix. The standard uses a modified fragmentation test in which a single filament embedded in a polymer film is incrementally strained while fibre breaks are observed and counted. Results are analyzed assuming a two‑parameter Weibull distribution for filament strength.

Key topics and requirements

• Test principle: modified fragmentation test to obtain filament break‑point density versus fibre strain; Weibull analysis yields tensile strength distribution and interfacial shear strength.
• Specimen preparation:
  • Single recycled carbon fibre embedded at the centre of a transparent polymer sheet.
  • Typical cut specimen size: 5 mm × 35 mm; specimen thickness > 200 µm; thickness variation < 5%.
  • Fibre length per batch: total ≥ 100 mm (preferably > 150 mm); individual fibre > 3 mm.
  • Press moulding recommended; vacuum pressing to remove air; control spacer thickness ≥ 200 µm.
  • Fibre straightness check: reject specimens with waviness ≥ 5°.
• Measurement equipment:
  • Tensile test machine with displacement accuracy < 1 µm; gauge length typically 20 mm.
  • Grips must prevent slippage and avoid local deformation.
  • Microscope (video/photography preferred) for observing and recording break points.
• Test procedure and parameters:
  • Begin at film strain ~3.5% (reduce if excessive breaks occur).
  • Incremental film strain Δεfilm: < 0.25% per step up to 7.5%; < 0.5% above 7.5%.
  • Strain rate < 0.05%/s; maximum strain > 10%.
  • Calculate fibre strain accounting for thermal shrinkage of the polymer.
• Data analysis & validity:
  • Count incremental break points per strain step; produce double‑log plots of break density vs strain.
  • Extract Weibull shape and scale parameters and the interfacial shear strength.
  • Follow clauses on reporting, validity checks and sample size requirements.

Applications and users

• Applicable to manufacturers and recyclers of carbon fibre and composite parts who need to:
  • Qualify recycled carbon fibres for reuse in structural composites.
  • Compare recycled vs virgin filament strength distributions.
  • Characterize fibre–matrix adhesion for process development and quality control.
• Typical users: materials and mechanical engineers, composite product developers, test laboratories, R&D groups, and recycling technology providers.

Related standards

• ISO 10618 - Carbon fibre: tensile properties of resin‑impregnated yarn
• ISO 11566 - Carbon fibre: tensile properties of single‑filament specimens
• ISO 11567 - Carbon fibre: filament diameter and cross‑sectional area

Keywords: ISO 19350:2025, recycled carbon fibre standard, tensile strength distribution, interfacial shear strength, modified fragmentation test, single filament testing, Weibull analysis, polymer matrix testing.

Standards Content (Sample)

International
Standard
ISO 19350
First edition
Recycled carbon fibre —
2025-01
Determination of tensile strength
distribution and interfacial
shear strength of single filament
embedded in matrix polymer
Fibre de carbone recyclée — Détermination de la distribution
de la résistance à la traction et de la résistance au cisaillement
interfacial d'un filament unique noyé dans une matrice polymère
Reference number
© ISO 2025
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ISO copyright office
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols. 1
3.1 Terms and definitions .1
3.2 Symbols .1
4 Principle . 2
5 Tensile test machine and specimen . 2
5.1 Tensile test machine .2
5.2 Grip.2
5.3 Microscope .2
5.4 Test specimens.2
5.5 Number of tests .4
6 Testing technique. 4
6.1 Test procedure .4
6.2 Validity of the test .6
7 Calculation of results . 6
7.1 Summary of measurement data .6
7.2 Calculation of tensile strength distribution .7
7.3 Calculation of interfacial shear strength .8
7.4 Validity of the test result .8
8 Reporting of test results . 9
Bibliography .10

iii
Foreword
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iv
Introduction
The properties of recycled carbon fibres are potentially different from those of the original virgin carbon fibres.
Therefore, it is very important to evaluate the properties of recycled carbon fibres in order to reuse them as
reinforcing fibres. The tensile strength distribution and interfacial shear strength of recycled carbon fibres are
essential for the production of composite materials using recycled carbon fibres. This document describes how
to measure the tensile strength distribution and interfacial shear strength of recycled carbon fibres.

v
International Standard ISO 19350:2025(en)
Recycled carbon fibre — Determination of tensile strength
distribution and interfacial shear strength of single filament
embedded in matrix polymer
1 Scope
This document specifies methods for the simultaneous measurement of the fibre tensile strength
distribution, and the fibre resin interfacial shear strength of recycled carbon fibres using the modified
[1]
fragmentation test .
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 10618, Carbon fibre — Determination of tensile properties of resin-impregnated yarn
ISO 11566, Carbon fibre — Determination of the tensile properties of single-filament specimens
ISO 11567, Carbon fibre — Determination of filament diameter and cross-sectional area
3 Terms, definitions and symbols
3.1 Terms and definitions
No terms and definitions are listed in this document.
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/
3.2 Symbols
Symbol Definition
E
fibre tensile modulus, GPa Tensile modulus of the recycled carbon fibres
D
average fibre diameter, μm Average fibre diameter of the recycled carbon fibres
L Gauge length, mm Initial distance between grips
Total fibre length, mm Total length of a fibre within the observed area of all speci-
l
mens
Length of a fibre within the observed area of each specimen i
l Fibre length, mm
i
m
Weibull shape parameter Shape parameter of the 2-parameters’ Weibull distribution
Total number of break points
N()ε Total number of fibre break points in all specimens at ε
fibre fibre
Δ Displacement, mm Displacement given between gauges
Incremental film strain The magnitude of the strain on the film in each step
Δε
film
Symbol Definition
Δn ε Incremental number of fibre break Incremental n
...