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.