Overview
ISO/TS 6857:2024 provides guidelines for determining void and fibre contents in polished cross sections of continuous fibre‑reinforced ceramic matrix composites (CMCs) using image analysis. Applicable to bidirectional (2D), tridirectional (3D) textile architectures and carbon‑fibre‑reinforced carbon (C/C) composites, the technical specification defines procedures for preparing specimens, acquiring microscope images (optical or SEM), and quantifying area content of voids and oriented fibres. Note: results are area content, not volumetric content.
Key topics and technical requirements
- Scope & applicability: Continuous‑fibre ceramic matrix composites (2D, 3D) and C/C composites; results reported as area fractions.
- Specimen preparation:
- Cut specimens perpendicular to the fibre orientation of interest.
- Recommendations: >3 plies for 2D textiles, >3 unit cells for 3D textiles.
- Mounting/impregnation recommended for delicate samples; careful grinding and polishing to remove subsurface damage.
- Apparatus & calibration:
- High‑resolution microscope (optical or SEM) with stage stitching recommended.
- Calibrated rule/scale (accuracy ±0.5 %) and image analysis software capable of histogram/binzarization and circular pattern detection.
- Resolution target: ~1/10 of filament diameter or void size.
- Image acquisition & processing:
- Acquire grayscale images with consistent conditions; enhance contrast to separate voids (darker) from matrix/fibres.
- Calibrate pixel size with a stage micrometer.
- Void area content:
- Use grayscale histogram binarization (threshold at valley of bimodal histogram) and pixel counting to compute void area fraction.
- Fibre area content:
- Simplified method: tow counting - determine mean filament area per tow and multiply by counted tows.
- Detailed method: pattern matching to detect circular filament cross sections and count filament pixels. Filaments must be cut within ±15° to axis; not suitable for heavily waved woven materials.
Applications and users
ISO/TS 6857:2024 is useful for:
- Materials scientists and researchers studying CMC microstructure.
- Quality control and incoming inspection in aerospace, defense, automotive, and industrial ceramics manufacturing.
- Failure analysis, process development, and comparative material characterization.
Benefits: provides reproducible image‑analysis workflows to quantify porosity and fibre distribution for material development and quality assurance.
Related standards
- ISO 13383‑1:2012 - guidance on grinding and polishing of ceramic materials (referenced for polishing practice).
- Produced by ISO/TC 206 (Fine ceramics).
Keywords: ISO/TS 6857:2024, fine ceramics, ceramic matrix composites, C/C, image analysis, void content, fibre content, polished cross section, microscopy, binarization, tow counting, filament detection.