Overview
ISO 7822:1990 specifies three calibrated laboratory methods for determining the void content (void fraction) of textile glass reinforced plastics (glass-fibre reinforced composites whose constituents are solids). The standard covers sample preparation, required apparatus, test procedures, calculation of void content (expressed as % by volume), and reporting requirements. It is intended for quality control, materials characterization and comparative testing of composite parts and laminates.
Key topics and technical requirements
- Three permitted methods
- Method A – Loss on ignition: Uses density calculations combined with loss-on-ignition resin content (referencing ISO 1172). Applicable when constituent behaviour under ignition is known. Accuracy ≈ ±2.5% by volume. Not suitable for resins/fillers that do not burn cleanly (e.g., some silicones, oxide/carbonate fillers).
- Method B – Mechanical disintegration: Destructive technique where specimens are crushed/delaminated and volumes measured (air/gas pyknometer). Suitable when constituent densities are unknown. Requires care with ductile matrices (may need embrittlement by cooling). Pyknometer volume accuracy should be better than ±0.1%.
- Method C – Statistical counting (micrography): Microscope grid point-counting on polished sections. Applicable to low-void materials (≤1% by volume). Accuracy ≈ ±1% by volume. Counting may be manual or automated; grid size and number of points chosen to meet required statistical error.
- Apparatus & specimen requirements
- Typical equipment: micrometer (±1 µm), balance (±0.1 mg), muffle furnace (625 °C ±5 °C for ignition), disintegrator/press, air/gas pyknometer, microscope up to ×400, polishing and encasing equipment.
- Specimen shapes/sizes specified (e.g., strips ~38 mm × 10 mm for pyknometer tests; parallelepipeds 40 × 10 × thickness up to 15 mm for micrography). At least five specimens/sections recommended.
- Conditioning & atmosphere
- Condition specimens per ISO 291 standard atmospheres for at least 16 hours unless otherwise stated.
- Reporting
- Test method used, material identification, sampling, number of determinations, individual and average results, and method-specific details (e.g., pyknometer type, freezing method, number of sections, grid parameters).
Applications and users
ISO 7822 is used by:
- Composite materials laboratories for quality control, acceptance testing and batch certification.
- R&D and materials engineers characterizing laminate integrity and manufacturing process optimization.
- Manufacturers and suppliers of glass-fibre reinforced components in industries such as aerospace, automotive, marine, wind energy and construction where porosity affects mechanical and environmental performance.
Related standards
- ISO 1172:1975 - Textile glass reinforced plastics - Determination of loss on ignition (used with Method A).
- ISO 291:1977 - Standard atmospheres for conditioning and testing (conditioning of specimens).
Keywords: ISO 7822:1990, textile glass reinforced plastics, void content, loss on ignition, mechanical disintegration, statistical counting, pyknometer, void fraction, composite testing.
Open preview (PDF)Textile glass reinforced plastics — Determination of void content — Loss on ignition, mechanical disintegration and statistical counting methods