Overview
ISO 4604:2011 - Reinforcement fabrics - Determination of conventional flexural stiffness - Fixed-angle flexometer method specifies a laboratory procedure for measuring the conventional flexural stiffness of reinforcement fabrics (e.g., fabrics used in composites) using a fixed-angle flexometer. The method determines the overhanging length of a fabric strip bent under its own weight and converts that measurement, together with mass per unit area, into stiffness values. The procedure is not suitable for limp fabrics or fabrics with a marked tendency to curl, twist or fray.
Key topics and requirements
- Test principle: A rectangular strip is moved over a platform until its tip aligns with sighting lines inclined at 41.5° below the horizontal; the overhanging length is measured and used to compute stiffness.
- Specimen dimensions and quantities: Cut strips 25 mm × 250 mm; test six warp and six weft specimens (three per face orientation as specified).
- Apparatus: Fixed-angle flexometer with a slide 25 mm wide and at least 300 mm long; slide mass specified as 10 g ± 2 g per centimetre of length. Cutting die and suitable cutting device are required.
- Conditioning and atmosphere: Condition specimens per ISO 291 for at least 6 hours until mass is stable to 0.25% (reweighed at 2 h intervals); test in the same atmosphere.
- Calculation and units: Conventional flexural stiffness is calculated from the average overhanging length and the fabric’s mass per unit area (ρ determined per ISO 3374). Results are reported in millinewton metres (mN·m); ρ is in g/m² and length in metres.
- Reporting: Test report must reference ISO 4604:2011, identify the fabric and test conditions (conditioning temperature/humidity per ISO 291), give warp/weft stiffness per face, and note any deviations or incidents.
Applications and users
- Useful for quality control, comparative testing and specification of reinforcement fabrics used in composite part manufacture, structural textiles and technical fabrics.
- Typical users:
- Textile and composite manufacturers assessing stiffness properties in warp and weft directions
- Materials test laboratories and certification bodies
- R&D teams developing reinforcement fabrics and process engineers selecting fabrics for molding or lay-up
- Procurement/specification writers who need standardized stiffness data for material selection
- Practical value: Provides reproducible, comparable stiffness data to inform handling, drapability and processing behavior of reinforcement fabrics in manufacturing.
Related standards
- ISO 291 - Plastics - Standard atmospheres for conditioning and testing (conditioning requirements referenced)
- ISO 3374 - Reinforcement products - Mats and fabrics - Determination of mass per unit area (ρ measurement referenced)
- Prepared by ISO/TC 61 (Plastics), Subcommittee SC 13 (Composites and reinforcement fibres)
Keywords: ISO 4604:2011, reinforcement fabrics, flexural stiffness, fixed-angle flexometer, fabric testing, warp weft stiffness, ISO 291, ISO 3374.
Open preview (PDF)Reinforcement fabrics — Determination of conventional flexural stiffness — Fixed-angle flexometer method
