Overview
ISO 3597-2:2003 specifies a standardized test method for determining the flexural strength of circular composite rods made from roving-reinforced resin (textile-glass-reinforced plastics). The method covers testing of “as‑moulded” rods or rods pretreated by immersion in boiling water (or another medium) for a specified time. It is intended for inspection and quality control of rovings and for evaluating their suitability in a resin system - not for producing design allowables.
Key topics and technical requirements
- Test geometry and apparatus:
- Based on ISO 14125 flexural-testing apparatus with specific modifications for circular rods.
- Support span = 16 × specimen diameter.
- Load applicator: waisted steel rod; the waist radius must be no more than 0.25 mm larger than the measured specimen radius (example illustrated for 6 mm diameter).
- Specimen preparation and conditioning:
- Prepare rods following ISO 3597-1.
- Minimum of eight specimens per condition (“as‑moulded” or pretreated); specimen length = 20 × diameter (e.g., 120 mm for 6 mm rods).
- Measure diameter at two points 90° apart to 0.1 mm accuracy and use the average.
- Test procedure:
- Test in the same atmosphere used for conditioning.
- Load applicator speed = 5 mm/min.
- Polyethylene film may be placed between supports and rod (influence on results not established).
- Mode of failure may be recorded; note that failures initiated by interlaminar shear are not acceptable for this method.
- Result calculation:
- Flexural strength σ (MPa) is calculated from the breaking force F (N), span l (mm) and diameter d (mm) using:
σ = (8 × F × l) / (π × d^3)
- Reporting and precision:
- Test report must identify roving, resin, mould diameter, release agent (if used), curing/postcuring, test atmosphere, individual and average strengths, pretreatment details if applicable.
- Inter‑laboratory precision is not established in this edition.
Applications and who uses it
- Quality control laboratories and composite manufacturers verifying roving quality and resin compatibility.
- Materials engineers and R&D teams evaluating processing effects (e.g., hydrothermal pretreatment) on flexural performance.
- Suppliers wanting standardized inspection methods for roving-reinforced rods.
- Not intended for structural design data; use for inspection, acceptance testing, and comparative screening.
Related standards
- ISO 3597-1 - General considerations and preparation of rods (preparation & conditioning).
- ISO 14125 - Fibre-reinforced plastic composites - Determination of flexural properties.
- ISO 3597 Parts 3 & 4 - Compressive strength and apparent interlaminar shear strength.
Keywords: ISO 3597-2:2003, flexural strength, roving-reinforced resin, textile-glass-reinforced plastics, composite rod testing, quality control, ISO 14125, specimen preparation, three-point bending.