Overview
ISO 13061-7:2014 - Physical and mechanical properties of wood - Test methods for small clear wood specimens - Part 7 specifies a standardized method for determining the ultimate tensile stress perpendicular to grain of wood. The method applies to small, clear specimens tested in the radial and tangential directions by measuring the breaking load applied statically perpendicular to the specimen’s longitudinal axis.
Keywords: ISO 13061-7:2014, tensile stress perpendicular to grain, wood testing, small clear specimens, ultimate tensile stress, radial tangential.
Key topics and technical requirements
- Scope & principle: Progressive static loading perpendicular to the grain until specimen failure; results expressed as stress (N/mm² or MPa).
- Apparatus:
- Testing machine able to apply constant load or crosshead speed and measure load to 1% accuracy.
- Jaws designed to apply load perpendicular to the longitudinal axis and prevent specimen torsion.
- Measuring instruments for specimen dimensions to 0.1 mm.
- Conditioning equipment for moisture determination (per ISO 13061-1).
- Specimen preparation:
- Follow ISO 3129 for sampling and general preparation.
- Calibrated section: rectangular or square; one side 10–25 mm, other 20–50 mm.
- If prismatic, length ≥ 5 mm or end radius ≥ 12 mm; end shapes must promote failure within the calibrated section.
- Conditioning & moisture:
- Tests may be on green specimens (≥ fibre saturation point) or air-dry specimens.
- Dry specimens conditioned to constant mass at (65 ± 5)% RH and (20 ± 2)°C. Mass constant when two weighings 8 h apart differ ≤ 0.2%.
- Test procedure:
- Measure cross-section, clamp ends at least 10 mm from calibrated section.
- Test speed chosen so failure occurs between 0.5 and 5 minutes after load application begins.
- Report maximum load and compute stress: σ⊥ = P_max / (b · h) (N/mm²), reported to 0.1 MPa.
- Moisture correction:
- If needed, adjust results to 12% moisture using recognized methods; an approximate correction formula with α = 0.015 is provided.
- Test report requirements: include specimen size, sampling info, time to failure, test speed, fracture mode, moisture content, density, statistics (mean, SD), direction (radial/tangential), and laboratory ID.
Applications and users
ISO 13061-7:2014 is used by:
- Timber testing laboratories and certification bodies for material characterization and quality control.
- Researchers studying wood anisotropy and failure mechanisms.
- Structural engineers and designers requiring perpendicular-to-grain strength data for joints, fasteners, adhesives and component design.
- Manufacturers of wood products who need standardized property data for product development and compliance.
Related standards
This standard ensures consistent, reproducible measurement of tensile strength perpendicular to grain-critical data for safe, reliable use of wood in engineered applications.