Overview
ISO 13061-6:2014 specifies a standardized method to determine the ultimate tensile stress (tensile strength) of wood parallel to grain using small clear specimens. The test measures the breaking load applied statically along the longitudinal axis of a test piece to produce reliable, comparable strength data for design, quality control and research.
Key Topics
- Principle: Apply a gradually increasing load parallel to the grain until failure occurs within the gauge portion of the specimen.
- Specimen geometry:
- Gauge cross-section: radial 10–30 mm, tangential 5–10 mm.
- Gauge length: 50–100 mm.
- Ends shaped (or laminated) to ensure failure in the gauge portion and to minimize stress concentrations.
- Moisture content:
- Test pieces may be green (moisture ≥ fibre saturation point) or air-dry.
- Air-dry conditioning: (65 ± 5) % RH at (20 ± 2) °C to constant mass (two weighings 8 h apart within 0.2 % mass).
- Test pieces must be stored to keep moisture content unchanged prior to testing.
- Apparatus and measurement:
- Testing machine capable of a constant rate of loading or movement; load measured to ±1 % accuracy.
- Grips arranged to load along the longitudinal axis and prevent longitudinal twisting.
- Dimensional measurement of the gauge portion to 0.1 mm.
- Procedure:
- Clamp test piece with grips at least 25 mm from the gauge portion.
- Select a rate so failure occurs between 0.5 and 5 minutes from start of loading.
- Discard results when failure occurs outside the gauge portion.
- After testing, determine moisture content and density as per ISO 13061-1 and ISO 13061-2.
- Calculations:
- Ultimate tensile stress, σ|| = P_max / (b h) (expressed in N/mm2 (MPa)).
- Results expressed to a precision of 1 N/mm2 (MPa).
- Optional adjustment to 12 % moisture content may be applied using recognized methods.
- Test report: Must reference ISO 13061-6 and include specimen sizes, sampling, time to failure, results and statistics, moisture and density, adjustment method (if used), mode of failure, speed of testing, test date and laboratory.
Applications
- Generates standardized tensile strength data for structural design and material selection.
- Supports quality control and batch verification in wood products manufacturing.
- Provides consistent test results for research, material characterization, and comparative studies across species and treatments.
Related Standards
- ISO 3129 - Sampling and general requirements for small clear wood specimens
- ISO 13061-1 - Determination of moisture content for physical and mechanical tests
- ISO 13061-2 - Determination of density for physical and mechanical tests
- ISO 24294 - Timber vocabulary
This part of ISO 13061 aligns tensile testing procedure details (apparatus, specimen preparation, conditioning, timing, calculations and reporting) to ensure reproducible and comparable tensile strength parallel to grain results across laboratories and programs.