Overview
ISO 34-2:2022 specifies a standardized laboratory method for determining the tear strength of small (Delft) test pieces of vulcanized or thermoplastic rubber. Designed for situations when material is limited or when small finished products must be tested, this Part 2 procedure complements ISO 34-1 (which uses trouser, angle and crescent specimens) and may give different numerical results - the two methods are not directly interchangeable.
Key technical topics and requirements
- Test specimen geometry: Rectangular Delft test pieces - nominal dimensions: length L = 60 mm, width B = 9.0 ± 0.1 mm, slit length b = 5.0 ± 0.1 mm; thickness d = 2.0 ± 0.2 mm.
- Apparatus:
- Tensile-testing machine meeting ISO 5893 (class 1 force accuracy) with traverse speed 500 mm/min ± 50 mm/min.
- Die for cutting Delft pieces and slit (drawings specified in the standard).
- Micrometer gauge per ISO 23529 (circular foot ≈ 6 mm, 22 kPa ± 5 kPa).
- Travelling microscope, ≥10× magnification with 0.01 mm graticule for certain measurements.
- Measurement methods:
- Thickness measured in accordance with ISO 23529 (Method A), with at least three readings near the slit.
- Total width outside the slit (rubber to be torn) may be determined by either:
- Method 1 - direct measurement of cut cross-section with a travelling microscope (theoretically more exact), or
- Method 2 - calculated from die dimensions (simpler, commonly used). Results from different methods are not comparable.
- Test procedure:
- Mount specimen so free length between grips is 30 mm (each grip 15 mm from the slit); pull until complete tearing; record maximum force.
- Conditioning and test temperature follow ISO 23529 guidance.
- Result expression & reporting:
- Tear force is normalized to a standard width and thickness (see Clause 10) and reported as tear strength.
- Minimum three specimens (preferably six); median or average of medians used per Clause 10.
- Full test-report requirements are listed (sample details, measurement methods, conditioning, temperature, grain direction, individual results if n=3, etc.).
- Calibration & precision:
- Equipment calibration per Annex B; interlaboratory precision data in Annex A.
Practical applications and who uses this standard
ISO 34-2 is used for:
- Quality control and acceptance testing of small rubber products (e.g., seals, gaskets, O‑rings, valve parts) where standard large specimens cannot be obtained.
- Material development, comparative testing, and failure analysis when only limited material is available.
- Test laboratories, rubber manufacturers, OEMs, and quality/continuity engineers who require a repeatable tear-strength measurement for small components.
Benefits include repeatable, standardized tear-strength data for small samples and clear reporting requirements to support material specifications, supplier agreements, and regulatory or contractual testing.
Related standards
- ISO 34-1 - Rubber - Determination of tear strength (trouser, angle and crescent test pieces)
- ISO 5893 - Tensile test equipment specification
- ISO 23529 - Preparation and conditioning of rubber test pieces
- ISO 18899 - Guide to calibration of test equipment
Keywords: ISO 34-2, tear strength, Delft test pieces, rubber testing standard, vulcanized rubber, thermoplastic rubber, tear testing, tensile-testing machine, specimen dimensions, rubber quality control.
Open preview (PDF)Rubber, vulcanized or thermoplastic — Determination of tear strength — Part 2: Small (Delft) test pieces