Overview
ISO 20872:2018 specifies a standardized method to determine the tear strength (tear resistance) of footwear outsoles, regardless of material, using trouser (pant) test pieces. The procedure defines specimen preparation, conditioning, test apparatus and instrumentation, test execution, result calculation and reporting so laboratories and manufacturers obtain reproducible, comparable tear-strength data for outsole materials.
Key Topics and Requirements
- Scope: Measurement of tear strength of outsoles irrespective of material using trouser test pieces (ISO 20872:2018).
- Specimen preparation
- Use an emporte‑pièce to cut trouser-shaped specimens; notch depth of 40 mm ± 5 mm with final ~1 mm cut made with a razor blade.
- Preferred specimen thicknesses: 2.0 mm ± 0.2 mm for compact polymer/elastomer outsoles; 4.0 mm ± 0.2 mm for semi‑expanded/cellular outsoles. For leather, test the initial thickness.
- Measure thickness at three points and use the average (median thickness used in calculation).
- Types of specimen surface: S2 (two skin surfaces), S1 (one skin), S0 (no skin) - results must be based on the same specimen type.
- Conditioning and sampling
- Sample and cut at least three specimens following ISO 17709.
- Condition specimens at the normal atmosphere per ISO 18454 for at least 24 h before testing.
- Apparatus
- Tensile testing machine complying with ISO 7500‑1 (class 2 accuracy), low inertia, constant crosshead speed of 100 mm/min ± 10 mm/min, and autographic force recording.
- Jaws that grip automatically and maintain uniform pressure; thickness gauge with a 10 mm diameter foot applying 10 kPa ± 3 kPa.
- Test procedure and results
- Apply increasing tensile load until propagation of tear and specimen rupture while recording force vs time.
- Determine the median peak force (Method A for