ISO 37

ISO 37 – Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties

Purpose:
Specifies the method for determining tensile stress–strain properties of vulcanized and thermoplastic rubber.

Properties Measured:

• Tensile strength
• Elongation at break
• Stress at a given elongation (modulus)
• Elongation at a given stress
• Stress and elongation at yield (for certain thermoplastic rubbers)

Principle:
Standard test pieces (dumb-bell or ring shapes) are stretched at a constant rate using a tensile-testing machine. Force and elongation are recorded until the specimen breaks.

Test Pieces:

• Dumb-bell types: 1, 1A, 2, 3, and 4
• Ring types: A (standard) and B (miniature)
  Type 1A is a newer design with more uniform strain distribution and improved repeatability.

Main Procedure:

• Prepare and condition samples per ISO 23529.
• Use a constant traverse rate (e.g., 500 mm/min for type 1, 2, 1A).
• Calculate tensile strength, elongation, and modulus according to standard formulas.
• Report median values of test results.

Apparatus:

• Tensile-testing machine (ISO 5893 compliant)
• Extensometer, dies, gauges for measuring specimen dimensions
• Temperature-controlled chamber (if needed)

Test Conditions:

• Standard laboratory temperature (per ISO 23529)
• Minimum of three test pieces per test
• Time between vulcanization and testing: at least 16 hours

Results & Reporting:
The test report must include:

• Reference to ISO 37
• Sample and test piece details
• Test temperature and conditions
• Median values of all measured properties

Annexes:

• Annex A: Preparation of Type B ring test pieces
• Annex B: Precision data from interlaboratory tests

Annex C: Analysis of dumb-bell shapes (Type 1A shows higher precision)