ISO 12493:2023

Overview

ISO 12493:2023 - Rubber, vulcanized or thermoplastic - Determination of stress in tension under non‑isothermal conditions specifies two laboratory methods to measure tensile thermal stress in rubber materials while temperature changes. It covers equipment, calibration, test‑piece dimensions, conditioning, test procedures and data evaluation for accelerated, non‑isothermal stress measurements. The standard is applicable to vulcanized and thermoplastic rubbers and supports comparative testing (e.g., ageing assessment) and estimating upper operating temperatures.

Key topics and technical requirements

• Two measurement methods
  • Method A: Measures thermal stress as a function of time for various pre‑strain and temperature conditions (rapid heating to target temperature).
  • Method B (TSSR): Temperature Scanning Stress Relaxation - measures stress change at a fixed strain while temperature varies at a constant heating rate, recording stress as a function of temperature.
• Principle: A sample is held at a constant pre‑strain; after reaching equilibrium pre‑stress, temperature is increased and the resulting thermal stress is recorded.
• Apparatus and accuracy
  • Test machines shall comply with ISO 5893 (tensile machines) with force measurement to class 1.
  • Machines must set pre‑strain within ±0.1 (unitless) and move at (20 ± 2.5) mm/min where specified.
  • A temperature‑controlled chamber with internal sensing (suitable volume ~3–5 L) capable of raising temperature at least 30 K/min is required.
  • Load cell and crosshead requirements reference ISO 18899:2013.
• Data considerations
  • Corrections for Gough–Joule effect (retractive forces) and thermal expansion (use of coefficient of thermal expansion, CTE) are necessary.
  • Derivative analysis of stress–temperature curves enables extraction of a relaxation temperature spectrum and can indicate crosslink density changes.
• Normative references: ISO 188, ISO 5893, ISO 18899, ISO 23529.

Practical applications and users

• Useful for materials engineers, test laboratories, quality control, and R&D teams working with vulcanized or thermoplastic rubber.
• Typical applications:
  • Accelerated comparative testing for ageing and formulation screening.
  • Estimating upper operating temperature limits and thermal‑mechanical behaviour.
  • Rapid characterization where conventional isothermal stress‑relaxation tests would be time‑prohibitive.
• Benefits include shorter test duration (hours instead of days/weeks) and enhanced sensitivity to specific relaxation processes.

Related standards

• ISO 188 - Accelerated ageing and heat resistance tests
• ISO 5893 - Tensile, flexural and compression test equipment
• ISO 18899:2013 - Calibration of test equipment
• ISO 23529 - Preparation and conditioning of rubber test pieces

Keywords: ISO 12493:2023, rubber testing, thermal stress, non‑isothermal, TSSR, stress relaxation, vulcanized rubber, thermoplastic rubber, test machine, heating rate.