ISO 18489:2015

Overview

ISO 18489:2015 specifies the Cracked Round Bar (CRB) test method to determine resistance to slow crack growth (SCG) in polyethylene (PE) materials for piping systems. The standard defines an accelerated fracture‑mechanics test performed at ambient temperature (23 °C) suitable for PE pipe grades-especially PE 80 and PE 100-and for specimens taken from compression‑moulded sheets, extruded pipes and injection‑moulded fittings. The method can be adapted for other thermoplastics by adjusting test parameters.

Key topics and technical requirements

• Test principle: cyclic tensile loading with a constant load range on a cylindrical specimen containing a circumferential razor‑sharp notch to promote crack initiation and SCG to final failure. Final result is failure cycles (Nf) as a function of initial crack length and stress range.
• Specimen geometry: preferred specimen diameter D = 14 mm and length L = 80–100 mm. Target initial crack length a* = 1.50 +0.15/‑0.0 mm, producing a target initial ligament diameter D*.
• Notching: notch tip radius < 10 µm (razor blade recommended) and notch location ≥ 20 mm from grips to avoid clamping effects.
• Loading and waveform: sinusoidal load control with maximum and minimum loads constant to ±1%. Load‑cycle frequency shall not exceed 10 Hz (accuracy 1%); reduce to 5 Hz or 1 Hz if hysteretic heating is suspected.
• Measurement accuracy: crack length measurement with a microscope or equivalent to 0.01 mm. Temperature control for tests other than 23 ± 2 °C.
• Apparatus: servo‑hydraulic or mechanically driven cyclic test machines, grips for cylindrical specimens, notching apparatus, temperature chamber (if required).
• Data and reporting: record cycles to failure, initial crack length, stress range and test conditions for fracture‑mechanical characterization.

Applications and users

ISO 18489:2015 is used for:

• Material ranking and pre‑selection in pipe system design
• QA/QC and type‑approval testing of PE pipes and fittings
• R&D for new PE formulations and compound optimization
• Failure analysis and lifetime prediction studies using accelerated SCG data

Typical users: pipe manufacturers, materials scientists, test laboratories, R&D teams, certification bodies, and regulators concerned with long‑term performance of PE piping systems.

Related standards

• ISO 291 - Plastics: standard atmospheres for conditioning and testing
• ISO 2818 - Plastics: preparation of test specimens by machining

ISO 18489:2015 provides a practical, accelerated CRB test for assessing SCG resistance of polyethylene piping materials, enabling faster, application‑relevant evaluation of PE 80/PE 100 grades without elevated temperatures or stress‑cracking liquids.