Overview
ISO/TS 28660:2022 - "Plastics - Determination of J‑R curves - Fracture toughness" specifies a standardized method to determine fracture toughness of plastics in terms of J (J‑integral) and J‑R curves (resistance to crack growth). The technique is a multiple‑specimen, nonlinear fracture mechanics approach suited to ductile and semi‑ductile polymers and blends. It is not intended for materials where the crack front cannot be distinguished from other deformation ahead of the crack tip or for fibre‑reinforced polymers. J‑R curves produced by this method characterize crack growth resistance beyond the scope of linear elastic fracture mechanics (LEFM) such as ISO 13586.
Key topics and technical requirements
- Test principle: Multiple‑specimen method with optical measurement of crack length and crack extension on fracture surfaces.
- Specimen geometries: Two options - three‑point bend (SENB) and pin‑loaded compact tension (CT). Bend specimens typically give a lower‑bound J‑R.
- Energy and J calculation: Total energy is split into elastic and plastic parts; corrected energy (U) is used to compute the J‑integral and construct J‑R curves.
- Apparatus and accuracy:
- Force measurement: class 1 accuracy per ISO 7500‑1.
- Displacement transducer: meets class 2 accuracy per ISO 9513 and be free from inertia lag at test speeds.
- Test speeds: recommended range provided (examples include 0.125 mm/min up to 500 mm/min with specified tolerances).
- Specimen preparation: Requirements for shape, size, notching, side grooves and conditioning (referenced to ISO 291 and ISO 2818).
- Measurement and correction: Optical crack length measurement along the crack front, indentation correction and validation procedures for J‑R curve construction.
- Reporting and precision: Requirements cover test reports, validation of results, and discussion of precision/bias.
Applications and practical use
- Determines fracture toughness and crack‑growth resistance of polymers where plasticity is significant.
- Useful for material selection, failure analysis, product design, quality control and comparison of polymer formulations or processing conditions.
- Helps engineers and researchers predict stable crack extension and resistance to fracture in structural plastics where LEFM is not applicable.
Who should use this standard
- Materials scientists, plastics engineers, test laboratories, quality assurance teams and R&D groups working with ductile polymers and blends.
- Manufacturers developing polymer components requiring fracture‑resistance data for safety or performance validation.
Related standards
- ISO 13586 (LEFM for plastics - GIC and KIC)
- ISO 7500‑1 (calibration/verification of testing machines)
- ISO 9513 (calibration of extensometers)
- ISO 291, ISO 2818 (conditioning and specimen preparation)
- ASTM D6068 (similar J‑R methodology)