Overview
ISO 15850:2014 - "Plastics - Determination of tension‑tension fatigue crack propagation - Linear elastic fracture mechanics (LEFM) approach" specifies a standardized test method to measure fatigue crack growth in notched plastic specimens under cyclic tensile loading. The standard uses a LEFM framework to report crack length as a function of load cycles and to derive fatigue crack growth rates (da/dN) versus stress intensity factor range (ΔK) and energy release rate range (ΔG). Test outputs can also include number of cycles to failure or time to failure versus ΔK for resistance-to-failure evaluations. ISO 15850:2014 detects and requires reporting of discontinuous crack propagation and is intended for rigid/semi‑rigid thermoplastics and thermosets (including filled and short‑fibre reinforced materials).
Key topics and technical requirements
- Test principle: constant‑amplitude cyclic tensile load between fixed positive minimum and maximum values; crack initiation from a notch and monitored propagation.
- Measured outputs: crack length a(N), crack growth rate da/dN, ΔK and ΔG relationships, and, when applicable, Nf or tf to failure.
- Specimen types and preparation: notched specimens such as compact tensile (CT) and single‑edge‑notched tensile (SENT); requirements for notch preparation, side grooves, machining and conditioning.
- Apparatus and setup: fatigue test machine, grips, load control, and crack‑length measurement systems (optical or other appropriate methods); control of test atmosphere and avoidance of out‑of‑plane crack growth.
- Data analysis: numerical differentiation of a(N) to obtain da/dN, application of crack curvature corrections, and use of stress intensity calibrations relating load and crack length to K (LEFM assumptions apply).
- Reporting: full documentation of specimen geometry, loading waveform, load ratio R, frequency, environmental conditions, and any discontinuities or abnormal behaviour (see informative Annex A).
Applications and users
ISO 15850:2014 is used for:
- Materials characterization: ranking fatigue crack propagation resistance of thermoplastic and thermosetting compounds.
- Product design and structural integrity assessment using da/dN vs ΔK/ΔG datasets for fracture‑mechanics based life prediction.
- Quality control, R&D, failure analysis, and certification testing in plastics manufacturing and material selection.
Primary users include materials engineers, test laboratories, plastics R&D teams, design engineers concerned with fatigue life, and regulatory or certification bodies.
Related standards
- ISO 291 - Conditioning and testing atmospheres for plastics
- ISO 527 - Determination of tensile properties of plastics
- ISO 2818 - Preparation of test specimens by machining
- ISO 13586 - Definitions related to stress intensity factor (referenced for K)
ISO 15850:2014 provides an LEFM‑based, geometry‑independent approach (within thickness and anisotropy limits) to generate fatigue crack growth data useful for design, comparison and fitness‑for‑service assessments of plastics.