Overview
ISO 20504:2022 specifies a standardized method for determining the compressive behaviour of ceramic matrix composites (CMCs) with continuous fibre reinforcement at room temperature. It covers uni‑directional (1D), bi‑directional (2D) and tri‑directional (xD) architectures and also applies to carbon‑fibre‑reinforced carbon (C/C) composites. Two test configurations are described: compression between platens and compression using grips. The standard defines measurement principles, apparatus, specimen preparation, test execution, data analysis and reporting.
Key topics and technical requirements
- Scope and principle: Compression testing is performed at a constant cross‑head displacement rate or constant deformation rate; constant force rate only for linear behaviour up to failure. Force and longitudinal deformation are recorded simultaneously.
- Apparatus and measurement:
- Test machines must have a force measurement system conforming to ISO 7500‑1 (grade 1 or better).
- Strain measurement by extensometers (meeting ISO 9513, class 1) or strain gauges; extensometer range linearity and gauge length considerations are specified.
- Load train alignment and mitigation of bending/torsion are required; misalignment verification follows ISO 17161.
- When using platens, parallelism of platen faces in the loading area is specified (very tight tolerance) and compliant interlayers (paper/cardboard) are allowed for inhomogeneous materials.
- For specimens prone to buckling, antibuckling devices (e.g., per ISO 14126 practices) are recommended.
- Test specimens and preparation:
- Requirements for calibrated length, initial gauge length and cross‑sectional area, machining and surface preparation to avoid local artefacts.
- Guidance on number of specimens and mounting techniques (platens vs. grips).
- Results and calculations:
- Determination of compressive strength, strain at maximum compressive force, proportionality ratio / pseudo‑elastic modulus and elastic modulus where applicable.
- Criteria for test validity and reporting requirements.
Practical applications and users
ISO 20504:2022 is intended for:
- Materials and mechanical testing laboratories performing routine or qualification compression tests on CMCs.
- R&D teams developing advanced ceramics for aerospace, automotive, energy, defense and industrial applications.
- Quality control and suppliers requiring consistent, reproducible compressive property data for specifications and acceptance testing.
- Standards developers and certification bodies comparing material performance across suppliers and designs.
Using ISO 20504 helps ensure comparable, traceable compressive property data for design allowables, failure analysis, and material selection.
Related standards
- ISO 7500‑1 - calibration/verification of force measurement systems
- ISO 9513 - calibration of extensometer systems
- ISO 17161 - misalignment verification for uniaxial tests
- ISO 14126 - guidance on antibuckling devices (practices referenced)
Keywords: ISO 20504:2022, compressive properties, ceramic matrix composites, fine ceramics, compression testing, strain measurement, extensometer, compressive strength, elastic modulus.