ISO 20975-1:2023

Overview

ISO 20975-1:2023 specifies standardized methods for determining the through-thickness properties of fibre-reinforced plastic composites using direct tension and compression tests. The standard applies to laminates with thermoset or thermoplastic matrices and a through-thickness range of 20 mm to 40 mm, and covers aligned and non-aligned, continuous and discontinuous fibre formats. It defines specimen types, test modes and data-expression procedures to measure strength, modulus of elasticity, Poisson’s ratio and strain-to-failure.

Key topics and technical requirements

• Specimen types
  • Type I: Fixed rectangular cross-section along specimen length - preferred for determining elastic properties.
  • Type II: Waisted, variable cross-section - suitable only for tensile strength testing and preferred for highly anisotropic and thermoplastic materials.
  • Type III: Waisted with fixed gauge cross-section - used to obtain both elastic and strength data and ideal for full stress–strain response.
  • Note: Types I & II are suitable for unreinforced plastics but unsuitable for rigid cellular materials and sandwich structures containing cellular cores.
• Testing modes
  • Method A - Tension
  • Method B - Compression
• Measured properties
  • Tensile/compressive strength, modulus of elasticity (chord), Poisson’s ratio, and failure strain (strain-to-failure).
• Apparatus and instrumentation
  • Calibrated uniaxial testing machines, load and strain indicators, strain gauges, micrometers and appropriate loading fixtures designed to minimize end effects and buckling.
• Test controls and reporting
  • Conditioning and test atmosphere per referenced standards, data acquisition, failure-mode criteria, statistical treatment (confidence intervals, precision) and detailed test reporting requirements.
• Design considerations
  • Specimen geometries and procedures are specified to reduce out-of-plane bending, end effects and Euler buckling, promoting failure away from ends for reliable through-thickness data.

Practical applications - who uses ISO 20975-1:2023

• Composite materials test laboratories and OEM quality control teams conducting through-thickness qualification.
• Design and structural engineers who need validated through-thickness strength and stiffness inputs for finite-element analysis and laminate design.
• Manufacturers of aerospace, automotive, wind energy, marine and sporting goods components where out-of-plane laminate behavior is critical.
• Certification bodies and R&D groups developing new fibre-reinforced plastics and comparing thermoset vs thermoplastic laminate performance.

Related standards

Common normative references used with ISO 20975-1 include:

• ISO 291 (conditioning and testing atmospheres)
• ISO 1268 (production of test plates)
• ISO 2602 (statistical interpretation)
• ISO 5893 (test equipment)
• ISO 7500-1 (calibration of testing machines)

Using ISO 20975-1:2023 helps ensure consistent, reproducible through-thickness test data for laminate qualification, material selection and structural design.