Overview
EN ISO 14129:1997 defines the ±45° tension test method to determine the in‑plane shear stress–shear strain response, including the in‑plane shear modulus and shear strength, of fibre‑reinforced plastic composites. The procedure is applicable to thermoset and thermoplastic matrix laminates manufactured from unidirectional layers and/or fabrics where the plies are arranged symmetrically and balanced about the mid-plane.
The standard emphasises practical measurement and test control for reliable material data used in design, material selection and quality control of composite components.
Key Topics
- Scope and applicability: Suitable for unidirectional and fabric laminates with fibres at ±45° to the specimen axis; not recommended for coarse fabrics.
- Specimen geometry: Typical specimen width 25 mm, length 250 mm, nominal thickness 2 mm (values and tolerances are stated in the standard). For layers thicker than 0.125 mm, a 16‑layer laminate is specified.
- Test setup and instrumentation:
- Strain measurement both parallel and perpendicular to the specimen axis using strain gauges or extensometers.
- Load measurement per ISO 5893 with accuracy better than ±1% full scale.
- Typical test speed: 2 mm/min (unless material-specific conditions apply).
- Termination and failure criterion: Tests are terminated at a shear strain g = 0.05 if failure has not occurred; this reduces uncertainty for high shear‑elongation materials.
- Calculations and reporting:
- In‑plane shear stress is calculated from instantaneous load and specimen cross section.
- Shear strain is obtained as the sum of longitudinal and transverse strains (εx + εy).
- Shear (chord) modulus is derived from shear stress and strain intervals (example points g' = 0.001 and g'' = 0.005 in the standard).
- Minimum five specimens are required; results include mean values, standard deviation and 95% confidence intervals if requested.
Applications
This test method provides practical material properties for:
- Structural design and finite element input where accurate in‑plane shear properties are required.
- Comparative evaluation of laminate lay‑ups and resin/fibre combinations.
- Quality control and acceptance testing of production panels and prepregs.
The method is most effective for materials that fail in the expected shear‑dominated manner; caution is advised when interpreting ultimate shear values for high‑elongation systems.
Related Standards
- ISO 5893 - tensile test machine requirements
- ISO 291 - conditioning and testing atmospheres
- ISO 1268 / ISO 2818 - specimen and panel preparation guidance
- ISO 2602 - statistical interpretation and confidence intervals
For full procedural details, formulas and annex guidance on specimen preparation, refer to the complete EN ISO 14129:1997 text. The standard provides the required test geometry, data collection, calculation method and mandatory reporting items for traceable in‑plane shear characterization.