Overview
ISO 20337:2018 specifies a standardized shear test method using a shear frame to determine the in‑plane shear stress–shear strain response, shear modulus and shear strength of fibre‑reinforced plastic composites. The method produces a state of pure shear in square specimens (fibres at 0° and 0°/90° orientations), avoiding edge effects and enabling reliable measurement in both the linear and nonlinear deformation ranges - including shear strains greater than 5%. It applies to thermoset and thermoplastic laminates, unidirectional layers, fabrics, non‑wovens, and short or long fibre composites when the lay‑up is symmetrical and balanced.
Key Topics and Requirements
- Test principle: Square specimen clamped along all sides in a shear frame, deformed into a rhombus under axial load to produce pure in‑plane shear.
- Measured outputs: In‑plane shear stress (τ12), shear strain (γ12), in‑plane shear modulus (G12) and maximum shear strength (τ12M).
- Specimen geometry: Typical specimen size (165 ± 0.5) mm square; shear (free) area at least (105 ± 0.5) mm square; nominal thickness (4 ± 0.1) mm (select to prevent out‑of‑plane deflection).
- Apparatus: Tensile testing machine compliant with ISO 7500‑1 (force measurement class 1); shear frame with uniform clamping and follower mechanism to maintain reproducible grip.
- Strain measurement: Strain gauges (front and back faces) accurate to ±1% full scale or optical 3‑D systems; measure at 45° to coordinate axes; verify out‑of‑plane deflection.
- Dimensional control: Micrometer or equivalent with maximum permitted error ≤ 0.01 mm for thickness measurement.
- Test conditions & procedure: Specimen conditioning per standard atmospheres (e.g., ISO 291); prescribed test speeds and data collection practices; defined failure modes and test termination criteria.
- Applicability: Suited for both linear and nonlinear shear characterization, including high shear‑elongation materials.
Applications and Users
ISO 20337:2018 is used by:
- Composite materials R&D teams for material characterization and model calibration (shear modulus and nonlinear behaviour).
- Quality control and test laboratories performing routine or comparative shear testing.
- Composite manufacturers validating lay‑ups, resins and reinforcement systems (thermoset/thermoplastic).
- Certification bodies and engineering teams for structural design data, finite element inputs, and failure analysis.
Practical benefits include consistent, reproducible shear properties across labs, capability to measure high‑strain shear behavior (>5%), and reduced edge‑related artefacts thanks to full‑edge clamping.
Related Standards
Keywords: ISO 20337:2018, shear test, shear frame, in‑plane shear, shear modulus, fibre‑reinforced plastic composites, composite shear testing, strain measurement.