Overview
ISO 19927:2018 specifies a standardized procedure to determine interlaminar shear strength and interlaminar shear modulus of fibre‑reinforced plastic composites using the double beam shear (DBS) test. The method is intended primarily for glass and carbon fibre‑reinforced plastics with thermoset matrices, and is applicable when an acceptable interlaminar failure (delamination) is obtained. The standard targets laminates with a symmetrical and balanced lay‑up (preferably unidirectional fibres aligned with the specimen length) to avoid bending/twist or coupling deformations.
Key Topics and Requirements
- Test principle: 5‑point flexure (double support spans) producing regions of near‑pure interlaminar shear in the specimen; critical load at delamination gives shear strength and load‑displacement slope gives shear modulus.
- Applicability: Suitable for typical glass/carbon thermoset composites; other fibres or lay‑ups (e.g., natural fibres) require trial tests to confirm correct delamination mode.
- Specimen design and preparation: Laminates must be symmetric and balanced; preferred unidirectional lay‑up. Specimen dimensions and machining tolerances are specified to ensure pure ILS regions.
- Apparatus and measurement:
- Test machine conforming to ISO 5893 with constant crosshead speed.
- Load indicator accuracy better than ±1% (Class 1).
- 5‑point flexure loading fixture with rollers positioned within ±0.2 mm; roller contact diameter 6 mm (tolerance 0 to –0.1 mm).
- Displacement transducer (DVRT/LVDT or extensometer) calibrated to ±1% (Class 1 of ISO 9513).
- Data and calculations:
- Interlaminar shear strength (τ13,max) calculated from critical load at delamination.
- Interlaminar shear modulus (G13) derived from load‑displacement slope; requires E11, E22, G12 and ν12 (measured or manufacturer data).
- Acceptance and reporting: Defines acceptable failure modes, number of specimens, conditioning (ISO 291), test speed, and required test report content.
Practical Applications and Users
ISO 19927:2018 is used by:
- Composite manufacturers and material suppliers for product data and quality control.
- Independent testing laboratories and certification bodies for material characterization.
- Design engineers and analysts for structural design, finite‑element modelling and failure analysis of laminated composites.
- R&D teams developing matrices, fibres or new lay‑ups to evaluate interlaminar performance.
- Repair and maintenance teams assessing delamination susceptibility in service components.
Practical uses include material selection, verification of manufacturing quality, comparison of DBS vs. other ILS methods (e.g., short beam shear), and deriving input properties for structural simulations.
Related Standards
Keywords: ISO 19927:2018, double beam shear test, DBS, interlaminar shear strength, interlaminar shear modulus, fibre‑reinforced composites, glass fibre, carbon fibre, thermoset matrices, symmetrical lay‑up, unidirectional.