Overview
EN ISO 6721-3:2021 - "Plastics - Determination of dynamic mechanical properties - Part 3: Flexural vibration - Resonance-curve method" (ISO 6721-3:2021) specifies a bending-vibration test based on resonance curves to determine the flexural complex modulus (E*f) and damping characteristics of homogeneous and laminated plastics. The method is particularly suited for materials and multi-layer systems used for acoustic insulation (for example, metal sheets with damping plastic layers or sandwich constructions). Measurements can be made as a function of temperature and frequency to characterise viscoelastic behaviour.
Key topics and technical requirements
- Principle: Forced flexural vibration is applied and resonance curves are recorded to derive the flexural complex modulus and damping parameters.
- Test apparatus: Includes clamps or suspension fibres, an exciter and detector, a temperature‑controlled enclosure, gas supply (if required), temperature sensors and devices for precise specimen dimension measurement.
- Specimens: Requirements for specimen shape, dimensions, preparation, number of specimens and conditioning are specified to ensure repeatability.
- Measurement procedures: Guidance on mounting (Methods A and B), transducer adjustment, varying temperature and frequency, and recording resonance curves.
- Data and calculations: Derivation of flexural storage modulus (E' f ), flexural loss modulus (E'' f ), and loss factor (tan δf ), plus plotting complex modulus versus temperature/frequency.
- Precision and validation: Precision statements, interlaboratory testing guidance (informative Annex A) and requirements for reporting test results.
- Normative references: Includes density measurement methods (ISO 1183 series) and ISO 6721-1 (general principles for dynamic mechanical properties).
Applications
- Characterising viscoelastic and damping performance of plastics, coated metals, and sandwich panels used in noise and vibration control.
- Evaluating material behaviour across temperature and frequency ranges for product design, acoustic insulation, automotive, aerospace and building applications.
- Quality control and acceptance testing during production of damping layers, laminated composites and hybrid metal–plastic systems.
- Research & development for new polymers, formulations and laminate constructions where flexural damping is critical.
Who should use this standard
- Materials testing laboratories and calibration facilities conducting dynamic mechanical analysis (DMA) by flexural vibration.
- Polymer scientists, acoustic engineers, product designers and manufacturers of damping systems and sandwich panels.
- Certification bodies and standards committees needing harmonised test procedures for elastic and damping properties.
Related standards
- ISO 6721-1 - Plastics: Determination of dynamic mechanical properties - General principles
- ISO 1183-1 / -2 / -3 - Methods for determining density of non-cellular plastics
Keywords: EN ISO 6721-3:2021, flexural vibration, resonance-curve method, dynamic mechanical properties, flexural complex modulus, damping properties, plastics testing, storage modulus, loss factor, temperature dependence.