ISO 6721-5:2019

Overview

ISO 6721-5:2019 - Plastics: Determination of dynamic mechanical properties - Part 5: Flexural vibration - Non‑resonance method specifies a flexural, non‑resonance test to determine the components of the flexural complex modulus (Ef*) of polymers. The method covers measurements typically from 0.01 Hz to 100 Hz, with reliable storage modulus measurement over 10 MPa to 200 GPa. It is especially suited to measuring loss factors (tan δ) > 0.02 and for studying temperature‑ and frequency‑dependent behaviour through the glass‑rubber relaxation region. Data can be used to construct master plots via frequency/temperature shift procedures.

Key topics and technical requirements

• Test principle: Apply a sinusoidal transverse force or displacement well below the specimen’s fundamental flexural resonance; measure force and displacement amplitudes and phase angle to calculate storage modulus (E′), loss modulus (E″) and loss factor (tan δ).
• Frequency and modulus ranges: Typical frequency range 0.01 Hz–100 Hz; storage modulus range 10 MPa–200 GPa. Note that higher frequencies risk significant measurement error.
• Specimen geometry: Rectangular cross‑section recommended; width and thickness variation ≤ 2% of mean. Recommended aspect ratios to minimize shear/anticlastic effects: L/h > 16 (clamped), L/h > 8 (simply supported); L/b > 6 (clamped), L/b > 3 (simply supported).
• Apparatus:
  • Loading assembly options (clamped or simply supported three‑point flexure).
  • Transducers for force and displacement with calibration traceable to national standards; calibration accuracy ±2% of minimum applied amplitudes.
  • Data acquisition accuracy: amplitude ±1%, phase angle ±0.1°, frequency ±10%.
  • Temperature measurement and control per ISO 6721‑1.
• Corrections and precautions: Avoid specimen resonance (see clause on resonance avoidance); apply corrections for transducer resonance, apparatus compliance, and specimen length where required.
• Measurement precision and reporting: Calculations and test report requirements include symbols, formulae, and procedures for presenting temperature‑dependent data and precision estimates.

Applications and who uses it

• Materials scientists and polymer R&D teams for characterizing viscoelastic behaviour of plastics.
• Quality control and product development labs for validating dynamic mechanical properties (storage modulus, loss factor).
• Designers using master curves for predicting long‑term mechanical behaviour across temperatures and frequencies.
• Instrument manufacturers and calibration laboratories to ensure compliance and traceability of dynamic mechanical analysis (DMA) equipment.

Related standards

• ISO 6721-1 - Plastics - Determination of dynamic mechanical properties - General principles (temperature control, terminology).
• ISO 6721-6 - Shear modes for low‑modulus materials (recommended for materials with modulus < 10 MPa).
• Other parts of the ISO 6721 series for complementary DMA methods and guidance.

Keywords: ISO 6721-5:2019, flexural vibration, non‑resonance method, plastics, dynamic mechanical properties, flexural complex modulus, storage modulus, loss factor, DMA.