ISO 6721-7:2019

Overview

ISO 6721-7:2019 specifies a torsional, non‑resonance method for determining the components of the shear complex modulus G* of solid polymers (bars or rods). The method measures torque and angular displacement amplitudes and the phase angle between them to calculate the shear storage modulus (G′), shear loss modulus (G″) and loss factor (tan δ) over a typical frequency range of 0.001 Hz to 100 Hz. It is tailored to study temperature- and frequency-dependent viscoelastic behaviour across glass–rubber relaxation regions and to generate master plots using frequency–temperature shift procedures.

Key topics and requirements

• Measurement principle: Apply sinusoidal torque or angular displacement well below the specimen’s torsional resonance and record torque, displacement and phase.
• Frequency & modulus ranges: Typical frequencies 0.001–100 Hz; suitable for G′ from about 10 MPa to 10 GPa. Higher frequencies are possible but can introduce significant errors.
• Specimens: Rectangular bars or cylindrical rods; cross‑section variation along length ≤ 2%. Clamps should prevent slippage and allow small separation adjustments to accommodate thermal expansion.
• Instrumentation & accuracy:
  • Transducer calibrations traceable to national standards; accuracy ±2% of minimum applied amplitudes.
  • Data acquisition accuracy: amplitude ±1%, phase angle ±0.1°, frequency ±10%.
• Corrections & calculations: Procedures described for avoiding specimen resonance, correcting for transducer resonance, apparatus compliance, and applying length corrections when needed (see Clause 10).
• Temperature control: Tests reference general principles in ISO 6721‑1 for temperature measurement and conditioning.
• Sensitivity: Particularly suitable for loss factors > 0.02. For very low loss factors (<0.1) torsion pendulum methods (ISO 6721‑2) may be more accurate.

Applications and users

• R&D and quality‑control laboratories performing dynamic mechanical analysis of plastics, rubbers and fibre‑reinforced composites.
• Materials scientists studying viscoelastic transitions (glass–rubber relaxations) and building master curves over wide frequency/temperature ranges.
• Manufacturers and suppliers of polymer products and test equipment who need standardized, traceable shear modulus and damping data.
• Certification bodies and materials databases requiring ISO‑compliant dynamic mechanical property data.

Related standards

• ISO 6721‑1 - General principles for dynamic mechanical property determination (temperature, terms).
• ISO 6721‑2 - Torsion pendulum method (recommended for very low loss factors).
• ISO 6721‑6 - Simple shear method (for lower modulus materials and thin layers).

Keywords: ISO 6721-7:2019, torsional non-resonance method, plastics dynamic mechanical properties, shear complex modulus G*, shear storage modulus G′, loss factor tan δ, torsional vibration testing.