ISO 6721-4:2019

Overview

ISO 6721-4:2019 specifies a forced, non‑resonance tensile vibration method for determining the components of the tensile complex modulus (E*) of plastics. The standard covers measurement of dynamic storage modulus (E′) and loss factors (tan δ) for polymers typically over frequencies from 0.01 Hz to 100 Hz and storage moduli in the range 0.01 GPa to 5 GPa. It is particularly suited to studying viscoelastic behaviour through the glass–rubber relaxation region and to producing master plots using frequency–temperature shift procedures.

Key topics and technical requirements

• Test principle: Apply a sinusoidal tensile force or displacement well below the specimen’s fundamental resonance; measure force and displacement amplitudes and their phase angle to calculate E′ and tan δ.
• Frequency & modulus ranges: Typical frequency 0.01–100 Hz; suitable storage modulus 0.01–5 GPa. Higher frequencies or outside-range moduli can produce significant errors.
• Apparatus:
  • Loading assembly with stiff, low-thermal-conductance members and accurate clamps.
  • Force and displacement transducers with calibrations traceable to national standards (accuracy ±2% of minimum applied amplitudes).
  • Data acquisition capable of recording amplitudes to ±1%, phase angle to ±0.1°, and frequency to ±10%.
• Specimens: Rectangular cross-section recommended; width and thickness variation ≤3% along length; specimen length between clamps usually >6× width; clamp separation of 50–100 mm recommended for high accuracy.
• Corrections & cautions:
  • Avoid specimen resonance (clamped/free longitudinal mode).
  • Apply corrections for transducer resonance, apparatus compliance and specimen length where required.
  • Control and measure temperature per ISO 6721-1 to enable frequency–temperature shifting.
• Output: Storage modulus E′, loss factor tan δ, and loss modulus; presentation of dynamic properties versus temperature and frequency, enabling master curves.

Applications

• Characterizing viscoelastic and damping behaviour of plastics across glass–rubber transitions.
• Material selection, formulation development and comparison of polymer grades.
• Generating input data for viscoelastic modelling, finite-element simulations and lifetime predictions.
• Quality control and R&D testing in polymer processing, automotive, consumer goods, and industrial applications.

Who should use this standard

• Polymer scientists, materials engineers and testing laboratories.
• R&D teams in plastics formulation and product development.
• Quality assurance professionals requiring standardized dynamic mechanical property data.

Related standards

• ISO 6721-1 - General principles for dynamic mechanical properties
• ISO 6721-3 / ISO 6721-5 - Flexural modes for higher stiffness materials
• ISO 6721-6 - Shear mode for very low modulus materials

Keywords: ISO 6721-4:2019, tensile vibration non-resonance, plastics dynamic mechanical properties, tensile complex modulus E*, storage modulus E′, loss factor tan δ, frequency–temperature shift, master curves.