Testing Principle
International standardization of plastics testing provides a unified framework for determining the dynamic mechanical properties of polymeric materials. The document designated as ISO 6721-1 establishes the general principles and introductory concepts for these measurements. It outlines the methodologies used to apply non-destructive sinusoidal forces to specimens under controlled thermal and frequency conditions.
Measurement Protocol
The standard describes the mathematical relationships used to calculate the storage modulus, the loss modulus, and the loss factor from the observed force and displacement. These parameters describe the ability of a polymer to store elastic energy and to dissipate energy as heat during cyclic deformation. Accurate determination of these properties requires precise control of the specimen geometry, as minor dimensional variations can introduce large errors in the calculated modulus.
The document mandates specific test configurations, including tension, compression, and torsion, each tailored to different stiffness ranges of the material under evaluation.
Calibration Mandate
Dynamic mechanical analyzers must undergo rigorous calibration of force, displacement, and temperature to comply with the standard. Thermal calibration requires using reference materials with known transition temperatures, such as indium, measured at the same heating rate as the test specimen. Force and displacement transducers are verified using precision calibration blocks and reference springs provided by the instrument manufacturer.
Operational Bound
The guidelines specified in the document assume that the specimen exhibits linear viscoelastic behavior during the test. If the strain amplitude exceeds the linear viscoelastic limit of the polymer, the calculated moduli become strain-dependent and the mathematical equations lose validity. The temperature range of the test is also bounded by the thermal degradation limits of the material.
