EUROLAB, with its state-of-the-art accredited laboratories and expert team, provides precise and fast testing services within the scope of EN ISO 6721-1 testing. Various parts of ISO 6721 specify methods for determining the dynamic mechanical properties of rigid plastics within the linear viscoelastic behavior region.
This section of ISO 6721 is an introductory section containing definitions and all aspects common to individual test methods described in the following sections.
Different deformation modes can produce results that are not directly comparable. For example, tensile vibration results in a stress that is uniform across the entire thickness of the sample, while bending measurements are preferably influenced by the properties of the surface regions of the sample.
The values obtained from the bending test data will only be comparable to the values obtained from the tensile test data for samples with a homogeneous structure and at strain levels where the stress-strain relationship is linear.
The methods outlined in the first nine sections of ISO 6721 can be used to determine the storage and loss modulus of plastics over a range of temperatures or frequencies by varying the temperature of the sample or the frequency of oscillation. Drawings of storage or loss modules, or both, are indicative of the viscoelastic properties of the sample.
Regions of rapid change in viscoelastic properties at certain temperatures or frequencies are normally referred to as transition regions. Also, from the temperature and frequency dependencies of the loss modulus, the sound and vibration damping of polymer or metal-polymer systems can be predicted.
Significant differences may arise in the results obtained under different experimental conditions. Without changing the observed data, full reporting of the conditions under which the data were obtained (as described in various parts of ISO 6721) will reconcile significant observed differences.
The complex module definitions are fully valid for sinusoidal oscillations of constant amplitude and constant frequency during each measurement. On the other hand, measuring small phase angles between stress and strain under these conditions presents some difficulties. These methods are often used because these difficulties are not contained in some methods that rely on freely decreasing vibrations or varying frequencies close to resonance.
In these cases, some equations describing viscoelastic properties are only approximately valid. The complex module definitions are fully valid for sinusoidal oscillations of constant amplitude and constant frequency during each measurement.
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