BS ISO 6721-6:2019 pdf free download – Plastics一Determination of dynamic mechanical properties.
9 Procedure
9.1 Test atmosphere
According to ISO 672 1-1.
9.2 Measuring the cross-section of the polymer specimen According to ISO 6721-1.
9.3 Clamping the test assembly
Mount the test specimen assembly in the load stage using a clamping force that is sufficient to prevent relative movement between each clamp and the associated end-piece under all test conditions.
9.4 Varying the temperature According to ISO 672 1-1.
9.5 Performing the test
Apply to the shear test-specimen assembly a dynamic force which yields force and displacement signal amplitudes which can be measured by the transducers to the accuracy specified in 5.1.3.
If the shear strain exceeds the limit for linear behaviour, then the derived dynamic properties will depend on the magnitude of the applied strain. This limit varies with the composition of the polymer and the temperature, and is typically in the region of 0,2 % for glassy plastics, but the effect is evident at very low dynamic strains in carbon-particle-filled rubbers. The dynamic strain range for linear behaviour can be explored by varying the dynamic displacement amplitude at a constant frequency and recording any change in dynamic stiffness with strain amplitude. A low frequency should be used for this purpose to minimize any temperature increase caused by mechanical loss. If nonlinear behaviour is detected in the strain range of interest, the dynamic strain limit should be recorded in the test report.
Record the amplitudes of the phase difference between and the frequencies of the force and displacement signals, as well as the temperature of the test. Where measurements are to be made over ranges of frequency and temperature, it is recommended that the lowest temperature be selected first and measurements made increasing frequency, keeping the temperature constant. The frequency range is then repeated at the next higher temperature (see ISO 672 1-1).
For test conditions under which the polymer exhibits medium or high loss (for example in the glass- rubber transition region), the energy dissipated by the polymer may raise its temperature sufficiently to give a significant change in dynamic properties. Any temperature rise will increase rapidly with increasing strain amplitude and frequency. If the data-processing equipement is capable of analysing the transducer outputs within the first few cycles, then the influence of any temperature rise will be minimized. Subsequent measurements will then change with time as the specimen temperature continues to rise, and such observations will indicate the need to exercise some caution in the presentation and interpretation of results.
10 Expression of results
10.1 Symbols.