BS ISO 6721-6:2019 download.Plastics-Determination of dynamic mechanical properties.
Plastics — Determination of dynamic mechanical properties — Part 6:
Shear vibration — Non-resonance method
1 Scope
BS ISO 6721-6 describes a forced, non-resonance method For determining the components of the shear complex modulus G’ of polymers at frequencies typically in the range 0.01 Hz to 100 Hz. Higher- frequency measurements can be made, but significant errors in the dynamic properties measured are likely to result (see 1D22 and 1O23). The method is suitable for measuring dynamic storage moduli in the range 0,1 MPa to SO MPa.
NOTE Although materials with modull greater than 50 MPa can be studied, more accurate measurements of their dynamic shear properties can be made using a torsional made of deformation (we ISO 6721-2 and b7ZI).
This method is particularly suited to the measurement of loss factors greater than 0,02 and can therefore be conveniently used to study the variation of dynamic properties with temperature and frequency through most of the glass-rubber relaxation region (see I 0h721- ). The availability of data determined over wide ranges of both frequency and temperature enables master plots to be derived. using frequency/temperature shift procedures, which display dynamic properties over an extended frequency range at different temperatures
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dared references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
150 6721-1. Plastics — Determination of dynamic mechanical properties — Part 1: General principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in 15L06221i apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses
4 PrInciple
A test-specimen assembly is subjected to a sinusoidal shear force or deformation at a frequency significantly below the fundamental shear resonance frequency (see 102.2). The amplitudes of the force and displacement cycles applied to the test-specimen assembly and the phase angle between these cycles are measured. The storage and loss components of the shear complex modulus and the loss factor are calculated using formulae given in Clause 10.
5.2 Hectronlc data-processing equipment
Data-processing equipment shall be capable of recording the force and displacement cycle amplitudes to an accuracy of ± 1 %, the phase angle between the force and displacement cycles to an accuracy of *0,1° and the frequency to an accuracy oft 10 %.
5.3 Temperature measurement and control According to ISO 6721-L
5.4 Devices for measuring test specimen dimensions According to 150 6721.1.
6 Test specimens
6.1 General
According to ISO 672 1-1.
6.2 Shape and dimensions
Various shear test specimen assemblies can be used. A suitable design is shown in Eigu.tL2. Here the metal end-pieces P are cylindrical, but any cross-sectional shape Is suitable as long as the end-pieces can be clamped rigidly in the shear load stage. The dimensions of the end-pieces and the polymer specimens S shall be chosen such that the deformation of the end-pieces under an applied load is negligible in comparison with that of the specimens. For a polymer whose shear modulus is less than 100 MPa, this wiLl mean that the thickness of the end-pieces may be comparable with the thickness I of the specimens.
The cross-sectional shape of the polymer specimens in the plane of their bonded faces is not critical. although a rectangular section is recommended In order to simpLify the application of a term representing the contribution to the specimen deformation from bending. See Eormula(1).
The specimens are typically cut from a sheet of the polymer and bonded to the end-pieces to construct the shear test-specimen assembly. The dimensions of each polymer specimen shall not vary by more than 3 % of the mean value. This dimension shall be sufficiently large to allow adequate accuracy to be achieved in the determination of dynamic strain and hence dynamic moduil Isee Eurmulai.1jI. In addition, It is recommended that the dimension h of the polymer in the direction of the applied load should be greater than 4L In order to make the correction for bending negligible.
NOTE A variation In dynamic properties can be observed between specimens of different thickness prepared by injection moulding owing to differences which can be present in the structure of the polymer in each specimen.
6.3 Preparation of polymer specimens According to ISO 6721.1.
7 Number of test specimens
According to iSD22.1d.
8 ConditionIng
According to ISD.h2211.
9 Procedure
9.1 Test atmosphere According to ISO 6721.L
9.2 MeasurIng the cross-section of the polymer specimen According to ISO 6721-1.
9.3 ClampIng the Lest assembly
Mount the test specimen assembly in the load stage using a damping 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 150.6221:1.
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 £,L.
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 oIO,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 sec 1S0.62Z11).
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 equlpement 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
bonded area of the specimens, in square metres
measurement frequency. In hertz
IF resonance frequency of the force transducer, In hertz
Is resonance frequency of the lest-sped men. In hertz
Ca. 6’ assembly apparent and corrected shear storage modulus, In pascals
C” shear loss modulus. In pascats
h mean of the specimen heights, in metres. in the direction of the applied load
ka. k measured and corrected magnitude of the complex stiffness of the test-specimen assembly, in newtons per metre
stiffness of the force transducer, in newtons per metre
k0, measured stiffness of a metal bar, in newtons per metre. whose cross-sectional dimensions are the same as those of the end-pieces of the shear test-specimen assembly (see Note), This bar shall be at least 100 times stiffer than the stiffest polymer specimen to be tested
L mean of dimension of each polymer specimen between bonded laces, in metres m mass of that part of the loading assembly between the force transducer and the test-specimen assembly, in kilograms
5A measured amplitude of the dynamic displacement, in metres
tan öGa. tan 66 apparent and corrected shear loss factor
66 measured and corrected phase difference, in degrees, between the force and displacement cycles
FA measured amplitude of the dynamic force, in newtons
NOTE The magnitude of k, will give an estimate of the stiffness of the loading assembly which is equivalent to a spring connected In series with the shear test-specimen assembly and will enable a correction for apparatus compliance to be deduced (see 1fl2A)
10.2 Calculation of the shear storage modulus C’
10.2.1 General
An approximate value for the shear storage modulus G’ Is determined from Formula (1).