ISO 6721-2:2019 pdf free.Plastics一Determination of dynamic mechanical properties -Torsion-pendulum method.
4 Principle
A test specimen of uniform cross-section is gripped by two clamps, one of them fixed and the other connected to a disc, which acts as an inertial element, by a rod. The end of the specimen connected to the disc is excited, together with the disc, to execute freely decaying torsional oscillations. The oscillation mode is that designated IV in Iso 6721-1, and the type of modulus is G0 as defined in ISO 6721-1. The inertial element is suspended either from the specimen (method A, see Figure 1) or from a wire (method 13, see Figure 2). In the latter case, the wire is also part of the elastically oscillating system.During a temperature run, the same inertial element can be used throughout the whole run, which results in a frequency decreasing naturally with increasing temperature, or the inertial element can be replaced at intervals by a member of different moment of inertia in order to keep the frequency approximately constant. During the test, the frequency and the decaying amplitude are measured. From these quantities, the storage component G0 and loss component G0 of the torsional complex modulus G0 can be calculated.
5 Test apparatus
5.1 Pendulum
Two types of torsion pendulum are specified for use with this document:
a) the inertial element is suspended from the test specimen and the lower end of the specimen is excited (method A, Figure 1)
b) the inertial element is suspended from a wire attached to a counterweight and the upper end of the specimen is excited (method B, Figure 2).
Both types of pendulum consist of an inertial element, two clamps for gripping the specimen (one of which is connected to the inertial element by a rod) and a temperature-controlled chamber enclosing the specimen and the clamps. For method B, a counterweight and connecting wire are also required.
5.2 Inertial element
5.2.1 General
The moment of inertia, 1, of the inertial element, which may be made of aluminium, for instance, shall be selected as a function of the torsional stiffness of the specimen, so that the temperature-dependent natural frequency of the system lies between approximately 0,1 Hz and 10 Hz.
When testing standard specimens (see &Z), a moment of inertia, I, of about 3 x 10 kgm2 is recommended if the same inertial element is to be used throughout a run.
NOTE For certain materials, e.g. filled polymers, a value of! of about 5 x 10 kg.m2 can be necessary.
If a constant frequency is desired over a broad temperature range, interchangeable inertial elements with different values of I may be used, thereby permitting the moment of inertia to be varied in steps of less than 20 %, i.e. the frequency to be corrected in steps of less than 10 %. When testing standard specimens (see 2) at a frequency of about 1 Hz, a maximum moment of inertia of about 3 x 10-s kgm2 is recommended.
5.2.2 Method A (see Figure 1)
The total mass of the inertial element, the lower clamp and the connecting rod shall be such that the weight, W, carried by the specimen is not too high [according to Annex A, Formula (A.2)J.
5.2.3 Method B (see Figure 2)
The total mass of the inertial element, the upper clamp and the rod must be balanced by a suitable counterweight, so that the longitudinal force, W, acting on the specimen is minimized [according to Annex A. Formula (A,2)1. The wire supporting these parts is part of the elastically oscillating system.
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