Torsion pendulum test

There are several other comparable rheological experimental methods involving linear viscoelastic behavior. Among them are creep tests (constant stress), dynamic mechanical fatigue tests (forced periodic oscillation), and torsion pendulum tests (free oscillation). Viscoelastic data obtained from any of these techniques must be consistent data from the others. 

Torsion property As noted, the shear modulus is usually obtained by using pendulum and oscillatory rheometer techniques. The torsional pendulum (ASTM D 2236 Dynamic Mechanical Properties of Plastics by Means of a Torsional Pendulum Test Procedure) is a popular test, since it is applicable to virtually all plastics and uses a simple specimen readily fabricated by all commercial processes or easily cut from fabricated products. 

Dynamic-Mechanical Measurement. This is a very sensitive tool and has been used intensively by Nielsen (17) and by Takayanagi (18). When the damping curves from a torsion pendulum test are obtained for the parent components and for the polyblend and die results are compared, a compatible polyblend will show a damping maximum between those of the parent polymers whereas the incompatible polyblend gives two damping maxima at temperatures corresponding to those of the parent components. Dynamic mechanical measurement can also give information on the moduli of the parent polymer and the polyblend. It can be shear modulus or tensile modulus. If the modulus-temperature curve of a polyblend locates between those of the two parent polymers, the polyblend is compatible. If the modulus-temperature curve shows multiple transitions, the polyblend is incompatible. 

The lowest temperature 6 peak appears at approximately -160 C in the vibrating reed measurement whereas only the onset of 6 relaxation can be seen near -18O C in the torsional pendulum test. As discussed below, this peak is not present in the Nafion acid or in its salt membranes in both mechanical and dielectric measurements. 

Part of the work performed on a sample will be converted irreversibly into random thermal motion by movement of the molecules or molecule segments. This loss passes through a maximum at the appropriate transition temperature or relaxation frequency in the associated alternating mechanical field (torsion pendulum test). A similar effect is obtained by the delayed response of the dipoles with dielectric measurements. Therefore, dielectric measurements can be made only on polar polymers. According to the... 

By applying free damped vibrations in torsion pendulum testing the mechanical vibration damping can be expressed in terms of the logarithmical decrement A which can be expressed as the ratio of two sequent amplitudes according to equation 3.13. 

When specimen is deflected from its equilibrium state by pulsed deformation, it returns to its state of equilibrium in free damped vibrations. The natural frequency of vibration, as well as the decrease of vibration amplitude with time, depends on the viscoelastic properties of the material. The principle of free damped vibrations has its practical application in torsion pendulum testing according to ISO 6721-2. The storage modulus G, the loss modulus G" and the loss factor tan S can be determined at frequency ranges from 10 Hz to 10 Hz. 

Table 3.7 G values from torsion pendulum testing according to DIN 53445 and ISO 6721-2, TC test conditions.

DIN 53445 Testing of polymer materials - Torsion pendulum test (withdrawn replaced by ISO (1986) 6721 2011)... 

Figure 2.39 Shear modulus vs. temperature (DIN 53 455 torsion pendulum test) for Styrolution Terlux 2802 TR MASS resin [4],...

Figure 2.50 Mechanical damping vs. temperature for Styrolution Luran S 778 T and Luran S KR 2863 C (ISO 537 torsion pendulum test) [5].

Figure 3-3. Torsion pendulum. Test equipment (schematic). (Reprinted with permission of McGraw-Hill Company.)...

Even though torsion pendulum tests run at elevated temperatures provide very useful information regarding the dynamic mechanical properties of plastics, one must not forget that it is, nevertheless, a short-term test. The data obtained from creep modulus and creep rupture tests conducted at elevated temperatures must be relied on for long-term effects. 

Glass transition temperature (DSC Test, 2nd heating cycle) Vulcanizate properties 65-75 Shore A Torsion pendulum test DIN 53445 (°C)... 

Fig. U. Shear modulus (G) and logarithmic decrement ( 4) vs. temperature, measured by torsion pendulum test DIN 53445, ISO/R537.

Two common types of dynamic tests are the torsional pendulum test and the vibrating reed test shown in Figure 2.10a and b. The first measures a shear response (a dynamic... 

FIGURE 2.10 Two common dynamic tests, (a) Torsional pendulum test and (b) vibrating reed test. (From Nielsen, L. E., Mechanical Properties of Polymers and Composites, Vol. 1, pp. 11-17, Marcel-Dekker, Inc., New York, NY, 1974.)... 

---