Torsion pendulum technique

The automation of the torsion pendulum utilizing a desktop computer eliminates the tedious data analysis previously associated with that technique. Any one of four data reduction methods can be used the experimental conditions will determine which is the optimum one to employ. The torsion pendulum technique provides quantitative values of shear modulus and logarithmic decrement and in the torsion braid mode provides a qualitative analysis of materia i, especially in the liquid-to-solid transition region. 

Sai] Inverted torsion pendulum technique, infinred analysis of C using a high frequency combustion technique Internal friction cold rolled C-Fe-Si samples with small amount of Si (0.050 to 0.832 mass%) and C (0.45 to 0.47 mass%) and decaburization annealing at 700°C... 

Characterization and evaluation of performance by means of the torsional pendulum technique has been discussed by Hussain Wierenga et al. have used ultramicro indentation measurements for the determination of the viscoelastic properties of coated optical fibers... 

Many different experimental techniques exist today to study the effects of elevated temperature on dynamic mechanical properties of plastics. Perhaps, the most meaningful and simplest technique is the torsion pendulum technique. Using this technique, one can derive a plot of short-time modulus versus temperature up to the beginning of melting and degradation. 

As discussed in section 15. 4.1, the shear modulus of fibers is important, and it determines the fiber torsional rigidity. The shear modulus of a fiber can be measmed by using the torsion pendulum technique. Figure 15.32 shows the schematic of a... 

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. 

One of most popular techniques for dynamic mechanical analysis is the torsion pendulum method. In a modification of this method designed to follow curing processes, a torsion bar is manufactured from a braid of fibers impregnated with the composition to be studied this is the so-called torsional braid analysis (TBA) method.61 62,148 The forced harmonic oscillation method has been also used and has proven to be valuable. This method employs various types of rheogoniometers and vibroreometers,1 9,150 which measure the absolute values of the viscoelastic properties of the system under study these properties can be measured at any stage of the process. The use of computers further contributes to improvements in dynamic mechanical analysis methods for rheokinetic measurements. As will be seen below, new possibilities are opened up by applying computer methods to results of dynamic measurements. 

Various types of vibration experiments can be carried out to measure E and E2 at a certain frequency. An example is the torsion pendulum, in which the sample, connected to an auxiliary mass, is brought into a free torsional oscillation. From the frequency of the pendulum (around 1 to 10 sec) E is calculated, from the rate of damping tan 8 and E2. Other types of dynamic mechanical measurements can be carried out at higher frequencies, such as bending vibrations with or without extra mass, wave propagation, etc. By combining a number of these different techniques, a time scale ranging from 10 to 10"8 sec can be covered. 

Some experimental techniques yield a modulus rather than a sound speed, but the underlying physical properties are the same. In a torsional pendulum, for example, the shear modulus, G, is measured while in a Rheovibron, Young s modulus, E, is measured. When there... 

The results of the characterization of cured phthalonitrile resins are presented. This includes their thermal properties from thermal gravimetric analysis and differential scanning calorimetry, spectroscopic properties from the infra-red and nuclear magnetic resonance techniques, and mechanical properties from torsional pendulum analysis and fracture mechanics evaluation. 

The methods used in this study are mainly the drop and bubble shape technique and the torsion pendulum rheometry. The drop and bubble shape technique, which is based on fitting the shape of an axisymmetric liquid meniscus to the respective Gauss Laplace equation, allows to continuously monitor the... 

Dynamic Mechanical Analysis (DMA) is a technique in which the elastic and viscous response of a sample under oscillating load, are monitored against temperature, time or frequency. This technique became well known by the impressive amount of information about the structure of polymers obtained with the torsion pendulum apparatus. The torsion pendulum DMA apparatus is a so-called resonant system i.e. the measuring frequency is not constant. The modern DMA systems are nearly always fixed frequency systems operating at frequencies between about 0.01 and 100 Hz. and in a temperature region ranging from about -150°C to 300°C. A survey of the DMA technique and the available commercial equipment was given by Wunderlich [1]. 

Since the early DM work on metals with unautomated torsion pendulum systems [21], few papers have been published, perhaps because of the limited temperature range available. In 1989 Duncan presented some DM traces on common metals to 800 C [124]. Glass has had a couple of papers recently. Of the major glass companies in Europe, only Schottglas use this technique to my knowledge, and of the few published papers in the open literature Hill [35] and Boeder et al. [36] are examples. Hill showed that liquid-liquid phase separation prior to crystal nucleation and real time studies of the kinetics of crystal-ization could be studied in glass ceramics, and activation energies could be matched to... 

A comparison of experimental techniques is essential for understanding the slight differences in the results. The maximum in G" at 0.2 Hz was taken as Tg in the torsional pendulum study. The DSC scanning rates were 10 C/min. Since a factor of 10 in the frequency raises Tg about 6-7 C, if the torsional pendulum frequency had been increased from 0.2 Hz to about 1.0 Hz, the values in Table 6.9 would be predicted to match virtually identically. (Raising the temperature at TC/min, in volume-temperature studies often matches shear modulus studies using 10 sec or 0.1 Hz as the deformation time.)... 

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