Torsion pendulum, automated

Fig. 2. Automated torsion pendulum schematic. An analog electrical signal results from using a light beam passing through a pair of polarizers, one of which oscillates with the pendulum. The penduluin is aligned for linear response and initiated by a computer that also processes the damped waves to provide the elastic modulus and mechanical damping data, which are plotted vs. temperature or time...

Automated Torsion Pendulum Control and Data Collection/Reduction Using a Desktop Computer... 

The purpose of this paper is to describe an automated torsion pendulum controlled by a desktop computer, to discuss four separate methods of data analysis, and to compare the results of a torsion pendulum experiment and a TBA experiment using the same epoxy resin. 

Figure 2. Automated torsion pendulum system schematic for interfacing with a...

Figure 4. Automated torsion pendulum control sequence. Key 1, previous wave decays, drift detected and correction begins II, reference level of polarizer pair reached III, wave initiating sequence begins. IV, decay of transients V, free oscillations begin VI, data collected and VII, control sequence repeated.

Discussion. The four methods of data reduction were used to analyze the raw data of the same TBA specimen during a slow (0.25°C/min) temperature scan (Figure 8). A comparison of the spectra indicates that they all gave similar results over the range of period (0.3 to 1.8 sec) and logarithmic decrement (0.01 to 1.08) encountered in the experiment. (The automated torsion pendulum has been used to reduce data with a range of 0.1 to 15 sec. for the period, and 0.001 to 4.0 for the... 

These results were measured with an automated torsion pendulum apparatus. A rectangular sample strip of 50 x 10 x 1 mm. acted in combination with a steel suspension wire and a rotating mass as a visco-elastic spring. The measurements were performed while the sample temperature continously increased at a rate of l°C/minute. The storage shear (6 ) modulus and the loss shear (G ) modulus were determined from the free, damped vibrations (frequency about 0.5 Hz.) according to (4) ... 

The measurements were performed with an automated torsion pendulum (DMA) apparatus working at a frequency of about 0.5 Hz. (varying frequency system, see Chapter 4). The use of a low-stiffness suspension wire permitted stiffness measurements as low as 5H4 N/m2. These DMA measurements were performed from 50°C up to 250°C using a heating rate of l°C/minute the samples were, during these experiments, purged with nitrogen. 

Winberg et al. [2005] investigated how the incorporation of clay into PA-6 affects the free-volume cavity size and the viscoelastic properties. The CPNC contained 4 to 35 wt% C20A. DMA tests were performed using an automated torsion pendulum while heating at 2°C/min from 173 to 473 K at 1 Hz. The authors reported enhancement of E with clay content (i.e., E = 1.3 to 1.6 at Tloss modulus, E" increased with increasing clay content. 

Dynamic shear moduli are conveniently determined with automated equipment, for instance, with the torsion pendulum. However, moduli derived from dynamic tests are often higher than the results from static tests for lack of relaxation. Examples are shown in Table 3.3. Young s moduli of the polymers A, B, C, D, derived from tensile tests (frequency 0.01 Hz) are compared with shear moduli S determined with the torsion pendulum (frequency > 1 Hz). For rubberlike materials is 3S/E = 1, according to Eq. 

A torsion pendulum interfaced with a desktop computer form an automated instrument for dynamic mechanical characterization of polymeric materials. The computer controls the initiation of the oscillations, collects the digitized data and calculates the shear modulus and loss modulus from the damped oscillations, utilizing one of four methods of analysis ... 

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. 

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