Dynamic-mechanical analyzer

Dynamic Mechanical Analyzer DMA7 C 10-"-50 Perkin-Ehner Corp., Norwalk, Conn. 

Anonymous. DMA 983 Dynamic Mechanical Analyzer. Brochure. New Castle, DE TA Instruments 1995. 

A torsional pendulum (Figure 5.80) is often used to determine dynamic properties. The lower end of the specimen is clamped rigidly and the upper clamp is attached to the inertia arm. By moving the masses of the inertia arm, the rotational momentum of inertia can be adjusted so as to obtain the required frequency of rotational oscillation. The dynamic shear modulus, G, can be measured in this manner. A related device is the dynamic mechanical analyzer (DMA), which is commonly used to evaluate the dynamic mechanical properties of polymers at temperatures down to cryogenic temperatures. 

Another resonant frequency instrument is the TA Instmments dynamic mechanical analyzer (DMA). A bar-like specimen is clamped between two pivoted arms and sinusoidally oscillated at its resonant frequency with an amplitude selected by the operator. An amount of energy equal to that dissipated by the specimen is added on each cycle to maintain a constant amplitude. The flexural modulus, E is calculated from the resonant frequency, and the makeup energy represents a damping function, which can be related to the loss modulus, E". A newer version of this instrument, the TA Instruments 983 DMA, can also make measurements at fixed frequencies as well as creep and stress—relaxation measurements. 

Fig. 45. TA Instmments DMA 2980 dynamic mechanical analyzer. Courtesy of TA Instmments, Inc.

Fig. 46. Schematic diagram of a dynamic mechanical analyzer based on the nonresonance-forced vibration principle (Rheovibron-type).

The phase separation behavior during curing of polyetherimide (PEI) modified diglycidyl ether of bisphenol A (DGEBA) epoxy and PEI modified bisphenol A dicyanate (BPACY) were studied using SEM, light scattering, and dynamic mechanical analyzer. 

Tg of blend was measured at the scan rate of 5°C/min by Dynamic Mechanical Analyzer (Du Pont DMA 981), which was a resonant frequency measuring type. Tgs were determined by the peaks of the loss modulus peaks. 

The physical properties of barrier dressings were evaluated using the Seiko Model DMS 210 Dynamic Mechanical Analyzer Instrument (see Fig. 2.45). Referring to Fig. 2.46, dynamic mechanical analysis consists of oscillating (1 Hz) tensile force of a material in an environmentally (37°C) controlled chamber (see Fig. 2.47) to measure loss modulus (E") and stored modulus (E ). Many materials including polymers and tissue are viscoelastic, meaning that they deform (stretch or pull) with applied force and return to their original shape with time. The effect is a function of the viscous property (E") within the material that resists deformation and the elastic property (E )... 

Fig. 2.45 Seiko model dynamic mechanical analyzer, the operator s finger is touching the test specimen between grips...

Dynamic mechanical analyzers can further be divided into free resonance analyzers and forced resonance analyzers. In the case of free resonance analyzers, samples are allowed to oscillate freely (e.g., at their natural frequency) until oscillations cease. Forced resonance analyzers are nevertheless more frequently used. They are designed to apply oscillating stress at a fixed frequency and are ideal for scanning material performance over a wide temperature range (Menard, 1999). Sample preparation includes selection of an appropriate clamp system, which is a function of... 

These tests form the classical methods of testing, but the use of dynamic mechanical analyzers are becoming more popular, especially those that can operate from subambient temperatures to 150°C and above. 

From the results obtained when used in a dynamic stress-strain mode, a hysteresis graph can be generated. As the machines were developed and computerized results obtained, a new group of instruments was developed, namely, the dynamic mechanical analyzers. 

Mechanical properties Dynamic mechanical analyzer Texture analyzer Compaction simulator Instron material test system... 

Scanning electron micrographs were taken with an ISIDS-130 microscope. Thermogravimetric analysis (TGA) was performed with an SDT Q600 (TA Instruments). A Seiko DMS 210 dynamic-mechanical analyzer was used for DMA measurements. For water content determination samples were allowed to equilibrate over saturated salt solutions in sealed jars at controlled relative... 

The viscoelastic properties such as storage modulus, loss modulus, and tan 8 are measured using a dynamic mechanical analyzer (DMA) and/or a rheometer. 

One instmment capable of measuring the dynamic shear modulus is a dynamic mechanical analyzer (DMA). A DMA measures the viscoelastic properties of a material by measuring the mechanical response that is deformed under periodic stress. Operation of a DMA tool offered by TA Instruments is as follows The sample is clamped between the ends of two parallel arms, which are mounted on low-force flexure pivots, allowing motion only in the horizontal plane. The distance between the two arms is adjustable by means of a precision mechanical slide to accommodate a wide range of sample lengths (from < 1 mm up to 65 mm). An electromagnetic motor attached to one arm drives the arm/sample to a strain (amplitude) selected by the operator. As the arm/sample system is displaced, the sample undergoes a flexural deformation [as depicted schemati-... 

Small deformation rheometry refers to testing procedures that do not cause structural damage to the sample. Constant stress rheometers, such as dynamic mechanical analyzers or oscillatory constant stress rheometers, are often used. 

Several other tests are used to correlate properties with the working conditions. The dynamic mechanical analyzer (DMA) is used to measure modulus and viscoelastic properties related to ductility. By using the DMA test method, the degradation in modulus could be imderstood and applied to the end use application. The effect of the environmental conditions is also tested the esthetic durability in heated environments is not restricted to warp and relaxation attributed to creep. Creep and stress relaxation tests are also done on SMC/BMC for their structural applications. The retention of color is critical for a heated appliance application. BMC/SMC can be formulated to offer excellent color stability when exposed to high temperatures. 

Dynamic mechanical analyzers are normally built to apply the stress or strain in three ways (Fig. 1). One can apply force in a twisting motion so one is testing the sample in torsion. Axial analyzers are normally designed for solid and semisolid materials, and apply... 

FIGURE 10.10 Diagrammatic representation of the design of the dynamic mechanical analyzer 2980. (Adapted from Dynamic Mechanical Analyser 2980 Operator s Manual, TA Instruments, New Castle, DE, 1996.)... 

The complex modulus of samples of the neat resins was determined at different temperatures and frequencies using dynamic mechanical analyzer (Seiko DMS 200). The sample was heated at 2 °C/min while holding the amplitude of the oscillation at 30 fxm for most samples. All tests were carried out in an atmosphere of nitrogen gas. 

Figure 5. Variation of the maximum value of tan 8 with rubber content Values of tan 8 were obtained using a Seiko DMS 200 dynamic mechanical analyzer in the tensile mode. The heating rate was 2 °C/min at 5 Hz.

Input to the model requires a knowledge of Young s modulus of the resin as a function of temperature. This was obtained using a DuPont DMA 980 dynamic mechanical analyzer and Is presented in Figure 1. TCE of the resin as a function of temperature was obtained on the Perkin Elmer TMS-2 and Is presented in Table I along with TCEs for the fibers as obtained from the supplier s literature. 

Dynamic Experiments. We will now consider the response of a Maxwell element subjected to a sinusoidal stress, as in a controlled-stress dynamic mechanical analyzer. In such a case the strain will also be sinusoidal but out of phase with the stress by the angle 8, as discussed in Chapter 2. Thus... 

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