Dynamic thermomechanical analysis DMTA

Dynamic properties are more relevant than the more usual quasi-static stress-strain tests for any application where the dynamic response is important. For example, the dynamic modulus at low strain may not undergo the same proportionate change as the quasi-static tensile modulus. Dynamic properties are not measured as frequently as they should be simply because of high apparatus costs. However, the introduction of dynamic thermomechanical analysis (DMTA) has greatly widened the availability of dynamic property measurement. 

A more common mechanical method is dynamic mechanical thermal analysis (DMTA). DMTA is also called dynamic mechanical analysis (DMA) or dynamic thermomechanical analysis. An oscillating force is applied to a sample of material and the resulting displacement of the sample is measured. From this the stiffness of the sample can be determined, and the sample modulus can be calculated. A plot of loss modulus as a function of temperature shows a maximum at Tg as shown in Figure 1.35. Figure 1.35 shows a series of blends of high-impact styrene (HIPS) and PPO. As the amount of PPO is increased, Tg increases. The single Tg indicates that these blends are miscible. 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

Figure 3.7 Schematic showing the effect of moisture absorption on the thermomechanical response (DMTA, dynamic mechanical thermal analysis) of a resin, (Left) tan 8 (right) storage modulus dry/as-cured...

Thermal properties Thermal properties are the properties of materials that change with temperature. They are studied by thermal analysis techniques, which include DSC, thermogravimetric analysis (TGA), differential thermal analysis (DTA), thermomechanical analysis (TMA), dynamic mechanical analysis (DMA)/dynamic mechanical thermal analysis (DMTA), dielectric thermal analysis, etc. As is well known, TGA/DTA and DSC are the two most widely used methods to determine the thermal properties of polymer nanocomposites. TGA can demonstrate the thermal stability, the onset of degradation, and the percentage of silica incorporated in the polymer matrix. DSC can be... 

Maximum deformation, parameter in cyclic, thermomechanical tests Free state deformation after cooling Volume fraction Critical volume fraction Volume resistivity Maximum stress 1,4-Butanediol Carbon black Carbon nanotube Dimethylformamide DMTA Dynamic mechanical analysis at varied temperatures DSC Differential scanning calorimetry / Frequency... 

Thermomechanical Analysis (TMA) measures unidirectional dimensional changes in materials as functions of time, temperature and applied force. The TMA measurements are coefficient of linear thermal expansion (CLTE), glass transition temperatures (Tg) and softening points (Ts). Newer applications of TMA include elasticity, melt viscosity, and heat deflection temperature. In addition to traditional TMA instruments, many modem dynamic mechanical thermal analysis (DMTA) instruments can operate in a TMA (static force) mode. The main differences between the two types of instruments are the size of the specimens and the materials used to fabricate the measurement fixtures (stage, probe, clamps, etc.). Most TMA instruments use quartz, while DMTA instruments use larger steel components. The specimens used in these experiments are... 

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