Dynamic mechanical analysis
Dynamic mechanical analysis (DMA) is a thermal method, to determine physical properties of plastics.
Dynamic mechanical analysis subjects the sample to be examined as a function of the temperature of a time-varying sinusoidal mechanical stress. Thus the sample deforms with the same period. It measures the force amplitude, the strain amplitude and the phase shift Δ between the force and the deformation signal.
As a result of the dynamic-mechanical analysis provides the complex modulus of the sample. The prerequisite is that the specimen is loaded in no case beyond the linear elastic range ( Hooke's area).
There are three fundamentally different behaviors of the sample:
- Pure elastic samples react instantaneously to the applied force, the phase angle = 0 swing lossless.
- Pure viscous samples reach their maximum deformation at the zero crossing of the force. For them, therefore, is the phase angle (90 °). They convert the excitation energy completely into heat.
- Viscoelastic materials are characterized by the fact that the deformation of the sample follows a certain delay of the applied force. Therefore applies to the phase angle Δ. The greater the phase angle, the more pronounced is the attenuation of the vibration.
The DMA allows, inter alia, the determination of:
- Visco-elastic material properties, for example modulus and the loss factor tan ()
- Temperatures, characterize the viscoelastic behavior,
- Specifically, the glass transition temperature, for which the DMA is the most sensitive method
- The curing behavior of resins
- The frequency- dependent mechanical behavior of materials
- Thermal analysis
- Material testing