# Dynamic mechanical analysis

Dynamic mechanical analysis (DMA) is a thermal method, to determine physical properties of plastics.

## Principle

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).

## Testify

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.

## Application

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,
- Damping
- 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