Dynamic Mechanical Analysis (DMA)

 Dynamic mechanical analysis (DMA)

Dynamic mechanical analysis (DMA) applies sinusoidally oscillating stresses to investigate the relationship between stress and strain of materials at various temperatures, oscillatory frequencies and loads, and durations. While originally developed for metals, the DMA technique has become extremely important for thermomechanical testing of engineering polymers and composites. Visco-elastic materials such as polymers display both elastic properties characteristic of solid materials and viscous properties characteristic of liquids. Polymer samples, under sinusoidal loading, show a phase lag (described by the phase angle ‘δ’), between the applied stress and measured strain. DMA testing of polymers provides measurements of elastic (storage) modulus; loss (viscous) modulus; complex modulus and loss tangent (tan‘δ’), as a function of frequency, time, or temperature. A range of temperatures and frequencies or shear rates can be investigated.

The main components of DMA test set-up include sample clamps to secure the test sample; drive mechanisms for oscillatory and torsional loadings, displacement sensors and a temperature-controlled chamber (furnace and liquid nitrogen line). The DMA can be either stress or strain controlled. While axial and torsional loads can be applied, axial instruments should not be used for fluid samples with viscosities below 500 Pa-s and torsional analyzers are not suitable for materials with high modulus. The test set-up is integrated with an automatic control panel and data processing system.

DMA is applicable to determination of the visco-elastic properties of thermosetting, thermoplastic resins and polymer composites. DMA can be used to study the glass transition of polymers or fatigue characteristics in laboratory. Creep recovery can also be tested using DMA equipment. The value of DMA lies in its ability to replicate actual operating conditions of the material under industrial conditions.

Common Uses of Dynamic mechanical analysis (DMA)

• Dynamic-mechanical characterization of polymers, composites and polymeric biomaterials
• Characterization of shape-memory polymers for biomedical applications
• Study of glass transition temperatures of polymeric substances
• Dimensional stability analysis of engineering polymers
• Determination of cross-link density

 Advantages of Dynamic mechanical analysis (DMA)

• Small size of test sample
• Wide range of frequencies, temperatures, loads and durations can be applied
• Controlled rates of heating and cooling can be applied
• Comparative DMA of different samples can be accomplished
• Provides information on phase transition of materials
• Reproduces real world operating conditions

Limitations of Dynamic mechanical analysis (DMA)

• The modulus value is influenced by sample dimensions so errors in measurement of sample dimensions leads to error in computed modulus value.
• Work done on the sample also changes its temperature apart from the controlled environment
• Instrument errors need to be considered

Industrial Applications of Dynamic mechanical analysis (DMA)

• Research and development of resins and polymers including polymeric biomaterials
• Process optimizations in polymer processing
• Quality control in Polymer processing
• Failure analysis of engineering polymers