Dynamic Mechanical Analysis (DMA) is done to determine elastic modulus, viscous modulus, and damping coefficient by using ASTM D4065, D4440, D5279 test methods. DMA outlines transition areas in plastics, such as the glass transition and may be used for quality assessment checks or product development.
Dynamic Mechanical Analysis (DMA) determines elastic modulus (or storage modulus, G’), viscous modulus (or loss modulus, G”), and damping coefficient (Tan D) as a function of temperature, frequency, or time. The results are usually determined graphically with G’, G”, and Tan D versus temperature. DMA outlines transition areas in plastics, such as the glass transition. It may be used for quality assessment checks or product development. DMA can identify small transition areas that are afar the resolution of DSC (Differential Scanning Calorimetry).
The test sample is mounted between the stationary and dynamic fixtures of a dynamic mechanical analyzer. Then it is enclosed in a thermal chamber and provided with appropriate inputs, e.g., amplitude, frequency, and a temperature range. While slowly moving through a defined temperature range, torsional oscillation is applied to the sample by the analyzer.
Various techniques for determination of Tg by DMA:
The highest point on the Tan Delta curve
Highest-point on Loss Modulus curve
Storage Modulus curve (half-height)
When reporting Tg by DMA, it is important to indicate how the Tg was figured because the difference between the various techniques can fluctuate as much as 25 °C. As a result, Tg provided by DMA is often about 10 degrees higher than DSC Tg.
Test samples are usually 56 × 13 × 3 mm in size, either incised from the center section of an ASTM tensile bar (Type 1) or an ISO multipurpose test sample.
Elastic Modulus (G’) vs (1) Temperature (2) frequency (3) strain
Viscous Modulus (G”) vs (1) Temperature (2) frequency (3) strain
Damping Coefficient (Tan D) vs (1) Temperature (2) frequency (3) strain
Key Properties from G‘ G”:
From the elastic modulus, we can calculate the Tan Delta, defined as the ratio of G” to G’. Tan D indicates the relative grade of damping of the material. This scale measures how efficiently a substance loses energy to molecular (or atomic) rearrangements and the built-in friction.
In Torsional Mode, Complex Shear Modulus (G*) is defined as the complex reaction of a material sample when stress or strain is applied. The vector sum of storage, G’ and loss, G” gives the shear modulus.