Curve Interpretation Part 6: Variation of DMA Measurement Conditions

DMA measurements can be performed under very different conditions to characterize the mechanical properties of materials. A great deal of information about a sample is obtained when the temperature, frequency or displacement amplitude is varied. The mechanical properties of composites or anisotropic materials can only be fully described by varying the direction of the deformation measurement or by using other measurement modes. This article discusses a number of typical examples.

Introduction

The most frequently used DMA measurement is a temperature scan at constant frequency. In this measurement, the storage modulus, loss modulus and loss factor (tan delta) are determined as a function of temperature.

Normally a frequency of 1 Hz is used and the measurement is often performed in the bending mode or (with films) in tension. However, since the introduction of modern DMA instruments like the METTLER TOLEDO DMA861e, much more information about the properties of materials can be obtained by varying the measurement conditions. The DMA861e is capable of measuring sample stiffness over a very large range. The possibilities now available are discussed using different polymers and composites as examples.

Conclusions

The amount of information that can be gained from DMA measurements can be greatly increased when the normal temperature scan measurements are complemented by frequency scan measurements and measurements in which the displacement amplitude is varied.

Variation of the measurement direction is recommended in particular for materials whose mechanical properties are directional. This applies to fiber-filled materials, laminates, or materials that have a preferred direction (films or injection molded parts) as a result of their production process. The shear mode is an ideal technique to use for this. Finally, with composites, it is also often advantageous to perform measurements in different measurement modes.

_{Curve Interpretation Part 6: Variation of DMA Measurement Conditions | Thermal Analysis Application No. UC 431 | Application published in METTLER TOLEDO Thermal Analysis UserCom 43}