Table of ContentsDefinition of DMA.
Modes of DMATensile mode of DMADifferentiate DMA from thermomechanical analysis.Working OF DMAMethodology to measure DMA.Comparison of storage modulus and young’s modulus in DMADampingWhy we scan modulus as a function of temperatureMethodology to get excellent data from DMAMethodology to select geometryHow can we detect a TgMethodology to know it’s required TgWhy does my Tg values sometimes not agree with my DSC valueCan we use DMA to study curingWhat Time-Temperature superposition tell us?How can I tell if TTS is valid?Should we use DMA to check humidity effect my sample?Common Symbols in the DMA literatureDefinition of DMA:Dynamic Mechanical Analysis also known as DMA is as technique that is use where small deformation is produce to a specimen in a cyclic way. Here material response to stress, time, temperature and other values studied. It is also known as DMTA.Differentiate DMA from thermomechanical analysis:In thermomechanical analysis we applies a constant static force to a specimen of material and notice the variations in material change as temperature or time varies. It shows dimensional changes.
However, DMA applies an oscillatory force at a frequency, which we set to the sample, and shows changes in stiffness and damping. DMA data used to obtain modulus information while TMA provides coefficient of thermal expansion. Both detect transitions, but DMA is much more sensitive. Modes of DMA:DUAL CANTILEVERSINGLE CANTILEVERCOMPRESSIONTENSIONSHEAR SANDWICH3 POINT BENDTensile mode of DMA:In this mode, the sample placed in tension between a fixed and moveable clamp. In oscillationExperiments, a small static force is applied in order to prevent buckling. The clamps feature verySimple mounting and because the drive shaft does not rotate, no twist is induced in the sample that can lead to inaccurate data. Fig1: films Fig2: FibersTwo clamps are available:Tension (film)5 to 30mm (L); up to 8mm (W) and 2mm (T)Tension (fibers)5 to 30mm (L); 5 denier (0.
57 tex) to 0.8mm diam.single fibers or fiber bundlesWorking OF DMA:DMA works by applying a sinusoidal deformation to a sample whose geometry known. The sample can be study by a controlled stress or a controlled strain.
For a stress of known amount, certain amount of deformation will produce in the sample. Deforms is related to the stiffness of material. Force produce sinusoidal waves and they transmitted to the sample by drive shaft. Our concern is the compliance of this drive shaft and stabilizing bearing which hold it in position.
Figure 3. Schematic of the DMA 8000 analytic train.Methodology to measure DMA:DMA measures stiffness as modulus and damping as tan delta. Because we are applying a sinusoidal force, here we can express the storage modulus as an in-phase component, the loss modulus as an out of phase component. The storage modulus, either E’ or G’, is the measure of the sample’s elastic behavior. Figure 4. The relationship of the applied sinusoidal stress to strain with the resultant phase lag and deformation.
Comparison of storage modulus and young’s modulus in DMA:Young’s modulus calculated from the slope of the initial part of a stress-strain curve and similarly calculate the storage modulus but they are not the same. We know that shear, bulk and compressive modulus for a material will differ, and similarly Young’s modulus will not have the same value as the storage modulus.Damping:The ratio of the loss to the storage is the tan delta also called damping. It is a measure of the energy dissipation of a material.Why we scan modulus as a function of temperature:Modulus values changes as the temperature and transitions of materials can be seen as changes with E’ or tan delta curves.
This includes not only the Tg and Tm, but also other transitions that occur in the glassy or rubbery state.Figure 5. Modulus values change with temperature and transitions in materials can be seen as changes in the E’ or tan delta curves.Methodology to get excellent data from DMA: