Differential Mechanical Analysis (DMA).pdf
- 1. Differential Mechanical Analysis (DMA)
- 2. 2 Thermo mechanical dynamic analysis, otherwise known as Dynamic Mechanical Analysis (DMA), is a technique where a small deformation is applied to a sample in a cyclic manner. This allows the materials response to stress, temperature, frequency and other values to be studied. The term is also used to refer to the analyzer that performs the test. Dynamic mechanical analysis (DMA) is an important technique used to measure the mechanical and viscoelastic properties of materials such as thermoplastics, thermosets, elastomers, ceramics and metals. THERMO-MECHANICAL DYNAMIC ANALYSIS (DMA)
- 3. 3 A sinusoidal stress is applied and the strain in the material is measured, allowing one to determine the complex modulus. The temperature of the sample or the frequency of the stress are often varied, leading to variations in the complex modulus; this approach can be used to located the temperature of the material, as well as to identify transitions corresponding to other molecular motions. THERMO-MECHANICAL DYNAMIC ANALYSIS - PRINCIPLE
- 4. 4 Forced resonance analyzers – Analyzers force the sample to oscillate at a certain frequency and are reliable for performing a temperature sweep. Free resonance analyzers – Free resonance analyzers measure the free oscillations of damping of the sample being tested by suspending and swinging the sample. TYPES OF THERMO MECHANICAL DYNAMIC ANALYZER
- 5. 5 Stress (force) control – The structure of the sample is less likely to be destroyed and longer relaxation times/ longer creep studies can be done. Strain (displacement) control – The better short time response for materials of low viscosity and experiments of stress relaxation are done with relative ease. MODE OF ANALYZER
- 6. 6 Transducer Sensor (Linear Variable Displacement Transducer LVDT) – It is which measures a change in voltage. Drive shaft or probe – It is a support and guidance system to act as a guide for the force from the motor to the sample. Drive motor – A liner motor for probe loading which provides load for the applied force. Stepper motor – It controls the specimen dimension and measurement. COMPONENTS
- 7. Cross sectional of Thermo mechanical dynamic analyzer 7
- 8. 8 The sample is clamped in the measurement head of the DMA instrument. During measurement, sinusoidal force is applied to the sample via the probe or driving shaft. Deformation caused by the sinusoidal force is detected and the relation between the deformation and the applied force is measured. Properties such as electricity and viscosity are calculated from the applied stress and strain plotted as a function of temperature or time. THERMO-MECHANICAL DYNAMIC ANALYSIS – WORKING
- 9. DIFFERENT LOADING CONDITION Modes Stress application Purpose Shear mode Used for evaluation of thin fibers or films or bundle of single fiber 3-point bending mode Best for medium to high modulus materials. Dual cantilever mode Highly damped materials can be measured. 65
- 10. DIFFERENT LOADING CONDITION Modes Stress application Purpose Single cantilever mode Suited best for thermoplastics Tension or compression mode Used for low medium modulus materials 10
- 11. 11 • The most suitable type should be selected depending on the sample shape, modulus and measurement purpose. DIFFERENT LOADING MODES
- 12. 12 • Displacement and force • Wide range of force 1mN to 40N • Wide range of frequency 0.001 to 1000Hz. • Wide stiffness range. • Coefficient of thermal expansion (CTE) • Glass Transition Temperature • Compression Modulus of polymeric materials • Viscoelastic properties such as : Storage modulus (purely elastic component) Loss modulus (purely viscous component) Loss tangent DMA MEASURES
- 13. 13 • It is an essential analytical technique to determining the viscoelastic properties of polymers. • Very soft and hard samples are measured. • Allows accurate temperature measurement. • It can provide major and minor transitions of materials • It is also more sensitive • It is able to quickly scan and calculate the modulus for a range of temperatures. • It is the only technique that can determine the basic structure of a polymer system. • This analytical method is able to accurately predict the performance of materials in use. ADVANTAGES
- 14. 14 • It leads to calculation inaccuracies. • The large inaccuracies are introduced if dimensional measurements of samples are slightly inaccurate. • The oscillating stress converts mechanicalenergy to heat and changesthe temperature of the sample. • The maintaining an exact temperature is important in temperature scans, this also introduces inaccuracies. • The final source of measurement uncertainty comes from computer error. LIMITATIONS
- 15. 15 • Measurement of the glass transition temperature of polymers • Varying the composition of monomers • Effectively evaluate the miscibility of polymers • To characterize the glass transition temperature of a material • Mechanical properties in the relevant frequency range • Modulus information • Nonlinear properties • Damping behaviour APPLICATION