Dynamic Mechanical Analysis
Dynamic Mechanical Analysis (DMA) is a technique used to characterize materials, specifically polymers. It applies a displacement to a sample and measures the mechanical response of the bulk material in a controlled temperature environment.
Dynamic mechanical analysis test conditions can be designed to study bulk mechanical properties of organic polymers to assist in determining key functional behavior related to:
Elasticity: Polymer resistance to permanent deformation due to resiliency of structure (recovery; stiffness)
Viscous Response: Deformation without breaking due to dissipation of mechanical energy by internal friction (damping)
![DMA](https://www.atomicecho.com/wp-content/uploads/2023/06/DMA.jpg)
DMA testing involves selection of the appropriate conditions of time, temperature, displacement and frequency to study the properties of interest. Some example selections are:
- Frequency sweep: frequencies can be specified to study the mechanical behavior of the sample as a function of oscillatory loading rate.
- Temperature ramp or isothermal temperature: precision heating and cooling allows the study of mechanical response as a function of temperature.
- Displacement modes:
- Tensile (stretch) for thin films and fibers
- Flexural (bend) for filled and crystalline polymers, thermoplastic polymers, thermosetting resins, elastomers.
- Controlled force / displacement: non-oscillatory test that measures mechanical response after applying instantaneous force or displacement distance.
- Creep/recovery test
- Stress relaxation test
- Force ramp (Young’s Modulus, linear modulus of elasticity) – “mini-tensile tester”
Examples of the various properties that can be measured through select test conditions:
- Storage Modulus
- Complex Modulus
- Loss Modulus
- Tan Delta
- Creep Compliance
- Storage/Loss Compliance
- Relaxation Modulus
- Sample Stiffness
- Stress/Strain
- Young’s/Linear Elastic Modulus
- Transition Temperatures (e.g. Tg)
- Secondary Transitions (e.g. β)
Ideal Uses of Dynamic Mechanical Analysis (DMA)
- Measuring glass transition temperature (Tg) of polymers, especially highly filled thermoplastics and rigid thermosets
- Determining temperature ranges where material properties change from hard/rigid to soft/rubbery; “viscoelastic spectrum” to use for process design
- Comparative failure analysis of plastics and thermosets
- Differences in elastic modulus before and after processing , post-curing or physical aging
- Detecting phase separation of polymer blends or copolymers
- Dimensional stability of parts at operating temperature and loading
- Damping capability of polymer: dissipation of energy through internal motion; toughness
- Time-Temperature Superpositioning (TTS): study the effect of changing frequency on temperature-induced changes in polymers
Strengths
- Small sample geometry
- Offers wide range of programmable frequencies, force and temperature parameters
- Two types of force alterations: oscillating and linear
- Programmable temperature: (1) heating and cooling ramps, (2) isothermal
Limitations
- Geometrically uniform test specimens
- Examples: rectangular specimens with maximum dimensions L = 60 mm; W ≤ 15 mm; T = ≤ 5 mm
- Films size range: rectangular specimens with max. dimensions L = 30 mm; W ≤ 8 mm; T ≤ 2mm; , also adaptive for analyzing small diameter flexible tubing (e.g. medical grade).
- Fiber size range: dimensions L = 30 mm; W = 5 denier; Dia. ≤ 0.8 mm
DMA Technical Specifications
- Temperature operation from -150 – 600°C
- Temperature ramp (Heating/Cooling) 0.1 – 10°C/minute
- Force Range: 0.0001 to 18 N
- Frequency Range: 0.01 – 200 Hz
- Dynamic Sample Deformation Range: ±0.5 to 10,000 micrometer