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A dynamic mechanical analyzer (DMA) is a laboratory instrument that applies a small oscillating force or deformation to a specimen and measures how stiff and how energy-dissipating the material is, usually while temperature, frequency or time is varied. It is used on plastics, elastomers and composites for transition temperatures, quality control and product development.
What is dynamic mechanical analysis?
Dynamic mechanical analysis is the test; the dynamic mechanical analyzer (sometimes called a dynamic thermomechanical analyzer) is the instrument. ASTM D4065-20 describes the practice as gathering and reporting dynamic mechanical data for plastic specimens subjected to oscillatory deformations, to determine transition temperatures and the elastic and loss moduli over a range of temperatures, frequencies or time. The output is a plot of those moduli against temperature or frequency, which shows elasticity and damping, and the transition regions where molecular motion in a polymer changes. (ASTM D4065-20, read 2026-11-07.)
What does a DMA measure?
DMA analysis reports three linked quantities, defined as in Intertek’s and the Madison Group’s technical notes:
- Storage modulus (E’ in tension and bending, G’ in shear): the elastic, stiffness-related response.
- Loss modulus (E” or G”): the viscous response, energy lost as heat through internal friction.
- Tan delta (loss modulus divided by storage modulus): a measure of damping. A tan delta peak marks where the material is proportionally most viscous.
In a transition region the elastic modulus falls rapidly with rising temperature (at near-constant frequency), and both the loss modulus and tan delta pass through a maximum (ASTM D4065-20, section 5.2).
What is it used for?
Per ASTM D4065-20 section 5, the practice can locate transition temperatures, and by comparison with reference or control materials can evaluate phase separation in multicomponent systems, filler type, amount and dispersion, and the effects of processing. It can also characterise stiffness of polymer composites as a function of temperature and degree of crystallinity, and the standard states it is useful for quality control, specification acceptance and research. Intertek adds that tan delta peaks below the glass transition are used to estimate impact performance.
Who uses it: materials-science, polymer and quality-assurance laboratory staff, and engineers who need modulus-versus-temperature data for design.
Test modes and standards
Deformation can be applied in different geometries, and the standard family changes with the mode.
| Standard | What it covers | Stated scope |
|---|---|---|
| ASTM D4065-20 | General practice for determining and reporting dynamic mechanical properties of plastics | Tensile, bending and shear modes via referenced test methods; free vibration and resonant or non-resonant forced vibration |
| ASTM D5026 | Plastics under oscillating tensile forces (as described by Centexbel) | Frequency usually 0.01-100 Hz; temperature commonly -100 C to +300 C |
| ISO 6721 (multi-part) | Dynamic mechanical properties, split into parts by mode | Part 4 covers tensile vibration of rigid plastics; ASTM D4065 notes it is equivalent to ISO 6721-1 |
Sources: ASTM D4065-20 store page; Centexbel testing page (both read 2026-11-07).
Operating envelope stated in ASTM D4065-20
Before assuming a method or instrument fits a material, check it against the practice’s stated limits:
| Parameter | Stated in D4065-20 |
|---|---|
| Temperature | Primarily useful from -140 C up to polymer softening |
| Frequency | Valid from 0.01 to 1000 Hz |
| Elastic modulus of material | 0.5 MPa to 100 GPa |
| Deformation range | Linear viscoelastic region assumed |
| Units | SI values are the standard |
The standard also notes that results differ under differing experimental conditions, which is why it asks for the conditions to be reported in full. Where a material specification modifies the procedure, the specification takes precedence over the practice. Intertek gives a typical specimen for torsion testing of 56 x 13 x 3 mm, cut from an ASTM Type I bar or ISO multipurpose bar.
Reading the glass transition temperature (Tg)
DMA does not produce a single Tg. Intertek lists several ways to read it: the tan delta peak, the loss modulus peak, the half-height of the storage modulus drop, and the onset of the storage modulus drop. It states the values can vary by as much as 25 C depending on the method. The Madison Group ranks them: storage modulus onset gives the lowest value, the loss modulus peak a higher one, and the tan delta peak the highest, which it describes as the most common DMA Tg value and one referenced in ASTM D4065. Intertek notes DMA Tg is often about 10 C higher than the Tg from differential scanning calorimetry (DSC), and that DMA can recognise small transitions beyond the resolution of DSC.
| Tg definition | Relative value (Madison Group) |
|---|---|
| Onset of storage modulus drop | Lowest |
| Loss modulus peak | Intermediate |
| Tan delta peak | Highest; most commonly reported |
Common mistakes
- Reporting a Tg without stating which definition was used; the spread between methods can reach 25 C.
- Comparing a DMA Tg directly with a DSC Tg; DMA often reads about 10 C higher.
- Omitting test conditions (mode, frequency, heating rate, specimen geometry); D4065 asks for full reporting because results vary with conditions.
- Running outside the linear viscoelastic region, which the practice assumes.
- Applying the general practice when a material specification prescribes its own procedure.
FAQ
What is dynamic mechanical analysis?
It is a test in which a specimen is subjected to oscillating deformation while temperature, frequency or time changes, yielding storage modulus, loss modulus and tan delta. ASTM D4065-20 is the general practice for plastics.
What is DMA analysis used to find?
Transition temperatures such as Tg, stiffness as a function of temperature, damping behaviour, and differences caused by fillers, phase separation or processing.
How is DMA different from DSC?
Intertek reports DMA can resolve small transitions that DSC misses, and its Tg is often about 10 C higher than the DSC value.
Related CASRAI pages
- X-ray diffraction (XRD), another materials-characterisation method
- ASTM D5276, a further ASTM test standard guide
- How to calibrate a thermometer, relevant to temperature verification
- Standard operating procedure (SOP)
Sources
- ASTM D4065-20, Standard Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Procedures, store.astm.org/d4065-20.html (read 2026-11-07)
- Intertek Testlopedia, Dynamic Mechanical Analysis, intertek.com/polymers-plastics/testlopedia/dynamic-mechanical-analysis (read 2026-11-07)
- Madison Group, dynamic mechanical analysis note, madisongroup.com (read 2026-11-07)
- Centexbel, DTMA according to ASTM D5026 and ISO 6721, centexbel.be (read 2026-11-07)
