Dynamic Mechanical Analysis (DMA)

DMA is short for Dynamic Mechanical Thermal Analysis (DMTA), which is another name for Dynamic Mechanical Rheological Testing (DMRT).

Rheometers for mechanical Rheometry are of two types:

1)   Linear displacement, RSA II Rheometrics Solids Analyzer

2)   Rotational, SR5 Rheometrics Controlled Stress Rheometer

Rheology is the science that studies the deformation and flow of materials, whether in liquid, gel, melt, solid, or composite form, in terms or their elasticity and viscosity.

Elasticity is the ability of a material to store deformational energy, and can be viewed simply as the capacity of a material to regain its original shape after being deformed.

Viscosity is a measure of a material’s resistance to flow and reflects the material’s rate of dissipation of deformational energy through flow.

Materials respond to an applied force or displacement by exhibiting either elastic, Hookean, or viscous, Newtonian, behavior, or through a combination of these, called viscoelastic behavior, in which the response of the material is time   and temperature dependent. Most polymeric materials are viscoelastic.

Dynamic mechanical measurements monitor the dynamic mechanical response of viscoelastic materials. The measurement is based on the difference in response of viscous and elastic elements to a sinusoidally varying strain. For Example, a material acting like a spring (elastic ball) would give a resulting stress in phase with the applied strain. The opposite, a material acting like a viscous element (poured liquid) would produce a resulting stress 90 degrees out of phase with the applied strain.

From these measurements, properties such as the elastic modulus E’ or G’, viscous modulus E” or G”, damping factor tangent δ, and the glass transition temperature Tg are easily and precisely obtained. Furthermore, if the rheometer is sufficiently sensitive, normal stress differences can also be measured.

E is the symbol for the modulus measured in tension, compression, and bending. G is the modulus measured in shear. The relationship is E(t)=3G(t). Tangent δ is the ratio of the viscous modulus to the elastic modulus; E”/E’ or G”/G’.

DMA is probably the most versatile thermal analysis method available, and no other single test method provides more information about a sample is a single test. Besides material properties, DMA provides a direct link between a material’s chemical makeup and its mechanical behavior.

Materials can be characterized by DMA regardless of their kind,  physical state, shape or the form in which they are used. The material may be:

o Thermoplastic, a thermoset, or an elastomeric polymer

o Polymer Blend, Alloy, or Recycled

o Liquid, Gel, Hydrogel, Melt, Solid, or Composite

o Soft solids like cheese, food, toothpaste, cosmetics

o Foams, wet or dry, soft or rigid, open or closed cell

o Dispersion, emulsion, suspension or solution

o Virgin “Neat”, or with fillers, pigments, plasticizers, fibers, nanotubes, and nano particles

Many tests are nondestructive and only small samples are needed. DMA can extend beyond the present. New and existing products are typically tested in the here and now. DMA can predict the materials performance in weeks, years, even decades from now. Using the Boltzmann superposition principle, time-temperature superposition, time-strain superposition or time-concentration superposition, rheological data generated in minutes or hours can be used to predict long term (shelf-life) material performance.

Dynamic mechanical measurements of materials yield insight and intrinsic information more than any other single measurement. These tests can be accomplished for a wide range of temperatures from -120C to 600C. Testing liquids to solids and everything in between. Geometries include torsion, three point bending, cantilever, tension, compression, indentation, cone and plate modes are available. Custom made fixtures assure the minimal material change. The different modes are used to characterize materials in any form including: composites, heterogeneous blends, plastics, foams, films, cosmetics, gels, medical devices, etc.

What does dynamic mechanical analysis (DMA) testing provide?

• Modulus as a function of temperature, time, frequency, or shear rate

• Storage Modulus (E’), Loss Modulus (E”), tan-delta, complex modulus, phase angle

• Important thermal transition temperatures, like Tg - glass transition, Tm – melt transition

• Maximum continuous use temperature

• Indications of impact and creep behavior

• Stress Relaxation behavior, time temperature superposition, Boltzmann Principle

• Shelf life and stability testing

• Predict product performance

• Failure analysis, residual stress and fractures

• Compatibility studies, mixing and blending

• Consequences of compounding, processing, extrusion, additives, foaming and molding

• Fatigue and yield behavior, when and how based on time and temperature limits

• Poisson’s ratio (G w/r E)                                                                                

ASTM methods used for DMA testing of plastics:

ASTM D4065 Standard Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Procedures

ASTM D4440 Standard Test Method for Plastics: Dynamic Mechanical Properties Melt Rheology

Companies contact Associated Polymer Labs for DMA and Rheology Service because of our decades of experience, innovation, and leadership in the science of rheology. We specialize in the following materials: Plastics, Polymers, Bio-resins, Elastomers, Rubbers, Thermosets, Epoxy, Composites, Prepregs, Nano and Aerospace Materials, Consumer and Protective Packaging, and Cosmetics