RUDIMENTS OF RHEOMETRICSAND DYNAMICMECHANICAL
The TA Instruments RSA-G2 Solids Analyzer
the science concerned with the study of deformation and flow of
materials. Dynamic mechanical analyzers such as the present-day TA
Instruments RSA-G2 or the earlier Rheometrics RSA II impose
mechanical deformation on a specimen and measure the resulting
Deformation is the relative change in shape of a body, or strain, under the influence of an external
force, or stress. Flow is a continuous relative change in shape per unit time, or strain rate,
under influence of external stress. The RSA-G2 is in fact a linear rheometer, or a precision instrument
which holds a specimen of the material of interest in a geometric configuration, controls the environment around
it and applies and measures wide ranges of stress, strain, and strain rate.
An alternative definition of rheology, relating more directly to the function of the rheometer, is the study of
stress-strain or stress-strain rate
A material's response to external forces can be purely
viscous or Newtonian behavior, purely elastic or Hookean behavior or a
combination of the two. Nearly all commercial materials of interest
respond with a combination of viscous and elastic behavior and are
referred to as viscoelastic materials.
Amoung others, polymer scientists use the RSA-G2 and
rheology theory to study these rigid-solid, soft-solid, and highly
viscous liquid materials in terms of a variety of material parameters
such as modulus, compliance, and elasticity. Modulus is a measure of a
material's overall resistance to mechanical deformation,
whilst compliance is a measure of the material's ability to respond to deformational stress and elasticity
is a measure of a material's ability to store and release deformational energy.
The TA Instruments RSA-G2 DMA seen in Fig. 2 is capable of applying a variety of deformation types over a wide
range of temperatures and time scales, or frequencies, and calculates these material parameters providing a wealth
of information about a material s structural property relationships and material performance characteristics.
An informative 10 minute movie on the TA Instruments RSA-G2.
Complete information on the operation of the, "RSA-G2".
A brochure on one of the RSA-G2's predecessors, the, "Rheometrics
RSA II Solids Analyzer" which includes info on the capabilities of the Orchestrator software
used to program and run the machine. Included in Ch. 5 is calibration information using the obsolete Rhios software.
An overview of, "High
Strain Rate Testing" from Veryst along with a paper
on an open-source 2D Digital Image Correlation (DIC) tool used to monitor in-situ, full-field deformation and strain
responses of structures during loading.
Preliminary info on, "Polyphene" a polymer/graphene nano-composite that, amoung many other things, will be PEARL, Inc's. new loudspeaker diaphragm material. ("Polyphenene" is
a portmanteau of polymer and graphene.)
Fig. 2. The new RSA-G2 is the most advanced platform
for mechanical analysis of solids. The separate motor and transducer technology of the RSA-G2 ensures the purest
mechanical data through independent control of deformation and measurement of stress. It is capable of performing
the most accurate DMA measurements as well as many additional experiments including creep and recovery, stress
relaxation, stress ramps, strain rate ramps, iso-strain, iso-force, fatigue, multi-wave, arbitrary waveform, and
dielectric thermal analysis. Being capable of such a broad range of solids analysis techniques, the RSA-G2 is uniquely
positioned to address a wide range of applications from the R&D bench to the quality control lab.
This high-performance instrument is the fourth generation of dual-head (separate motor/transducer) mechanical analyzers
and features a new, forced-convection oven for precise and accurate temperature control, an extensive array of
sample holding geometries accommodating a wide range of sample shapes and stiffness, along with immersion testing
capability. Additionally, the RSA-G2 doubles as a DETA, or Dielectric Thermal Analyzer, for stand-alone or simultaneous
Fig. 3. The Wikipedia article seen here
provides good overview of the basic theory of dynamic mechanical analysis. Fig. 4. Viscoelastic material trends as a function of driving frequency.
A DMA frequency scan showing the changes in a viscoelastic material's apparent morphology as driving frequency
is varied. Forces at low frequencies allow polymeric chains time to relax and respond whereas forces at higher
frequencies do not, with the result that materials exhibit higher Young's modulus.
Base graphic excerpted from: Dynamic Mechanical Analysis by Menard, 2nd edition.
Fig. 5. There is no such thing as a negative value
loss modulus, the DMA used to run that data was out of cal' and wasn't properly measuring phase angles. Even so,
the illustration is somewhat instructive but will be replaced as soon as possible.
Base graphic retrieved from Wikipedia: Dynamic Mechanical Analysis Fig. 5