RUDIMENTS OF RHEOMETRICSAND DYNAMICMECHANICAL
The TA Instruments RSA-G2 Solids Analyzer
Rheology is the science concerned with the study of deformation and flow of materials. A dynamic
mechanical analyzer such as the earlier RSA II or the present RSA-G2 imposes a mechanical deformation on a specimen
and measures the resulting stress response.
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 contains 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 relationships. A material's response to external
forces can be purely viscous or Newtonian behavior, purely elastic or Hookean behavior or a combination of both.
Nearly all commercial materials of interest respond with a combination of viscous and elastic behavior and are
referred to as viscoelastic materials. 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
Fig. 1. Text to follow
ability to store and release deformational energy. The RSA-G2 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 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 what will be PEARL's new loudspeaker diaphragm
material"Ultiphene" on which we want to generate DMA data.
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. Text to follow.
Fig. 4. Viscoelastic material trends as a function of driving
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