TA Instruments RSA-G2, Manual

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RSA-G2 Getting Started Guide Page 57
Selecting and Installing a Geometry
The sections below detail recommendations for selecting geometries, as well as procedures for installation.
General Recommendations
Although the physical properties of the sample generally dictate the appropriate sample geometry, it is
sometimes possible to test a given sample using more than one geometry.
Ideally, the test results should be identical in the different geometries. However, there exist experimental
limitations that may make testing in one geometry preferable to testing in another. Additionally, factors
such as anisotropy and differences in strain dependence may yield inconsistent results for different
geometries.
Recommendations for selection of a geometry based upon sample type are as follows:
•
Thin films : Test thin films (such as magnetic recording tape) using the linear tension geometry.
• Fibers : Test fibers using the linear tension geometry.
• Rubbers and other elastomers : Below the glass transition, these samples are best tested using the
clamped bending geometry. Above the glass transition, these samples can be tested in either compres -
sion using the compression (parallel plate) geometry, or in shear using the shear sandwich geometry.
• Solid polymer bars : These materials can be tested using either the clamped bending or three-point
bending geometry for samples that are up to 4 mm in thickness and up to 12 mm in width.
• Polymer melts : Melts can be tested using the shear sandwich geometry or parallel plates, provided
that the sample viscosity is high enough to prevent the material from flowing out of the tool.
• High performance composites, ceramics, and metal bars : These materials are best tested in a three-
point bending geometry.
• Foams : Foams are best tested in either compression using the compression (parallel plate) geometry,
or shear using the shear sandwich geometry.
Testing Limits and Compliance
The following factors limit the sample size that can be tested on the RSA-G2:
• Motor/transducer force and displacement ranges
• Sample compliance and stiffness
• Size of the test geometry
Transducer compliance and sample stiffness play a major role in the selection of sample size that can be
accurately tested on the RSA-G2.