Standard Uniaxial Testing Deficiencies in Amorphous Polymer Characterization
Uniaxial tensile tests misrepresent multi-axial yield, physical aging, and strain-rate sensitivity in amorphous polymers, causing structural failure in real parts.
Optical Extensometry
Meaning
Non-contact optical measurement systems track surface gauge marks on deformation specimens using high-resolution digital cameras and image processing algorithms. Utilizing optical extensometry captures high-rate, true strain data across complex strain fields without applying mechanical knife-edge forces to fragile or soft specimens. The method applies to tensile testing of flexible films, elastomers, highly extensible polymers, and micro-molded components, but requires clear line of sight and high contrast surface markings.
Tracking Kinematics
Digital image correlation algorithms track vector movements of contrast patterns across sequential image frames. System software calculates real-time longitudinal and transverse strain vectors across the specimen gauge section simultaneously. Eliminating physical extensometer clips prevents local stress concentrations and early specimen tearing at grip points.
High-speed cameras capture rapid strain localization during high-rate impact tensile testing.
Noncontact Advantage
Flexible film testing relies on non-contact measurement because mechanical clips distort light polymer webs. Modulus measurements for soft thermoplastic elastomers require weightless tracking to prevent premature sagging and gauge displacement errors. Molders testing thin-wall test specimens obtain reliable true strain data across local necking zones.
Regrind-rich samples exhibit non-uniform strain field distributions that optical tracking maps across the full specimen area.
Strain Resolution
Digital pattern matching provides accurate non-contact strain mapping across full specimens.