Deriving Ogden Constitutive Parameters from Biaxial Stretch Testing Data
Deriving Ogden constitutive parameters pairs non-linear biaxial stretch data with Drucker stability constraints to ensure reliable finite element simulations.
DIC Strain Measurement
Meaning
Non-contact optical metrology tracks surface deformation by capturing gray-level digital image patterns across a loading cycle. Applying dic strain measurement delivers full-field surface strain maps during high-speed stretch blow moulding or biaxial tension tests of polymer membranes. The optical technique quantifies localized necking, strain concentrations, and shear band formation across flat or curved surfaces, provided the speckle pattern remains bonded and visually resolveable under high stretch ratios.
Pattern Density
Surface preparation requires applying contrasting paint speckles that deform conformally with the underlying polymer substrate. Executing dic strain measurement demands uniform speckle size distributions relative to camera sensor pixels to maintain high correlation confidence. Coarse speckles reduce spatial resolution around narrow transition radii in thermoformed parts, while overly fine patterns blur into grey noise under high magnification.
Flexible paint formulations prevent speckle flaking during elastomer testing at several hundred percent elongation.
Optical Resolution
Sub-pixel pattern tracking algorithms calculate displacement vectors across discrete facet arrays. Dense facets capture sharp strain gradients near injection gates, though computational processing time scales exponentially with image grid density.
Out-of-Plane Distortion
Dual-camera stereoscopic setups eliminate false strain readings caused by sample motion toward or away from lenses. Single-camera systems misinterpret perpendicular movement as planar stretch, generating spurious strain values across target zones.