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.
Shear Strain Artifacts
Meaning
Fictitious strain concentrations appear in optical measurement fields when out-of-plane rotations or improper specimen clamping corrupt planar displacement tracking. Detecting shear strain artifacts prevents erroneous material calibration during biaxial tensile testing and planar shear evaluations of polymer sheets. The analytical concern applies specifically to optical displacement metrology systems such as digital image correlation, becoming irrelevant in direct contact extensometry or rigid body displacement tracking.
Error Generation
Misalignment between mechanical test axes and optical camera planes projects false shear vectors onto two-dimensional displacement maps. Experiencing shear strain artifacts leads numerical optimization routines to fit incorrect coupling parameters during hyperelastic model calibration. Specimen tilting under high tensile loads shifts pattern focus, causing facet correlation algorithms to calculate spurious shear strain values near sample edges.
Unsymmetric grip friction during cruciform testing similarly distorts uniform tension fields into false shear fields.
Alignment Control
Rigid test frames and laser-aligned camera mounts keep optical sensors parallel to the specimen plane throughout testing. Minimizing mechanical frame flex prevents out-of-plane rotation vectors from corrupting planar strain calculations.
Calibration Correction
Algorithmic filtering and rigid body motion subtraction identify and remove fictitious strain fields prior to material model fitting. Eliminating spatial artifacts ensures accurate hyperelastic parameter extraction from empirical DIC datasets.