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.
Elastomer Characterization
Meaning
Empirical physical testing measures hyperelastic, viscoelastic, and temperature-dependent responses of crosslinked or thermoplastic rubbers. Performing elastomer characterization supplies essential stress-strain curves needed to calibrate constitutive material models for finite element simulations of seals, bladders, and flexible components. The evaluation process covers physical testing across multiple strain modes, temperature ranges, and strain rates, stopping short of predicting long-term chemical degradation or oxidative aging effects.
Multiaxial Testing
Capturing complete mechanical behavior requires subjecting test samples to pure tension, planar shear, equibiaxial extension, and volumetric compression. Executing elastomer characterization across only one deformation mode produces incomplete datasets that fail to predict complex stress states in 3D moulded seals. Planar shear tests isolate crosslink response without lateral contraction interference, while equibiaxial tension mimics inflation forces seen in membrane structures.
Combining data from four distinct strain modes resolves hyperelastic model constants with minimal numerical ambiguity.
Data Quality
Hysteresis and Mullins softening mask baseline elastic response during initial loading cycles. Pre-conditioning test specimens through repeated pre-stretching stabilizes stress-strain responses before logging data for model fitting.
Thermal Influence
Temperature shifts alter rubber elasticity dramatically by modifying polymer chain mobility and entropic recovery forces. Testing must match expected processing or operating temperatures to produce valid simulation inputs.