Fitting Hyperelastic Ogden Model Parameters to Biaxial Stretch Test Data
Simultaneous fitting of multi-axial stretch data to Ogden parameters prevents FEA solver instability and accurately predicts material thinning under strain.
Tensile Strain
Meaning
Elongation of a polymer specimen under an applied pulling load divided by its original gauge length constitutes the measured value. Tensile strain expresses this relative deformation as a dimensionless ratio or percentage. It quantifies how much a plastic component stretches before reaching its point of failure or permanent deformation.
Processing Mechanics
Injection moulding parameters govern the development of this internal state within a cooling cavity. High hold pressures increase the density of the solidified part and restrict the molecular movement that leads to premature yielding. Operators adjust the gate freeze time and packing profile to ensure the polymer chains remain stable during the transition from melt to solid.
Variations in the cooling rate across thick and thin sections create non-uniform distributions of this property throughout a finished article. A drift in mould temperature changes the crystalline structure and forces a shift in how the material responds to later mechanical loading.
Material Performance
Datasheet specifications for raw resins provide a controlled benchmark based on standard test bars produced under optimal conditions. Moulders must distinguish these lab values from the performance observed in complex geometries that contain sharp corners or variations in wall thickness. Virgin resin typically exhibits a predictable elongation curve while the inclusion of regrind material introduces impurities that shorten the distance to break.
Production batches might deviate from the initial target when the molecular weight distribution narrows during the repeated heating cycles of the extrusion process. Excessive elongation during field use signals a design failure where the component undergoes stress beyond its elastic limit.
Cost Implications
Quality management relies on keeping this metric within a defined window to avoid the financial penalties of structural rejection. High rates of breakage during assembly require the secondary screening of lots and the potential disposal of expensive sub-assemblies. Scrapped parts represent the loss of both raw material costs and the energy invested in machine cycle time.
Consistent monitoring of the tensile strain ensures that the final component maintains the structural integrity demanded by the end application. Accurate calibration of the test equipment prevents the false acceptance of brittle parts that fail prematurely in the field.