Test Protocol
Mechanical testing procedures measure force decay over time while holding elastomeric or polymeric specimens at constant compressive or tensile strain. Executing stress relaxation validation confirms that long-term material load decay follows predicted viscoelastic constitutive models. Tests record load relaxation curves across designated time intervals to confirm force decay or structural load retention.
Validity requires maintaining constant specimen deformation without mechanical drift in loading frames.
Fixture Compliance
Loading frame deflection under initial application of force introduces strain variations that corrupt load relaxation curves. Compliance calibration measures load frame stiffness to correct applied strain calculations. High-rigidity load frames minimize machine deformation during rapid strain application phases.
Load cell thermal drift must remain orders of magnitude below expected material force decay.
Temperature Control
Polymer relaxation rates exhibit high sensitivity to environmental temperature fluctuations during long duration evaluations. Environmental chambers maintain specimen temperatures within narrow band limits across multi-day testing periods. Thermal expansion of test fixtures introduces artificial strain changes that alter measured relaxation forces.
Multi-temperature testing allows time-temperature superposition mapping to predict multi-year seal behavior.
Acceptance Criteria
Engineering standards specify allowable percentage force loss over defined operational lifetimes. Seals and gaskets undergo validation testing to ensure retention of minimum sealing contact pressure under operational compressive strains. Deviation from exponential relaxation models indicates material degradation or microstructural damage.
Test certificates document initial strain and total load decay.
