Silicon Piezoresistive Pressure Diaphragm Encapsulation Selection Criteria
Encapsulation selection balances gel potting low cost against oil-filled cell thermal stability to control long term zero drift and field recalibration expenses.
Shear Modulus Hardening
Elastic Transition
Elastomeric compounds and metallic alloys exhibit changes in their resistance to shearing forces when subjected to continuous deformation or aging. The phenomenon of shear modulus hardening represents the rise in shear modulus that occurs as the material undergoes cyclic strain or environmental curing. This change determines the stiffness and vibration damping performance of elastomer mounts used in sensitive metrological enclosures.
Metrological Characterization
Quantification of this property involves dynamic mechanical analysis or rotational rheometer testing. The shear modulus is measured by applying a sinusoidal shear strain to a sample and recording the resulting stress response. This test must be conducted under precise thermal control because polymer stiffness is highly sensitive to temperature.
The displacement and force sensors of the rheometer are calibrated against a steel reference specimen with a known, stable elastic profile. This calibration ensures that measured increases in stiffness are due to material hardening rather than instrument drift.
Aging Variable
Environmental aging and chemical cross-linking are the primary drivers of this hardening over time. In rubbers and polyurethane elastomers, the continuous exposure to oxygen and heat causes additional molecular cross-linking, which reduces the elasticity of the material. This process shifts the resonant frequency of vibration isolation mounts, which can degrade the performance of high-precision sensors.
Engineers use thermal-accelerated aging models to predict the long-term hardening behavior of these materials based on short-term high-temperature tests.
Structural Boundary
Elastic modeling does not apply to plastic deformation regimes where the strain is irreversible. If the strain exceeds the linear elastic region, micro-voids form and the material softens. This damage alters the stress-strain curve.