Quadrupolar Fiber Coil Potting Material Selection for Tactical Gyroscope Thermal Stability
Select low-modulus addition-cure silicones with sub-minus 100 Celsius glass transitions to decouple thermal stress from quadrupolar gyroscope fiber coils.
Cure Shrinkage
Dimensional Variation
Volumetric reduction occurring during the transition of a liquid resin into a solid state affects the structural integrity of encapsulated components. This phenomenon, known as cure shrinkage, occurs as monomer units form closer covalent bonds to reorganise into denser polymeric networks. If the dimensional changes are not controlled, they can induce mechanical stress on embedded electronics.
Volumetric Reduction
The transition from liquid to solid involves both chemical and thermal effects that contribute to the overall change in dimensions. In addition cure systems, the shrinkage is minimal because no volatile compounds are emitted, whereas condensation cure systems experience more significant reductions in volume as reaction byproducts escape. Thermosetting resins like epoxies can shrink by up to several percent during cross-linking, depending on the filler load and the chemistry of the curing agent.
Applying specific fillers like silica or glass beads is a standard method to reduce this volumetric change.
Stress Generation
Internal stresses result when the curing material is constrained by the rigid walls of a housing or by the surface of the encapsulated sensor. When the compound shrinks, it pulls against these boundaries, creating tensile forces within the polymer and compressive forces on the embedded electronics. These forces can cause physical damage, such as the cracking of delicate ceramic capacitors or the delamination of the potting material from the housing wall.
In optical fibers, these compressive stresses can bend the waveguide, causing signal attenuation or altering the polarization of the transmitted light. This mechanical tension can also drift the calibration of pressure and strain transducers, necessitating recalibration after the resin has fully stabilized.
Metrological Assessment
Measurement of this volumetric contraction is typically performed using density displacement methods or optical dilatometry under controlled temperature conditions. Standard ASTM methods provide the framework for quantifying the percentage of cure shrinkage by measuring the density of the liquid resin prior to curing and comparing it to the density of the fully cured solid. Instrument designers use these precise metrics to calculate the clearance required within sensor housings.
Accurate tracking of the dimensional change ensures that the final assembly remains within the mechanical tolerances specified for the completed instrument.