Epoxy Strain Transfer Efficiency Loss under Cyclic Thermal Loading
Cyclic thermal loading degrades epoxy shear modulus, causing strain transfer loss that demands strict bondline guard-banding in technical files.
Fiber Bragg Grating
Optical Strain
Optical strain measurement relies on a fiber bragg grating inscribed directly into the core of a silica glass strand by ultraviolet laser exposure. Ultraviolet interference patterns alter local refractive indices permanently along a predetermined length of the optical pathway. Periodic variations in this internal profile reflect specific wavelengths of light while transmitting all other spectral components forward without interruption.
Mechanical tension applied to the host structure stretches the microscopic grating pitch and shifts the reflected wavelength upward in proportion to the applied elongation.
Thermal Drift
Temperature fluctuations alter both the physical length of the glass waveguide and the thermo optic coefficient of the core material. Wavelength shifts caused by ambient thermal variations introduce measurement errors during structural monitoring unless dual cavity compensation or physical decoupling isolates the strain response. Uncompensated sensors register apparent mechanical loads when subjected to thermal gradients alone because silica expands predictably upon heating.
Calibration matrices convert raw spectral shifts into accurate values by subtracting the known thermal sensitivity component from the combined optical reading.
Interrogation Limits
Optical spectrum analyzers and specialized interrogation hardware sample returning wavelengths at discrete frequency intervals to determine absolute peak positions with high resolution. Signal processing algorithms calculate the centroid of the reflected spectrum to resolve subpicometer shifts despite inherent noise in the photodetector circuit. Maximum acquisition rates depend on the sweep frequency of the tunable laser source within the interrogation unit.
Extended lead lengths between the sensor array and the processing hardware degrade signal amplitude through inherent insertion losses and connector back reflections.