A typical procedure involves illuminating the sample with laser light of a known wavelength, causing the material to release its own radiation in response (see fluorescence).
By measuring the emitted radiation and comparing the location of the peaks to a stress-free sample, stresses in the material can be revealed without any destructive interaction.
[2] Piezospectroscopy takes advantage of both the microstructure and composition of TBCs to generate accurate results.
Because the TGO is buried beneath a thick layer of ceramic, subsurface stresses are generally difficult to detect.
[4] Within the TGO, it is the chromium (Cr3+) ions that produce strong emission spectra and allow for piezospectroscopic analysis.
Because the energy levels are discrete, the spectrum for stress-free aluminum oxide always exhibits two peaks at wavelengths 14,402 cm−1 and 14,432 cm−1.
Because TBC failure can begin at microscopic scales, magnification is often essential to accurately detect stresses.
[citation needed] A monochromator is used to filter out weakly scattered light and permit the strong emission peaks from the fluorescent response.
[citation needed] Many types of detectors are used with piezospectroscopy, the two most common being dispersion through a spectrograph or an interferometer.
[citation needed] It is critical that TBCs be applied properly in order to prevent premature microfractures, delamination, and other structural failure.