Characterization of residual stresses in a sapphire-fiber-reinforced glass-matrix composite by micro-fluorescence spectroscopy

Residual stress in fibers of a sapphire-fiber-reinforced glass-matrix composite arising from thermal expansion mismatch is characterized by measuring the shift of the optical fluorescene lines of Cr⁺³ in sapphire. The stress is found to vary along the fiber length as well as across the fiber cross-section for an uncoated fiber embedded in a glass matrix. Some finite residual stress is also measured at the fiber ends. Analytical models to explain the experimentally measured stress variations are proposed. The high spatial resolution of the microprobe spectrometer is demonstrated for mapping stresses across a specific section of the composite.