MEASUREMENT OF RESIDUAL-STRESSES IN SAPPHIRE FIBER COMPOSITES USING OPTICAL FLUORESCENCE

The residual stresses in c-axis sapphire fibers in a gamma-TiAl matrix and in a polycrystalline Al2O3 matrix as a function of distance below a surface are determined. They are obtained from the shift in frequen cy of the characteristic R2 fluorescence line of chromium in sapphire obtained by focusing an optical probe at different depths in a sapphir e fiber intersecting the surface of the composite. The method is descr ibed together with its calibration. Both the axial and radial componen ts of the residual stress in the fiber are observed to vary over a dep th of approximately the fiber diameter and are then almost independent of depth.