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 frequency of the characteristic R2 fluorescence line of chromium in sapphire obtained by focusing an optical probe at different depths in a sapphire fiber intersecting the surface of the composite. The method is described together with its calibration. Both the axial and radial components of the residual stress in the fiber are observed to vary over a depth of approximately the fiber diameter and are then almost independent of depth.