MECHANICS OF THE PUSH-OUT PROCESS FROM IN-SITU MEASUREMENT OF THE STRESS-DISTRIBUTION ALONG EMBEDDED SAPPHIRE FIBERS

The basic mechanics of the fiber push-out process are studied by measu ring the stress distributions along c-axis sapphire fibers in gamma-Ti Al matrices. The stress measurements were made in situ during fiber pu sh-out tests using a piezo-spectroscopy method. By focussing an optica l microprobe into a sapphire fiber, the frequency shift distribution o f the characteristics R lines of Cr3+, and hence the stress distributi on along the fiber were determined at each increment of applied load. By comparing the measured stress distributions with ones calculated us ing finite element method, key mechanical parameters including residua l stress before composite slicing, debond length at each load, debond energy and the frictional stress along the interface in both debonding and sliding phases were determined. Two coating systems (Mo/Al2O3 and CVD-C/Al2O3) were studied. The results also show that while the debon d energies differ by an order of magnitude, the frictional stresses ar e very similar in magnitude, suggesting that the interface morphology is of greater importance than the nature of the coating.