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 measuring the stress distributions along c-axis sapphire fibers in γ-TiAl matrices. The stress measurements were made in situ during fiber push-out tests using a piezo-spectroscopy method. By focussing an optical microprobe into a sapphire fiber, the frequency shift distribution of the characteristics R lines of Cr3+, and hence the stress distribution along the fiber were determined at each increment of applied load. By comparing the measured stress distributions with ones calculated using finite element method, key mechanical parameters including residual 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 debond energies differ by an order of magnitude, the frictional stresses are very similar in magnitude, suggesting that the interface morphology is of greater importance than the nature of the coating.