Residual and bridging microstress fields in Al2O3/Al interpenetrating network composite evaluated by fluorescence spectroscopy

Experimental recognition of toughening by crack-wake bridging mechanism in liquid-metal infiltrated Al2O3/Al composite has been substantiated by microscopic stress analysis involving the determination of both residual and bridging stress fields developed on the microstructural level. A piezo-spectroscopic technique, based on microprobe measurements of the Cr3+ optical fluorescence in the Al2O3-matrix phase, has been employed to assess microscopic stresses. Microscopic stress fields which developed during cooling from the temperature of liquid-metal infiltration were mapped and their overlapping effect on the bridging stress field, developed during fracture on the advancing crack, analyzed in situ. Emphasis is placed on developing a microstress measurement procedure which, taking into account the interaction between residual and bridging stress fields, enables one to relate the microscopic fracture behavior to the macroscopic fracture mechanics characteristics (i.e. the rising R-curve behavior) of the Al2O3/Al composite.