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 micro scopic stress analysis involving the determination of both residual and bri dging stress fields developed on the microstructural level. A piezo-spectro scopic technique. based on microprobe measurements of the Cr3+ optical fluo rescence in the Al2O3-matrix phase, has been employed to assess microscopic stresses. Microscopic stress fields which developed during cooling from th e temperature of liquid-metal infiltration were mapped and their overlappin g effect on the bridging stress field, developed during fracture on the adv ancing crack, analyzed in situ. Emphasis is placed on developing a microstr ess measurement procedure which, taking into account the interaction betwee n residual and bridging stress fields, enables one to relate the microscopi c fracture behavior to the macroscopic fracture mechanics characteristics ( i.e. the rising R-curve behavior) of the Al2O3/Al composite. (C) 2000 Elsev ier Science B.V. All rights reserved.