Micromechanics of fracture in a ceramic/metal composite studied by in situ fluorescence spectroscopy I: Foundations and stress analysis

in situ

microstress fields that develop during fracture in an exemplary ceramic/metal composite. Stress maps are obtained over a relatively large area in the neighborhood of a propagating crack at both zero and critical loading conditions. Theoretical and experimental issues of concern for measurement of local complex stress fields are dealt with. In particular, a review of the fluorescence spectroscopy technique in context with ceramic materials is presented and experimental procedures are proposed to deconvolute the experimental peak-shift in individual components arising from (pre-existing) residual stress fields and microstress fields additionally developed during fracture (e.g., bridging stresses). The results illustrate that, despite the approximations involved with applying piezo-spectroscopic equations for assessing microstress fields, fluorescence microprobe spectroscopy is a viable method for quantitative investigations of crack-wake microfracture mechanisms in ceramic materials.