Raman microprobe evaluation in bridging stresses in highly anisotropic silicon nitride

The microscopic bridging stress distribution developed behind the crack tip of a highly anisotropic silicon nitride has been measured along the crack profile using Raman microprobe spectroscopy with a micrometer spatial resolution. The near\u2010tip rising R\u2010curve behavior and the crack\u2010opening displacement (COD) profile of the material were also determined and discussed in comparison with the Raman microstress data. A comparison with the fracture behavior of a previously investigated silicon nitride material with a three\u2010dimensional random microstructure is also proposed. According to this set of micro/macroscopic fracture characterizations, a self\u2010consistent view of toughening behavior in silicon nitride ceramics is obtained, and the role on toughness of anisotropically oriented acicular grains clarified. In agreement with previous studies, it is confirmed that crack\u2010face bridging is the most effective mechanism for toughening silicon nitride ceramics