In Situ Measurements of Frictional Bridging Stresses in Alumina Using Fluorescence Spectroscopy |
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| Authors: | Giuseppe Pezzotti Orfeo Sbaizero Valter Sergo Naoki Muraki Ken Maruyama Toshihiko Nishida |
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| Affiliation: | Department of Materials, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606, Japan;Materials Engineering and Applied Chemistry Department, University of Trieste, 34127 Trieste, Italy;Toray Research Center, Inc., 3-3-7 Sonoyama, Otsu 520, Japan |
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| Abstract: | Fracture of a large-grained alumina polycrystal has been examined in situ by optical microscopy. Concurrently, local bridging stresses, as generated by friction or tension of unbroken ligaments in the wake of the crack path, were measured by piezospectroscopy. Stress measurements were performed both at fixed sites as a function of the external load and at a fixed external load along the crack profile. Frictional stresses were similar/congruent50 MPa, while unbroken ligaments between the crack faces were found to support tensile stresses up to similar/congruent100 MPa. The maximum bridging stress was dictated by the weak (intrinsic) interface bonding of the polycrystal. Average bridging stresses, either theoretically calculated from R -curve data or experimentally measured by piezospectroscopy on frictional/bridging sites, were similar. Such a circumstance enables us to explain the fracture behavior of polycrystalline alumina by considering crack-wake shielding as the main micromechanism contributing to toughening. |
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