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Measurement of Microscopic Bridging Stresses in an Alumina/Molybdenum Composite by In Situ Fluorescence Spectroscopy
Author(s) -
Pezzotti Giuseppe,
Suenobu Hiroyuki,
Nishida Toshihiko,
Sbaizero Orfeo
Publication year - 1999
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1999.tb01904.x
Subject(s) - materials science , bridging (networking) , composite material , fracture mechanics , ceramic , composite number , fracture toughness , stress intensity factor , computer network , computer science
The R ‐curve behavior of an Al 2 O 3 ceramic with 25 vol% of molybdenum‐metal particles added was studied by using fracture‐mechanics experiments and in situ piezospectroscopic measurements of microscopic bridging tractions. Cracks were propagated by using a crack stabilizer, which allowed stable crack growth in a bending geometry. Microscopic bridging stresses were measured in situ during fracture propagation by detecting the shift of the Cr 3+ fluorescence lines of Al 2 O 3 . Laser spots ∼1 µm in diameter and ∼10 µm deep were focused at the ceramic/metal interface of the bridging sites, and the closure stresses that acted on the crack faces were recorded as a function of external load. The maximum stress that was experienced by the stretched metal particles prior to final failure was ∼0.4 GPa. The maximum stress magnitude was not markedly different in relatively small (i.e., <5 µm) metal particles, failing with large ductility, as compared with larger particles which, instead, fractured in semibrittle fashion. A map of bridging tractions along the crack wake was constructed under a constant stress intensity factor, almost equal to that which is critical for crack propagation. Using this map to theoretically predict the rising R ‐curve behavior of the composite led to results that were consistent with the fracture‐mechanics experiments, thus enabling us to explain the observed toughening, primarily in terms of a crack‐bridging mechanism.