ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
The R-curve behavior of an Al2O3 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 Cr3+ fluorescence lines of Al2O3. 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.1999.tb01904.x
