SEDL / STP / STP1409-EB / STP10476S

Crack Deflection Toughening Mechanism in Brittle Materials

Awaji, H
Professor, and graduate students, Nagoya Institute of Technology, Nagoya,

Ebisudani, M
Professor, and graduate students, Nagoya Institute of Technology, Nagoya,

Choi, S-M
Professor, and graduate students, Nagoya Institute of Technology, Nagoya,

Ohashi, T
Professor, and graduate students, Nagoya Institute of Technology, Nagoya,

Pages: 15    Published: Jan 2002

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Abstract

Toughening mechanisms in polycrystalline ceramics and ceramic-based composites were discussed based on Griffith's energy equilibrium and classified into three groups: (A) the frontal process-zone toughening mechanism, (B) the crack-bridging mechanism, and (C) the macroscopic crack-deflection mechanism. The increase in fracture toughness caused by enforced macroscopic crack-deflection was estimated using the energy equilibrium between the energy-release rate and the fracture-energy rate. The analytical results revealed that the fracture toughness under Mode I loading was enhanced by twice the normal value when the crack propagates in the direction 90° from its original plane. Under Mode II loading the fracture toughness is increased 1.2 times the normal value when the crack propagates in its original plane. Crack-deflection tests were carried out by using wooden, thin rectangular plates with a central crack. The increase in the fracture toughness caused by crack deflection was confirmed and the experimental data was coincident with the calculated results.