Chapter 20. Investigation of “Halos” Associated with Fracture Toughness Precracks

  1. J. P. Singh
  1. Jeffrey J. Swab1 and
  2. George D. Quinn2

Published Online: 26 MAR 2008

DOI: 10.1002/9780470294444.ch20

Proceedings of the 21st Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 18, Issue 4

Proceedings of the 21st Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 18, Issue 4

How to Cite

Swab, J. J. and Quinn, G. D. (1997) Investigation of “Halos” Associated with Fracture Toughness Precracks, in Proceedings of the 21st Annual Conference on Composites, Advanced Ceramics, Materials, and Structures - B: Ceramic Engineering and Science Proceedings, Volume 18, Issue 4 (ed J. P. Singh), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470294444.ch20

Author Information

  1. 1

    U.S. Army Research Laboratory-Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005

  2. 2

    National Institute of Standards and Technology, Gaithersburg, MD 20899

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 1997

ISBN Information

Print ISBN: 9780470375532

Online ISBN: 9780470294444

SEARCH

Keywords:

  • fractographic;
  • reorientation;
  • indentation;
  • ceramics;
  • elucidate

Summary

The surface crack in flexure (SCF) method, which is used to determine the fracture toughness of dense ceramics, necessitates the measurement of precrack sizes by fractographic examination. Optical examination of the fracture surfaces of a high-purity Al2O3, an AIN, and a glass-ceramic revealed the presence of a “halo” around the periphery of each precrack. The halo in the AIN was merely an optical effect due to crack reorientation. However, for the Al2O3 and the glass-ceramic the halo was due to environmentally-assisted slow crack growth. The stable crack extension in the alumina must be included as part of the critical crack size in order to determine the appropriate fracture toughness.