skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Effect of precrack halos on kic determined by the surface crack in flexure method. Final report, August 1995-May 1997

Abstract

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. Stable crack extension may occur from flaws under ambient room-temperature conditions, even in the relatively short time under load during fast fracture strength or fracture toughness testing. In this paper, fractographic techniques are used to characterize evidence of stable crack extension, a halo, around Knoop indentation surface cracks. Optical examination of the fracture surfaces of a high-purity Al2O3, an AlN, a glass-ceramic, and a MgF2 revealed the presence of a halo around the periphery of each precrack. The halo in the AlN was merely an optical effect due to crack reorientation, while the halo in the MgF2 was due to indentation-induced residual stresses initiating crack growth. However, for the Al2O3 and the glass-ceramic, environmentally assisted slow crack growth (SCG) was the cause of the halo. In the latter two materials, this stable crack extension must be included as part of the critical crack size in order to determine the appropriate fracture toughness.

Authors:
;
Publication Date:
Research Org.:
Army Research Lab., Aberdeen Proving Ground, MD (United States)
OSTI Identifier:
575004
Report Number(s):
AD-A-335068/3/XAB; ARL-TR-1575
TRN: 80750935
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Dec 1997
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRACK PROPAGATION; FRACTOGRAPHY; FRACTURE PROPERTIES; MAGNESIUM FLUORIDES; PROGRESS REPORT; ALUMINIUM NITRIDES; ALUMINIUM OXIDES; KNOOP HARDNESS

Citation Formats

Swab, J J, and Quinn, G D. Effect of precrack halos on kic determined by the surface crack in flexure method. Final report, August 1995-May 1997. United States: N. p., 1997. Web.
Swab, J J, & Quinn, G D. Effect of precrack halos on kic determined by the surface crack in flexure method. Final report, August 1995-May 1997. United States.
Swab, J J, and Quinn, G D. 1997. "Effect of precrack halos on kic determined by the surface crack in flexure method. Final report, August 1995-May 1997". United States.
@article{osti_575004,
title = {Effect of precrack halos on kic determined by the surface crack in flexure method. Final report, August 1995-May 1997},
author = {Swab, J J and Quinn, G D},
abstractNote = {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. Stable crack extension may occur from flaws under ambient room-temperature conditions, even in the relatively short time under load during fast fracture strength or fracture toughness testing. In this paper, fractographic techniques are used to characterize evidence of stable crack extension, a halo, around Knoop indentation surface cracks. Optical examination of the fracture surfaces of a high-purity Al2O3, an AlN, a glass-ceramic, and a MgF2 revealed the presence of a halo around the periphery of each precrack. The halo in the AlN was merely an optical effect due to crack reorientation, while the halo in the MgF2 was due to indentation-induced residual stresses initiating crack growth. However, for the Al2O3 and the glass-ceramic, environmentally assisted slow crack growth (SCG) was the cause of the halo. In the latter two materials, this stable crack extension must be included as part of the critical crack size in order to determine the appropriate fracture toughness.},
doi = {},
url = {https://www.osti.gov/biblio/575004}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1997},
month = {12}
}

Technical Report:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that may hold this item. Keep in mind that many technical reports are not cataloged in WorldCat.

Save / Share: