ISSN: 0090-3973
Page Count: 6

The Effects of Residual Stress, Loading, and Crack Geometry on SEPB Fracture Toughness Test Results

Grendahl, S
Worcester Polytechnic Institute,MA,
Presently with the Army Research Laboratory,MD,

Bert, R
Worcester Polytechnic Institute,MA,
Presently with Howmet Corporation,CT,

Cho, K
Worcester Polytechnic Institute,MA,
Presently with the Army Research Laboratory,MD,

Bar-On, I
Worcester Polytechnic Institute,MA,

(Received 18 August 1999; accepted 29 November 2000)

Abstract

Use of the single-edge precracked beam (SEPB) specimen with the “bridge indentation” method is one of the new ASTM standard test methods for the determination of fracture toughness of advanced ceramics. In support of this effort, the effects of several test parameters on the fracture toughness values were established. The effects of the residual stress due to the indent, the alignment in three- and four-point bending, and the crack front straightness on the fracture toughness values were determined using aluminum nitride specimens. The results show that indent loads should be kept below 100 N (10 kg), and the crack plane angle should be less than 5° in order to prevent artificially high fracture toughness values. Crack front straightness requirements can be less stringent than generally accepted.

Keywords:
fracture toughness, residual stress, aluminum nitride, crack plane, crack front straightness

Paper ID: JTE12255J
DOI: 10.1520/JTE12255J
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