Location

La Jolla, CA

Start Date

1-1-1987 12:00 AM

Description

Machining damage to structural ceramics is complex; a single machining crack consists of a series of continuous and overlapping semielliptical surface flaws between about 10 and 100 μm deep, as shown schematically in Fig, 1a. The mouths of these flaws are held closed by a layer of compressive residual stresses induced by the irreversible plastic deformations and material removal occuring during machining. Beneath the compressive layer is a zone of weak tension which separates the subsurface portions of the flaw faces. These residual stress fields permit stable crack growth to about 4.5 times the initial flaw depth prior to fracture, and are responsible for as much as a 40% reduction in material strength. Figure lb shows a series of closely-spaced machining cracks, such as might be produced during multipoint grinding. In the absence of significant internal flaws prior to shaping, these surface cracks assume a strength-controlling role [1]. To successfully predict the failure strength of a ceramic part then, we need to determine the depth of the deepest machining flaw.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

6B

Chapter

Chapter 8: Materials Characterization

Section

Cracks and Deformation

Pages

1617-1623

DOI

10.1007/978-1-4613-1893-4_182

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Resolution of Closely-Spaced Machining-Damage-Induced Surface Cracks in Ceramics

La Jolla, CA

Machining damage to structural ceramics is complex; a single machining crack consists of a series of continuous and overlapping semielliptical surface flaws between about 10 and 100 μm deep, as shown schematically in Fig, 1a. The mouths of these flaws are held closed by a layer of compressive residual stresses induced by the irreversible plastic deformations and material removal occuring during machining. Beneath the compressive layer is a zone of weak tension which separates the subsurface portions of the flaw faces. These residual stress fields permit stable crack growth to about 4.5 times the initial flaw depth prior to fracture, and are responsible for as much as a 40% reduction in material strength. Figure lb shows a series of closely-spaced machining cracks, such as might be produced during multipoint grinding. In the absence of significant internal flaws prior to shaping, these surface cracks assume a strength-controlling role [1]. To successfully predict the failure strength of a ceramic part then, we need to determine the depth of the deepest machining flaw.