Appearance features provide extensive and valuable information about fracturing. Descriptive analysis, one finds, can be based upon a relatively simple model which assumes the crack is a flat internal free surface embedded in a linear elastic stress field. The crack-extension force G corresponding to this model is the Griffith crack theory strain energy release rate. A factor K, proportional to √G, represents the stress elevation near the crack border. Crack toughness may be defined as the critical value Kc (or Gc) for onset of rapid crack extension.
A crack traversing a plate converts from the transverse tensile to the oblique shear fracture mode as the size of the crack border plastic strain zone begins to exceed the plate thickness. When fracture mode transition is suppressed by elastic constraint a brittleness temperature of fundamental significance is not observed. For high strength pressure vessels an estimated plastic zone size of twice the plate thickness corresponds to a “leak before break” toughness criterion.
For structural metals Gc exceeds solid state surface energy by a factor of the order of 104. Apparently lattice slip and the non-coplanor character of crack border elements each provide a hundred-fold increase of crack toughness. In its general aspects fracture strength is dominated by flaws and flaw growth rates.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
TAM R 202
1967-0498
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/111915
Copyright and License Information
Copyright 1961 Board of Trustees of the University of Illinois
TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.
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