ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 6

Surface-Crack Shape Change in Bending Fatigue Using an Inexpensive Resonant Fatiguing Apparatus

Pierce, WS
Materials engineer and headmember of ASTM, Strength of Materials Section, National Aeronautics and Space Administration Lewis Research Center, Cleveland, Ohio

Shannon, JL
Materials engineer and headmember of ASTM, Strength of Materials Section, National Aeronautics and Space Administration Lewis Research Center, Cleveland, Ohio

Abstract

An inexpensive device for producing surface cracks of controlled size and shape is described along with results of its use which show how the shape of the surface crack changes as it grows in bending fatigue from a variety of crack starter shapes. The growth pattern for any crack is uniquely defined by the crack starter configuration and appears to be independent of alloy. Shape changes are substantial and all growth curves tend toward a common growth curve. Circular cracks tend to become elliptical with an associated increase in stress intensity factor. This increase accelerates the crack growth rate and proximity to the critical flaw size. Through-cracks produced by the extension of a surface crack in a bending stress field will have length ten times the section thickness. The results demonstrate the necessity of taking into account changing crack shape in the calculation of structural life when bending is a significant component of the stress field.

Keywords:
fractures (materials), crack propagation, bending, crack growth, fracture toughness, crack shape

Paper ID: JTE10940J
DOI: 10.1520/JTE10940J
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