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The surface crack embedded with cylindrical components such as shaft, bar, bolt and
wire is the most common crack model and has received widespread attention in the
past. Due to geometrical complexity, some simplification had been made for the
crack profile such as straight-edged, circular, notch and elliptical crack model to
analyze such crack problem.
Cylindrical components have many applications in aircraft design. These structural
components are subjected to cyclic stresses, which can cause damage and premature
failure by fatigue crack growth. As it is well known, the design of engineering
components in the past was only based on the S-N curves and did not consider the
crack initiation and crack growth phases to predict life. Most of the mechanical failures by fatigue process on rotor shafts have origin on surface cracks that grow with a notch
shape. Surface cracks emanating from stress concentrating locations are the most
common phenomena of fatigue failure. Bars with variable cross-sections are a category
of cylindrical parts and components extensively used in engineering mechanisms.
Surface fatigue cracks are frequently initiated in such components at the stress
concentrating locations, then they propagate into the interior of the parts and can
cause final fracture abruptly (Brown, 1975).
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