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Development of Crack Growth Rate at Multiple Overloads
Last modified: 2013-05-03
Abstract
To improve the knowledge of fatigue crack propagation the development of the
crack growth rate at multiple overloads with constant stress intensity, K, in steels
has been experimentally studied. To keep K constant, a special test equipment has
been developed at the Institute of Materials Science. Using a very high-resolution
DC-potential drop method and recording the potential signal about 50 times per
load amplitude, the crack propagation could be observed continuously with a
cycle by cycle resolution of about 1μm. In multiple overloads the crack
propagation within the first cycle ΔaOL,1 was found to be about hundred times
greater than in the following cycles. This behaviour cannot be explained by
LEFM. It was found that ΔaOL,1 may be explained by the crack tip opening
displacement. However, in the following overload cycles the dislocation structure
in front of the crack tip seems to control the crack growth as assumed by
J. Weertman.
crack growth rate at multiple overloads with constant stress intensity, K, in steels
has been experimentally studied. To keep K constant, a special test equipment has
been developed at the Institute of Materials Science. Using a very high-resolution
DC-potential drop method and recording the potential signal about 50 times per
load amplitude, the crack propagation could be observed continuously with a
cycle by cycle resolution of about 1μm. In multiple overloads the crack
propagation within the first cycle ΔaOL,1 was found to be about hundred times
greater than in the following cycles. This behaviour cannot be explained by
LEFM. It was found that ΔaOL,1 may be explained by the crack tip opening
displacement. However, in the following overload cycles the dislocation structure
in front of the crack tip seems to control the crack growth as assumed by
J. Weertman.
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