Cumulative Damage in Fatigue of a Structure Subjected to Random Loading
Engineering and Technology Journal,
2007, Volume 25, Issue 7, Pages 897-917
AbstractWhen a structure is subjected to a random loading, its dynamic response
changes, characterized by shifts in the eigenvalues and modification of eigenvectors.
The peaks in the dynamic response spectrum will give indications of the natural
frequencies of the structure. Any damage in the structure will be reflected in the
spectrum as a shift in natural frequencies.
Crack initiation and early growth of fatigue cracks in 0.4% carbon steel and
2024-T4 aluminum are investigated using spectral density approach for applied
random loading. Energetic consideration and spectral density approach lead to the
formulation of a model used to predict the behavior of short and long cracks
initiation, propagation, and paths taking into account the microstructural variables
relevant to fatigue crack initiation and early crack growth.
The model indicates that crack arrest occurs when crack-tip is blocked by a
grain boundary. In the short crack region, propagation and non-propagation occurs
depending on random loading stress level and slip band energy released. The
application of the present model to cumulative damage is compared with the
experimental data and a reasonable agreement is found. The introduction of material
specification shows a quantitative description of the parameters which affect the
reliability of a structural component subjected to random loading. The power of the
analytic model and the simulation analysis in the present work give some insight to
the behavior of the structure under random loading showing the different mode
shapes, eigenvalues/vectors, deformation, propagation and non-propagation of cracks,
and the stresses caused by such random loading that can lead to fatigue failure. A life
predication model is presented for long-life fatigue , to control the hardware design
and to find a proper combination of random load and life .
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