الفهرس 
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Abstract
A3-D elastic-plastic finite element model has been developed to
simulate the behaviour of a single edge cracked specimen under monotonic
and cyclic loading. The finite element model was composed of four-noded
tetrahedral elements. Relevant kinematic parameters corresponding to
loading-unloading and reloading phases of the cycle were computed and
correlated. The commonly used Von Mises yield criterion and the Prandtl-
Reuss flow rule were adopted. In the plastic regime, the stress-plastic
strain behaviour of the material was assumed to obey a simple power law.
A 2-D finite element analysis under plane stress and plane strain
conditions was also invoked and compared with the correspondence from
the 3-D analysis. The numerical analysis was performed for different
specimen thickness, applied stress and different shapes of crack front
geometry at zero stress ratio. Idealization of specimen thickness by
unequal layers was compared to that of equal layers.
The development of plastically deformed zones, stationary and
cyclic crack tip opening displacement along the crack front were recorded
and correlated. Step by step tracing of the crack front formation during
fatigue crack growth and the relevant changes in the crack tip deformation
parameters and crack surface closure were also investigated.
The results demonstrated that, the equal layers idealization simulate
well the stress-strain and deformation fields existing along the crack front
compared to that of unequal layers. The variation of stress-strain and
deformation fields along the front of straight through thickness crack were