Three dimensional finite element analysis of fatigue crack closure

A3-D elastic-plastic finite element model has been developed tosimulate the behaviour of a single edge cracked specimen under monotonicand cyclic loading. The finite element model was composed of four-nodedtetrahedral elements. Relevant kinematic parameters corresponding toloading-unloading and reloading phases of the cycle were computed andcorrelated. The commonly used Von Mises yield criterion and the Prandtl-Reuss flow rule were adopted. In the plastic regime, the stress-plasticstrain behaviour of the material was assumed to obey a simple power law.A 2-D finite element analysis under plane stress and plane strainconditions was also invoked and compared with the correspondence fromthe 3-D analysis. The numerical analysis was performed for differentspecimen thickness, applied stress and different shapes of crack frontgeometry at zero stress ratio. Idealization of specimen thickness byunequal layers was compared to that of equal layers.The development of plastically deformed zones, stationary andcyclic crack tip opening displacement along the crack front were recordedand correlated. Step by step tracing of the crack front formation duringfatigue crack growth and the relevant changes in the crack tip deformationparameters and crack surface closure were also investigated.The results demonstrated that, the equal layers idealization simulatewell the stress-strain and deformation fields existing along the crack frontcompared to that of unequal layers. The variation of stress-strain anddeformation fields along the front of straight through thickness crack were