Three-dimensional finite element analysis of fatigue crack closure behavior in surface flaws

Finite element technique has been widely used in 2-D fatigue crack closure problems for almost three decades. However, the reported 3-D surface crack closure results obtained from this technique are scarce. One possible cause could be the meshing difficulty. In the present study, meshing issues are discussed. Subsequently, both semi-circular and semi-elliptical crack closure behaviors at various loading conditions are calculated. The calculated results show that the closure and opening phenomena of surface cracks are caused by two types of plastic wake, that is, the near-surface type and the interior region type. In the stress ratio R=0 cases, the final crack-front opening always takes place at the free surface. However, the calculated R=−1 results show a different crack opening sequence. In the semi-elliptical crack results, along the crack front, different opening levels are found at various locations of the interior region. Finally, surface crack shape development incorporating the crack closure effect is also briefly discussed.