3D vs. 2D fatigue crack initiation and propagation in notched plates

This paper analyses the influence of crack shape and the procedure used to calculate the stress distribution on the estimated fatigue life in a notched specimen. To estimate the crack shape, a series of interrupted tests at a various number of cycles was performed. Afterward, the specimens were broken to analyse crack shape. The stress intensity factor was calculated using weight functions from the stress distribution in uncracked specimens. The stresses were numerically calculated and three possibilities were analysed: plane stress, plane strain and three dimensional (3D). For each case (two dimensional (2D) or 3D geometries), an appropriate weight function was used. Each combination exhibited a different evolution of the stress intensity factor and therefore, different values of the propagation life. A life estimation model that combines the initiation and propagation phases without defining a one phase finishes and the other phase begins was applied in these tests. Finally, the lives described in the numerical analysis were compared with the experimental lives.