Fatigue crack propagation in complex stress fields: Experiments and numerical simulations using the Extended Finite Element Method (XFEM)

This work presents the numerical simulation and validation of a fatigue propagation test of a semi-elliptical crack located at the side of the rectangular section of a beam subjected to four-point bending. For most common fatigue test configurations there are equations that allow calculating the stress intensity factors (SIFs). However, no solution is provided if the crack is located on any of the lateral sides of the rectangular section, since one part of the crack is located in the tractive zone while the other is at the compressive zone. In these cases, it is necessary to use alternative methods. The Extended Finite Element Method (XFEM) provides a new alternative for the calculation of SIFs, and to simulate crack propagation, by using special interpolation functions. Furthermore, XFEM-based LEFM approach offers the advantage of performing crack growth analysis without the need for updating the mesh (re-meshing). The experimental tests have been carried out in an Instron 8874 biaxial testing machine. Crack growth was controlled by optical microscopy and by progressive crack surface heat tinting. For the numerical simulations, the Extended Finite Element Method (XFEM) implemented in the Abaqus® 2017 software has been used. The comparison between the experimental and numerical results shows very good correlation regarding crack shape and number of cycles to failure. The capabilities of the XFEM-based LEFM approach to simulate fatigue crack growth in complex crack fronts are validated.