Finite element analysis of a laser-processed fracture specimen

Finite element analysis was used to simulate the static failure of a AISI 4140, three-point bend, Charpy specimen. Non-linear finite element models (FEM) were constructed to represent standard Charpy, fatigue-precracked Charpy, and laser-processed Charpy specimens. For the laser-processed Charpy FEM, a strain-based failure criterion was used to simulate crack propagation through the 0.5 mm thick laser-processed zone. For comparison, a 0.5 mm long crack was used in the fatigue-precracked FEM and similarly loaded. Results showed that the numerically calculated load for crack initation through this zone compared favorably to that reported in earlier experiments. Furthermore, after the crack had propagated through the laser-processed zone within the FEM-comparison of plastic strain contours for this model and that for a fatigue-precracked model showed that similar patterns exist around the crack tip. These results indicate that laser-processing and fatigue-precracking should provide a similar basis for fracture toughness measurements.