Mixed mode II and III fatigue crack growth in a rail steel

International audienceRolling contact fatigue cracks in rails undergo non-proportional mixed-mode I+II+III, in variable proportionsalong their front. In order to determine the crack growth thresholds and kinetics in mixed-mode II/III, asymmetricfour point bending tests are run on a rail steel with different angles between the crack front and theshearing load, so as to vary the mode mixity ratio. For sufficiently high loading ranges, these tests give rise tocoplanar shear-mode crack growth. The effective stress intensity factors (SIFs) are derived by an inverse methodfrom the measured crack face relative displacements. It appears to be 10–70% lower than the nominal SIFs andto allow a reasonable correlation of the measured crack growth rates. The local application, ahead of the crackfront, of shear-driven or tension-driven fatigue damage models – after 3D elastic-plastic computations of localstress and strain ranges – allows a successful prediction of crack fronts paths and growth rates