A study on dynamic stress intensity factors of rail cracks at high speeds by a 3D explicit finite element model of rolling contact

A 3D explicit finite element model has been developed with ANSYS/Ls-dyna to study the dynamic interaction between a wheelset and a cracked rail at high speeds. Two contact pairs are separately defined in the wheel-rail interface and between the crack faces, for which Coulomb׳s law of friction is implemented. By incorporating a self-developed program, the dynamic stress intensity factors (SIFs) at the crack tip are calculated from the dynamic solutions using the virtual crack closure technique. As the first step, this work investigates the vertical rail crack being perpendicular to the contact surface. Significant difference between the dynamic and the static contact solutions illustrates that the cracking behavior is essentially a dynamic phenomenon, and the moving Hertzian loading usually assumed in the literature is not strictly valid. It is further found that the vertical cracks are completely closed during the wheel passage, resulting in the absence of SIF KI along the crack tip, and larger KII with respect to KIII. A parameter variation analysis confirms that the traction effort and the lubrication on crack faces can significantly enhance the potential of crack propagation, while the rolling speed is found to have negligible influence under the assumption of linear elastic material. Considering the minimum fracture toughness of 26 MPa m1/2 of a rail material (U71MnG), a vertical crack can hardly propagate into the bulk, being in line with field observations that RCF cracks usually propagate at shallow angles to the contact surface.