INFLUENCE OF WHEEL-RAIL ADHESION COEFFICIENT ON TRANSIENT PROPAGATION OF A VERTICAL RAIL CRACK

A 3D explicit finite element model has been established with ANSYS/LS-DYNA to simulate the high-speed transient rolling contact between a wheelset and a cracked rail, for which a vertical rail crack is considered. By defining another contact pair, the normal as well as tangential contact forces between the crack faces and the resulted dynamic stress intensity factors (SIFs) at the crack tip are analyzed in the time domain. The virtual crack closure technique is employed to calculate the SIFs, so that the discrete nodes on the two crack surfaces are kept coincident. No gap between the crack faces has been considered. The wheel-rail contact and the contact between crack faces are both defined by a ‘surface-to-surface’ contact algorithm, and the Coulomb's law of friction is implemented to treat tangential contact problems for both contact pairs. The results under traction have shown that the normal and tangential contact forces between the wheel and rail do not change with the adhesion coefficient, while those between crack faces decrease correspondingly. As the wheel reaches the crack, the two faces are pressed against each other due to rail bending under wheel loading, i. e., the crack is closed and K_I is zero value, while the maximum of K_Ⅱ is 8.1 times that of K_Ⅲ. This means that mode II shear probably dominates the propagation of the vertical crack, if it can, under traction conditions and without lateral shift. With the increase of the adhesion coefficient from 0.1 to 0.5, the maximum of K_Ⅱ increases by only 3.98% under traction conditions and without lateral shift, while the maximum of K_Ⅲ decreases by 20.8%.