Fitting formation under rolling contact

The mechanism of pitting caused by rolling contact is analyzed using the fr acture mechanics approach. The governing factors are the initial crack leng th, crack angle, contact force, friction, strain hardened layer, and the hy draulic pressure of trapped fluid acting on the crack surface. Mode I and I I stress intensity and the strain energy density factors are calculated by application of the two-dimensional finite element method. The strain energy density criterion is applied to show that shallow angle crack under small rolling contact force and friction enhances the probability of pitting unde r the roller's running surface. The presence of a strain hardened surface l ayer also tends to affect the fracture behavior. The analytical results agr ee well with the experimental observations. (C) 2000 Elsevier Science Ltd. All rights reserved.