The concept of the average stress in the fracture process zone for the search of the crack path

The concept of the average stress has been employed to propose the maximum average tangential
stress (MATS) criterion for predicting the direction of fracture angle. This criterion states that a crack grows
when the maximum average tangential stress in the fracture process zone ahead of the crack tip reaches its
critical value and the crack growth direction coincides with the direction of the maximum average tangential
stress along a constant radius around the crack tip. The tangential stress is described by the singular and
nonsingular (T-stress) terms in the Williams series solution. To demonstrate the validity of the proposed MATS
criterion, this criterion is directly applied to experiments reported in the literature for the mixed mode I/II crack
growth behavior of Guiting limestone. The predicted directions of fracture angle are consistent with the
experimental data. The concept of the average stress has been also employed to predict the surface crack path
under rolling-sliding contact loading. The proposed model considers the size and orientation of the initial crack,
normal and tangential loading due to rolling–sliding contact as well as the influence of fluid trapped inside the
crack by a hydraulic pressure mechanism. The MATS criterion is directly applied to equivalent contact model
for surface crack growth on a gear tooth flank.