2.1 Subsurface shear stress
Most of the rolling contact fatigue failure originates from subsurface,
so it is important to analyze the subsurface stress field during rolling
contact. Note that the traditional Hertz contact theory is no longer
applicable to subsurface stress analysis. Johnson26calculated the principal stress at any depth under contact surface
theoretically, and then used the Mohr circle to calculate shear stress.
The subsurface shear stress reaches its maximum and minimum values at a
certain depth, and changes alternately along the direction paralleling
to bearing raceway. In this work, a two-dimensional (2D) finite element
model was established to simulate the contact between ball and raceway.
Due to the normal stress on subsurface is compressive, and compressive
stress will hinder crack growth, the alternating shear stress is the key
factor to result in damage accumulation and microcrack
propagation.27 Therefore, only shear stress is used in
the following research. Fig. 2 shows the distribution of shear stress in
the contact area between ball and raceway. Ball has a diameter of 5.5 mm
and inner race has a radius of 9.63 mm in the 2D contact model (shown in
Fig. 2a). Contact analysis implemented in ABAQUS was used. Fig. 2b shows
the nephogram of shear stress distribution in the contact area. It shows
that the distribution of shear stress along the raceway has maximum and
minimum values. Note that we are only interested in the stress
distribution and ignore the specific stress value. Fig. 2c shows the
maximum shear stress and the maximum orthogonal shear stress on the
subsurface under contact load. The x -axis represents the
direction along raceway, and \(\tau_{\max}\) represents the maximum
orthogonal shear stress which will change alternately as bearing runs.\(\tau_{y\max}\) stands for the maximum shear stress along they -axis.