Analysis of Micro-Elastohydrodynamic Lubrication and Prediction of Surface Fatigue Damage in Micropitting Tests on Helical Gears

Micropitting predominantly in the dedendum region of a helical test gear tooth

Sections through micropits showing crack growth

Sections through micropits showing the characteristic direction of cracks in the dedendum (left) and addendum (right) of the same tooth on the driven gear. Arrows above the surface indicate the direction of rolling over the contact (R), and the direction of the sliding traction (S) acting on the tooth.

The 160 mm helical gear test rigs with a close-up view of exposed test gears (inset)

Three-dimensional representation of the surfaces produced by the two types of finish grinding processes: (a) generation-ground, and (b) form-ground

Graph showing the average gear profile deviation versus the running cycles. It shows the progression of cumulative micropitting damage on gears ground by the generation and form grinding processes during two stepwise micropitting tests under the same operating conditions. The final load stage corresponds to a pinion torque of 4 kN m.

Helical test gear with illustration of the position of surface profiles

Illustration (to scale) showing the setup for measurement of the tooth profile. Here, AB is the datum line of the profilometer, which is tangential to the tooth at the working pitch point z and x is the distance along the profile measured from the tooth tip.

Typical raw profilometer trace of the gear tooth showing the tooth tip location on the right (origin of the x-coordinate)

Illustration of contact between gears at s = +9.4 mm; z is the pitch point

Typical tooth profile from the wheel of test A corresponding to s = −5.0 mm

Pressure profile (lower curve) and deflected surface profiles (upper curves) at a particular timestep during the micro-EHL simulation. The operating condition corresponds to gear set B; s = +5.0 mm. The dashed line shows the corresponding Hertzian pressure with a maximum value of 1.0 GPa. The Hertzian contact dimension is a = 0.247 mm.

Contours of the subsurface damage (D) on the pinion tooth from gear set A at s = +5.0 mm (the pinion is the faster surface). The upper graph shows the corresponding section of the pinion surface profile. The Hertzian contact dimension is a = 0.247 mm.

Contours of the subsurface damage (D) on the pinion tooth from gear set B at s = +5.0 mm (the pinion is the faster surface). The upper graph shows the corresponding section of the pinion surface profile. The Hertzian contact dimension is a = 0.247 mm.

Cumulative damage distribution for the pinion (slower surface) corresponding to s = −9.4 mm at a series of depths below the surface. The solid lines are for gear set A and the dashed lines are for gear set B.

Cumulative damage distribution for the pinion (slower surface) corresponding to s = −5.0 mm at a series of depths below the surface. The solid lines are for gear set A and the dashed lines are for gear set B.

Cumulative damage distribution for the pinion (faster surface) corresponding to s = +5.0 mm at a series of depths below the surface. The solid lines are for gear set A and the dashed lines are for gear set B.

Cumulative damage distribution for the pinion (faster surface) corresponding to s = +9.4 mm at a series of depths below the surface. The solid lines are for gear set A and the dashed lines are for gear set B.