What if gear surface durability is lower than bending strength?
Gear surface durability below bending strength: design to the contact-fatigue limit
If surface durability is lower than bending strength, the tooth flank is the limiting condition: pitting, micropitting, scuffing or wear may govern before tooth-root fracture does. Do not simply increase torque or assume a stronger core solves it. PairGears should review the contact rating, lubricant and temperature, flank finish, alignment, load spectrum and material/heat-treatment route against the required life.
What to check before accepting the setup
- Separate the two ratings: contact fatigue and tooth-root bending are different failure modes with different stress concentrations and factors.
- Review the contact conditions: include torque spectrum, speed, temperature, lubricant viscosity and contamination control.
- Protect the flank geometry: alignment, runout, crowning or microgeometry, surface finish and stiffness affect load distribution.
- Choose the material route for the duty: hardness and case-depth targets must support the applicable rating method and manufacturing distortion control.
The PairGears hardness and surface-treatment overview gives project context; use a formal rating method for release decisions.
Example: make the review measurable
For a gearset with adequate root safety but low pitting margin, the corrective path may be better lubrication control, lower contact stress through geometry or face width, improved alignment, a revised surface-finish/heat-treatment route, or a lower duty target. Which route is valid depends on the calculated rating and application evidence.
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