The stress at the tooth root produced by the tooth acting as a short cantilever under load, calculated from tangential load, face width, module and a geometry factor that captures tooth shape and fillet stress concentration. Rating standards compare it with an allowable bending stress for the material and heat treatment, adjusted for cycles, reliability and reversed loading. Exceeding it leads to tooth breakage by fatigue.
Bending stress is fine on the gear but the pinion's over, go up a module or add face width.
Also heard as
- root stress
- tooth bending stress
- Lewis stress
Do not mix it up with
- Contact stress: Contact stress is the surface pressure on the flanks that drives pitting, not the root stress that breaks teeth.
Related terms
Tooth breakage
A gear tooth cracking off, most often by bending fatigue starting in the root fillet on the loaded side.
Contact stress
The compressive stress where two tooth flanks press together, which governs pitting life.
Shot peening
Blasting gear roots with hard steel shot to build compressive stress and raise bending fatigue strength.
Idler
A gear placed between a driver and a driven gear to change direction or span distance, without changing ratio.