A finite element/contact mechanics formulation is used to analyze the dynamic tooth forces that arise from damage-induced vibrations in spur gear pairs. Tooth root crack damage of varying sizes are analyzed for a wide range of speeds that include resonant gear speeds. The added localized compliance from tooth root crack damage leads to a re-distribution of the forces on the individual gear teeth in mesh. At speeds away from resonance, smaller dynamic forces occur on the damaged tooth and larger dynamic forces occur on the tooth that engages immediately after it. These dynamic tooth contact forces cause additional transient dynamic response in the gear pair. For certain speeds and sufficiently large tooth root cracks, the damage-induced dynamic response causes large enough vibration that tooth contact loss nonlinearity occurs. For some speeds near resonance, the damage-induced vibrations cause teeth that normally lose contact to remain in contact due to vibration. Tooth contact loss nonlinearity in this cause briefly seizes but then occurs again after several mesh cycles when the damage-induced transients diminish. The features of the dynamic tooth loads shown in this work may be used in analyses that predict the propagation of damage, determine conditions that will likely cause healthy teeth to become damaged, and give insight into the fundamental mechanisms driving vibration in damaged geared systems.
