RIM THICKNESS EFFECTS ON GEAR CRACK-PROPAGATION LIFE

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRa cture ANalysis Code) computer program was used to simulate crack propa gation. The FRANC program used principles of linear elastic fracture m echanics, finite element modeling, and a unique re-meshing scheme to d etermine crack tip stress distributions, estimate stress intensity fac tors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gear s were installed with special crack propagation gages in the tooth fil let region to measure bending fatigue crack growth. Good correlation b etween predicted and measured crack growth was achieved when the fatig ue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear to oth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.