Correlation study between FEA and physical testing for a hypoid gear set

Abstract: This thesis describes a correlation study of gear tooth bending stresses between physical testing and Finite Element modelling. It was conducted after a discovery at GKN that there were inconsistencies between the measured and calculated tooth root stresses for a hypoid gear set. The aim of the thesis was to investigate to what extent the stresses are correlated and if the program used is reliable for bending stress calculation. This would then be used to create S/N-curves for the gear set. The correlation was studied for several different aspects of the gear set. The contact pattern for the gear set was compared visually for a range of torque levels to see how well they matched and if this would contribute to the discrepancy. The root bending stress had been measured using a number of strain gauges in the root of the teeth. The location of these strain gauges was measured using a digital microscope and coordinate-measuring machine and the strain in the corresponding location in the Finite Element model was evaluated. The calculated contact pattern showed a slight under-approximation for lower torque levels but the agreement increased with increasing torque levels. The stress showed good correlation in the highly stressed middle area of the tooth for both the pinion and the ring gear while the lowly stressed heel and toe were worse. As the maximum stress is the deciding factor for bending fatigue the program was deemed reliable and the results used to evaluate fatigue life for the gear set.