Abstract
The test programme involves the analysis, using two and three-dimensional photoelastic model techniques, of an epicyclic gear assembly incorporating typical features of production gear units. Two three-dimensional models are tested, one subjected to torque loading, i.e. tooth forces, alone and the other to combined torque and inertia loading. Particular attention is devoted to the analysis of contact loads and load distribution, maximum sub-surface stresses, maximum root fillet bending stresses and the geometry of the lines of contact. An extensive two-dimensional test programme is reported in which stress concentration factors in the root fillet radii due to shear, bending and radial loads are evaluated. It has been found convenient to express the stress distributions around the fillet boundaries in terms of the stress concentration factors and details are given of the various attempts which have been made to derive a simple analytical procedure for adequately defining the gear deformation behaviour. Evidence is produced of "proximity effects" associated with load positions near the fillets, particularly in the tensile fillet; efforts made to isolate and quantify the effect are reported. A theoretical analysis has been carried out and a computer programme produced which enables the results of the stress concentration factor tests on the two-dimensional models to be used as the basis for the prediction of the maximum root fillet stresses present in a three-dimensional helical gear configuration. Correlation with the results of the three-dimensional model tests is excellent. Proposals are made for the application of the programme to a new design procedure for the prediction of bending strengths of helical gears.