David G. Lewicki

Vibration Based Sun Gear Damage Detection

Seeded fault experiments were conducted on the planetary stage of an OH-58C helicopter transmission. Two vibration based methods are discussed that isolate the dynamics of the sun gear from that of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Three damaged sun gears: two spalled and one cracked, serve as the focus of this current work. A non-sequential vibration separation algorithm was developed and the resulting signals analyzed. The second method uses only the time synchronously averaged data but takes advantage of the signal/source mapping required for vibration separation. Both algorithms were successful in identifying the spall damage. Sun gear damage was confirmed by the presence of sun mesh groups. The sun tooth crack condition was inconclusive.

Simulating Fatigue Crack Growth in Spiral Bevel Gears Using Computational Fracture Mechanics

Development of practical and accurate numerical tools for evaluating gear performance and life assists in the design of new and better gears. This paper summarizes new results for predicting crack trajectory and fatigue life for a spiral bevel pinion using the parallel finite element method (FEM) and computational fracture mechanics. The predictions presented are based on linear elastic fracture mechanics (LEFM) theories combined with FEM, and incorporating plasticity-induced fatigue crack closure and moving loads. The analyses are carried out using a parallel FEM solver, which calculates stress intensity factors (SIF) using the equivalent domain J-integral method. We show that we can simulate arbitrarily shaped fatigue crack growth in a spiral bevel gear more accurately and efficiently than with a previous boundary element based approach [1] using the parallel FEM along with a better representation of moving loads.Copyright

Seeding Cracks Using a Fatigue Tester for Accelerated Gear Tooth Breaking

This report describes fatigue-induced seeded cracks in spur gears and compares them to cracks created using a more traditional seeding method, viz. notching. Finite element analysis (FEA) compares the effective compliance of a cracked tooth to the effective compliance of a notched tooth where the crack and the notch are of the same depth. In this analysis, cracks are propagated to the desired depth using FRANC2D and effective compliances are computed in ANSYS. A compliance-based feature for detecting cracks on the fatigue tester is described. The initiated cracks are examined using both non-destructive and destructive methods. The destructive examination reveals variability in the shape of crack surfaces.