Bending Fatigue Tests of Helicopter Case Carburized Gears: Influence of Material, Design and Manufacturing Parameters

A single tooth bending (STB) test procedure has been developed to optimally map the AgustaWestland gear design parameters and a test program on case carburized, aerospace standard gears, has been conceived and performed in order to appreciate the influence of various technological parameters on fatigue resistance, and to draw the curve shape up to the gigacycle region. In a first phase, tests up to 10 million cycles have been performed on four test groups differing by material (VAR and VIM-VAR 9310, and VIM-VAR EX-53) and by manufacturing process (ground fillet versus unground fillet); in the second phase, VIM-VAR 9310 ground fillet specimen have been tested up to 100 million cycles. All the gear types were shotpeened. FEM analysis, strain gauge measurements and rating formula of AGMA standard are used to express test loads in terms of tooth root stresses. The program has been completed by failure analysis, based on SEM, on failed specimens and by ultimate load tests.