Fatigue Crack Growth Arrestor for High Speed Flexible Coupling of Fighter Aircraft Transmission Systems

A lightweight High Speed Flexible Coupling (HSFC) is used to connect the engine gear box (EGB) with an accessory gear box (AGB) for fighter aircrafts. The HSFC transmits the power at high speeds ranging from 10000 to 18000 rpm from the EGB to AGB. The HSFC also accommodates larger angular and axial misalignments resulting from differential thermal expansion of the aircraft engine and mounting arrangement. The HSFC utilizes series of metallic contoured annular thin flexible plates. These flexible plates are susceptible to fatigue failures in the presence of minuscule surface defects. The present work describes the analysis carried out on a typical HSFC with incipient flaw for various kinds of imposed misalignments. Based on the sensitivity study of the flaw on the stress levels, a Fatigue Crack Growth Arrestor (FCGA) is designed. In order to contain the crack propagation, drilling a hole at the tip of the crack on the flexible plate as a FCGA is adapted. The fatigue life of the flexible plates is improved by finding appropriate size and location of FCGA through finite element analysis and simulations.