STRUCTURAL ANALYSIS OF LARGE TITANIUM CASTINGS IN A HIGH-CYCLE, ROTOR-INDUCED VIBRATORY LOAD ENVIRONMENT

Large titanium hot isostatic pressed (HIP) castings, with a beta-solution heat treatment, are cost-effective alternatives to machined forgings for the fabrication of structural components subjected to a high-cycle-load fatigue environment. The V-22 Osprey transmission adapter provides the load path between the proprotor gearbox and the pylon support fitting; this component is being fabricated from a titanium investment casting for the V-22 EMD program. To alleviate concerns regarding the use of castings in a high-cycle fatigue environment, extensive coupon testing and finite-element analysis was conducted to develop the V-22 transmission adapter. Coupon testing was conducted to fully characterize the material for both fatigue and damage tolerance allowables. Damage tolerance to a 0.025-inch flaw was the primary design driver for the transmission adapter. To ensure conformity to this criterion, extensive finite-element modeling of the transmission adapter was done to fully quantify the stress magnitudes throughout the component. Multiple solid-element fine-grid models were constructed during the design process. The results of coupon tests and finite element stress analysis show that the cast titanium transmission adapter meets fatigue and damage tolerance requirements. This will be verified by fatigue tests of five full-scale transmission adapters.