Finite element analysis of helicopter main rotor hub plates to evaluate the possibility of increasing the time to retirement

Rotorcraft main rotor systems have multiple components that are subject to very high loads and moments. These loads and moments dictate the life expectancy of the parts based upon the components material of composition. This project will focus on the upper and lower hub plates on the main rotor system of a typical four bladed commercial helicopter. The upper and lower plates are machined from 7075-T73 aluminum forgings. The upper and lower plates were laboratory fatigue tested during product development as supporting parts in the test of the main rotor assembly. With recent advances in finite element analysis, there are situations were a computer generated three dimensional model analysis would be more economical and time beneficial to determine if the life expectancy of a part can be increased above the published safe life component retirement time. The applied loads are measured flight loads under maximum peak conditions and also ground-air-ground cycle loads. The stress values obtained from the loads are plotted on a Soderberg diagram and evaluated to determine if the retirement time of the part can be increased above the current value based on the steady and oscillatory stresses encountered.