Fatigue failure analysis on the 2nd bulkhead beam of the Portuguese Air Force Epsilon TB-30 aircraft

Abstract

Military aircraft perform demanding maneuvers with a wide range of load factor levels, allowing the growth of fatigue cracks that shall be duly monitored to prevent unexpected failures. In order to monitor the operation of the Portuguese Air Force Epsilon TB-30 fleet that performs basic and elementary piloting training, two systems were installed in these aircraft, allowing the recording of load factor data in the aircraft center of gravity and strain data in two critical locations.This study aims to evaluate and compare the growth of fatigue cracks on the 2nd bulkhead beam, one of the aircraft critical locations, through experimental tests and computational simulations. The methodology used in this work comprised the application of real flight load sequences to a 2024-T351 aluminum specimen that is representative of this critical location.Main results from these fatigue crack growth tests and simulations showed that NASGRO model is the one that comes closest to experimental data with maximum deviations of approximately 8%, presenting a deviation of 18% between the representative and real structures at the final rupture of the specimen. Additionally, experimental results provided knowledge about the component behavior regarding fatigue of materials, namely the evolution of the local strain as a function of the crack length.This study can be used by the Portuguese Air Force engineers to adjust the aircraft maintenance program according to the actual operation regime and consider a possible life extension of this fleet.