Fatigue crack propagation study on the Portuguese Air Force Epsilon TB-30 aircraft

Abstract

Fatigue is a phenomenon caused by dynamic loads which is characterised by the propagation of cracks and can culminate in the complete fracture of a material. In the military aeronautical sector, particularly in pilot training, this problem takes on special importance given the diversity of missions and manoeuvres that are carried out. The Epsilon TB-30 aircraft is used in the Portuguese Air Force for basic piloting instruction in the 101st Fleet, at the Air Base 11 in Beja. Within the scope of Structural Integrity monitoring, a fleet aircraft was recently instrumented with a system that includes the installation of an accelerometer at the aircraft's centre of gravity and five strain gauges in critical locations of the aircraft, ,which led to the definition of the main objectives of this work: the development of an automatic crack propagation tool for a critical location in the aircraft structure, as well as the comparison of the crack growth rate when subjected to a severe and non-severe flight regime, typical flights in the operation of the Epsilon fleet. In order to simulate the crack propagation, this work included a finite element model developed in Ansys software to obtain the stress intensity factor values for several crack sizes. It was also carried out, with the resource to Matlab, the crack propagation modeling using the Walker and NASGRO propagation laws to get an expression for the geometric factor Y. Subsequently, a comparison analysis of crack growth behaviour for different flight severity regimes, propagation laws and initial crack sizes was conducted. Finally, a web application was developed to straightforwardly and automatically simulate the crack propagation for a real-world flight. ; A fadiga é um fenómeno causado por cargas dinâmicas que se caracteriza pela propagação de fissuras e pode culminar na rotura total de um material. No sector aeronáutico militar, particularmente na formação de pilotos, este problema assume especial importância dada a diversidade de missões e manobras que são levadas ...