Damage tolerance design of transport aircraft

Abstract

In a transport aircraft, there are normally two spars to withstand bending loads. A large part of this bending moment is drawn from the main spar. The main spar in large transport wings is an integrally machined part that is physically connected to the skin and ribs. At some fastener openings, the mechanical fastening contributes to extreme tension concentration where a fatigue crack can originate. This crack will form first in the flange under service loading and then expand into the spar network. If not detected during service and repaired, this crack growth can lead to catastrophic failure. This investigation aims at examining the main spar’s alternate structural design to make it damage tolerant. With one more intermediate flange and at a height of one-third from the bottom flange, the spar construction will be in two separate parts. The bottom flange and web can fail in the case of fatigue cracking, but the top flange, web, and intermediate flange will remain intact and can be designed to bear the requisite load limit design. An approach to finite element modelling and analysis is also used to analyze all forms of spar constriction and test the principle of harm tolerance nature.