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Damage Tolerance Evaluation of the Front Spar in a transport aircraft wing

Abstract

For the continued airworthiness of an aircraft during its entire economic service life, fatigue and damage tolerance design, analysis, testing and service experience correlation play a pivotal role. In a transport aircraft there are usually two spars to take the bending loads. The main spar takes a major portion of this bending moment. It is the major critical structural elements in a transport wing. Most service structural failures in structures are due to fatigue cracks. Fatigue cracking cannot be avoided but can be tolerated by suitable damage tolerance design. In large transport wings the main spar is an integrally machined component which gets mechanically fastened to the skin and ribs. The mechanical fastening leads to severe stress concentration at a few fastener holes. Under service loading a fatigue crack can initiate from the most severe stress concentrator. This fatigue crack will grow under service loading first in the flange and then grow into the spar web. This crack growth can lead to catastrophic failure if not detected during service and repaired. This project work will investigate alternate structural design of the main spar to make it damage tolerant. The spar construction here will be having one more intermediate flange and at an assumed height of 1/3rd from the bottom flange of the spar. In the event of fatigue cracking the bottom flange and web may fail but the top flange, web and the intermediate flange will remain intact and can be designed to carry the required design limit load. A finite element modeling and analysis approach will be employed to study both types of spar constriction and validate the damage tolerance design concept

Diganth Kumar B N, Dr.K.Mahesh Dutt

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