172. The Weight Engineer’s Approach to the Problem of Fatigue in Aircraft Structures


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S Sichveland, F M DeGraan, R H Trelease: 172. The Weight Engineer’s Approach to the Problem of Fatigue in Aircraft Structures. 1958.



The structure of an aircraft must be designed to be fatigue resistant. This is a reasonable statement, and one with which no straight thinking aircraft engineer will argue, for it is based on the principle of ‘safety before all else’. The designing of structures to be fatigue resistant can be said to be mandatory. What does this mean to the Weight Engineer: does it imply that large weight penalties will be incurred, and if so how can these penalties be held to a minimum? These are a few of the questions which the authors of this paper have attempted to answer by defining ‘The Weight Engineers Approach to the Problem of Fatigue in Aircraft Structures’.
To assist the Weight Engineer to better understand the problem of fatigue, the paper has been designed in a series of three steps or parts leading the engineer through from the basic principles of the problem to the practical aspect of structural failure from fatigue.
Part I – Fatigue in Structural Materials
Part I introduces the problem and describes the mechanism of fatigue failure in the crystal structure of the material. The resistance to fatigue in relation to mechanical strength for various materials is briefly described.
Part II – The Problem of Fatigue in Aircraft Structures
This second part of the paper is partially historical, recalling the accidents which ought the problem out of the laboratory and placed it squarely in the lap of the Aircraft engineer. The causes of these accidents are discussed together with the preventive methods which have been adopted by structural engineers to ensure that such catastrophes will not occur again. The two basic preventive methods are described and compared.
Part III – The Approach of the Weight Engineer to the Design of Fatigue Resistant Structures
Part III discusses the implications of designing fatigue resistant structures and the weight penalties which can be incurred by over insuring the structure. The weight engineers approach to the problem is also considered. The fatigue resistance properties end weight advantages of several unconventional methods of construction are highlighted.


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