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About this book

This book provides a state-of-the-art review of the fail-safe and damage tolerance approaches, allowing weight savings and increasing aircraft reliability and structural integrity.

The application of the damage tolerance approach requires extensive know-how of the fatigue and fracture properties, corrosion strength, potential failure modes and non-destructive inspection techniques, particularly minimum detectable defect and inspection intervals. In parallel, engineering practice involving damage tolerance requires numerical techniques for stress analysis of cracked structures. These evolved from basic mode I evaluations using rough finite element approaches, to current 3D modeling based on energetic approaches as the VCCT, or simulation of joining processes. This book provides a concise introduction to this subject.

Table of Contents


Damage Tolerance of Aircraft Structures


Chapter 1. Introduction

This book concisely reviews the different design philosophies which have been employed in fatigue design of aircraft structures and the recent evolution of the subject. Figure 1.1 contrasts percentage of failures in general engineering components and in aircraft components, and shows that fatigue is the main source of failure in aircraft structures. Diversification of airframes, from completely metallic to the current high interest on composites and use of a variety of materials may impact the percentile distribution of failure cases, but the predominance of fatigue will certainly continue for metallic materials. Of course the figures cited correspond to a certain universe of cases; Nishida, reporting on the experience of failure analysis of mechanical components in his laboratory, mentions an even greater percentage attributable to fatigue, see Table 1.1, from Nishida (Failure analysis in engineering applications. Butterworth-Heinemann, 1992.)
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 2. Maintenance

Airworthiness involves the interplay of authorities, manufacturers, operators and maintenance providers (Fig. 2.1).
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 3. Fatigue Crack Growth

Readers of this book will have previous knowledge of fracture mechanics, and as such no effort will be made to delve here into fundamental concepts.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 4. Materials

High strength/density ratio and toughness, ease of manufacture, long term performance, joinability by riveting and welding, and recyclability, justify the long period of preeminence of aluminum as the main material for structures of aircraft, Merati [1]. Facing competition from composite fiber reinforced plastics, aluminum producers are trying to reduce weight and improve performance developing new alloys. In parallel, joining techniques as laser beam welding (LBW) or friction stir welding (FSW) originate integral structures, with manufacturing weight and part count advantages vis a vis traditional riveting. The dominance of Al was challenged with the Boeing 787 with increased use of titanium alloys and almost 50% by weight of aircraft structure constructed from composites, and by Airbus with even more 53% of structure composites weight in the A350 XWB.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 5. Widespread Fatigue Damage and Limit of Validity

Multiple site damage (MSD) and multi element damage (MED) decrease the number of cycles up to failure, and concomitantly decrease the interval for inspection.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Design of Monolithic Aeronautical Structures


Chapter 6. Alloys and Fatigue Crack Propagation

Aluminium alloys were for many decades the material of choice for aircraft structures. Although this prominence no longer exists, these alloys still represent a substantial part of the aircraft. This section briefly reviews the fatigue crack propagation behaviour of typical Al alloys, including Al-Li alloys of interest because of their low weight and high strength. Al prominence is now disputed by composites; other alloys as Ti alloys and steel are used for specific applications.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 7. Residual Stress

Integral structures, fabricated using welding, present residual stresses, and these affect their behaviour in particular fatigue crack propagation. Residual stresses of welded metallic structures are discussed with an emphasis on numerical modelling using the finite element method and experimental measurement using the contour technique. Modelling of residual stress created by welding was carried out using the ESI software Sysweld. The reference to this software highlights aspects of interest for engineering applications through a number of examples found in the literature; these were chosen because of their exemplary nature, even if coming from a variety of applications.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro

Chapter 8. Fatigue Crack Propagation of a Structural Detail

Fatigue cracking is the most common problem in aeronautical structures, requiring a damage tolerant design philosophy in order to increase their reliability.
Sérgio M. O. Tavares, Paulo M. S. T. de Castro


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