Introduction

Fatigare (L)—to tire (translated term first used for metals in 1839, in France, and 1854, in England). Fatigue occurs under cyclic loading and can significantly degrade the operational capability and safety of metallic aircraft components and structures. Fatigue is also important in other engineering sectors. This book provides summaries of some metallic aircraft structural integrity issues; innovative but established examples of maintaining operational capability (airworthiness) and assessments of safe in-service fatigue lives. These topics are based on a through-life fatigue management philosophy that ensures safe and continued operation, including during life extensions that are almost inevitably required. This philosophy is underpinned by observations of the behaviour of fatigue cracks in actual structures subjected to realistic service loading conditions. More specifically, the book chapters consider aircraft design requirements, individual aircraft fatigue loads monitoring, airframe fatigue testing, sources of fatigue-nucleating discontinuities and prediction of fatigue crack growth from these discontinuities. All these aspects contribute to discussing methods of assuring the structural integrity and operational capability of realistically cracked structures. Detailed subjects include the exponential behaviour of lead or dominant cracks (i.e. those leading to first failure), and the practical significance of differences between fatigue fracture topographies produced under constant amplitude and variable amplitude loading. Also, the many observations of lead crack growth have enabled comparing the efficiencies of alternative (or competing) aircraft design standards, and developing procedures for countering in-service cracking. The book described has been developed through the pragmatic need to safely manage in-service aircraft structures for extended periods and with limited resources. The principles and analyses described in this book have contributed significantly to the efficient and effective structural integrity management of aircraft operated by the Royal Australian Air Force.