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Fatigue of structures and materials covers a wide scope of different topics. The purpose of the present book is to explain these topics, to indicate how they can be analyzed, and how this can contribute to the designing of fatigue resistant structures and to prevent structural fatigue problems in service. Chapter 1 gives a general survey of the topic with brief comments on the signi?cance of the aspects involved. This serves as a kind of a program for the following chapters. The central issues in this book are predictions of fatigue properties and designing against fatigue. These objectives cannot be realized without a physical and mechanical understanding of all relevant conditions. In Chapter 2 the book starts with basic concepts of what happens in the material of a structure under cyclic loads. It illustrates the large number of variables which can affect fatigue properties and it provides the essential background knowledge for subsequent chapters. Different subjects are presented in the following main parts: • Basic chapters on fatigue properties and predictions (Chapters 2–8) • Load spectra and fatigue under variable-amplitude loading (Chapters 9–11) • Fatigue tests and scatter (Chapters 12 and 13) • Special fatigue conditions (Chapters 14–17) • Fatigue of joints and structures (Chapters 18–20) • Fiber-metal laminates (Chapter 21) Each chapter presents a discussion of a speci?c subject.
This book offers a concise introduction to fatigue crack growth, based on practical examples. It discusses the essential concepts of fracture mechanics, fatigue crack growth under constant and variable amplitude loading and the determination of the fracture-mechanical material parameters. The book also introduces the analytical and numerical simulation of fatigue crack growth as well as crack initiation. It concludes with a detailed description of several practical case studies and some exercises. The target group includes graduate students, researchers at universities and practicing engineers.
The life prediction of aerospace structures subjected to service loading conditions can be complex and expensive. Fortunately, many flight-by- flight loadings can be analyzed as constant amplitude loading if the variability in crack growth rate is low. A test program was designed such that the stress intensity factor (Kmax) was held constant by uniformly reducing the load as the fatigue crack grew. With a constant Kmax, the crack growth rate remains constant throughout the life of the test. The baseline fatigue crack growth rate variability was established for the 7075-T6 center-cracked panels under a flight-by-flight load history. The effect of introducing overloads to the baseline flight history on the crack growth rate variability was reported. The results indicate that the delay region for the applied 114% overloads was predicted by Irwin's plastic zone model and was equal to 0.0382 inches which was equal to 225 flights. The delay behavior was consistent for the several overload conditions that were studied. When the occurrence of overload increased, the fatigue crack growth decreased. The standard error of estimate remained relatively constant, suggesting that a block approach to life prediction is feasible for flight-by-flight load history.