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Author: J. Schijve Publisher: Springer Science & Business Media ISBN: 1402068085 Category : Science Languages : en Pages : 627
Book Description
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.
Author: C. M. Hudson Publisher: ISBN: Category : Airframes Languages : en Pages : 28
Book Description
VARIABLE-AMPLITUDE FATIGUE-CRACK-GROWTH TESTS WERE CONDUCTED ON SIMPLE SHEET SPECIMENS MADE OF 7075-T6 ALUMINUM ALLOY. THE NUMBERS AND THE AMPLITUDES OF THE HIGH-LOAD CYCLES APPLIED IN THESE TESTS WERE SYSTEMATICALLY VARIED TO STUDY THEIR EFFECTS ON SUBSEQUENT LOW-LOAD FATIGUE-CRACK GROWTH. THE HIGH-LOAD CYCLES CONSISTENTLY DELAYED SUBSEQUENT FATIGUE-CRACK GROWTH AT LOWER LOAD LEVELS. FOR A GIVEN LOW-LOAD LEVEL, THE HIGHER THE PRECEDING HIGH-LOAD LEVEL WAS, THE GREATER THE DELAY IN CRACK PROPAGATION. FURTHERMORE, THE DELAY IN CRACK GROWTH INCREASED WITH INCREASING NUMBERS OF HIGH-LOAD CYCLES UP TO A LIMIT. ONE HIGH-LOAD CYCLE CAUSED APPROXIMATELY ONE-FOURTH OF THE MAXIMUM DELAY, AND TEN HIGH-LOAD CYCLES CAUSED APPROXIMATELY ONE-HALF OF THE MAXIMUM DELAY. THESE DELAYS PROBABLY RESULTED FROM RESIDUAL COMPRESSIVE STRESSES GENERATED IN THE MATERIAL IMMEDIATELY AHEAD OF THE CRACK TIP DURING THE APPLICATION OF THE HIGH-LOAD CYCLES. ELECTRON FRACTOGRAPHIC STUDIES SHOWED THAT A GIVEN STRESS LEVEL, FATIGUE CRACKS PROPAGATED MORE SLOWLY IMMEDIATELY AFTER THE APPLICATION OF A HIGH-LOAD CYCLE THAN THEY DID IMMEDIATELY BEFORE ITS APPLICATION. THIS LOWER CRACK-GROWTH RATE IS CONSISTENT WITH THE DELAY IN CRACK GROWTH OBSERVED ON THE MACROSCOPIC LEVEL.
Author: Attilio Salvetti Publisher: ISBN: Category : Airplanes Languages : en Pages : 220
Book Description
Thirty three specimens were tested both at constant and variable amplitude loading. The specimens, cut from sheets of 7075-T6 aluminium alloy, coming from the same batch were both simple sheets and riveted stiffened panels. The constant amplitude tests on simple sheet specimens were carried out in order to obtain the average K-rate relationship and the relevant scatter of the batch of sheets. The constant amplitude tests on stiffened panel were aimed at obtaining information on rivet flexibility and friction forces. Variable amplitude tests were performed utilizing the FALSTAFF spectrum. The data on sheet specimens was used to assess the reliability of prediction methods such as those devised by Wheeler and Willenborg, and the stiffened panels test data to establish how these methods work in the case of built-up structures. The results, especially those concerning the spectrum tests on stiffened panels, are still preliminary, but significant in as far as they allow us to assess the reliability of crack grow prediction methods and to obtain a qualitative but deep insight into the phenomenon of crack growth in built-up structures.