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This comprehensive overview of the whole field of fatigue and fracture of metallic materials covers both the theoretical background and some of the latest experimental techniques. It provides a summary of the complex interactions between material microstructure and cracks, classifying them with respect to the overall damage process with a focus on microstructurally short cracks and dynamic embrittlement. It furthermore introduces new concepts for the numerical treatment of fatigue microcrack propagation and their implementation in fatigue-life prediction models.This comprehensive overview of the whole field of fatigue and fracture of metallic materials covers both the theoretical background and the latest experimental techniques. It provides a summary of the complex interactions between material microstructure and cracks, classifying them with respect to the overall damage process. It furthermore introduces new concepts for the numerical treatment of fatigue microcrack propagation and their implementation in fatigue-life prediction models.
Fatigue failures occur in aerospace,marine,nuclear structures and automobile com ponents from initiation and propagation of cracks from holes,scratches or defects in the material. To design against these failures, crack propagation life and fracture strength need to be accurately predicted. It is reported in the literature, that these failures often initiate as surface cracks, corner cracks and cracks emanating from fastner holes. Such cracks are with elliptic or nearly elliptic in shapes. The deviation from elliptic shape is due to varying constraint effect along the crack front. Even in situations, when the cracks are through the thickness of the material, there would be thicknesswise variation of constraint effects leading to three dimensional nature of crack growth. Accurate predictions of the crack growth in these cases by numerical methods can be made only by solving three-dimensional boundary value problems. Empirical relationships have been developed [1] based on Linear Elastic Fracture Mechanics over years describing fatigue crack growth response. Some of these empirical relationships required modifications in the later stages, to meet the design applications. The Crack closure phenomenon discovered by Elber[2, 3] during the crack growth phase is mainly attributed to the local material yielding near the crack tip and the consequent residual plastic wake behind the crack tip. It helped considerably in understanding several aspects of fatigue crack growth and rewrite these relations.
In this book, the authors present current research in the study of the mechanisms, behaviour and analysis of fatigue crack growths. Topics discussed in this compilation include the unified fatigue crack growth rate model; practical tools for statistical fatigue design; probablistic algorithms performance evaluation and application in multi-fractured structures; three dimensional effects in the fracture mechanics of bi-dimensional specimens; fatigue crack propagation mechanism in porous open pore metal foams; lifetime predictions for short fatigue crack's initiation-propagation by basic mechanical properties; variable amplitude fatigue crack growth in selected aluminium alloys; fatigue threshold R-curves for analysis of short fatigue cracks; and multiaxial fatigue life prediction for lateral notched round bars made of high strength steel.
This book explains the numerical method for fatigue life analysis of adhesive joints using the CZM technique. CZM is a robust approach that is widely used for failure analysis of adhesive joints exposed to various stress conditions including fatigue. In this book, various aspects of the numerical evaluation of adhesive bonds using CZM are discussed. First of all, it is explained how different load and environmental parameters influence the service life of adhesive connections. Various types of CZM shapes and their applications are then discussed. It was answered how different parameters of a CZM should be defined. It is also discussed which CZM form should be used for each condition. The book then describes how the CZM parameters should be degraded to simulate the cyclic loading behavior of bonded structures. Various CZM strategies for the fatigue life assessment of adhesive joints are discussed. The book presents various techniques that can be followed for the simulation of load cycles for both high-cycle and low-cycle fatigue regimes based on the concepts of the CZM. Details of numerical methods to be considered in the FE software for the fatigue life assessment of adhesives with CZM are also described in this book. Finally, some numerical examples using CZM are also provided.
Cold working has been widely used for enhancing the fatigue life of open holes. The process imparts compressive residual stresses around the hole which slows down the progression of crack under cyclic loading conditions. In the present study, fatigue crack growth in open holes in R260 grade steel, a typical railroad material, has been analyzed using the Extended Finite Element Method (XFEM). Along with the experimental studies, numerical simulation emerges as a powerful tool to predict the fatigue crack growth in rail steel and may deliver important insights to consider more situations by saving time and cost. XFEM modifies the standard displacement-based approximation by adding enrichment functions in the crack region. The investigation explored the capability of the XFEM, for a plate containing plain hole (baseline), pad coined, or split-sleeve cold-worked hole using the commercial finite element package, Abaqus, as a means of fatigue crack growth under constant amplitude loading. The effect of residual stress redistribution has been added to the numerical model to accurately predict the crack evolution. Stress Intensity Factors (SIF) are obtained from the XFEM calculations and the crack growth is estimated until the SIF reaches the fracture toughness of the modeled coupon material. The obtained simulation results are in good agreement with the fatigue experimental results in terms of the fatigue crack growth rates for plain hole (baseline), pad coined, or split-sleeve cold-worked holes. Results from the performed analysis show that cold working of an open hole increases the fatigue life when compared to the one without residual stresses due to the delay of crack initiation and propagation. The results also indicated fatigue life increase almost by a factor of three during crack propagation due to split-sleeve cold expansion in correlation to the baseline and pad coined sample.
Adhesively-bonded joints provide many advantages over conventional mechanical fasteners and are increasingly receiving attention as an alternative to mechanical joints in engineering applications. The traditional fasteners usually result in the cutting of fibers and hence the introduction of stress concentrations, both of which reduce structural integrity. By contrast, bonded joints are more continuous and have potential advantages of strength-to-weight ratio, design flexibility, and ease of fabrication. This book provides an overview of available analytical methods as well as numerical methods.
By adopting the principles of sustainable design and cleaner production, this important book opens a new challenge in the world of composite materials and explores the achieved advancements of specialists in their respective areas of research and innovation. Contributions coming from both spaces of academia and industry were so diversified that the 28 chapters composing the book have been grouped into the following main parts: sustainable materials and ecodesign aspects, composite materials and curing processes, modelling and testing, strength of adhesive joints, characterization and thermal behaviour, all of which provides an invaluable overview of this fascinating subject area. Results achieved from theoretical, numerical and experimental investigations can help designers, manufacturers and suppliers involved with high-tech composite materials to boost competitiveness and innovation productivity.