The Life Of Cracks

Many people find the concept of fracture and damage mechanics to be somewhat problematic, mainly because, until recently, close attention in mechanics was focused especially on the strength and resistance of materials. In this sense, to speak of fracture is as uncomfortable for some as it is to speak of a deadly disease. In confronting and preventing a fatal disease, one must understand its complexity, symptoms, and behavior; by the same token, in securing the strength of an engineering structure, one must understand the reasons and type of its potential failure. This book will provide knowledge and insights on this matter to its readers.

Fatigue failure is a multi-stage process. It begins with the initiation of cracks, and with continued cyclic loading the cracks propagate, finally leading to the rupture of a component or specimen. The demarcation between the above stages is not well-defined. Depending upon the scale of interest, the variation may span three orders of magnitude. For example, to a material scientist an initiated crack may be of the order of a micron, whereas for an engineer it can be of the order of a millimetre. It is not surprising therefore to see that investigation of the fatigue process has followed different paths depending upon the scale of phenomenon under investigation. Interest in the study of fatigue failure increased with the advent of industrial ization. Because of the urgent need to design against fatigue failure, early investiga tors focused on prototype testing and proposed failure criteria similar to design formulae. Thus, a methodology developed whereby the fatigue theories were proposed based on experimental observations, albeit at times with limited scope. This type of phenomenological approach progressed rapidly during the past four decades as closed-loop testing machines became available.

Cracks and Fracture consists of nine chapters in logical sequence. In two introductory chapters, physical processes in the vicinity of the crack edge are discussed and the fracture process is described. Chapter 3 develops general basic concepts and relations in crack mechanics, such as path independent integrals, stress intensity factors and energy flux into the crack edge region. Chapters 4-7 deal with elastostatic cracks, stationary or slowly moving elastic-plastic cracks, elastodynamic crack mechanics and elastoplastic aspects of fracture, including dynamic fracture mechanics. Appendices include general formulae, the basic theory of analytic functions, introduction to Laplace and Hankel transforms and description of certain basic relations, for instance for stress waves in solids. There is an extensive bibliography, containing references to both classical and recent work, and a comprehensive index. Presents an extensive bibliography containing references to both classical and recent works and a comprehensive index Appendices include general formulas, the basic theory of analytic functions, introduction to Laplace and Hankel transforms, and descriptions of certain basic relations, for instance for stress waves in solids

An “eerie, elliptical masterpiece set in a South African boarding school in the early 1960s. . . . First-rate psychological suspense . . . played out flawlessly” (Kirkus Reviews). The members of an elite girls swim team are the reigning queens at their South African boarding school. And then Italian student Fiamma Coronna joins their ranks. Beautiful, athletic, and suddenly commanding all the coach’s attention, Fiamma is the envy of every girl on the team—until the summer she walks into the rural grasslands surrounding the school and disappears. Forty years later, the former teammates return to the school for a reunion, and the memory of that summer emerges like a long buried secret, the shocking, violent truth of what really happened to Fiamma no longer able to be contained . . . “Riveting . . . while evocative of The Prime of Miss Jean Brodie and Picnic at Hanging Rock, Kohler’s writing is so smoothly confident and erotic that she has produced a tale resonant with a chilling power all its own.” —Elle “A stunning and singular tale of the passion and tribalism of adolescence, Cracks lays bare the violence that lurks in the heart of even the most innocent. Shocking, reminiscent of Lord of the Flies . . . conjures up the wildness of the veld and the passion and drama of adolescence . . . peculiarly satisfying.” —The Times Literary Supplement “A disturbing, note-perfect novel. Dissection of evil has rarely been so extravagantly executed.” —San Francisco Chronicle “Polished, compact and chilling . . . Powerful.” —Publishers Weekly A Library Journal and Newsday Best Book of the Year, now a major motion picture starring Eva Green

Cancer disappearing without trace. A premature baby confounding the medical predictions about his prognosis. A teenager seeing her long-term debilitating illness vanish in an instant. A church receiving cash out of thin air, ensuring it survives the threat of closure. A man defying death, multiple times, following life-threatening injuries sustained in a head-on road collision. Light through the Cracks contains ten true stories, united by a common theme: All of them feature ordinary people encountering God, in extraordinary ways, in the toughest of life's circumstances. Starting with her own dramatic story of the car accident that could have left her dead or paralysed, Joanna Watson writes authentically and compellingly of how God breaks in when life turns tough. Each story raises faith, builds hope, and encourages readers to look for God's Light through the cracks in their own challenging situations.

Failures of many mechanical components in service result from fatigue. The cracks which grow may either originate from some pre-existing macroscopic defect, or, if the component is of high integrity but highly stressed, a region of localized stress concentration. In turn, such concentrators may be caused by some minute defect, such as a tiny inclusion, or inadvertent machining damage. Another source of surface damage which may exist between notionally 'bonded' components is associated with minute relative motion along the interface, brought about usually be cyclic tangential loading. Such fretting damage is quite insidious, and may lead to many kinds of problems such as wear, but it is its influence on the promotion of embryo cracks with which we are concerned here. When the presence of fretting is associated with decreased fatigue performance the effect is known as fretting fatigue. Fretting fatigue is a subject drawing equally on materials science and applied mechanics, but it is the intention in this book to concentrate attention entirely on the latter aspects, in a search for the quantification of the influence of fretting on both crack nucleation and propagation. There have been very few previous texts in this area, and the present volume seeks to cover five principal areas; (a) The modelling of contact problems including partial slip under tangentialloading, which produces the surface damage. (b) The modelling of short cracks by rigorous methods which deal effectively with steep stress gradients, kinking and closure. (c) The experimental simulation of fretting fatigue.

This book contains the fully peer-reviewed papers presented at the Third Engineering Foundation Conference on Small Fatigue Cracks, held under the chairmanship of K.S. Ravichandran and Y. Murakami during December 6-11, 1998, at the Turtle Bay Hilton, Oahu, Hawaii. This book presents a state-of-the-art description of the mechanics, mechanisms and applications of small fatigue cracks by most of the world's leading experts in this field. Topics ranging from the mechanisms of crack initiation, small crack behavior in metallic, intermetallic, ceramic and composite materials, experimental measurement, mechanistic and theoretical models, to the role of small cracks in fretting fatigue and the application of small crack results to the aging aircraft and high-cycle fatigue problems, are covered.

Introduction to Fracture Mechanics presents an introduction to the origins, formulation and application of fracture mechanics for the design, safe operation and life prediction in structural materials and components. The book introduces and informs the reader on how fracture mechanics works and how it is so different from other forms of analysis that are used to characterize mechanical properties. Chapters cover foundational topics and the use of linear-elastic fracture mechanics, involving both K-based characterizing parameter and G-based energy approaches, and how to characterize the fracture toughness of materials under plane-strain and non plane-strain conditions using the notion of crack-resistance or R-curves. Other sections cover far more complex nonlinear-elastic fracture mechanics based on the use of the J-integral and the crack-tip opening displacement. These topics largely involve continuum mechanics descriptions of crack initiation, slow crack growth, eventual instability by overload fracture, and subcritical cracking. Presents how, for a given material, a fracture toughness value can be measured on a small laboratory sample and then used directly to predict the failure (by fracture, fatigue, creep, etc.) of a much larger structure in service Covers the rudiments of fracture mechanics from the perspective of the philosophy underlying the few principles and the many assumptions that form the basis of the discipline Provides readers with a "working knowledge" of fracture mechanics, describing its potency for damage-tolerant design, for preventing failures through appropriate life-prediction strategies, and for quantitative failure analysis (fracture diagnostics)