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A variety of ceramic materials has been recently shown to exhibit nonlinear stress strain behavior. These materials include transformation-toughened zirconia which undergoes a stress-induced crystallographic transformation in the vicinity of a propagating crack, microcracking ceramics, and ceramic-fiber reinforced ceramic matrices. Since many of these materials are under consideration for structural applications, understanding fracture in these quasi-brittle materials is essential. Portland cement concrete is a relatively brittle material. As a result mechanical behavior of concrete, conventionally reinforced concrete, prestressed concrete and fiber reinforced concrete is critically influenced by crack propagation. Crack propagation in concrete is characterized by a fracture process zone, microcracking, and aggregate bridging. Such phenomena give concrete toughening mechanisms, and as a result, the macroscopic response of concrete can be characterized as that of a quasi-brittle material. To design super high performance cement composites, it is essential to understand the complex fracture processes in concrete. A wide range of concern in design involves fracture in rock masses and rock structures. For example, prediction of the extension or initiation of fracture is important in: 1) the design of caverns (such as underground nuclear waste isolation) subjected to earthquake shaking or explosions, 2) the production of geothermal and petroleum energy, and 3) predicting and monitoring earthquakes. Depending upon the grain size and mineralogical composition, rock may also exhibit characteristics of quasi-brittle materials."
Portland cement concrete is a relatively brittle material. As a result, mechanical behavior of concrete, conventionally reinforced concrete, prestressed concrete, and fiber reinforced concrete is critically influenced by crack propagation. It is, thus, not surprising that attempts are being made to apply the concepts of fracture mechanics to quantify the resistance to cracking in cementious composites. The field of fracture mechanics originated in the 1920's with A. A. Griffith's work on fracture of brittle materials such as glass. Its most significant applications, however, have been for controlling brittle fracture and fatigue failure of metallic structures such as pressure vessels, airplanes, ships and pipe lines. Considerable development has occurred in the last twenty years in modifying Griffith's ideas or in proposing new concepts to account for the ductility typical of metals. As a result of these efforts, standard testing techniques have been available to obtain fracture parameters for metals, and design based on these parameters are included in relevant specifications. Many attempts have been made, in the last two decades or so, to apply the fracture mechanics concepts to cement, mortar, con crete and reinforced concrete. So far, these attempts have not led to a unique set of material parameters which can quantify the resistance of these cementitious composites to fracture. No standard testing methods and a generally accepted theoretical analysis are established for concrete as they are for metals."
FRACTURE MECHANICS OF CONCRETE AND ROCK Over the past few years, researchers employing techniques
borrowed from fracture mechanics have made many groundbreaking
discoveries concerning the causes and effects of cracking, damage,
and fractures of plain and reinforced concrete structures and rock.
This, in turn, has resulted in the further development and
refinement of fracture mechanics concepts and tools. Yet, despite
the field's growth and the growing conviction that fracture
mechanics is indispensable to an understanding of material and
structural failure, there continues to be a surprising shortage of
textbooks and professional references on the subject. The most timely, comprehensive, and authoritative book on the subject currently available, Fracture Mechanics of Concrete is both a complete instructional tool for academics and students in structural and geotechnical engineering courses, and an indispensable working resource for practicing engineers.
Current economics often dictate the use of structures well beyond their design lives. Today, there is an increased reliance on nondestructive evaluation (NDE) to provide accurate data about the health of materials in these aging systems. Examples of such structures include aircraft, bridges, nuclear reactors, roads, ships, industrial manufacturing facilities, storage vessels for both toxic and nontoxic substances, electronic hardware, etc. This book looks at ways to develop new NDE techniques for aging materials. Special emphasis is given to the structural health of concrete, defects in high-strength aircraft materials and the characterization of steels in nuclear reactors. One intriguing new technology, borrowed from the semiconductor industry, is the use of very small micro-electro-mechanical systems (MEMS) to monitor materials properties in situ. Using these devices in networks should permit both real-time monitoring of materials properties during operation and the anticipation of component failure. The book also explores the many potentially fertile collaborative research opportunities between NDE and noninvasive medical diagnostic procedures.
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