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This report is a three part study of indentation fracture in the plastic contact regime. The first part summarizes the observations of fracture and develops a fracture classification scheme. The second part discusses the implications of the fracture characterization for fracture toughness determinations, and abrasive wear and low velocity erosion prediction. Finally, the third part discusses indentation friction and its measurements, as needed to determine the role of friction in the indentation fracture process. (Author).
Several basic aspects concerning the effects of grain boundaries in niobium bicrystals were explored. The investigation led to the following findings: (1) A new method of growing oriented niobium bicrystals (the Y shaped seed technique) was developed. Large cylindrical bicrystals, 0.63 cm in diameter and over 10 cm in length, have been grown from the melt using this method. (2) Niobium bicrystals exhibit excess hardening at the grain boundary, as shown by microhardness measurements. The degree of boundary hardening increased as the angle of misorientation increases. In addition, hardening is greater in bicrystals with tilt boundaries than with twist boundaries. (3) In tensile deformation of niobium bicrystals, Stage I hardening is absent. In Stage II, extra slip traces are activated from the boundary. In some cases, the primary slip system of the bicrystal differs from that of the single crystal of similar orientation. (4) In conjunction with the experimental program, a refined analysis was made to examine the dislocation-boundary interaction. It was found that in non-symmetrical bicrystals an edge dislocation wall has a long-range stress field which contrasts with the classical result in a single crystal. (Author).
Comprehensive in scope and readable, this book explores the methods used by engineers to analyze and predict the mechanical behavior of materials. Author Norman E. Dowling provides thorough coverage of materials testing and practical methods for forecasting the strength and life of mechanical parts and structural members.
This book concentrates on both understanding and development of nanocrystalline materials. The original relation that connects grain size and strength, known as the Hall-Petch relation, is studied in the nanometer grain size region. The breakdown of such a relation is a challenge. Why and how to overcome it? Is the dislocation mechanism still operating when the grain size is very small, approaching the amorphous limit? How do we go from the microstructure information to the continuum description of the mechanical properties?
This book focuses on the emerging class of new materials characterized by ultra-fine microstrucures. The NATO ASI which produced this book was the first international scientific meeting devoted to a discussion of the mechanical properties and deformation behavior of materials having grain sizes down to a few nanometers. Topics covered include superplasticity, tribology, and the supermodulus effect. Review chapters cover a variety of other themes including synthesis, characterization, thermodynamic stability, and general physical properties. Much of the work is concerned with the issue of how far conventional techniques and concepts can be extended toward atomic scale probing. Another key issue concerns the structure of nanocrystalline materials, in particular, what is the structure and composition of the internal boundaries. These ultra-fine microstructures have proved to challenge even the finest probes that the materials science community has today.
This collection gives broad and up-to-date results in the research and development of materials characterization and processing. Topics covered include characterization methods, ferrous materials, non-ferrous materials, minerals, ceramics, polymer and composites, powders, extraction, microstructure, mechanical behavior, processing, corrosion, welding, solidification, magnetic, electronic, environmental, nano-materials, and advanced materials The book explores scientific processes to characterize materials using modern technologies, and focuses on the interrelationships and interdependence among processing, structure, properties, and performance of materials.