A recent study indicated that the behavior of single-ended dislocation sources contributes to the flow strength of micrometer-scale crystals. In this study 3D discrete dislocation dynamics simulations of micrometer-sized volumes are used to calculate the effects of anisotropy of dislocation line tension (increasing Poisson's ratio, [nu]) on the strength of single-ended dislocation sources and, to compare them with the strength of double-ended sources of equal length. This is done by directly modeling their plastic response within a 1 micron cubed FCC Ni single crystal using DDS. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with Poisson ratio ([nu]), exhibiting an increase of about 50% at u = 0.38 (value for Ni) as compared to the value at [nu] = 0. Independent of dislocation line direction, for [nu] greater than 0.20, the strengths of single-ended sources depend upon the sense of the stress applied. The value for [alpha], in the expression for strength, [tau] = [alpha](L)[mu]b/L is shown to vary from 0.4 to 0.84 depending upon the character of the dislocation and the direction of operation of the source at [nu] corresponding to that of Ni, 0.38 and a length of 933b. By varying the lengths of the sources from 933b to 233b, it was shown that the scaling of the strength of single-ended and double-ended sources with their length both follow a ln(L/b)/(L/b) dependence. Surface image stresses are shown to have little effect on the critical stress of single-ended sources at a length of ≈250b or greater. The relationship between these findings and a recent statistical model for the hardening of small volumes is also discussed.

A recent study indicated that the behavior of single-ended dislocation sources contributes to the flow strength of micrometer-scale crystals. In this study 3D discrete dislocation dynamics simulations are used to calculate the effects of anisotropy of dislocation line tension on the strength of single-ended dislocation sources in micrometer-sized volumes with free surfaces, and to compare them with the strength of double-ended sources of equal length. This is done by directly modeling their plastic response within a 1-micron cubed volume composed of a single crystal FCC metal. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with Poisson ratio, exhibiting an increase of about 50% at v = 0.38 (value for Ni) as compared to the value at v= 0. Independent of dislocation line direction, for v greater than 0.20, the strengths of single-ended sources depend upon the sense of the stress applied.

Three-dimensional (3D) discrete dislocation dynamics simulations were used to calculate the effects of anisotropy of dislocation line tension (increasing Poisson's volumes with free surfaces) and to compare them with the strength of double-ended sources of equal length. Their plastic response was directly modeled within a 1um3 volume composed of a single crystal fcc metal. In general, double-ended sources are stronger than single-ended sources of an equal length and exhibit no significant effects from truncating the long-range elastic fields at this scale. The double-ended source strength increases with v, exhibiting an increase of about 50% at v=0.38 (value of Ni) as compared to the value at v=0. Independent of dislocation line direction, for v greater than 0.20, the strengths of single-ended sources depended upon the sense of the stress applied.

This work deals with the experimental investigation of the mechanical properties of nanowires. Experiments are conducted in a dedicated system inside the electron microscope. The mechanical response of various material systems is probed, the underlying deformation mechanisms are elucidated and subsequently put into context with mechanical size effects.

This book is a printed edition of the Special Issue "Crystal Indentation Hardness" that was published in Crystals

Presents a comprehensive treatment of the fundamentals of dislocations. This book covers the elastic theory of straight and curved dislocations, and includes a chapter on elastic anisotropy. It also presents applications to the theory of dislocation motion at low and high temperatures.

Successor of the highly acclaimed, first full-color introduction to nanomaterials - now including graphenes and carbon nanotubes This full-colored introduction to nanomaterials and nanotechnology in particular addresses the needs of engineers who need to know the special phenomena and potentials, without getting bogged down in the scientific detail of the physics and chemistry involved. Based on the author's own courses, this textbook shows how to produce nanomaterials and use them in engineering applications for novel products. Following an introduction, the text goes on to treat synthesis, characterization techniques, thermal, optical, magnetic and electronic properties, processing and, finally, emerging applications. A sound overview of the "nano world" from an application-oriented perspective. Reviews for the first edition: "The reader [of this book] profits from the broad scientific teaching experience of the author.... This book is highly recommended for everyone who wants to step onto the new and fascinating field of nanomaterials." (International Journal of Materials Research, May 2009) "The practical presentation and clarity in writing style makes this book a winner for anyone wanting to quickly learn about the fundamentals and practical side of nanomaterials." (IEEE Electrical Insulation Magazine, March/April 2009)

KEY FEATURES: - A unified, fundamental and quantitative resource. The result of 5 years of investigation from researchers around the world - New data from a range of new techniques, including synchrotron radiation X-ray topography provide safer and surer methods of identifying deformation mechanisms - Informing the future direction of research in intermediate and high temperature processes by providing original treatment of dislocation climb DESCRIPTION: Thermally Activated Mechanisms in Crystal Plasticity is a unified, quantitative and fundamental resource for material scientists investigating the strength of metallic materials of various structures at extreme temperatures. Crystal plasticity is usually controlled by a limited number of elementary dislocation mechanisms, even in complex structures. Those which determine dislocation mobility and how it changes under the influence of stress and temperature are of key importance for understanding and predicting the strength of materials. The authors describe in a consistent way a variety of thermally activated microscopic mechanisms of dislocation mobility in a range of crystals. The principles of the mechanisms and equations of dislocation motion are revisited and new ones are proposed. These describe mostly friction forces on dislocations such as the lattice resistance to glide or those due to sessile cores, as well as dislocation cross-slip and climb. They are critically assessed by comparison with the best available experimental results of microstructural characterization, in situ straining experiments under an electron or a synchrotron beam, as well as accurate transient mechanical tests such as stress relaxation experiments. Some recent attempts at atomistic modeling of dislocation cores under stress and temperature are also considered since they offer a complementary description of core transformations and associated energy barriers. In addition to offering guidance and assistance for further experimentation, the book indicates new ways to extend the body of data in particular areas such as lattice resistance to glide.

Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.