Effects of High Shearing Stress Combined with High Hydrostatic Pressure
TL;DR: In this article, the effects of shearing stress at the plastic flow point were investigated and it was found that many substances normally stable become unstable and may detonate, and conversely combinations of substances normally inert to each other may be made to combine explosively.
Abstract: Mean hydrostatic pressures up to 50,000 kg/${\mathrm{cm}}^{2}$ combined with shearing stresses up to the plastic flow point are produced in thin disks confined between hardened steel parts so mounted that they may be subjected to normal pressure and torque simultaneously Qualitative and quantitative studies are made of the effects of such stresses Among the qualitative effects it is found that many substances normally stable become unstable and may detonate, and conversely combinations of substances normally inert to each other may be made to combine explosively Quantitatively, the shearing stress at the plastic flow point may be measured as a function of pressure The shearing stress at plastic flow may rise to the order of 10 or more times greater at 50,000 kg/${\mathrm{cm}}^{2}$ than it is normally at atmospheric pressure; this is contrary to the usually accepted results in a narrower range of pressure If the substance undergoes a polymorphic transition under these conditions of stress, there may be a break in the curve of shearing stress vs pressure This gives a very convenient tool for the detection of transitions 57 elements have been explored in this way, and a number of new polymorphic transitions found
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TL;DR: In this paper, the authors defined severe plastic deformation (SPD) as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal.
Abstract: Processes of severe plastic deformation (SPD) are defined as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal The objective of the SPD processes for creating ultra-fine grained metal is to produce lightweight parts by using high strength metal for the safety and reliability of micro-parts and for environmental harmony In this keynote paper, the fabrication process of equal channel angular pressing (ECAP), accumulative roll-bonding (ARB), high pressure torsion (HPT), and others are introduced, and the properties of metals processed by the SPD processes are shown Moreover, the combined processes developed recently are also explained Finally, the applications of the ultra-fine grained (UFG) metals are discussed
849 citations
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...The HPT process was first investigated by Bridgman [89]....
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TL;DR: In this paper, the analysis of the orthogonal cutting with a type 2 chip is extended by introducing those physical properties of the work material which control its plastic behavior, and a simple additional plasticity condition is obtained by application of the principle of minimum energy.
Abstract: The analysis of the mechanics of orthogonal cutting with a type 2 chip as presented in the first paper of this series can be extended by introducing those physical properties of the work material which control its plastic behavior. One evident plasticity condition is the equality of the shear stress on the plane of shear to the shear strength of the metal. If it is also assumed that the shear strength of the work material is a constant and is the only quantity controlling its plastic behavior, then a very simple additional plasticity condition is obtained by application of the principle of minimum energy. This condition is 2φ+τ−α=90°, where φ is the shear angle, τ the friction angle, and α the rake angle. This condition, however, is found by experiment to be a poor approximation in the case of polycrystalline metals. A very good approximation is obtained, though, if use is made of the fact that the shear strength of the polycrystalline metal is actually a function of the compressive stress on the shear pl...
725 citations
TL;DR: In this article, an overview of the more recent developments in this field, with special emphasis on the opportunities for achieving homogeneity in the as-processed materials and on the general characteristics of the mechanical properties achieved after SPD processing.
614 citations
TL;DR: This paper reviews the history of mechanochemistry, which begins with prehistoric times, when reactions could be initiated during grinding and rubbing accidentally, and follows the main developments until recent results and current trends.
Abstract: This paper reviews the history of mechanochemistry. It begins with prehistoric times, when reactions could be initiated during grinding and rubbing accidentally, and follows the main developments until recent results and current trends. There are very few records on mechanochemistry until the first systematic investigations by Spring and Lea at the end of the 19th century. For the next decades, mechanochemistry developed slowly; minerals, inorganic compounds, and polymers were the main subjects of investigation. The area became more organized in the 1960s, when several large groups were established and the first dedicated conferences were held. Mechanical alloying was invented in 1966 independently and it became a subject of intense research. Interaction between the two topics was established in the 1990s. In recent years, the mechanochemical synthesis of organic compounds was added to the main subjects and the invention of the atomic force microscope provided new ways to manipulate atoms and molecules by direct mechanical action. The theoretical explanation of mechanochemical phenomena is difficult, as the mechanism is system specific and several length and time scales are involved. Thiessen proposed the first theory, the magma–plasma model, in 1967, and deeper insight is being obtained by computer modelling combined with empirical work. Practical applications have been an important motivation throughout the history of mechanochemistry. It is used alone or in combination with other steps in an increasing number of technologies.
454 citations
15 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors reviewed the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarized their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.
Abstract: High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.
390 citations