Showing papers by "Marc A. Meyers published in 1981"

Shock Waves and High-Strain-Rate Phenomena in Metals

Abstract: These proceedings of EXPLOMET 90, the International Conference on the Materials Effects of Shock-Wave and High-Strain-Rate Phenomena, held August 1990, in La Jolla, California, represent a global and up-to-date appraisal of this field. Contributions (more than 100) deal with high-strain-rate deforma

Shock Waves and High-Strain-Rate Phenomena in Metals. Concepts and Applications.

Abstract: : The subject matter addressed by the chapters which compose this book is organized into nine sections followed by a number of appendices. Section 1 consists of a Historical Perspective followed by sections on High Strain-Rate Deformation, Dynamic Fracture, and Adiabatic Shearing (2,3,4). The next three sections deal with shock waves and constitute the core of the book: Shock Waves I: Experimental Techniques, Shock Waves II: Fundamentals, and Shock Waves III: Microstructural and Mechanical Effects, (5,6,7). The last two chapters treat the major applications: Dynamic Compaction of Powders (8) and Explosive Metal Working and Welding (9).

Defect Generation in Shock-Wave Deformation

Abstract: A theoretical framework elucidating the generation of shock-induced defects is presented. Three different mechanisms responsible for the generation of point, line, and planar defects (twins and stacking faults), respectively, are described. Dislocations are homogeneously nucleated at or slightly behind the shock front by the powerful deviatoric stresses generated by the shock pulse; they are accelerated by the residual deviatoric stresses either towards or away from the front. Dislocation dynamical considerations limit their velocity to the velocity of shear waves in the medium. Their self-energy and stiffness are very high at the high velocities; hence, their ability to generate point defects upon intersecting each other is greatly enhanced, because the drag stress produced by the jogs is essentially independent of the velocity.

Shock-Wave Consolidation of Rapidly Solidified Superalloy Powders

Abstract: The feasibility of consolidating rapidly solidified MAR M-200 powders by explosive means is demonstrated. MAR M-200 powders produced by the rapid solidification rate (RSR) technique and exhibiting a microdendritic structure were consolidated in an axisymmetric set-up, consisting of a steel pipe (in which the powder was placed) surrounded by explosives. The converging shock waves produced full densification, after optimization of the process parameters. The microindentation hardness showed a dramatic increase: 357 HV in the as-received condition, to 700 HV in the shock-consolidated condition. The substructure was analyzed by TEM, and two distinct regions were identified. The center of the particles exhibited planar arrays of dislocations, stacking-faults, and twin faults characteristic of shock-loaded superalloys, while the melted and re-solidified interfacial layers consisted of a microcrystalline structure with homogeneous composition.

The Attenuation of Shock Waves in Nickel

Abstract: The attenuation of planar shock waves generated by plate impact was monitored by their decay throughout massive nickel blocks. This was accomplished, during the passage of the wave, by manganin piezoresistive gages connected to oscilloscopes and, in the post-shocked condition, by hardness measurements and TEM observations at various distances from the impact surface in the nickel blocks. The nickel systems exhibited different metallurgical microstructures before shock loading: preshocked (grain size 150 μm), annealed (grain size 150 μm)and annealed (grain size 32 μm). For each system two different initial shock pressures were used: 10 and 25 GPa. The pulse duration was held constant at 2 μs. The experimental records of oscilloscopes showed that there are no significant effects of grain size and pre-deformation on the attenuation in nickel. The observed attenuation was compared with the calculated one according to hydrodynamic theory and poor agreement was found, An “accumulation” model based on the conservation of energy is presented herein to explain the dissipative processes of shock waves in metals.

Thermomechanical Processing by Shock Waves: An Overview

Abstract: Research efforts assessing the potential of shock TMP for a number of alloy systems are reviewed. Shock loading seems to be a promising deformation technique in TMP when (a) the initial strength of the alloy is such that conventional deformation is precluded and (b) when the shock wave induces property improvements that are significantly superior to those of conventional deformation.