Showing papers by "Marc A. Meyers published in 1979"
TL;DR: In this article, a method for the determination of nucleation times for martensitic transformation is described, which utilizes a shock wave that, upon being reflected at a free surface, generates a tensile wave with a pulse duration that increases as it moves away from the surface.
Abstract: A method for the determination of nucleation times for martensitic transformation is described. The method utilizes a shock wave that, upon being reflected at a free surface, generates a tensile wave with a pulse duration that increases as it moves away from the surface. Once the duration of the reflected pulse is large enough for nucleation to occur, transformation can take place. The width of the martensite free layer adjoining the surface is measured and compared with wave predictions. A nucleation time can be obtained. The method requires that the temperature, pulse amplitude, and alloy composition be such that only the reflected tensile wave induce martensite transformation. For the experimental conditions used by Snell, Shyne, and Goldberg10 the nucleation time is found to be less than 55 nanoseconds.
17 citations
TL;DR: In this article, two simple tests are presented to verify whether the mechanical response of the substructure remains constant during stress relaxation, and a method is developed for the determination of the time dependence of the mobile dislocation density, using the decrease in relaxation rates in repeated cycling.
Abstract: Two simple tests are presented to verify whether the mechanical response of the substructure remains constant during stress relaxation. They consist of a) subjecting the sample to repeated relaxation cycles from the same reference load and b) reloading the sample after the last cycle. Either exhaustion of relaxation after repeated cycles or yield-point formation on reloading are indicative of a decrease in the mobile dislocation density. Accordingly, a method is developed for the determination of the time dependence of the mobile dislocation density, using the decrease in relaxation rates in repeated cycling. The exhaustion of relaxation in Armco iron is found to be in good agreement with predictions for the decrease of mobile dislocation density by a pinning mechanism.
17 citations
01 Jan 1979
TL;DR: In this article, a model for dislocation generation in shock-wave deformation is described, which does not require the dislocations to move with the shock front; therefore no supersonic disllocations are needed.
Abstract: A model for dislocation generation in shock-wave deformation is described. Contrary to earlier models proposed by Smith (1958) and Hornbogen (1960), this model does not require the dislocations to move with the shock front; therefore no supersonic dislocations are needed. Dislocations are homogeneously nucleated at the shock front by the deviatoric component of the applied stress pulse; after generation, they are left behind, organizing themselves into more stable arrangements. Dislocation generation may also take place at the rarefaction part of the wave; however the mechanism is thought to be the conventional multiplication mechanism in this part of the wave. Dynamical considerations for nickel show that dislocations moving at velocities higher than the transverse sound velocity would lead to exceedingly high temperatures; experiments show that such is not the case. What renders the proposed model especially attractive is that, for the first time, quantitative predictions of residual dislocation densities are made possible. Accordingly, calculated dislocation densities are compared to observed densities for nickel reported in the literature.
5 citations