A Comparison of Microplastic Strain Produced Statically and Dynamically

The object of this investigation was the microscopic comparison of the structure of alpha brass resulting from strain produced statically and dynamically. The dynamic strain was produced at an impact velocity of 150 ft/sec. It was observed that for the same strain produced at the two rates of loading, there was no observable difference in the resulting microstructure. The strains varied from 1.3 percent to 10.9 percent. For this same range of strain, it was also observed that except for the apparent amount of slip on each individual slip plane and the distortion of the surface, the resulting microstructure was practically independent of the amount of strain. In the grains which had only one slip system acting and in which the slip lines were distinct enough so that a count could be made of them, the average spacing of the slip lines was about o.6 micron, varying from a minimum of 0.38 to a maximum of 1.0 micron. The slip line spacing for grains in which more than one slip system was acting appeared to vary from 0.4 to 4 or 5 micron. Approximately 40 percent of the grains observed had two slip systems acting, and this percentage did not vary appreciably with strain. Not enough grains were found with three systems of slip acting at the same point to form any valid conclusion concerning this phenomenon. At least 95 percent of the grains showed slip lines, even at the smallest strains observed. No conclusions could be made concerning the possibility of twinning in the deformation of alpha brass, except that it is certain that no large mechanical twins are produced. Twinning in this material is still a controversial issue, and its detection involves more elaborate investigation.