Choice of the mechanical testing to plot the dependence of the microhardness of metal on the plastic strain

Abstract

The comparative analysis of the results of the tests on uniaxial compression and uniaxial tension of the metal alloys was caried out. The goal of the analysis was to reveal the advantages and disadvantages of the tests in terms of using them to plot the calibration dependence of microhardness on the plastic strain. There were four alloys tested: copper, brass L60, steel 15 and aluminum-magnesium alloy AMg5. There were from 8 to 12 cylindrical samples tested on uniaxial compression. The compression of each sample was conducted to different strain value. Being compressed the samples were cut either along the section containing the axis of a cylinder, or perpendicularly to the axis of the compressed cylinder in the middle of the cylinder height. The testing on the tension was carried out until failure; then the two parts of the broken specimens of the copper, brass L60 and steel 15 were cut along the axis. The surfaces of the sections was first ground on the abrasive paper of different grit, and then polished on the wet cloth with polishing paste. And on the torn samples of the alloy AMg5 the zone of the uniform deformation was marked and cut into a few cylindrical samples of the length-to-diameter ratio equal to 2, the cylindrical samples were subjected to plastic deformation in uniaxial compression and then the deformed samples were cut either along the section containing the axis of a cylinder, or perpendicularly to the axis of the compressed cylinder in the middle of the cylinder height. The obtained sections were ground and polished.  The measurements of the microhardness of the sections obtained were conducted. The measurements for the compressed specimens were performed in the center of the section; for the torn specimens — along the axis on the different distances from the specimen butt. The microhardness was measured using three loads on the indentor: 0,196 N; 0,490 N and 0,980 N. There were produced 6 impressions on each load, that is 18 impressions in all. The final value of microhardness was obtained as mean arithmetical magnitude over 18 impressions. For the most alloys it does not matter which testing to apply — uniaxial compression or uniaxial tension — in order to obtain the calibration dependence of microhardness on the plastic strain for the zone of strain not exceeding 0,3, the uniaxial compression being preferable as less costly. In the area of comparatively high plastic strains to avoid the considerable error in evaluation of the strain distribution in plastically deformed parts according to  the microhardness measurements it is recommended to plot the calibration curve based on the uniaxial compression tests.