Determination of measurement uncertainties of mechanical properties and plastic anisotropy ratios of material at tensile tests

Abstract

Paper deals with determination of measurement uncertainties of mechanical properties and plastic anisotropy ratios of material at the tensile tests at usage of either three or five test specimens in orientations 0º, 45º and 90º towards sheet-metal rolling direction. Standard for tensile tests ČSN EN ISO 6892-1 contains determining of uncertainties partly for input dimensions of test specimens, partly for testing device, no for values of measured mechanical properties. The standard for determination of plastic anisotropy ratios ČSN ISO 10113 does not include the determination of measurent uncertainties, hence the standard does not solve achieve results accuracy. In this contribution the selective averages, selective standard deviations and combined measurement uncertainties of directional and medium values of mechanical properties and plastic anisotropy ratios of steel strip DD11 (11 320) are calculated using statistical methods. For calculations the software MS Excel was used. Based on the values of weighted average of plastic strain ratio of tested steel strip and with the use of sheet-metal classification concept according to Shawki, the suitability of tested steel for drawing operations at which predominate pressure-pull mechanical diagrams of stress was evaluated.