Development of innovative indentation system and its application to cyclic ball indentation test for small-sized specimens

Abstract

An innovative indentation system has newly been developed with major features of precise measurements of load and profile of indentations, a wide range of load and test temperature, setting of two indenters, automatically controlled operations with various patterns and computer aided data processing. The system was applied to the cyclic ball indentation test for small-sized specimens. Since the test results showed poor reproducibility, improvements of the test technique have been made. Results of the improved test on FeMnCuC and Al3 at.% Mg alloys to evaluate stress-strain curves, strain-hardening exponents, strength coefficients and yield strengths as a function of heat treatment are shown in comparison with tensile test results. It is also presented that cracks occur around indents, which is the first to observe in the ball indentation test of metals. Empirical relationships between the critical strain, ε c at which the crack formation may start and the uniform elongation, ε u or the fracture strain, ε f are shown.