Instrumentation of a conventional hardness tester for load-displacement measurement during indentation

A conventional microhardness tester has been instrumented with a piezoelectric load cell and capacitance displacement gages to measure load and displacement during indentation. As in other recently-developed load and displacing sensing indentation instruments, the new device can be used to measure a variety of mechanical properties, but has the advantage of being relatively inexpensive to assemble since many of its components are standard equipment. Tests were performed on soda-lime glass and an aluminum alloy, demonstrating the diversity of material elastic-plastic responses under indentation, particularly in the unloading cycle. The data suggest that models of elastic unloading based on invariant indenter-surface contact area may not be general, and may lead to underestimates of hardness and modulus.