Determining of the machine compliance using instrumented indentation test and finite element method

Abstract

At present time the importance of indentation measurements once again increases. As modern and perspective measurement method it allows to measure various mechanical properties while only needing micro volumes of materials. While standard hardness measurement methods examine only the plastic response of sampled material, Depth Sensing Indentation (DSI) testing is founded on real-time recording of applied force and resulting travel of indenter. This allows to evaluate both plastic and elastic response of examined material during the indentation process which in turn allows for calculation of various static material properties in very small volumes of samples. The big advantage of this approach is saving of time (especially on sample preparation), however the data analysis – and thus results – could be influenced by certain factors. Those worth noting are surface quality of the sample, wear of the indenter head, its shape and material, and also the compliance of testing machine’s frame. If we consider the frame of testing machine having non-zero compliance, inevitably there will occur not only displacement of indenter but also displacement of frame itself, especially noticeable while using high loads. This negatively influences the results of such measurement. This work’s aim is to calculate the compliance of test machine’s frame using Finite Element Method model and 1 mm in diameter steel ball indenter. The result of this work is addition of virtual spring to the FEM model and fine tuning of its stiffness. This should allow us to minimize the influence of frame’s compliance on the results of future measurements.