New instrumentation and analysis methodology for nano-impact testing

The nano-impact test is a technique for high strain rate mechanical characterization of materials at the nano/microscale. However, its use has been limited so far due to the lack of appropriate methods to determine the dynamic hardness under impact conditions. The main limitation up to date has been the determination of the true applied force due to considerable inertia effects. For this reason, dynamic hardness from nano-impact tests has traditionally been computed using an energy-based approach. This work overcomes this limitation by instrumenting the test device with force-sensing capability by means of a piezoelectric load cell. The methodology was evaluated on six materials covering a wide spectrum of mechanical behaviour. The work shows that the energy-based approach used so far yields significant errors on the determination of dynamic hardness, explaining contradictory results existing in literature, and identifies the main sources of error with the aid of finite element simulations. As a result, a new energy-based approach to determine dynamic hardness that overcomes the current limitations is proposed. (C) 2020 The Authors. Published by Elsevier Ltd.