Understanding and modeling plasticity error during nanoindentation with continuous stiffness measurement

Abstract

Over the years, there have been many improvements to the depth sensing indentation testing methodology and measurement electronics. These advancements provide opportunities to develop novel testing capabilities and also improve the reliability of the measurements. In this regard, a comprehensive model for simulating a constant indentation strain rate continuous stiffness measurement (CSM) test that includes the elastic-plastic response of the material and the response of the phase lock amplifier (PLA) is developed to understand the parameters affecting the precision and accuracy of the measurements. A novel test methodology that does not require closed-loop feedback is developed based on the model predications, and is found to improve the precision and accuracy of the CSM based indentation measurements. A procedure to correct for the plasticity error during CSM testing is also developed. Guidelines for selecting test parameters to stay within an acceptable level of error are established.