Strain Rate and Nanoindentation

The deformation behavior of materials is often time dependent. During uniaxial mechanical testing at higher deformations speeds, most metals display higher strengths. This time dependence is called strain rate sensitivity, and it is an important factor to consider in nanoindentation testing, as well. 

In this application note, we discuss the relationship between indentation test profiles and the resulting measured hardness values, and we demonstrate techniques for measuring strain rate sensitivity using constant strain rate and strain rate jump indentation. We show that displacement control and continuous stiffness measurement are valuable features for both test methods. Hardness and strain rate sensitivity values measured on fused silica, single-crystalline and ultrafine-grained aluminum are seen to be in good agreement with literature values. This illustrates how strain rate control can be used to achieve both more consistent measurements and provide insight into the operative deformation mechanisms during indentation.