On the effective load during nanoindentation creep testing with continuous stiffness measurement (CSM)

The ability to accurately determine the applied load is critical in measuring hardness, which is traditionally defined as the ratio of the applied load to the projected contact area in the case of instrumented indentation. The magnitude of the applied load is unambiguous when the load is monotonically increased or held constant. However, in the case of nanoindentation testing with continuous stiffness measurement (CSM), wherein an oscillatory load is superimposed on the primary load, what one should use for the load has significant implications especially for rate-dependent materials. In this work, a concept of an effective load during nanoindentation creep testing with CSM is proposed based on a theoretical analysis. The analytical model is experimentally validated, and good agreement is found with the experimental results, even when the material exhibits a strong indentation size effect (ISE). The findings of this work have important implications for accurately measuring the rate dependence of hardness, especially during high-temperature nanoindentation testing.