An analysis of nanoindentation in elasto-plastic solids

This paper examines the accuracy of the extracted elastic properties using the nanoindentation technique on elasto-plastic materials. The application of the correction factor evaluated in the linearly elastic case [Poon, B., Rittel, D., Ravichandran, G., 2008. An analysis of nanoindentation in linearly elastic solids. Int. J. Solids Structures 45 (24), 6018–6033.] on elastic–plastic materials is critically examined. It is then established that the accurate determination of the projected area of contact is found to be crucial for the accurate determination of elastic material properties. The conventional methods for the accurate determination of contact area are generally limited to ratios of Young’s modulus over yield stress, E/σy < 30 for elastic-perfectly plastic materials, which is too stringent for most materials. Thus, a new electrical resistance method is proposed to measure directly the projected contact area. Using numerical simulations, it was found that with the accurate determination of A, the error associated with the extracted elastic material properties is reduced by more than 50% in some cases. Using the newly proposed procedure, the error is also found to be independent of E/σy and the tip radius, ρ, and it is only a function of Poisson’s ratio, ν. This suggests that the errors might be due to the residual stresses at the plastic imprint that were found to depend on ν as well.