INFLUENCES OF STRESS ON THE MEASUREMENT OF MECHANICAL-PROPERTIES USING NANOINDENTATION .2. FINITE-ELEMENT SIMULATIONS

The finite element method has been used to study the behavior of alumi num alloy 8009 during elastic-plastic indentation to establish how the indentation process is influenced by applied or residual stress. The study was motivated by the experiments of the preceding paper which sh ow that nanoindentation data analysis procedures underestimate indenta tion contact areas and therefore overestimate hardness and elastic mod ulus in stressed specimens. The NIKE2D finite element code was used to simulate indentation contact by a rigid, conical indenter in a cylind rical specimen to which biaxial stresses were applied as boundary cond itions. Indentation load-displacement curves were generated and analyz ed according to standard methods for determining hardness and elastic modulus. The simulations show that the properties measured in this way are inaccurate because pileup is not accounted for in the contact are a determination. When the proper contact area is used, the hardness an d elastic modulus are not significantly affected by the applied stress .