Development of pile-up during spherical indentation of elastic-plastic solids

摘要

Finite element modeling has been used to study the development of pile-up during indentation with a rigid sphere as it relates to the measurement of mechanical properties by load and depth sensing indentation. A wide range of materials with different elastic moduli, yield stresses, strain-hardening exponents, and friction coefficients were examined. Results show that during a significant portion of the spherical indentation process, the amount of pile-up cannot be related solely to the strain-hardening exponent, as is often assumed. Rather, after initially sinking-in at small depths of penetration, the pile-up for many materials evolves and increases gradually as the indenter is driven into the material. Even when deformation enters the fully developed plastic stage, the pile-up geometry continues to change in manner that can significantly affect the contact area. It is also shown that contact friction affects the pile-up geometry, and that the pile-up heights before and after the indenter is unloaded can be quite different. Implications for the measurement of mechanical properties by load and depth sensing indentation methods are discussed. (C) 2004 Elsevier Ltd. All rights reserved.