Analysis of indentation creep

摘要

Finite element analysis is used to simulate cone indentation creep in materials across a wide range of hardness, strain rate sensitivity, and work-hardening exponent. Modeling reveals that the commonly held assumption of the hardness strain rate sensitivity (m_H) equaling the flow stress strain rate sensitivity (m_(σ)) is violated except in low hardness/ modulus materials. Another commonly held assumption is that for self-similar indenters the indent area increases in proportion to the (depth)~2 during creep. This assumption is also violated. Both violations are readily explained by noting that the proportionality "constants" relating (ⅰ) hardness to flow stress and (ⅱ) area to (depth)~2 are, in reality, functions of hardness/modulus ratio, which changes during creep. Experiments on silicon, fused silica, bulk metallic glass, and poly methyl methacrylate verify the breakdown of the area-(depth)~2 relation, consistent with the theory. A method is provided for estimating area from depth during creep.