Effects of viscoelasticity and time-dependent plasticity on nanoindentation measurements of human cortical bone.

The viscoelastic and time-dependent plastic effects on the nanoindentation measurement of osteonal lamella in a human cortical bone were investigated. The elastic modulus of osteonal lamella obtained from the quasi-static technique was strongly affected by the indentation rate and time-dependent plasticity. The effects of time-dependent plasticity can be diminished by multiple loading-unloading cycles and a long holding period at maximal load. After minimizing the contribution of time-dependent plasticity to unloading data, it was surprisingly found that the elastic modulus was proportional to indentation strain rate raised to the 0.06 power, which is similar to conventional test results. Copyright 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 208-214, 2003