Use of dynamic test methods to reveal mechanical properties of nanomaterials

Abstract

Dynamic indentation techniques like micro and nanoscratch compared to static nanoindentation offer more robust extraction of mechanical properties of thin films, with higher level of control during experimentations. The velocity of the scratch indenter can be changed for probing the material properties at a wide range of strain rate. Considering the potential of this technique, detailed knowledge about the applicability of scratch method to different material systems is essential to create strategies for controlling appropriate physical feature for better mechanical properties at nanoscale.

Micro-scratch testing of free-standing micro-to-nano porous and dense metal foils shows a different rate sensitivity exponent at higher strain rate, suggesting a different mode of deformation. Continuous and interrupted tensile testing have been done on foils to provide a base line for comparison of strain rate sensitivity as well as possible stiffening effect under progressive load. Tensile testing of nanocrystalline metal alloys has been conducted to do the comparison with prior micro-scratch results. Nano-scratch testing on nanocrystalline nanolaminates and artificial ceramic bone (coatings of hydroxyapatite) are tested to reveal strength and strain rate sensitivity. In addition, a new technique known as the tapping mode measurement is investigated to determine the elastic-plastic transition and measure the elastic modulus of metallic nanolaminates and hydroxyapatite thin films for comparison to static nanoindentation.