Quasi-static and dynamic nanoindentation of particle-reinforced soft composites

The mechanical properties of ferromagnetic particle-reinforced silicone-rubber matrix composites are examined with quasi-static and dynamic nanoindentation measurements using Berkovich and flat punch indenters, respectively. Quasi-static nanoindentation is performed to examine primary factors such as the loading and holding time, particle volume fraction, and indentation depth for these particle-reinforced soft composites (PRSCs). The Einstein-Guth-Smallwood equation based on macroscopically mechanical property testing is utilized to describe the relationship between elastic modulus and particle content of PRSCs in quasi-static tests. A good agreement between the nanoindentation and simulation prediction is obtained. To characterize the storage modulus and loss factors of PRSCs, the dynamic nanoindentation is then conducted over the force frequency range of 0-45 Hz to show that the dynamic properties are dominated by the particle content and the force frequency, and independent of indentation depth and oscillation amplitude. It is indicated that the nanoindentation is a versatile methodology to assess mechanical properties of microsized particulate soft composites. (C) 2016 Wiley Periodicals, Inc.