Characterization and modeling of specific strain gradient modulus of epoxy

Microscale sensing and actuating components are prevalent in microelectromechanical systems. Deformations of microscale components are dependent not only on the strains in the body, but also on the strain gradients. The contribution of strain gradients to plastic hardening is characterized by the specific strain gradient modulus of the material. The specific strain gradient modulus has been predicted to vary with the plastic strain. The moduli of plastically prestrained epoxy specimens were experimentally characterized in this investigation using nanoindentation Prestraining induced softening and an energy model are developed to separate the effect of prestrain softening from the effect of strain gradient. The results indicated that the contribution of strain gradient to hardening was initially large but diminished with increased plastic deformation. A model was developed for power law material and was shown to compare well with the experimental results.