Effects of strain rate on mechanical properties of nanosilica/epoxy

The mechanical properties (i.e., stress-strain relationship and peak stress) of nanosilica filled epoxies were studied using an Instron machine and a split Hopkinson pressure bar apparatus over a range of strain rates from 8 × 10^-4 s^-1 up to ∼5 × 10³ s^-1 under uniaxial compression. It was found that the nanosilica particles only reinforce epoxies slightly under both quasi-static and dynamic loading conditions. With a unit cell model, it was observed that owing to the existence of nanosilica, the surrounding strain field was changed and the strain-softening characteristics of the epoxy introduced a negative effect of the nanosilica particles as a reinforcement agent. That is, the particle strengthening effect depended on the mechanical characteristics of epoxy matrix. This was further confirmed by numerically simulating the mechanical behaviors of the composites for which (a) the matrix might assume different strain-softening or strain-hardening characteristics and (b) there were higher loadings of rigid silica particles.