Size effect and strain rate sensitivity in benzocyclobutene film

The mechanical properties of benzocyclobutene film are investigated at the nanoscale by nano-indentation using atomic force microscopy (AFM). The force versus indentation depth data were collected with two different AFM tips of radii ∼20 and ∼380nm. A strong size effect of the plastic flow stress was observed as the radius of the indenter tip was reduced. More important, the material exhibited pronounced strain rate sensitivity when probed at the nanoscale, while it was rate insensitive at larger scales. These two size effects were quantified by analytic and finite element modeling.