Size effects on the onset of plastic deformation during nanoindentation of thin films and patterned lines

Abstract

Plastic deformation of materials exhibits a strong size dependence when the relevant physical length scales are in the range of microns or below. Recent progress in experimental and computational nanoindentation allows us to investigate the mechanical response of nanoscale material volumes, particularly the transition from elastic to plastic deformation and the early stages of plastic deformation. We present a systematic experimental study of nanoindentation on continuous films and unidirectionally patterned lines on substrates to explore the effects of two size scales (film thickness t and linewidth w) on the early stages of plastic deformation via the investigation of the nanoindentation P–h response. The observed experimental trends indicate that early stage plasticity is strongly size dependent, a feature that cannot be rationalized on the basis of continuum concepts. Computational simulations of these nanoindentation experiments through finite element modeling and molecular dynamics are conducted to elucidate the mechanisms by which this incipient plasticity progresses in the material by correlating observations from both experiments and computations.