Micro-indentation tests at scales on the order of sub-micron have shown tha
t the measured hardness increases strongly with the indent depth or indent
size decreasing, which is frequently referred to as the size effect. Howeve
r, the trend is at odds with the size-independence implied by conventional
elastic-plastic theory. In this paper, strain gradient plasticity theory is
used to model the size effect for materials undergoing the micro-indenting
, Meanwhile, the micro-indentation experiments for single crystal copper an
d single crystal aluminum are carried out. By the comparison of the theoret
ical predictions with experimental measurements, the micro-scale parameter
of strain gradient plasticity theory is predicted, which is fallen into the
region of 0.8-1.5 micron for the conventional metals such as copper (Cu),
aluminum (Al) and silver (Ag). Moreover, the phenomena of the pile-up and s
ink-in near micro-indent boundary are investigated and analyzed in detail.