Strain path influence on size effects during thin sheet copper microforming

The influence of the size effects on the forming processes for micro-sized parts is not yet well known. This work follows experimental and numerical studies of the effect of a reduction in thickness (t) over grain size (d) ratio on the mechanical properties of high purity copper. Under tensile conditions, copper exhibits softer mechanical properties if t/d < 6, in agreement with previous results concerning Al or Ni. To assess the influence of complex loadings linked to forming processes on size effects, Nakazima tests were performed with 20 mm hemispherical punch on a universal sheet metal testing machine associated to a 3D video extensometer. Our results revealed that size effects are strongly sensitive to strain paths. Depending on these latter, the deterioration of the mechanical properties shown for tension is modified.