Experimental evaluation of loading mode effect on plasticity of microscale single-crystal copper

Abstract

Abstract This study aims to experimentally elucidate the effect of loading mode on plastic behavior of microscale single-crystal copper. Tensile and bending tests involving in situ observations in a scanning electron microscope are carried out by fabricating dog-bone shaped specimens and cantilever beams, respectively, with the same size (2 μm) and the same single-slip orientation. The experimental results show that for microscale single-crystal copper the maximum stress at global failure under bending (288 MPa) is much higher than that of tension (82 MPa), while the yield stress at which the first group of dislocations are generated is similar for both tension (76 MPa) and bending (69 MPa). For tensile tests, the stress increases linearly and monotonically before yielding. The dislocations go through the tensile specimen and synchronously form surface steps at two opposite sides. However, the slip lines in bending specimens are initiated from the surface edges and terminated somewhere inside, and these local strain bursts lead to several intermittent stress drops. Assuming dislocation pile-up mechanism inside of bending specimens, the pile-up stress in the bending is evaluated as about 200 MPa, which agrees well with the experimental results.