Different response mechanisms of yield strength and ultimate tensile strength in pure copper considering size effect

The ultimate tensile strength (UTS) and the yield strength (YS) are two key performances of copper wire, which vary synergistically under macroscopic conditions. However, they exhibit different dimensional sensitivity at small dimensions, which provides new ideas for designing materials. This study tested the UTS of copper wire with different dimensions after annealing. It was found that the UTS became weaker in a smaller dimension. Dislocations in the surface grains moved quickly to the sample surface of the microstructure. The density of dislocations in the grains decreased, which significantly reduced the strength at small dimensions. The YS arises with smaller dimensions because the growth of hard grains increased the difficulty in opening the slip system. The evolution of the Taylor factor (M) with dimensions explains the size effect in YS. The rapid increase in M value for small-size samples resulted in higher YS.