Understanding scale-dependent yield stress of metals at micrometre scales

Abstract

The mechanical softening behaviour of micrometre-scale metals (free-standing metal foils and wires) with decreasing either the geometrical or the microstructural scale (i.e. the smaller, the weaker) has recently been reported. Here, we present a mechanism-based model to understand the softening behaviour, which is based on competition between the effects of surface grain relaxation and the interior grain strengthening effect. The model describes well the yield stress of Cu foils with different ratios of the thickness to grain size.

Keywords:

• copper foils
• yield stress
• dislocations
• size effect
• mechanical softening

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 50971125 and 51171045) and the National Basic Research Program of China (Grant No. 2010CB631003).