Unique tension-compression asymmetry of nanoporous metallic glasses induced by surface effects

The mechanical properties of nanoporous (NP) metallic glasses (MGs) under uniaxial tension and compression are studied via molecular dynamics simulations in this work. The shrinking tendency within NP MGs, induced by the surface effects, results in the unique tension-compression asymmetry, i.e., the tensile yield strength is stronger than the compressive yield strength and the tensile yield strain is bigger than the compressive yield strain. This unique tension-compression asymmetry of NP MGs is contrary to that of the pore-free bulk MGs and the MGs with macroscopic pores. The strengthening phenomenon with the increase of the pore size is more remarkable for compression than tension due to the difference of elastic energy release during the deformation. Moreover, with the pore size decreasing, the deformation mechanism of NP MGs changes from catastrophic fracture with a single dominant shear band to homogeneous plastic deformation with multiple shear bands under both tensile loading and compressive loading. Our results are helpful in understanding the surface effects on NP materials and important for optimization design of NP materials.