Review of experimental observations on the gradient-enhanced continuum plasticity

Abstract The conventional plasticity theory cannot predict the size effects, in particular, when materials in nano- or microscales are subjected to the heterogeneous plastic deformation during short time period. In addition, higher-order continuum theories need to be used when addressing material instabilities due to shear bands and necking. Under this condition, one main mechanism to cause the size effects is strain gradient strengthening due to inhomogeneous plastic deformation. Following the experimental works on torsion of the copper thin wires by Fleck et al., numerous researchers have developed the strain gradient plasticity models targeting the size effects in the theoretical as well as the experimental contexts. This chapter reviews the experimental studies in terms of uniaxial tests, bending tests, torsion tests, indentation tests, bulge tests, and shear tests.