Size-dependent Tensile Behavior of Micron-Scale Materials Under Pre-Torsional Deformation: A Strain Gradient Plasticity Analysis

With the continued miniaturization of structural components, metallic materials often exhibit pronounced size-dependent mechanical behavior at the micron scale. Such size dependence is commonly associated with non-uniform plastic deformation and the resulting strain gradient effects. Pre-torsional deformation is efficient in enhancing mechanical strength with minimal impact on the shape and dimensions. However, when pre-deformation is applied at the micron scale, the associated size effect must be carefully considered. To address this issue, this study delves into the relatively unexplored realm of size effect arising from pre-torsional deformation. A finite element model grounded in the conventional mechanism-based strain gradient plasticity (CMSG) theory was employed to examine the impact of pre-torsion on mechanical behavior. Through comprehensive computational examinations, this research endeavors to unveil the intricate size-dependent alterations in the material response at the micron scale, drawing comparisons with classical plasticity theory. The results show that the CMSG theory can effectively capture the size effect of the uniaxial tensile strength of a sample after pre-torsional deformation. The yield and ultimate strengths increased with the degree of pre-torsional deformation, while the necking strain decreased. These findings highlight the essential role of strain gradient effects in governing the tensile response of pre-torsioned metallic samples at small scales.