Numerical verification of torsion-bar models based on the modified couple stress theory

This study verifies the suitability of the classical Saint–Venant’s displacement field, originally intended for macroscale torsional behavior, to microscale torsion-bar models within the modified couple stress theory framework. Finite element analysis was conducted for bars with circular and rectangular cross-sections, and the results align closely with analytic solutions, which is confirmed by the energy ratio analysis. These results affirm the appropriateness of the displacement field for microscale torsion bars. Additionally, warping effects are observed to be minimal, even at the microscale. These findings validate torsion experiments for determining a material’s length scale parameter, advancing the understanding of microscale torsion.