A new form of equivalent stress for combined axial–torsional loading considering the tension–compression asymmetry of polymeric materials

Abstract

Although the von Mises criterion has been generally adopted to obtain the equivalent stress for materials under multiaxial loading, it does not consider the influence of the tension–compression asymmetry of pressure-sensitive materials. For polymeric materials, to include the non-negligible effect of the tension–compression asymmetry, this work proposes a new form of equivalent stress in which the tensile and compressive yield strengths are presented. This form is compared with the work of von Mises, Bai and Christensen with the support of experimental data. It was found that the proposed form is more suitable for polymeric materials under combined axial–torsional loading conditions. The implications of the present findings for designing stress-controlled combined axial–torsional loading experiments are also discussed.