A new perspective on bounding surface plasticity: The moving projection origin

Abstract

This technical note attempts to validate the radial mapping rule for a bounding surface plasticity model with testing data from the stress probe experiment. The projection origin mapping the current stress point into an imaginary stress point on the bounding surface is an essential element of the bounding surface plasticity because the magnitude and direction of the plastic strains are eventually calculated based on the location of the imaginary stress point. The adequacy of the projection origin that has been frequently assumed fixed was criticized by tracking the possible location of the projection origin using experimental values of the plastic strains without prior assumption. When the projection origin is fixed at the origin of the stress space, the difference between the angular directions of the measured plastic strain increments and the tangential plane at the imaginary stress point can be significant, indicating that the projection origin should be allowed to move. The trace of the moving projection origin that can be located via the intersection of two straight lines passing the current and imaginary stress points reveals that the movement of the projection origin depends on both current and preshear stress paths, especially at the early stages of loading. A new mapping rule for the bounding surface plasticity model is proposed in the discussion.