Elastoplastic buckling of structures is much more complicated to analyse and to understand than nonlinear elastic buckling. The reason is that the critical load predictions strongly depend on which theory of plasticity, \(J_2\) flow theory or deformation theory, is used. This is also well-known as the plastic buckling paradox.
In this clearly written paper, the usual single-load parameter buckling analysis is extended to the case where a rectangular plate is biaxially loaded by compression in one direction, and by tension in the direction orthogonal to the direction of compression. Critical loads are calculated both for \(J_2\) flow and deformation theories for various boundary conditions for the plate. The critical stresses are determined by using numerical solution of an eigenvalue problem for a range of plate geometry and loading ratio. Various different loading paths are compared to each other. Additionally, the authors obtain a striking contradiction in the buckling behaviour from the two competing theories, adding a new observation to the plastic buckling paradox.