A yield-surface corner lowers the buckling stress of an elastic-plastic plate under compression

The bifurcation stress is calculated for a simply-supported elastic-plastic plate in uniaxial compression, in the case when the stress is at a vertex of the yield surface which is locally similar to that of Tresca. The effect of coupled hardening between yield-surface facets which meet at the vertex is included. It is found that the bifurcation stress may be substantially lower than that associated with the von Mises yield surface. The latter is known to give results too high to be reconciled with experiment. Reductions of order 10–30 per cent are shown to be unexceptional, even with the retention of an elastic value for the shear modulus.