CONCEPTUAL MODELS FOR UNDERSTANDING THE ROLE OF THE R-NODES IN PLASTIC COLLAPSE

The r-nodes (redistribution nodes) are locations in mechanical compone nts and structures that are load-controlled, and therefore insensitive to material constitutive relationships. These locations and their res pective equivalent stress values can be approximately determined on th e basis of two linear elastic analyses. By invoking equilibrium consid erations, a simple relationship can be established between the ''combi ned r-node equivalent stress'' and the plastic collapse loads. On acco unt of its lend-controlled nature, the combined r-node equivalent stre ss can be identified with the reference stress, which is extensively u sed in carrying out pressure component integrity assessments. The conc ept of r-nodes is also related to the primary stresses in pressure com ponents, and in designing mechanical components and structures for min imum weight, This paper proposes simple phenomenological models in an attempt to characterize the functioning of r-nodes.