Conceptual Models for Understanding the Role of the R-Nodes in Plastic Collapse

The r-nodes (redistribution nodes) are locations in mechanical components and structures that are load-controlled, and therefore insensitive to material constitutive relationships. These locations and their respective equivalent stress values can be approximately determined on the basis of two linear elastic analyses. By invoking equilibrium considerations, a simple relationship can be established between the “combined r-node equivalent stress” and the plastic collapse loads. On account of its load-controlled nature, the combined r-node equivalent stress can be identified with the reference stress, which is extensively used in carrying out pressure component integrity assessments. The concept of r-nodes is also related to the primary stresses in pressure components, and in designing mechanical components and structures for minimum weight. This paper proposes simple phenomenological models in an attempt to characterize the functioning of r-nodes.