Validation of the Nonlinear Superposition Method (NSM) for elastic shakedown limit pressures via comparison with experimental test results of spherical vessels with radial and oblique nozzles

The present research revisits rare experiments which determined elastic shakedown (SD) limit pressures of full scale radial and oblique nozzles partially penetrating spherical vessels. The experiments were conducted at Berkeley Nuclear Laboratories in England [1]. The SD limit pressures were determined via conducting consecutive series of internal pressure cycles and observing cyclic strain variation recorded by strain gauges cemented at predetermined various critical locations within the junctions' vicinities. The Nonlinear Superposition Method (NSM), formulated for computing elastic SD limit loads based on Melan's lower bound SD theorem, is successfully validated against recorded experimental outcomes for both nozzle configurations. Furthermore, full elastic-plastic cyclic loading finite element simulations were executed and illustrated very good correlation to the NSM results.