Neuber’s rule is commonly applied in fatigue analysis to estimate the plasticity of purely elastic FEA results. In certain cases, this is more efficient than running elastic-plastic models. However, the applicability of Neuber’s rule is not well understood for complex models and may not always be appropriate. In this paper, the applicability of Neuber’s rule is investigated. The background of Neuber’s rule is discussed, theoretical limitations are derived, and algorithmic outlines of the procedures are presented. Neuber’s plasticity correction procedure is applied to both the Ramberg-Osgood elastic-plastic constitutive relation and the advanced Chaboche isotropic/kinematic nonlinear hardening relation. Throughout the manuscript, the aspects of each model are discussed from an educational perspective, highlighting each step of the implementation in sufficient detail for independent reproduction and verification. This level of detail is often absent from similar publications and, it is hoped, may lead to the wider dissemination of Neuber’s rule for plasticity correction. The final component of the paper presents a multiaxial correction of the Chaboche hardening model. To the best of the authors’ knowledge, this is the first published application of Neuber’s rule to the multiaxial plasticity correction of the Chaboche combined isotropic/kinematic hardening model. Examples are used to illustrate the behavior of the method and to present some of the commonly overlooked components when assessing the applicability of Neuber’s method.
A coke drum experiences operating conditions that are severe and unrelenting, and their lifespans reflect this. In this paper, a coupled thermal-mechanical model of an operating coke drum is presented. The impacts of important operating parameters, such as the cycle time and quench rate, on an ideal operating cycle and a cycle that produces hotspots are discussed. The model is constructed in three stages: (i) the through-wall temperature distribution is probabilistically determined using a Bayesian inverse approach that calculates the heat flux profile on the inside of the drum wall from a temperature reading on the outside of the wall; (ii) a thermal-mechanical finite element analysis of the drum wall is conducted using the heat flux profile as a spatially and temporally varying boundary condition — to obtain the stress and strain behavior at a critical location (weld seam) on the drum; and (iii) hotspots are introduced in the vicinity of the weld through a novel approach, and their impact on the plastic behavior of the drum wall is examined. The influence of the operating conditions on the behavior of the coke drum is to be incorporated into a financial analysis of the entire coke drum’s life cycle — in a companion paper — to determine an optimal operating strategy.
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