Using Nonlinear Kinematic Hardening Material Models for Elastic–Plastic Ratcheting Analysis

Abstract

Applicable design codes for power plant components and pressure vessels demand for a design check against progressive plastic deformation. In the simplest case, this demand is satisfied by compliance with shakedown rules in connection with elastic analyses. The possible noncompliance implicates the requirement of ratcheting analyses on elastic–plastic basis. In this case, criteria are specified on maximum allowable accumulated growth strain without clear guidance on what material models for cyclic plasticity are to be used. This is a considerable gap and a challenge for the practicing computeraided engineering engineer. As a followup to two independent previous papers PVP201398150 ASME (Kalnins et al., 2013, “Using the Nonlinear Kinematic Hardening Material Model of Chaboche for ElasticPlastic Ratcheting Analysis,â€‌ ASME Paper No. PVP201398150.) and PVP201428772 (Weitze and Gilman, 2014, “Additional Guidance for Inelastic Ratcheting Analysis Using the Chaboche Model,â€‌ ASME Paper No. PVP201428772.), it is the aim of this paper to close this gap by giving further detailed recommendation on the appropriate application of the nonlinear kinematic material model of Chaboche on an engineering scale and based on implementations already available within commercial finite element codes such as ANSYSآ® and ABAQUSآ®. Consistency of temperaturedependent runs in ANSYSآ® and ABAQUSآ® is to be checked. All three papers together constitute a comprehensive guideline for elastoplastic ratcheting analysis. The following issues are examined and/or referenced: (1) application of monotonic or cyclic material data for ratcheting analysis based on the Chaboche material model, (2) discussion of using monotonic and cyclic data for assessment of the (nonstabilized) cyclic deformation behavior, (3) number of backstress terms to be applied for consistent ratcheting results, (4) consideration of the temperature dependency (TD) of the relevant material parameters, (5) consistency of temperaturedependent runs in ANSYSآ® and ABAQUSآ®, (6) identification of material parameters dependent on the number of backstress terms, (7) identification of material data for different types of material (carbon steel, austenitic stainless steel) including the appropriate determination of the elastic limit, (8) quantification of conservatism of simple elasticperfectly plastic (EPP) behavior, (9) application of engineering versus true stress–strain data, (10) visual checks of data input consistency, and (11) appropriate type of allowable accumulated growth strain. This way, a more accurate inelastic analysis methodology for direct practical application to real world examples in the framework of the design code conforming elastoplastic ratcheting check is proposed.