USING NONLINEAR KINEMATIC HARDENING MATERIAL MODELS FOR ELASTIC-PLASTIC RATCHETING ANALYSIS

摘要

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 non-compliance 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 CAE (Computer Aided Engineering) engineer. As a follow-up to two independent previous papers PVP2013-98150 ASME and PVP2014-28772 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 ANSYS~® and ABAQUS~®. Consistency of temperature-dependent runs in ANSYS~® and ABAQUS~® is to be checked. All three papers together constitute a comprehensive guideline for elasto-plastic 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 (non-stabilized) cyclic deformation behavior 3. Number of backstress terms to be applied for consistent ratcheting results 4. Consideration of the temperature dependency of the relevant material parameters 5. Consistency of temperature-dependent runs in ANSYS~® and ABAQUS~® 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 elastic-perfectly plastic behavior 9. Application of engineering versus true stress-strain data 10. Visual checks of data input consistency 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 elasto-plastic ratcheting check is proposed.