Finite Element Prediction of Creep-Plastic Ratchetting and Low Cycle Creep-Fatigue for a Large SPF Tool



Industrial experience shows that large superplastic forming (SPF) tools suffer from distortion due to thermal cycling, which apparently causes high temperature creep and plasticity. In addition to distortion, thermomechanical fatigue and fatigue-creep interaction can lead to cracking. The aim of this study is to predict the life-limiting thermomechanical behavior of a large SPF tool under realistic forming conditions using elastic-plastic-creep FE analyses. Nonlinear time-dependent, sequentially coupled FE analyses are performed using temperature-dependent monotonic and cyclic material data for a high-nickel, high-chromium tool material, XN40F (40% Ni and 20% Cr). The effect of monotonic and cyclic material data is compared vis-à-vis the anisothermal, elastic-plastic-stress response of the SPF tool. An uncoupled cyclic plasticity-creep material model is employed. Progressive deformation (ratchetting) is predicted locally, transverse to the predominant direction of the creep-fatigue cycling, but at the same spatial location, due to creep and cyclic plasticity, during the so-called minor cycles, which correspond to comparatively small-amplitude temperature changes associated with opening of the press doors during part loading and unloading operations.


creep ratchetting heating-cooling cycles major cycle minor cycle part-forming cycles plastic shakedown superplastic forming thermomechanical fatigue and creep 



The authors wish to thank Ian Leaver and John Chippendale of BAE Systems, Salmesbury for helpful discussions. The first author would also like to thank BAE Systems for funding.


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© ASM International 2010

Authors and Affiliations

  1. 1.Division of Materials, Mechanics and StructuresUniversity of NottinghamNottinghamUK
  2. 2.Mechanical and Biomedical Engineering, College of Engineering and InformaticsNational University of IrelandGalwayIreland

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