Thermo-Mechanical Analysis and Lifing of Ni-Cr SPF Tool
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The paper describes the aniso-thermo-mechanical analysis of a representative large industrial SPF (XN40F, high nickel-chromium) tool. Sequentially coupled thermo-mechanical analyses under realistic loading conditions are developed within a general purpose non-linear FE code, ABAQUS to predict and analyse the complex temperature-stress-strain cycles of the SPF tool. A temperature-dependent, two-layer visco-plasticity model which combines both creep and combined isotropic-kinematic plasticity is chosen to represent the material behaviour. The material constants are identified from multiple strain-range isothermal cyclic tests and stress relaxation tests, over a range of temperatures between 20°C and 900°C. The FE predicted stress-strain data is used in stress-strain-life equations obtained from isothermal fatigue lifing tests at 900°C and the identified constants are validated against the TMF tests and simulative SPF tool test, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the tool cycle. The predicted SPF tool life is consistent with the simulative SPF tool test life and industrial observations.
Keywordsthermo-mechanical fatigue superplastic forming XN40F tools Ostergren model Zamrik model two-layer visco-plasticity model
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