Modeling of coupled thermoplasticity at finite strains

Detta är en avhandling från Div. of Solid Mechanics, Lund University, P.O. Box 118, SE-221 00 Lund

Sammanfattning: In this thesis, models for simulation of inelastic phenomena, such as plastic anisotropy, texture evolution, void growth and phase transformation are presented. Special emphasized is put on the modeling of heat generation due to plastic work. All models are formulated within a thermodynamic framework that allows large deformations. The thermodynamic framework is used as a base for the formulation of the coupled thermomechanical problem, where the mechanical dissipation will serve as a heat source in the heat equation. Heat generation effects are studied for plastic anisotropic materials. The first investigation is performed using a mixed isotropic and kinematic hardening constitutive mode. The non-associated formulation of the model makes it possible to, in addition to the mechanical behavior, predict an accurate heat generation. A thermodynamically consistent single crystal plasticity model is developed. The model is used study the heat generation in textured material during cyclic loading. One failure mechanism in ductile metals involves nucleation and growth of voids, which eventually leads to crack propagation. Temperature evolution and heat generation in connection with void growth are studied with a Gurson model. The Gurson model, which is extended to also consider non-local porosity effects, is used in fully coupled thermomechanical simulations, including localization problems and crack propagation. Many austenitic stainless steels undergo a change of microstructure from austenite to martensite when they are loaded. A model that considers the evolution of phase transformation, as well as plastic flow in form of slip, is developed within a thermodynamic framework for large deformations. The model is used in necking simulations where it is studied how the phase transformation affects the localizations. The effects of phase transformation in sheet metal forming are also studied.

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