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AbstractAn extensive plasticity model base useful to predict stresses in thermo-mechanical processes where the microstructure changes has been established. The densities of mobile and immobile dislocations are the basic ingredients in the model. The motion of the former corresponds to plastic strain rate. The interaction between moving dislocations and various obstacles contributes to the material resistance. The focus is on the developed recrystallization model that is based on dislocation densities. The results show that recrystallization at high strain rates leads to a large number of nuclei that grow after the test. This means that most of the recrystallization occurs after the test. [ABSTRACT FROM AUTHOR]

A previously published dislocation density based flow stress model has been refined and made more consistent with underlying physical assumptions. The previous model included many temperature dependent parameters that are taken as constant in the current work. The model has also been simplified with respect to dynamic strain aging. Additional contributions to flow stress from the Hall-Petch effect and solute hardening have now been explicitly included in the model. Furthermore, the dynamic recovery part of the model has been improved. [ABSTRACT FROM AUTHOR]

Abstract: A physical based model for the evolution of flow stress of AISI 316L from room temperature up to 1300°C, strains up to 0.6 and strain rates from 0.0005 up to 10s−1 is developed. One set of tests have been used for model calibration and another more complex set of tests for its validation. The model is based on a coupled set of evolution equations for dislocation density and (mono) vacancy concentration. Furthermore, it includes the effect of diffusing solutes in order to describe dynamic strain ageing (DSA). The model described the overall flow stress evolution well with exception of the details of the effect of the DSA phenomenon. Its numerical solution is implemented in a format suitable for large-scale finite element simulations. [Copyright &y& Elsevier]

• A flow stress model including microstructure evolution for friction stir additive manufacturing is established. • Numerical simulations reveal the effect of microstructure evolution on mechanical properties. • Multiple reheating promotes the generation of precipitates and increases the yield strength. • Multiple reheating depletes solid solution elements and reduces net flow stresses. The Complex reheating phenomenon during friction stir additive manufacturing (FSAM) has a significant impact on the microstructural evolution. This, in turn, affects its mechanical properties. A flow stress model including the precipitate, solid solution and dislocation density evolution was proposed to reveal the relationship between the microstructure and constitutive behavior in FSAM of Al-Mg-Si alloys. The microstructure and mechanical properties of single-layer and multi-layer FSAM were investigated using experimental and numerical simulation methods. The results revealed that during the first reheating process, the precipitates exhibited dissolution and coarsening behavior in the heating stage. In the third reheating process, precipitates were generated during the heating stage because of the lower temperature. The multiple reheating process in FSAM promoted the generation of precipitates in the stirring zone. This phenomenon increased the yield strength from 183.46 MPa to 189.95 MPa. Meanwhile, the precipitate nucleation and growth during reheating process depleted the concentrations of Si and Mg in the matrix. A comparison of the stress-strain curves before and after the reheating process, revealed that the reheating process reduces the net flow stress in the plastic deformation stage. A decrease in the concentration of solid solution elements caused a decrease in the statistically stored dislocation density, and thereby, decreased the net flow stress. [Display omitted] [ABSTRACT FROM AUTHOR]

Simulating the additive manufacturing process of Ti-6Al-4V is very complex due to the microstructural changes and allotropic transformation occurring during its thermomechanical processing. The α -phase with a hexagonal close pack structure is present in three different forms—Widmanstatten, grain boundary and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases was used here. Furthermore, a physically based flow-stress model coupled with the metallurgical model was applied in the simulation of an additive manufacturing case using the directed energy-deposition method. The result from the metallurgical model explicitly affects the mechanical properties in the flow-stress model. Validation of the thermal and mechanical model was performed by comparing the simulation results with measurements available in the literature, which showed good agreement. [ABSTRACT FROM AUTHOR]

The flow stress of an as-cast Al-Si based alloy was modeled using a dislocation density based model. The developed dislocation density-based constitutive model describes the flow curve of the alloy with various microstructures at quite wide temperature range. Experimental data in the form of stress-strain curves for different strain rates ranging from 10 −4 to 10 −1 s −1 and temperatures ranging from ambient temperature up to 400 °C were used for model calibration. In order to model precisely the hardening and recovery process at elevated temperature, the interaction between vacancies and dissolved Si was included. The calibrated temperature dependent parameters for different microstructure were correlated to the metallurgical event of the material and validated. For the first time, a dislocation density based model was successfully developed for Al-Si cast alloys. The findings of this work expanded the knowledge on short strain tensile deformation behaviour of these type of alloys at different temperature, which is a critical element for conducting a reliable microstructural FE-simulation. [ABSTRACT FROM AUTHOR]