Friction Stir Welding (FSW) is one of the most effective solid state joining processes and has numerous potential applications in many industries. The simulation process can provide the evolution of physicals quantities such as temperature, metallurgical phase proportions, stress and strain which can be easily measured during welding. The numerical modelling requires the modelling of the complex interaction between thermal, metallurgical and mechanical phenomena. The aim of this paper is to describe the thermal-fluid simulation of FSW using the finite element method. In the theoretical part of paper heating is provided by the material flow and contact condition between the tool and the welded material. Thermal-mechanical results from the numerical simulation using SYSWELD are also presented for aluminium alloy.

Friction Stir Welding (FSW) is one of the most effective solid state joining processes and it has numerous potential applications in many industries. The simulation process can provide the evolution of physical quantities such as temperature, metallurgical phase proportions, stress and strain which can be easily measured during welding. The numerical modelling requires the modelling of a complex interaction between thermal, metallurgical and mechanical phenomena. The aim of this paper is to describe the thermal-fluid simulation of FSW using the finite element method. In the theoretical part of the paper heating is provided by the material flow and contact condition between the tool and the welded material. The thermal-fluid results from the numerical simulation for aluminium alloy using SYSWELD are also presented in this paper.

In this paper a universal mathematical model using fully coupled thermal-structural finite element analysis capable of predicting ductile-to-brittle failure mode transition at high strain rates is presented. Appropriate equivalent strain measures describing the onset and the growth of ductile and total damage and heat generation rate per unit volume for dissipation-induced heating have been proposed. The model was implemented into a finite element code using the updated Lagrangian formulation for finite strains, the von Mises material model with isotropic hardening and the Jaumann rate, in the form of the Green-Naghdi rate, in the co-rotational Cauchy's stress update calculation. Plastic bending of a cantilever was studied, applying constant pressure as stepped load to 1/3 of the upper surface of the beam. The analysis result shows that at higher strain rates the ductile damage value is significantly lower than the value of the total damage, while at low strain rates their values are approximately identical, thus the model is likely to open new perspectives in the study and numerical simulation of the behaviour of ductile materials.

In this paper an alternative material model using a generalized J2 finite-strain flow plasticity theory with isotropic hardening is presented. The model is based on a new nonlinear continuum mechanical theory of finite deformations of elasto-plastic media which allows for the development of objective and thermodynamically consistent material models. As a result, the constitutive equation, the evolution equation and even the ‘normality rule’, characterising the plastic flow in the material during return mapping, can be expressed in various forms, using several instances of the yield surface and corresponding pairs of stress measures and strain rates, respectively, which are conjugate with respect to the internal mechanical power and its arbitrary higher order time derivative. Therefore the results of the material model when used in numerical analyses are not affected by the description and particularities of the material model formulation. Here, we briefly outline the nonlinear continuum theory along with a detailed description of the material model and finally present the model in a numerical example using a cross-shaped specimen in biaxial tension.

Contemporary plasticity theories and their related material models for finite deformations are either based on additive decomposition of a strain-rate tensor or on multiplicative decomposition of a deformation gradient tensor into an elastic part and a plastic part. From the standpoint of the nonlinear continuum mechanics, the former theories, which are used to model hypoelastic-plastic materials, are rather incomplete theories, while the latter theories, which are used to model hyperelastic-plastic materials, are not even continuum-based theories, while none of their related material models are thermodynamically consistent. Recently, a nonlinear continuum theory for finite deformations of elastoplastic media was proposed, which allows for the development of objective and thermodynamically consistent material models. Therefore, the analysis results of the models are independent of the description and the particularities of their mathematical formulation. Here by the description we mean total or updated Lagrangian description and by the particularities of formulation, the ability to describe the model in various stress spaces using internal mechanical power conjugate stress measures and strain rates. In this chapter, an alternative framework for developing objective and thermodynamically consistent hypoelastic-plastic-and hyperelastic-plastic-based material models is presented using the first nonlinear continuum theory of finite deformations of elastoplastic media. Keywords: nonlinear continuum theory for finite deformations of elastoplastic media, objective and thermodynamically consistent formulation, J 2 generalised plasticity with isotropic hardening, hypoelastic-plastic-and hyperelasticplastic-based material models with internal damping