Simulation of material consequences induced by fsw for a trigonal pin

The numerical simulation of Friction Stir Welding processes involves the coupling of a solid mechanics approach under large strains and large strain rates and heat transfer. The eulerian formalism leads to specially efficient finite element simulations of the matter flow under steady conditions. But with such a formulation, the calculation of the consequences induced by the stirring on the material (stirred state, microstructure, etc.) requires the coupling of advection equations for integrating the associated state variables. In this paper, a moving mesh strategy is proposed for the numerical simulation of Friction Stir Welding and material consequences, for complex pin’s geometries. The numerical processing is detailed and the efficiency of the proposed method is discussed on a Friction Stir Welding simulation of 7075 series aluminum alloy

Challenges in thermo-mechanical analysis of Friction Stir Welding processes

This paper deals with the numerical simulation of friction stir welding (FSW) processes. FSW techniques are used in many industrial applications and particularly in the aeronautic and aerospace industries, where the quality of the joining is of essential importance. The analysis is focused either at global level, considering the full component to be jointed, or locally, studying more in detail the heat affected zone (HAZ). The analysis at global (structural component) level is performed defining the problem in the Lagrangian setting while, at local level, an apropos kinematic framework which makes use of an efficient combination of Lagrangian (pin), Eulerian (metal sheet) and ALE (stirring zone) descriptions for the different computational sub-domains is introduced for the numerical modeling. As a result, the analysis can deal with complex (non-cylindrical) pin-shapes and the extremely large deformation of the material at the HAZ without requiring any remeshing or remapping tools. A fully coupled thermo-mechanical framework is proposed for the computational modeling of the FSW processes proposed both at local and global level. A staggered algorithm based on an isothermal fractional step method is introduced. To account for the isochoric behavior of the material when the temperature range is close to the melting point or due to the predominant deviatoric deformations induced by the visco-plastic response, a mixed finite element technology is introduced. The Variational Multi Scale method is used to circumvent the LBB stability condition allowing the use of linear/linear P1/P1 interpolations for displacement (or velocity, ALE/Eulerian formulation) and pressure fields, respectively. The same stabilization strategy is adopted to tackle the instabilities of the temperature field, inherent characteristic of convective dominated problems (thermal analysis in ALE/Eulerian kinematic framework). At global level, the material behavior is characterized by a thermo–elasto–viscoplastic constitutive model. The analysis at local level is characterized by a rigid thermo–visco-plastic constitutive model. Different thermally coupled (non-Newtonian) fluid-like models as Norton–Hoff, Carreau or Sheppard–Wright, among others are tested. To better understand the material flow pattern in the stirring zone, a (Lagrangian based) particle tracing is carried out while post-processing FSW results. A coupling strategy between the analysis of the process zone nearby the pin-tool (local level analysis) and the simulation carried out for the entire structure to be welded (global level analysis) is implemented to accurately predict the temperature histories and, thereby, the residual stresses in FSW

Friction stir welding (FSW) simulation using an arbitrary Lagrangian -Eulerian (ALE) moving mesh approach

Material flow in the solid-state Friction Stir Welding (FSW) is quite a complex process. The Investigation of the material flow can be carried out either by experimentation or by numerical simulation. However, compared to experimentation, numerical simulation is inexpensive, efficient and convenient, but quite challenging to model.;This work concerns the choice and development of numerical methods for efficient and reliable simulation of the material flow during FSW. The two objectives of this work are: to develop a mesh motion scheme for simulating the large deformations of the workpieces during FSW and to assess the material flow behavior of the rigid-elastoplastic problem of FSW using the moving mesh approach.;The challenging issue in modeling FSW is to deal with large deformations of the workpiece material. The Lagrangian simulations of FSW show that the severely distorted finite elements are caused due to the large deformation of workpiece material, which makes the Lagrangian approach inappropriate for modeling FSW. Thus, Arbitrary Lagrangian-Eulerian (ALE) formulations are used to overcome the shortcoming of Lagrangian formulations. The basic idea of the ALE approach is that the mesh is not obliged to follow the material flow. Thereby the excessively distorted elements can be avoided.;An important consideration in applying the ALE approach is an advection method which determines the mesh motion in every step of the analysis. Due to the characteristics of FSW, the moving mesh approach based on ALE formulations is developed for the modeling of FSW. Several case studies that document the material flow during FSW are presented using this approach.;Based on the simulation results, it is concluded that the material motion characteristics on the top surface and through the depth (volume) of friction stir welds have been made for the advancing and retreating sides. The motion trends are consistent with the reported experimental evidence. The case studies demonstrate the capabilities and potential of the mesh motion scheme in simulating the FSW process

Numerical modeling of friction stir welding processes

This work describes the formulation adopted for the numerical simulation of the friction stir welding (FSW) process. FSW is a solid-state joining process (the metal is not melted during the process) devised for applications where the original metallurgical characteristics must be retained. This process is primarily used on aluminum alloys, and most often on large pieces which cannot be easily heat treated to recover temper characteristics. Heat is either induced by the friction between the tool shoulder and the work pieces or generated by the mechanical mixing (stirring and forging) process without reaching the melting point (solid-state process). To simulate this kind of welding process, a fully coupled thermo-mechanical solution is adopted. A sliding mesh, rotating together with the pin (ALE formulation), is used to avoid the extremely large distortions of the mesh around the tool in the so called stirring zone while the rest of the mesh of the sheet is fixed (Eulerian formulation). The orthogonal subgrid scale (OSS) technique is used to stabilize the mixed velocity–pressure formulation adopted to solve the Stokes problem. This stabilized formulation can deal with the incompressible behavior of the material allowing for equal linear interpolation for both the velocity and the pressure fields. The material behavior is characterized either by Norton–Hoff or Sheppard–Wright rigid thermo-visco-plastic constitutive models. Both the frictional heating due to the contact interaction between the surface of the tool and the sheet, and the heat induced by the visco-plastic dissipation of the stirring material have been taken into account. Heat convection and heat radiation models are used to dissipate the heat through the boundaries. Both the streamline-upwind/Petrov–Galerkin (SUPG) formulation and the OSS stabilization technique have been implemented to stabilize the convective term in the balance of energy equation. The numerical simulations presented are intended to show the accuracy of the proposed methodology and its capability to study real FSW processes where a non-circular pin is often used

An apropos kinematic framework for the numerical modelling of Friction Stir Welding

This paper describes features of a fully coupled thermo-mechanical model for Friction Stir Welding (FSW) simulation. An apropos kinematic setting for different zones of the computational domain is introduced and an efficient coupling strategy is proposed. Heat generation via viscous dissipation as well as frictional heating is considered. The results of the simulation using the proposed model are compared with the experimental evidence. The effect of slip and stick condition on non-circular pin shapes is analyzed. Simulation of material stirring is also carried out via particle tracing, providing insight of the material flow pattern in the vicinity of the pin

In-plane/out-of-plane separated representations of updated Lagrangian descriptions of viscoplastic flow models in plate domains

A new efficient updated Lagrangian strategy for numerical simulations of material forming processes is presented. The basic ingredient is the tensorial decomposition of the velocity field into a finite sum of in-plane and an out-of-plane components, giving rise to an equivalent computational complexity of some two-dimensional problems and some one-dimensional ones (therefore, much less than the true three-dimensional complexity of the original problem). This is efficiently achieved by using Proper Generalized Decomposition (PGD) techniques, which are here employed in an updated Lagrangian framework for the very first time. This updated Lagrangian nature of the method needs the use of a robust numerical integration technique (in this case, the Stabilized Conforming Nodal Integration has been chosen) for addressing the highly distorted projected meshes. The resulting strategy is of general purpose, although it is especially well suited for addressing models defined in plate or shell (in general, parallelepipedic) domains. The basics of the just-developed method are shown, together with some numerical examples to show the potential of the technique

Material flow visualization in Friction Stir Welding via particle tracing

This work deals with the modeling of the material flow in Friction Stir Welding (FSW) processes using particle tracing method. For the computation of particle trajectories, three accurate and computationally efficient integration methods are implemented within a FE model for FSW process: the Backward Euler with Sub-stepping (BES), the 4-th order Runge-Kutta (RK4) and the Back and Forth Error Compensation and Correction (BFECC) methods. Firstly, their performance is compared by solving the Zalesak's disk benchmark. Later, the developed methodology is applied to some FSW problems providing a quantitative 2D and 3D view of the material transport in the process area. The material flow pattern is compared to the experimental evidence.Peer ReviewedPostprint (author’s final draft

A Mesh-Free Solid-Mechanics Approach for Simulating the Friction Stir-Welding Process

In this chapter, we describe the development of a new approach to simulate the friction stir-welding (FSW) process using a solid-mechanics formulation of a mesh-free Lagrangian method called smoothed particle hydrodynamics (SPH). Although this type of a numerical model typically requires long calculation times, we have developed a very efficient parallelization strategy on the graphics processing unit (GPU). This simulation approach allows the determination of temperature evolution, elastic and plastic deformation, defect formation, residual stresses, and material flow all within the same model. More importantly, the large plastic deformation and material mixing common to FSW are well captured by the mesh-free method. The parallel strategy on the GPU provides a means to obtain meaningful simulation results within hours as opposed to many days or even weeks with conventional FSW simulation codes

Estudo das capacidades do método Smoothed Particle Hydrodynamics (SPH) na simulação de processos de manufactura

Challenging problems of computational mechanics may often be characterized by large deformations that are common in manufacturing processes such as friction stir welding. The finite element method faces difficulties in simulating large deformations, due to severe mesh distortion. Over the last few, years, meshfree methods have been an alternative applied to the studies, pointing a new generation of more effective computational methods for solving more complex problems such as Smoothed Particle Hydrodynamics (SPH). The present work focus on the application of the SPH method on the numerical simulation of the friction welding process, using the Abaqus numerical simulation software. However, Abaqus presents some limitations, since it includes the SPH formulation but with a reduced functionality, not allowing to analyze temperature variations throughout the process. In order to overcome these limitations, several numerical simulations were performed with changes in the material properties according to the analysis temperature, and in the friction coefficient between the work material and the toolProblemas desafiadores da mecânica computacional podem muitas vezes ser caracterizados por grandes deformações em processos de manufactura, tais como a soldadura por fricção, mais conhecido por ”friction stir welding” (FSW). Os métodos mais comuns, como o método de elementos finitos apresentam grande dificuldade na simulação de grandes deformações, devido à severa distorção presente na malha. Nos últimos anos, métodos que não envolvam malha têm sido uma alternativa aplicada a este tipo de problemas, apontando uma nova geração de métodos computacionais mais eficazes para resolver problemas mais complexos, tais como o método ”Smoothed Particle Hydrodynamics” (SPH). O presente trabalho centra-se na aplicação do método SPH na simulação numérica do processo de soldadura por fricção, com resurso ao software de simulação numérica Abaqus. Contudo o Abaqus apresenta algumas limitações, uma vez que inclui a formulação SPH mas com uma funcionalidade reduzida, não permitindo analisar variações de temperaturas ao longo do processo. De maneira a superar estas limitações foram realizadas várias simulações numéricas com alterações das propriedades do material consoante a temperatura de análise, e do coeficiente de atrito entre o material de trabalho e a ferramenta.Mestrado em Engenharia Mecânic