|Karim Agrebi||Laboratory of Applied Mechanics and Engineering, University of Tunis EL Manar, National Engineering School of Tunis, BP 37, Le Belvédère, 1002, Tunisia|
|Asma Belhadj||Laboratory of Applied Mechanics and Engineering, University of Tunis EL Manar, National Engineering School of Tunis, BP 37, Le Belvédère, 1002, Tunisia|
|Mahmoud Bouhafs||Laboratory of Applied Mechanics and Engineering, University of Tunis EL Manar, National Engineering School of Tunis, BP 37, Le Belvédère, 1002, Tunisia|
Welding processes are widely used in many industries. The determination of welding parameters and the study of their influence on the mechanical and metallurgical behavior of materials require multiple experiments, and the relevant studies are costly in terms of time and resources. Thus, numerical simulations can serve as a solution when it comes to choosing the appropriate welding process and optimizing its parameters while minimizing costs. The present work contributes to the development of a finite element code, using MATLAB software, for the prediction of thermo-mechanical and metallurgical behavior during the Tungsten inert gas (TIG) welding process. Numerical computation is based on the mathematical formulation of physical phenomena and thermal exchanges. In this paper, results dealing with the prediction of the temperature field evolution during the C50 steel TIG-welding process are presented. In this case, the thermal problem is solved numerically using the finite element method. The memory and computation time problems are solved using optimal stocking and resolution algorithms. To validate the developed computation code, numerical results are first compared with other published numerical results, then with our experimental data. A satisfactory concordance between simulated temperature evolutions and those measured with thermocouples implanted in the welded sheets was found.
Finite elements; Mathematical formulation; Thermal simulation; TIG welding
During welding, highly complicated phenomena occur due to the coupled interactions between heat transfer, metallurgical transformation, and mechanical behavior. To be able to predict the evolution of these phenomena, numerical methods—especially the finite element method (FEM)—are widely used. This method, which is performed using calculation codes like TRANSWELD (Hamide & Bellet, 2007; Hamide et al., 2008), ASTER CODE (Delmas, 2013) and SYSWELD, is based on mathematical formulation of the coupled physical phenomena.
Several works have been published on numerical simulation of the welding process. Simulating thermal behavior during welding processes is based on numerically solving three-dimensional transient heat equations with temperature-dependent material properties (Belhadj et al., 2010; Anca et al., 2011; Seleš et al., 2018). Numerical calculations require a longer time calculation, high storage capacity, and significant computer resources to predict the thermal, followed by metallurgical and mechanical, history. For this reason, using an adaptive mesh can be a solution for solving calculation problems (Hamide & Bellet, 2007; Hamide et al., 2008). For the validation of thermal simulation results during welding processes, researchers have compared temperature evolutions with experimental data, analytical solutions, or simulation results with other FEM code calculation. Anca et al.(2011) compared simulated temperature evolutions during welding processes with a semi-analytical solution developed by Weiner and Boley (1963). Moreover, Belhadj et al.(2010) simulated thermal behavior during CO2 laser welding and compared the temperature evolution according to time with the thermocouple-measured temperature in many positions on a welded sheet.
The TIG welding process is one of the most common methods used in the aerospace, automotive, and pipe industries (Lundbäck, 2003; Baskoro et al., 2011).TIG process welding, especially of stainless steel, has been studied numerically and experimentally by many authors (Del Coz Diaz et al., 2010;Ganesh et al., 2014; Aissani et al., 2015; Chuaiphan & Srijaroenpramong, 2018). These numerical simulations have been developed with software like ABAQUS, ASTER CODE, and ANSYS. These software programs offer a significant computing potential, especially for thermo-mechanical modeling. However, they are limited for modeling other phenomena occurring during the welding of some materials, such as metallurgical transformations or convection flow in the melt. Nevertheless, these limitations can be overcome via the user’s ability to develop and integrate functions, employing subroutines to extend the possibilities of this software and providing the flexibility required for any research work. In this study, we have opted for the development of a specific numerical calculation tool, integrating all the welding phenomena, using the MATLAB software to simulate material behavior during the TIG welding of phase transformation steel. This computer code gives the possibility to predict the thermo-mechanical and metallurgical transformations in the welded sheets from the beginning of the welding until the end of the cooling.
In this paper, thermal history prediction and its validation are presented. A thermal model with a moving heat source is developed to calculate the temperature on each element of an adaptive mesh during the welding and cooling stages. The developed thermal model considers the nonlinearity introduced by thermo-physical properties, which depends on the temperature. The numerical results are presented in the form of isotherms at different times of welding and temperature evolutions according to time in each point of the mesh. In addition to numerical model development, an experimental protocol is performed to optimize the TIG welding parameters of the C50 steel, realize automatic welding lines, and specifically, measure temperature data during welding using K-thermocouples implanted in several points on the welded sheet. These experimental results aim to validate the numerical results from the developed model. Therefore, finite element simulated temperature evolutions according to time are compared with those measured experimentally.
In the work, we have developed a computer finite element code using MATLAB software. This code aims to predict thermal behavior during C50-steel TIG-welding. The suggested model gives the possibility to determinate the space-time temperature evolutions in each point of the welded sheet from the beginning of welding until the return to thermal balance. In addition to numerical study, experimental investigations are made in order to measure temperature evolutions according to time during the welding of a 7mm sheet. Comparison of numerical and experimental results shows a good consistency.The validated temperature fields at various time steps, resulting from the developed model, are used as an input data on the mechanical and metallurgical behavior simulation models during the TIG welding of C50 steel. Results of these models will be published subsequently.
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