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The evolutionary optimization of selected welded structures

Kokot G., John A., Kuś W.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 43, nr 2

667--675

Purpose: of this paper is to present the recent possibility of evolutionary optimization method application to predicting the proper welding parameters in the weld process. The objective of the welding simulation is to study the temperature generated during the welding process and to investigate residual stresses in the component after the welding. Such results give the possibility to determine stress and strain state of welded parts and properties of materials in welding zones. From other side it gives the possibility to perform optimization process looking for welding parameters (welding speed, welding power source etc.) or initial shape of welded sheets according to displacement state (welding of thin metal sheets with stiffeners - T joints). Those results are the base for fatigue analysis too. Design/methodology/approach: In the paper the foundations of FEM simulation of welding process are presented. Also a grid based evolutionary optimization of welding parameters influences on strength parameters in the heat affected zone (HAZ) is shown. Numerical simulation of a welding process using the finite element method is applied. Findings: Results for coupled thermo-mechanical problem are prescribed. Two examples, the grid based evolutionary optimization of HAZ parameters and grid based evolutionary optimization of T-joint component deformation, illustrate the possibility of computational simulation and optimization of welding are presented. Practical implications: Computational simulation and evolutionary optimization give a lot of information very important for engineers. An undesirable side-effect of welding is the generation of residual stresses and deformations in the component and the quality of the weld has a substantial impact on the fatigue life of the structure. These resultant deformations may render the component unsuitable for further use. Originality/value: The presented the grid based evolutionary optimization procedure is a new tool for better understanding and predicting the welding behaviour from the thermo-mechanical process point of view. It gives the possibilities to optimize main welding parameters in order to achieve better structures, taking into account nearly full set of welding parameters, temperature dependent material parameters and simulating the coupled thermo-mechanical problem.

Modification of plastic strain localization induced by hydrogen absorption

Aubert I., Plessier F., Saintier N., Olive J.-M.

Advances in Materials Science

2008

Vol. 8, nr 1(15)

5-13

In order to highlight hydrogen effects on the plasticity, the slip morphology after straining (under tension up to 4% of plastic strain in ambient air) of hydrogenated (at 135 wt.ppm) and non-hydrogenated 3161 stainless steel polycrystals was compared. A statistical analysis of both slip band spacings (SBS) and slip band heights (SBH) was performed using atomic force microscopy. Tensile tests were performed at low strain rate, specimens being previously charged at controlled hydrogen concentration. The plastic strain field heterogeneity in polycrystals was taken into account thanks to numerical simulation of crystalline plasticity. On each grain, the calculated plastic shear was correlated with the distribution of SBS and the average number of emerging dislocations per slip band. In comparison with uncharged specimen and for an equivalent cumulated plastic strain, the hydrogenated specimen shows an increase of the slip band spacing (SBS) and of emerging dislocations. This result confirms a plastic localization induced by absorbed hydrogen.