A coupled thermo-mechanical model was developed to study the temperature fields, the plunge force and the plastic deformations of Al alloy 2024-T351 under different rotating speed: 350, 400 and 450 rpm, during the friction stir welding (FSW) process. Three-dimensional FE model has been developed in ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb’s Law of friction. Numerical results indicate that the maximum temperature in the FSW process is lower than the melting point of the welding material. The temperature filed is approximately symmetrical along the welding line. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface. With increasing rotation speed, the low plastic strain region is reduced. When the rotational speed is increased, the plunge force can be reduced. Regions with high equivalent plastic strains are observed which correspond to the nugget and the flow arm
This paper presents experimental and numerical analysis of the change of temperature and force in the vertical direction during the friction stir welding of high-strength aluminium alloy 2024 T3. This procedure confirmed the correctness of the numerical model, which is subsequently used for analysis of the temperature field in the welding zone, where it is different to determine the temperature experimentally. 3D finite element model is developed using the software package Abaqus; arbitrary Lagrangian-Eulerian formulation is applied. Johnson-Cook material law and Coulomb's Law of friction are used for modelling the material behaviour. Temperature fields are symmetrical with respect to the welding line. The temperature values below the tool shoulder, i. e. in the welding zone, which are reached during the plunge stage, are approximately constant during the entire welding process and lie within the interval 430-502 °C. The temperature of the material in the vicinity of the tool is about 500 °C, while the values on the top surface of the welding plates (outside the welding zone, but close to the tool shoulder) are about 400 °C. The temperature difference between the top and bottom surface of the plates is small, 10-15 °C.
Original scientific paper The subject of this paper is testing of complex geometrical structures, i.e. stress analysis of a pipe branch model of A6 third pipeline at Hydropower Plant Perućica, Nikšić. Analysis of pipe branch model stress distribution was carried out by using finite element method and experimental methods. Finite element method defined 3D pipe branch model. Numerical calculation defined critical locations on model, i.e. locations with the greatest stress concentration. Strain gauges were placed on identified critical locations. Measured stress values confirmed values obtained by using numerical calculation. Experimental measurements were also taken by using new digital image correlation (DIC) method. DIC method is an optical non-contact method that can provide full 3D stress field and enables better understanding of complex structures such as pipe branches. The aim of this paper was to determine stress concentration factor for the pipe branch model by using numerical and experimental analysis.Keywords: finite element method; pipe branch model; strain gauges; stress concentration factor; 3D DIC method Numeričko i eksperimentalno određivanje faktora koncentracije naprezanja na modelu cijevne račve Izvorni znanstveni članak Predmet ovog rada je ispitivanje struktura složene geometrije, odnosno analiza naprezanja modela cijevne račve A6 trećeg cjevovoda u hidroelektrani Perućica, Nikšić. Analiza stanja naprezanja modela cijevne račve provedena je numeričkom metodom konačnih elemenata i eksperimentalnim metodama. Metodom konačnih elemenata definiran je 3D model cijevne račve. Numeričkim putem određena su kritična mjesta na modelu, odnosno mjesta najveće koncentracije naprezanja. Mjerne trake su pozicionirane na identificirane kritične zone. Izmjerene vrijednosti naprezanja metodom mjernih traka potvrdile su vrijednosti dobivene metodom konačnih elemenata. Mjerenja su provedena i uporabom 3D optičke beskontaktne metode koja se bazira na digitalnoj korelaciji slika. Tom metodom se može dobiti cjelokupno 3D polje naprezanja, odnosno ona omogućava bolje razumijevanje kompleksnih struktura kao što su cijevne račve. Cilj ovog rada je bio određivanje faktora koncentracije narezanja na modelu cijevne račve uporabom numeričkog i eksperimentalnog pristupa.Ključne riječi: faktor koncentracije naprezanja; konačni elementi; mjerne trake; model cijevne račve; 3D DIC metoda
This work presents the results of studying harmful substances in the air, released in the case of tungsten inert gas (TIG) and metal inert gas (MIG) welding of 1460 aluminum alloy (Al-Cu-Li). It is shown that the TIG process is accompanied by smaller evolution of the solid component and gas component of welding fumes than in MIG welding. Ozone concentrations during TIG and MIG welding are significantly (1.3 and 7.4 times, respectively) higher than the maximum permissible concentration. It is found that ultraviolet radiation, accompanying the welding process, is the main factor of toxic gas generation in the working zone of the studied aluminum-lithium alloys. Also, this paper presents analyses of microstructure, hardness, strength characteristics and fatigue behavior of 1460 TIG weld joints.
The paper analyses the impact of the tool geometry on the friction stir welding (FSW) method on fracture toughness values of the base metal (BM) and weld metal (WM) of a butt welded joints of a high strength aluminium alloy. Values of fracture toughness KJIc were obtained using single-edge notched bend (SENB) specimens with fatigue precrack sampled from the BM and TMAZ (thermomechanically affected zone). Single specimen method was used according to ASTM E 1820 and parameters of elastic-plastic fracture mechanics were determined (CTOD crack tip opening displacement and the J integral). Although the welding tools had different values of cone angle (α = 2.5°-10°) and the variable length of the pin (h = 5.1 mm-5.4 mm) at a constant ratio of the number of tool revolutions and the speed of welding, the largest value of fracture toughness has the retreating side of the weld, then the advancing side of the WM, while the BM has the lowest value. This is the effect of recrystallization process in the retreating side of the WM due to combined rotating-straight forward motion of the tool during which the softened material is repeatedly transformed from one side to the other side around the centre of the tool.
The influence of friction stir welding (FSW) parameters on thermo-mechanical behaviour of the material during welding is analysed. An aluminium alloy is considered (Al 2024 T351), and different rotating speed and welding speed are applied. Finite element model consists of the plate (Al alloy), backing plate and welding tool, and it is formed and solved in software package Simulia Abaqus. The influence of the welding conditions on material behaviour is taken into account by application of the Johnson-Cook material model. The rotation of the tool affects the results: if increased, it contributes to an increase of friction-generated heat intensity. The other component of the generated heat, the plastic deformation of the material, is negligibly changed. When the welding speed is increased, the intensity of friction-generated heat decreases, while the heat generation due to plastic deforming increases. Combined, these two effects cause small change of the total heat generation. For the same welded joint length, the plate welded by lower speed will be heated more intensively. The changes of the heat generation influence both the temperature field and reaction force, which are also considered.
This paper describes pipeline stress analysis, primarilybranch junctions, as a structural element in hydro-power plants. Pipelines are exposed to internal pressure,which is present under working conditions. Analysis of stresses in the pipeline of the hydropower plant is based on analytical, numerical, and experimental methods. In this paper, we will define the critical elements of the pipeline. After that, we will determine critical areas in the branch junction, under experimental conditions, where strain gauges should be installed. The obtained resultsshow that a boiler formula can be efficiently applied in the stress analysis. Also, a correlation between the internal pressure and the maximum circumferential stresses in the elastic zone is given. In the final sections of the paper, the limit value of the internal pressure as a load for which stress in the zone of plasticity appears and the safety factor of the branch junction in the exploitation conditions are determined. The contribution of this work is the unification and deepening of the topic related to the problem of the testing ofhydro-power structural elements.
This research paper presents hardness, structure and tensile strength analysis of 1460 alloy of Al-Cu-Li system, welded joints made by Tungsten Inert Gas (TIG) welding and Friction Stir Welding (FSW). Characteristics of acoustic noise at the welding operator workplace during mechanized TIG and FSW of aluminium-lithium alloy with the purpose to develop recommendations for the improvement of health and safety during welding processes were studied. Analyzing results, we concluded that during TIG welding the values of welding noise at the workplace, are much higher than the admissible noise level limit. Results showed that the values of the welding nose reach 95 dB. The noise level at the workplace for FSW is also dangerous and reaches up a value of 84.3 dB. Also, this paper presents hardness, structure, and tensile strength measurements of 1460 alloy welded joints made by TIG and FSW welding.
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