Localisation of deformation is a problem in several manufacturing processes. Machining is an exception where it is a wanted feature. However, it is always a problem in finite element modelling of these processes due to mesh sensitivity of the computed results. The remedy is to incorporate a length scale into the numerical formulations in order to achieve convergent solutions. Different simplifications in the implementation of a non-local damage model are evaluated with respect to temporal and spatial discretisation to show the effect of different approximations on accuracy and convergence.
Modelling and simulation of manufacturing processes may require the capability to account for localization behavior, often associated with damage/fracture. It may be unwanted localization indicating a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying physics, as well as the robustness of the simulation procedure. Two different approaches for achieving mesh-independent solutions are compared in this paper. They are the multiresolution continuum theory (MRCT) and nonlocal damage model. The MRCT theory is a general multilength-scale finite element formulation, while the nonlocal damage model is a specialized method using a weighted averaging of softening internal variables over a spatial neighborhood of the material point. Both approaches result in a converged finite element solution of the localization problem upon mesh refinement. This study compares the accuracy and robustness of their numerical schemes in implicit finite element codes for the plane strain shear deformation test case. Final remarks concerning ease of implementation of the methods in commercial finite element packages are also given.
One of the aims of this work is to show that thermal softening due to the reduced flow strength of a material with increasing temperature may cause chip serrations to form during machining. The other purpose, the main focus of the paper, is to demonstrate that a non-local temperature field can be used to control these serrations. The non-local temperature is a weighted average of the temperature field in the region surrounding an integration point. Its size is determined by a length scale. This length scale may be based on the physics of the process but is taken here as a regularization parameter.
Non-local damage model for strain softening in a machining simulation is presented in this paper. The coupled damage-plasticity model consists of a physically based dislocation density model and a damage model driven by plastic straining in combination with the stress state. The predicted chip serration is highly consistent with the measurement results.
A finite element model of cold pilgering with elastic roll dies have been developed and used to investigate the influence of roll die deformation on the material flow, contact region, roll separating force and tube dimensions. Full scale experiments were performed to validate the contact surface and tube dimensions. The results show that the influence of roll die flattening is not significant on the contact length. However, elastic deformation of roll die has strong influence on both the wall thickness reduction and roll separating force. Thus it is recommended to consider elasticity of roll dies when forces and tube dimensions are estimated.
A three-dimensional finite element model of cold pilgering of stainless steel tubes is developed in this paper. The objective is to use the model to increase the understanding of forces and deformations in the process. The focus is on the influence of vertical displacements of the roll stand and axial displacements of the mandrel and tube. Therefore, the rigid tools and the tube are supported with elastic springs. Additionally, the influences of friction coefficients in the tube/mandrel and tube/roll interfaces are examined. A sensitivity study is performed to investigate the influences of these parameters on the strain path and the roll separation force. The results show the importance of accounting for the displacements of the tube and rigid tools on the roll separation force and the accumulative plastic strain.
Cold pilgering is a cold forming process used during manufacturing of seamless tubes. The tube with a mandrel inside is fed forward and rotated in stepwise increments, while the roll stand moves back and forth. The total plastic deformation of the tube is such that the cross-sectional area of the tube decreases and the length of the tube increases during the process. However, this is performed in many small incremental steps, where the direction of deformation in a material point changes at each stroke. Most published models of cold pilgering use simplified material models. In reality, the flow stress is dependent on temperature, strain rate, strain history and microstructure. In this work, temperature and strain rate distributions are computed, using a 3D thermo-mechanical FE model, and the influence of temperature and strain rate on the rolling force is investigated. The Johnson-Cook model is employed to describe the flow stress using isotropic hardening. The results show that strain rate and temperature have a significant influence on the roll separation force
Understanding and modelling the plastic behavior of a material are essential for simulation and design of metal forming processes. Cold pilgering of tubes is a process with very complex strain history with alternating loading direction. This makes evaluation of the work hardening challenging. Cold deformation applied in a single direction predominantly exhibit work hardening, while changes of the loading direction may even cause softening in other directions. The influence of alternating loading directions on work hardening has been experimentally investigated for 316L stainless steel (SS). Cubic specimens were cut out from the preform of the tube. The specimens are subjected to uniaxial compressions in alternating directions along two perpendicular axes. From the results, a cyclic elastic-plastic constitutive model based on a Chaboche-type approach is calibrated and implemented in the commercial finite element code MSC.Marc.
The principal challenge in producing aerospace components using Ti-6Al-4V alloy is to employ the optimum process window of deformation rate and temperature to achieve desired material properties. Qualitatively understanding the microstructure-property relationship is not enough to accomplish this goal. Developing advanced material models to be used in manufacturing process simulation is the key to compute and optimize the process iteratively. The focus in this work is on physically based flow stress models coupled with microstructure evolution models. Such a model can be used to simulate processes involving complex and cyclic thermo-mechanical loading.
Although Ti-6Al-4V has numerous salient properties, its usage for certain applications is limited due to the challenges faced during manufacturing. Understanding the dominant deformation mechanisms and numerically modeling the process is the key to overcoming this hurdle. This paper investigates plastic deformation of the alloy at strain rates from 0.001s−1 to 1s−1 and temperatures between 20° C and 1100° C. Pertinent deformation mechanisms of the material when subjected to thermo-mechanical processing are discussed. A physically founded constitutive model based on the evolution of immobile dislocation density and excess vacancy concentration is developed. Parameters of the model are obtained by calibration using isothermal compression tests. This model is capable of describing plastic flow of the alloy in a wide range of temperature and strain rates by including the dominant deformation mechanisms like dislocation pile-up, dislocation glide, thermally activated dislocation climb, globularization, etc. The phenomena of flow softening and stress relaxation, crucial for the simulation of hot forming and heat treatment of Ti-6Al-4V, can also be accurately reproduced using this model.
Simulating the additive manufacturing process of Ti-6Al-4V is very complex owing to the microstructural changes and allotropic transformation occurring during its thermo-mechanical processing. The alpha-phase with a hexagonal close pack structure is present in three different forms; Widmanstatten, grain boundary, and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases is used in this work. Furthermore, a physically based flow-stress model coupled with the metallurgical model is applied in the simulation of direct energy deposition additive manufacturing case.
Simulating the additive manufacturing process of Ti-6Al-4V is very complex due to the microstructural changes and allotropic transformation occurring during its thermomechanical processing. The α -phase with a hexagonal close pack structure is present in three different forms—Widmanstatten, grain boundary and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases was used here. Furthermore, a physically based flow-stress model coupled with the metallurgical model was applied in the simulation of an additive manufacturing case using the directed energy-deposition method. The result from the metallurgical model explicitly affects the mechanical properties in the flow-stress model. Validation of the thermal and mechanical model was performed by comparing the simulation results with measurements available in the literature, which showed good agreement
One of the main challenges in the simulation of machining is accurately describing the material behavior during severe plastic deformation at strain rates ranging six orders of magnitude and temperature between room temperature to nearly melting temperature. High strain rate measurements are performed using Split-Hopkinson Pressure Bar (SHPB) technique at a range of temperatures. The temperature change during deformation is included by computing the plastic work converted to heat energy. A physics-based material model published earlier (Babu and Lindgren, 2013) is extended in this paper to include the high strain rate mechanisms of phonon and electron drag. Characterization of the microstructure is performed using Electron Backscatter Diffraction (EBSD), and a novel method is proposed in this work to quantify the extent of globularization which is compared with model predictions.
Residual stress studies (by centre-hole drilling and finite element analysis) and microstructural computations (using temperature measurements) were carried out on multirun butt welded steel plates. The plates, 200 mm thickness, were in SIS 2134 material (0.12%C, 1.42%Mn, 0.044%V, 0.014%Ti, 0.038%Al). Welding was by submerged arc welding using ESAB OK AUTROD 12.10 filler material and ESAB OK FLUX 10.80 flux
Multipass butt welding of two 0.2 m thick steel plates has been investigated. The purpose of the project is to evaluate the residual stresses by experiment and simulations. Temperature dependent material properties were assumed in previous studies. We account for the dependency on temperature history in this work. This has been done by computing the microstructure evolution. This is combined with mixture rules for computing material properties.
Multipass butt welding of two 0.2 m thick steel plates has been investigated. The objective is to calculate residual stresses and compare them with measured residual stresses. The material properties depend on temperature and temperature history. This dependency is accounted for by computing the microstructure evolution and using this information for computing material properties. This is done by assigning temperature dependent material properties to each phase and applying mixture rules to predict macro material properties. Two different materials have been used for the microstructure calculation, one for the base material and one for the filler material
In view of developing a physics-based constitutive material model for AA7075-T651, the mechanical behavior and microstructure evolution of the material has been studied through compression tests using Gleeble thermo-mechanical simulator. The tests were performed at wide range of temperatures (room temperature (RT), 100, 200, 300, 400 and 500 °C) with two constant strain rates (0.01 and 1 s-1). The true stress-strain curves depicted an increase in the flow stress with increase in the strain rate and decrease in the deformation temperature, with an exception at RT. The effects of softening mechanisms, such as adiabatic heating, dissolution of precipitates, dynamic recovery (DRV) and dynamic recrystallisation (DRX), on the flow stress level, strain rate sensitivity (SRS) and temperature sensitivity over the entire range of temperatures were analyzed. Pertaining to the microstructure analysis, the intermetallic particles present in the initial as-received (AR) material were identified as (Al,Cu)6(Fe,Cu) and SiO2 with the help of back-scattered electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS). The microstructure of the material after the deformation processes were analyzed and compared with that of the AR state using inverse pole figures (IPF), grain orientation spread (GOS) and grain boundary rotation maps generated from electron back-scattered diffraction (EBSD) scans. DRV was observed for deformation at 300 °C, whereas a combination of DRV and incomplete DRX took place for 400 and 500 °C depending on the strain rate. The fraction of recrystallized grains was higher in case of deformation at higher temperature and lower strain rate. Furthermore, the difference in microstructure evolution on different surfaces of the deformed samples as well as at different locations on individual surfaces was also investigated.
The current study presents the effects of strain and temperature on the mechanical response and microstructure evolution in AA7075-T651 at high strain rates. Compression tests have been performed at room temperature (RT), 200, 300 and 400 °C using a Split-Hopkinson pressure bar (SHPB) setup with strain rates ranging between 1400 and 5300 s−1. For deformation at RT, the flow stress increases with increase in strain rate. Whereas deformation at elevated temperatures show a non-monotonous behavior of the flow stress with respect to the strain rate. This trait is attributed to the pronounced effects from the adiabatic shear bands (ASBs); namely, distorted shear bands (DSBs) and transformed shear bands (TSBs); and cracks resulting from the plastic deformation instability during hot deformation. The sequence of microstructure evolution is: inhomogeneity in the initial microstructure – DSB – TSB – crack –fracture. The feasibility of formation and growth of ASBs and cracks increases with increase in strain and temperature, neglecting any significant effect from the strain rate. During the compression tests, temperature of the material rises due to adiabatic heating. Considering a certain strain developed in the material, this adiabatic temperature rise decreases as the deformation temperature is increased. Furthermore, during individual deformation processes, the temperature rise increases with increasing strain. The adiabatic temperature leading to the formation of TSB is approximated to be 0.7 times of the melting temperature of the alloy. These results from the current study are to be used in developing a physics-based material model for the alloy.
In this paper the parameter identification using dislocation density based material model is studied. The model is rate-dependent and includes isotropic strainhardening/ softening as well as kinematic hardening. The model is implemented as a part of the custom toolbox for parameter identification (described in the accompanying paper) using Matlab®. A general stress-strain algorithm is used in the calculations, so the same logic can also be used when implementing the material models into a finite element code. The stressupdate algorithm of rate-dependent plasticity is chosen in the form that has the yield surface for which a so-called consistency condition exists. The amount of plasticity in a strain increment is determined by the consistency condition, whereas the internal variables history and yield stress depend on the plastic strain-rate. The paper focuses on the use of physically based material models. The dislocation density concept links the macroscopic stresses and strains to the underlying micro-structural processes of plastic deformation. The material models define evolution equations for the densities of mobile, immobile locked and immobile recoverable dislocations. The physical significance of the model parameters is highlighted. The developed toolbox is used to determine material parameters of a high-strength steel for a chosen dislocation density model fitted to the constant amplitude fully reversed strain controlled cyclic test curves. Parameter sensitivity is briefly discussed.
Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair and, if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.
Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model for computing the pressure and the thickness of the grain boundary liquid film, which are required to evaluate the crack criterion in paper 1. The third and final paper describes the application of the model to Varestraint tests of Alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.
Several advanced alloy systems are susceptible to weld solidification cracking. One example is nickel-based superalloys, which are commonly used in critical applications such as aerospace engines and nuclear power plants. Weld solidification cracking is often expensive to repair, and if not repaired, can lead to catastrophic failure. This study, presented in three papers, presents an approach for simulating weld solidification cracking applicable to large-scale components. The results from finite element simulation of welding are post-processed and combined with models of metallurgy, as well as the behavior of the liquid film between the grain boundaries, in order to estimate the risk of crack initiation. The first paper in this study describes the crack criterion for crack initiation in a grain boundary liquid film. The second paper describes the model required to compute the pressure and thickness of the liquid film required in the crack criterion. The third and final paper describes the application of the model to Varestraint tests of alloy 718. The derived model can fairly well predict crack locations, crack orientations, and crack widths for the Varestraint tests. The importance of liquid permeability and strain localization for the predicted crack susceptibility in Varestraint tests is shown.
Several nickel-based superalloys are susceptible to weld solidification cracking. Numerical simulation can be a powerful tool for optimizing the welding process such that solidification cracking can be avoided. In order to simulate the cracking, a crack model inspired by the RDG model is proposed. The model is based on a crack criterion that estimates the likelihood for a preexisting pore in a grain boundary liquid film to form a crack. The criterion depends on the thickness and the liquid pressure in the grain boundary liquid film, as well as the surface tension of the pore. The thickness of the liquid film is computed from the macroscopic mechanical strain field of an FE model with a double ellipsoidal heat source. A temperature-dependent length scale is used to partition the macroscopic strain to the liquid film. The liquid pressure in the film is evaluated using a combination of Poiseuille parallel plate flow and Darcy’s law for porous flows. The Poiseuille flow is used for the part of the grain boundary liquid film that extends into the region with liquid fraction less than 0.1, while Darcy’s law is used for the rest of the liquid film that extends into the regions with liquid fraction greater than 0.1. The proposed model was calibrated and evaluated in Varestraint tests of Alloy 718. Crack location, width, and orientation were all accurately predicted by the model.
Large tensile strains acting on the solidifying weld metal can cause the formation of eutectic bands along grain boundaries. These eutectic bands can lead to severe liquation in the partially melted zone of a subsequent overlapping weld. This can increase the risk of heat-affected zone liquation cracking. In this paper, we present a solidification model for modeling eutectic bands. The model is based on solute convection in grain boundary liquid films induced by tensile strains. The proposed model was used to study the influence of strain rate on the thickness of eutectic bands in Alloy 718. It was found that when the magnitude of the strain rate is 10 times larger than that of the solidification rate, the calculated eutectic band thickness is about 200 to 500% larger (depending on the solidification rate) as compared to when the strain rate is zero. In the paper, we also discuss how eutectic bands may form from hot cracks.
LKAB has tried new iron ore wagons for the 30 tonnes axle load. They got problems with cracking and material removal from the rim of the wheels during the tests. Martensite, which is more prone to cracking than other microstructures, was found at these locations. The initial material microstructure is supposed to contain no martensite. The purpose of this investigation is to find whether the thermal cycle due to braking, possibly with assistance of the mechanical load, can cause martensite formation
Rolling is simulated by a three-dimensional finite-element model with elastoplastic constitutive equations. The use of an explicit finite-element formulation, instead of the more commonly used implicit formulation, has reduced the required computing time. The larger of the models used in one step towards a general and complete computational model of rolling. Results from experiments and from two and three-dimensional calculations are compared.
A method for the evaluation of friction models is described. A wedge is rolled to uniform thickness, a range of reductions being investigated thereby in one experiment. Finite-element simulations are performed in order to estimate the friction parameters that can be used in the simulation of hot rolling. The influence of the material parameters and the friction parameters on the calculated results are investigated and the latter are compared with experimental results. It is shown that it is possible to separate the influence of the material parameters and the friction parameters, thus enabling the friction parameters to be evaluated from a minimum number of experiments.
A flow stress model describing precipitate hardening in the nickel based alloy Inconel® 718 following thermal treatment is presented. The interactions between precipitates and dislocations are included in a dislocation density based material model. Compression tests have been performed using solution annealed, fully-aged and half-aged material. Models were calibrated using data for solution annealed and fully-aged material, and validated using data from half-aged material. Agreement between experimental data and model predictions is good.
Induction hardening is a useful method for improving resistance to surface indentation, fatigue and wear that is favoured in comparison with through hardening, which may lack necessary toughness. The process itself involves fast heating by induction with subsequent quenching, creating a martensitic layer at the surface of the workpiece. In the present work, we demonstrate how to simulate the process of induction hardening using a commercial finite element software package with focuses on validation of the electromagnetic and thermal parts, together with evolution of the microstructure. Experiments have been carried out using fifteen workpieces that have been heated using three different heating rates and five different peak temperatures resulting in different microstructures. It is found that the microstructure and hardening depth is affected by the heating rate and peak temperature. The agreement between the experimental and simulated results is good. Also, it is demonstrated that the critical equilibrium temperatures for phase transformation is important for good agreement between the simulated and experimental hardening depth. The developed simulation technique predicts the hardness and microstructure sufficiently well for design and the development of induction hardening processes.
Gas Tungsten Arc Welding is simulated using the finite element method. The material model that has been used is a physically based plasticity model, coupled with a model for nucleation, growth, and coarsening of second phase particles. The material model is well suited for thermo-mechanical simulations and is used to predict microstructural changes, residual stresses and stress relaxation after post weld heat treatment. The residual stress state after welding is compared, using two different material models. One were the evolution of the precipitates is included and one where it is not. It is shown that the welding direction has an impact on the precipitate size and its distribution and thereby the residual stress state.
Induction heating is used in many industrial applications to heat electrically conductive materials. The coupled electromagnetic-thermal induction heating process is non-linear in general, and for ferromagnetic materials it becomes challenging since both the electromagnetic and the thermal responses are non-linear. As a result of the existing non-linearities, simulating the induction heating process is a challenging task. In the present work, a coupled transient electromagnetic-thermal finite element solution strategy that is appropriate for modeling induction heating of ferromagnetic materials is presented. The solution strategy is based on the isothermal staggered split approach, where the electromagnetic problem is solved for fixed temperature fields and the thermal problem for fixed heat sources obtained from the electromagnetic solution. The modeling strategy and the implementation are validated against induction heating experiments at three heating rates. The computed temperatures, that reach above the Curie temperature, agree very well with the experimental results.
Propagating bending waves are studied in plates made of glass-fiber reinforced polyester. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as light source, is used to record the out of plane motion of the waves. The interferograms have an elliptic-like symmetry for an orthotropic plate, while the wave pattern for a symmetric angle-ply reinforced plate has a symmetry about the axes of reinforcements. Experimental data are compared on one hand to analytical results obtained by assuming that the orthotropic plate can be described as if isotropic along the main axes, and on the other hand to numerical results from calculations using the finite-element method. The effective Young's modulus raised to power 1/4 is shown to be an important parameter for the description of the dispersive wave pattern. A defect in the plate alters the wave pattern in the interferograms significantly. This may have technical use.
The current work aims at developing models supporting design of the rolling and quenching processes. This requires a martensite formation model that can account for effect of previous plastic deformation as well as evolution of stress and temperature during the quenching step. The effect of deformation prior to the cooling on the transformation is evaluated. The experimental result shows that prior deformation impedes the martensite transformation due to the mechanical stabilisation of the austenite phase. Larger deformation above 30 % reduces the effect of the mechanical stabilisation due to increase in martensite nucleation sites. The computed transformation curves, based on an extended version of the Koistinen-Marburger equation, agree well with experimental results for pre-straining less than 30 %.
In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10−2 s−1, as compared to 10−3 s−1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson–Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.
The strain-induced martensitic transformation in a metastable austenitic stainless steel is investigated by high-energy x-ray diffraction and material modeling. Two different deformation modes are used (cold rolling and uniaxial tensile loading) and the effect on the strain-induced martensitic transformation behavior is investigated. Moreover, three different strain rates during the uniaxial tensile loading are evaluated. The results show a sigmoidal transformation behavior of the strain-induced martensite in respect to true strain, for tensile loading. The effect of different strain rates is also clearly seen and it alters both the amount of transformed martensite and the transformation behavior. The martensite transformation is drastically decreased already at moderate strain rates such as 10-2 s-1, due to adiabatic heating of the sample. The material model used gives an accurate prediction of the strain-induced martensitic transformation behavior during tensile loading. This is valuable for further implementation of the current material model in industrial forming mulations of real components.
Adaptive meshing is not only beneficial but also essential when simulating manufacturing processes. It can be used to reduce element distortions and to obtain accurate solutions in an efficient way. The versatility of combining different meshing capabilities when simulating a chain of manufacturing processes is demonstrated. The techniques have been implemented in a finite element code that is geometry oriented. This is convenient for the user and the additional complexity in the processing of the input file is compensated by the possibility to reuse this logic for transfer model definition data from old to new mesh
Smoothing improves the mesh quality by repositioning nodes while h-adaptive remeshing changes the topology of the mesh. The combination of these two schemes is indispensable when dealing with models with distorted elements and/or moving gradients in the solution. Different smoothing techniques for creating a mesh of high quality are studied. The quality of the mesh is quantified by a distortion metric. The adaptive remeshing procedure uses a generic error estimate for determining the size of new elements. The combined techniques are implemented for a graded finite element.
Simulation of automatic butt-welding of large plates was investigated. Two different steels were considered. The plates were tack-welded before the butt-welding. The simulation includes the tack-welding, the butt-welding and the cooling to room temperature. The simulations should lead to an understanding of the mechanics behind the change in gap width in front of the moving arc, which is of importance in automatic welding production. The residual stresses due to the butt-welding were also studied. The magnitude and the distribution of the residual stress are important in design of welded structures.
Many difficulties in welding result from the fact that heat input causes uneven heating of the welded object. This article reports on the results of an investigation carried out with the object to find out whether it is possible to predict residual stresses in welding and weld deformations with the aid of new computational methods used in continum mechanics. Butt welding of flat plates was studied in this investigation. Deformations, residual stresses, and gap width variations during the welding process were calculated.
In this paper root-bead welding of plates of two different sizes was experimentally and theoretically analysed. The material of the plates was a fine-grain steel with yield limit 360 MPa. The finite element method was used for both the thermal analyses and the mechanical analyses. Temperature-dependent material properties and volume changes due to phase transformations were considered. Plane stress conditions were assumed. Good agreement between calculated and measured values were obtained.