Transient Thermo-mechanical Simulation Research Articles

Numerical assessment of welding sequences in single-pass pipe welding for minimizing residual stresses

This research aims to investigate the impact of different welding sequences in the circumferential direction on the welding process of 304 stainless steel pipes. A fully coupled transient thermo-mechanical simulation technique used to numerically replicate welding behaviour on a single-pass butt-welded cylinder joint with a nominal diameter of 300 mm and a thickness of 8.38 mm. Five distinct welding sequences are considered, and temperature profiles are measured at four circumferential positions. The findings reveal that the residual stresses within and near the weld deposit are indeed influenced by the chosen welding sequence. In case 1, the value of maximum temperature reached 1840 Degree K at point T4, achieving equilibrium between the flux input and heat losses during welding. In case 3, the maximum temperature value (1530 Degree K) is lower than all other cases due to better heat distribution. Respective to the temperature distribution the maximum stress values in case-1 to 5 are 211, 201, 138, 146, and 147 Mpa. Based on a comprehensive analysis of these factors, case 3 emerges as the preferable welding sequences for pipes falling in the NPS 10 to NPS 24 size category.

Thermo-viscoelastic analysis of an inductive charging system included in an eRoads. Incit-ev project

This paper presents work carried out in WP4 of the European project INCIT-EV, to develop a thermo-mechanical model, for simulating the performance of electrified roads using an inductive system for the charging of electric vehicles. The system consists of a charging unit, made of a box containing a litz coil, inserted into the road, at low depth under the surface, and sealed using a resin. In previous studies [1], several solutions for the insertion of this system in the road structure were evaluated, using experimental and numerical studies. The purpose of this paper is to highlight the potential of thermo-viscoelastic FEM structural simulations to predict the response of the electric road system (ERS) taking into account daily thermal variations, and heat released by the inductive charging system. Firstly, thermal laboratory tests were performed to evaluate the temperature variations due to the operation of the charging system, and compared with FEM simulations, in order to validate different modelling assumptions (material characteristics, boundary conditions). Then, transient thermo-mechanical simulations were performed, considering different materials for the coil block (polyethylene, or concrete), and for the sealing resin, in order to evaluate different possible designs of the charging elements. The variations of the deformations of the different structures, and of the strain and stress fields, during representative temperature cycles, were studied and compared. Differences in mechanical response obtained with different sealing resins (elastic or viscoelastic) and different coil block materials (polyethylene, and concrete) were analysed and compared.

Heat Transfer and Structural Characteristics of Dissimilar Joints Joining Ti-64 and NiTi via Laser Welding

This study investigates the thermal-stress characteristics of a bi-metallic Ti-6Al-4V-Nitinol butt joints manufactured via laser welding. Particularly, the thermal profile along the weld interface and the deformation profile of the finished welded workpiece. A decoupled transient thermomechanical simulation model was constructed to recreate the welding process. This decoupled thermomechanical simulation model consisted of two transient simulation models. A transient thermal simulation model and a transient structural simulation model, with the thermal history of the transient thermal model being fed into the transient structural model. Both the thermal and structural portions of the model utilized temperature-dependent thermal and structural properties of Ti-6Al-4V and Nitinol. The temperature profile of the transient thermal-stress model aligns with the experimental thermal profile within 5% error. The deformation profile also matches the experimental results within 5% error. This approach to modeling laser welding can stand as a guide to predict both thermal and deformation profiles generated during the laser welding process.

Large-Scale Welding Process Simulation by GPU Parallelized Computing

The computational design of industrially relevant welded structures is extremely time consuming due to coupled physics and high nonlinearity. Previously, most welding distortion and residual stress simulations have been limited to small coupons and reduced order (from three-dimensional [3D] to two-dimensional [2D]), or inherent strain approximations were used for large structures. In this current study, an explicit finite element code based on a graphics processing unit was utilized to perform 3D transient thermomechanical simulation of structural components during welding. Laser brazing of aluminum alloy panels as representative of automotive manufacturing scenarios was simulated to predict out-of-plane distortion under different clamping conditions. The predicted deformation pattern and magnitude were validated by laser scanning data of physical assemblies. In addition, the code was used to investigate residual stresses developed during multipass arc welding of a nuclear industry pressurizer surge nozzle and subsequent welding repair where a 3D simulation was necessary. Taking the experimental data as reference, the 3D model predicted better residual stress distribution than a typical 2D asymmetrical model. Stress evolution in welding repair was also presented and discussed in this study. The efficient numerical model made it feasible to use integrated computational welding engineering to simulate welding processes for large-scale structures.

Effective residual stress prediction validated with neutron diffraction method for metal large-scale additive manufacturing

Metal Big Area Additive Manufacturing (MBAAM), an additive manufacturing based on wire-arc process, is progressively evolving from rapid prototyping to the industrial scale production. In MBAAM, the height of printed part can easily reach eight feet, and the printing can last for hours or days. For such large printed structures, distortion and residual stress management are primary challenges in production process. Although transient thermo-mechanical simulations with very small time increments have resulted in accurate process predictions on small parts, such time resolutions are not computationally feasible for large components. Hence, the time increment in thermo-mechanical simulations of large structures needs to be evaluated with respect to simulation accuracy and computational feasibility. In this work, two thin walls were printed using MBAAM, and temperature and process parameters were recorded and used to calibrate and validate the model results. The part distortion and residual stresses were measured before and after stress relaxation by neutron beam diffraction in High Flux Isotope Reactor (HFIR). These measurements were compared to the predicted simulation results. In this work, we investigated the robustness of the computational model and the effects of time increment magnitude on the large-scale MBAAM simulations in terms of accuracy and model efficiency. We found that a coarse time increment of 20 s effectively captured the overall part distortion, but the model was not able to capture the development of residual stresses in the base plate. We determined a combination of fine and coarse time increments that offers an optimal computational efficiency and accuracy for residual stress prediction. A fine time increment of 1 s can be used to resolve the thermal interactions between the wall and base plate during the printing of the first few layers, as well as for other transitions in the geometry or process conditions. These findings provide general guidelines for selection of simulation time increments and offer a general understanding of the effect of time increments on computational efficiency and accuracy in prediction.

Optimization of synchronizer cone angle with regard to manufacturing tolerances of cone roundness and cone angle

The effects of manufacturing tolerances on the maximum focal temperature has been investigated by transient thermomechanical simulations. Both relative cone angle and cone out-of-roundness for molybdenum and carbon fibre reinforced polymer synchronizers were evaluated. It was shown that cone out-of-roundness significantly increases the focal contact temperature for that specific cone but has little impact on the opposing cone. Two populations of measured synchronizers were evaluated, and it was shown that the maximum focal surface temperature can be decreased in almost all tolerance cases by introducing a relative angle between the cones.

A comparative study of the transient thermomechanical behavior of friction of the ceramic brake discs: Temperature field effect

During braking, a heat flow is generated by friction and heated the brake components, the heating causes thermal expansion in the disc and the pads and these expansions alternate the contact. This paper proposes a transient thermomechanical simulation of friction by the finite element method of disc/pads of a sport cars brake using ABAQUS. In this comparative study, three different ceramic composite materials (A359/SiC p20, Al6061/SiC, C/C-SiC) are used for the disc which is in friction with organic (C/C) lining bonded to steel back plates of the brake pads. This will allow us to emphasize the importance of the distribution and the variation of the temperature on the contact pressure and the stress field and the braking torque.

EFFICIENT QUANTIFICATION OF FREE AND FORCED CONVECTION VIA THE DECOUPLING OF THERMO-MECHANICAL AND THERMO-FLUIDIC SIMULATIONS OF MACHINE TOOLS

Thermo-elastic deformations represent one of the main reasons for positioning errors in machine tools. Investigations of the thermo-mechanical behaviour of machine tools, especially during the design phase, rely mainly on thermo-elastic simulations. These require the knowledge of heat sources and sinks and assumptions on the heat dissipation via convection, conduction and radiation. Forced convection such as that caused by moving assemblies has both a large influence on the heat dissipation to the surrounding air. The most accurate way of taking convection into account is via computational fluid dynamics (CFD) simulations. These simulations compute heat transfer coefficients for every finite element on the machine tool surface, which can then be used as boundary conditions for accurate thermo-mechanical simulations. Transient thermo-mechanical simulations with moving assemblies thus require a CFD simulation during each time step, which is very time-consuming. This paper presents an alternative by using characteristic diagrams to interpolate the CFD simulations. The new method uses precomputed thermal coefficients of a small number of load cases as support points to estimate the convection of all relevant load cases (i.e. ambient conditions). It will be explained and demonstrated on a machine tool column.

The effect of manufacturing tolerances on the thermomechanical load of gearbox synchronizers

Transmission performance is crucial for heavy trucks and connected vehicles in general and for platooning of trucks in particular. Gearbox synchronizers are highly loaded conical friction brakes used during gear shifts. Service life and, thus, the gear shifting reliability, of the synchronizer depend on the local thermomechanical loading of the contact surface. To achieve a robust and cost-efficient system, more knowledge is needed of how manufacturing tolerances affect the local thermomechanical loading and therefore service life and reliability of a synchronizer. The effects from angle deviations between the mating cones and cone out-of-roundness on focal maximum temperature during a synchronization sequence have been studied with transient thermomechanical simulations. It is shown that thermomechanical effects will significantly magnify the nominal effects on synchronization performance caused by shape deviations given by the specified manufacturing tolerances.

High performance computation of residual stress and distortion in laser welded 301L stainless sheets

Transient thermo-mechanical simulation of stainless plate laser welding process was performed by a highly efficient and accurate approach-hybrid iterative substructure and adaptive mesh method. Especially, residual stress prediction was enhanced by considering various heat effects in the numerical model. The influence of laser welding heat input on residual stress and welding distortion of stainless thin sheets were investigated by experiment and simulation. X-ray diffraction (XRD) and contour method were used to measure the surficial and internal residual stress respectively. Effect of strain hardening, annealing and melting on residual stress prediction was clarified through a parametric study. It was shown that these heat effects must be taken into account for accurate prediction of residual stresses in laser welded stainless sheets. Reasonable agreement among residual stresses by numerical method, XRD and contour method was obtained. Buckling type welding distortion was also well reproduced by the developed thermo-mechanical FEM.

Multifidelity Multidisciplinary Whole-Engine Thermomechanical Design Optimization

Traditionally, the optimization of a turbomachinery engine casing for tip clearance has involved either two-dimensional transient thermomechanical simulations or three-dimensional mechanical simulations. This paper illustrates that three-dimensional transient whole-engine thermomechanical simulations can be used within tip clearance optimizations and that the efficiency of such optimizations can be improved when a multifidelity surrogate modeling approach is employed. These simulations are employed in conjunction with a rotor suboptimization using surrogate models of rotor-dynamics performance, stress, mass and transient displacements, and an engine parameterization.

Numerical Computation of Component Shape Distortion Manufactured by Selective Laser Melting

The main aim of this paper is to effectively replicate the process heat effects during Selective Laser Melting (SLM) using a commercial FE package in terms of modeling effort and computation time, in order to achieve reliable residual stress distributions and distortions compared to experimental measurements. Since each build-up layer consists of hundreds of scan vectors, it is impracticable to model and execute a transient thermo-mechanical simulation without appropriate simplifications. By managing to provide reliable numerical results of the final component shape the volume-by-volume (VBV) method will allow performing a parameter sensitivity analysis on the final shape distortion. With the VBV method three layers of materials are being brought into melt simultaneously. The parameters investigated are the overall heat input and the stiffness of the component; both being directly related to the number of layers being deposited.

Finite element simulation of residual stresses and their measurement by contour method

A three-dimensional transient thermo-mechanical simulation has been performed on a welded Tee-joint using the finite element method, to predict longitudinal residual stresses. The uncoupled thermo-mechanical simulation consists of two stages. The first stage involves the prediction of the complete thermal history of the weldment. The second stage involves the thermo-mechanical simulation on the basis of the results of the first stage. Temperature dependent thermal and mechanical properties were incorporated in the simulation. A relatively new contour method was used to experimentally validate the longitudinal residual stresses obtained by the thermo-mechanical simulation. The experimental results agree well with the simulated results of residual stresses.