Thermo-mechanical FE Analysis Research Articles

Coupled thermomechanical FE analysis of multi-pass welding in thick pipe

Coupled thermomechanical FE analysis of multi-pass welding in thick pipe

A new method to estimate the residual stresses in additive manufacturing characterized by point heat source

Residual stress in additive manufacturing (AM) is one of the key challenges in terms of structural integrity and the finish quality of printed components. Estimating the distribution of residual stresses in additively manufactured components is complex and computationally expensive with full-scale thermo-mechanical FE analysis. In this study, a point heat source is utilized to predict the thermal field and residual stress distribution during the manufacturing processes. Numerical results show that the residual stress at a single material point can be expressed as a function of its spatial position and the peak nodal temperature it has experienced during thermal cycles. The distribution of residual stress can be divided into three segments according to the peak nodal temperature. The peak nodal temperature only depends on the heat flux and the distance to the point heat source center. A semi-analytical approach to predict the peak nodal temperature and residual stresses, once the heat flux is known, is proposed. The proposed approach is further validated by a numerical case study, and a very good agreement has been achieved. Compared with traditional thermo-mechanical FE analysis of additive manufacturing, the proposed method significantly improves the computational efficiency, showing great potential for prediction of residual stresses and distortion.

3D Coupled Thermo-Mechanical FE analysis of effect of process parameters in ring rolling process

3D Coupled Thermo-Mechanical FE analysis of effect of process parameters in ring rolling process

Study on thermal field in fly-cutting process of DKDP crystal

As an important nonlinear optical material, deuterated potassium dihydrogen phosphate (DKDP) crystal is used in laser beams as the core element of inertial confinement fusion. The most general method to produce smooth and crack-free DKDP surface is single point diamond fly-cutting (SPDF). However, the phase-changed temperature of DKDP is only about 120 °C which could be exceed in fly-cutting process. To analyze temperature field in cutting process, the formula based on the heat source method was introduced to calculate the temperature values on tool rake face under different cutting speed in DKDP crystal cutting process; then, thermo-mechanical FE analysis under the same process parameters was carried out to simulate the distribution of temperature field. The calculation and simulation results are basically in agreement, and the conclusion can be deduced: as the cutting speed increases, the temperature in the cutting zone increases, the highest temperature under common cutting parameter is up to 140 °C, which is validated by the dynamic infrared camera; however, the cutting temperature growth rate decreases with the same trend. The experiment results indicate that the chip morphology appears small spherical structure at high cutting speed, which illustrates the great possibility that the temperature exceed the phase transition temperature.

Partial strengthening method for cold stamped B-pillar with minimal shape change

The partial strengthening method for pre-stamped panels both avoids excessive strength enhancement over the entire product and substantially reduces the processing cost compared to conventional hot press forming. In this paper, we propose two types of partial strengthening processes to selectively increase the local strength of a cold stamped B-pillar by utilizing an induction coil system and water spray quenching to induce the martensitic transformation in the target region. Thermo-mechanical FE analyses were conducted to evaluate the effect of the process parameters such as the quenching rate, quenching time, and heating width on the shape changes during the partial strengthening processes while simultaneously considering the thermal dilatation and transformation plasticity.

Two-way coupled CFD fire and thermomechanical FE analyses of a self-supporting sandwich panel façade system

A self-supporting sandwich panel façade system under fire is studied. First, a thermomechanical FE model, which comprises the complete façade system, and incorporates material degradation and geometrical nonlinear behaviour except for the insulation material and connections, is loaded by a fire temperature curve. Eurocode design rules then predict the screw connections of a sandwich panel will fail in shear. Secondly, an existing programme, FDS-2-Abaqus, is extended to allow its two-way coupled analyses, in which CFD fire simulations are updated for changes in the thermomechanical FE model, to be applicable to the façade system. Again, these simulations show the shear failure of the screws. Parameter studies show differences in system behaviour for improved screw properties; a fuel-controlled vs. ventilation-controlled fire; and different panel thicknesses. Interestingly, as thermal bowing of the panel retards screw failure, and thicker sandwich panels bow less than thinner panels, thicker façade panels will decrease failure time. This and other insights obtained, and the predicted failure of two tiny but critical screws within 80 s, as compared to 150 min lasting sandwich panels in standard fire tests, stresses the need to study complete systems under realistic fires, rather than to study individual components in standard fire tests. Future research will focus on detailed FE models of the connections; full-scale fire experiments; CFD temperature measurement points at the façade outside; detailed modelling of the insulation; and the effects of high temperature creep.

Automated two-way coupling of CFD fire simulations to thermomechanical FE analyses at the overall structural level

Coupled CFD fire simulations and thermomechanical FE analyses typically consist of fire simulations, heat transfer analyses and structural response analyses, mutually coupled by three coupling steps. There are two coupling approaches, one-way and two-way coupling, where two-way coupling includes the effects of the structural response on fire propagation. In the first part of this paper, one- and two-way coupling approaches including the coupling steps are proposed to include coupling at the structural level. Then a case study comprising an office space with a 12-plate thin-walled steel façade under fire conditions is introduced, as well as the related CFD and FE models. A newly developed automated coupling interface and subprograms are used to perform several one-way and two-way coupled analyses using a coarse and fine CFD mesh for the case study. Slight differences are found in the results of identical simulations due to random effects in the fire simulations. Nevertheless, it can be concluded that two-way coupling is feasible, and that significant differences in the façade failure progression illustrate its effectiveness. Future research includes additional developments of both the fire and structural models, as well as verification and parametric studies to further confirm the findings.

Trail Rolling Method for Control of Buckling Distortion in AA5083 GMA Butt Weldment

This study deals with the proper conditions of the trail rolling method (TRM) for the prevention of the buckling welding distortion at the AA5083 GMA butt weldment. For it, the effect of the working conditions of TRM including the rolling depth and the rolling distance between the welding torch and the roller on the longitudinal welding shrinkage force of the weldment was evaluated by using 3 dimensional thermo-mechanical FE analyses. The longitudinal welding shrinkage force inducing the buckling welding distortion at the GMA butt weldment was mitigated with an increase in the rolling depth and the rolling distance between the welding torch and the roller. Based on the results, the proper conditions of trail rolling method were established to reduce the longitudinal welding shrinkage force of the GMA butt weldment to below the critical value corresponding to the bucking distortion.

3D finite element modeling of in-service sleeve repair welding of gas pipelines

The present work investigates the influence of welding sequence and scheme on residual stresses induced during in-service sleeve repair welding of gas pipelines. For this purpose, a 3D thermo-mechanical FE analysis is conducted on an 8″-Schedule-20, API 5L-X65 steel pipe. Two welding sequences for the sleeve-pipe circumferential fillet welds are compared in the present study: sequential welding in which one side of the sleeve is welded first and then the other side is welded by the same welder, and simultaneous welding in which both sides of the sleeve are welded concurrently by two welders. Within the simultaneous welding sequence, four different welding schemes, designed to investigate the influence of the number of welders and welding directions on residual stresses, are investigated. The results show that the sequential welding sequence induces less residual stresses and distortions. Within the simultaneous welding sequence, the back-step welding scheme is found to induce the least average residual stresses as compared to other welding schemes.

The effect of in-service steam temperature transients on the damage behavior of a steam turbine rotor

This study was aimed at identifying the influence of the temperature transient on the creep–fatigue behavior of a steam turbine rotor. Especially, the steam temperature fluctuations during the steady state operation phase could lead the stress to the oscillation, which also contributes to the fatigue damage. Toward this end, in-service operating data during startup, shutdown and steady state operation phases was chosen to investigate the creep–fatigue damage of a 1000MW steam turbine rotor. A viscoplastic constitutive model with damage was presented to describe creep–fatigue deformation behavior. A significant growth in creep damage was found under the influence of the temperature fluctuation compared to the creep damage under the stable temperature condition. In addition, steam temperature fluctuation induced the larger thermal gradient and temperature difference at the location where is closer to the rotor surface. The correlation of the stress range due to these temperature fluctuations has been established by carrying out the transient thermo-mechanical FE analysis. Frequent thermal fluctuations during the steady state operation phase were identified as one of the most influential factors for the creep–fatigue damage of the steam turbine rotor.

CI ENGINE AS A CASE STUDY OF THERMOMECHANICAL FE ANALYSIS OF THE PISTON – PISTON RINGS – CYLINDER SYSTEM

The compression-ignition engine as a case study of a methodology of the numerical modelling and simulation of the piston – piston rings – cylinder system was presented in the paper. Thermomechanical FE analysis, taking into account thermal and mechanical loads, was carried out using the MSC.Marc/Mentat software. The mechanical loads included loads due to inertial and gas forces as well. A three dimensional solid geometrical model of the considered set was developed using AutoCAD software, whereas the finite element mesh was generated using Altair HyperMesh. Kinematic boundary conditions – the vertical displacement and acceleration of the piston – were described by the corresponding curves as a function of time for selected engine speed. Changes in pressure on the piston crown were estimated based on data from the engine manufacturer and the corresponded indicator diagram available in the literature. The results of thermomechanical FE analysis were presented in the form of stress and/or displacement contours. The main aim of the analysis was to determine the deformation of the piston depending of on the piston material. Two types of material were compared – the actual one PA12 aluminum alloy and the new composite material with low hysteresis. The second material was characterized by slight differences of the coefficient of thermal expansion for heating and cooling.

Methods for the Numerical Modelling of the Adhesive Interlayer of Sandwich-Sheets in Case of Coupled Thermo-Mechanical FE-Analysis

Bending of multilayered sheets like lightweight sandwich sheets or fiber reinforced thermoplastics is dominated by the mechanism of interply-slip. FE-analysis is performed to predict defects depending on this mechanism. The shear and damage behavior of the adhesive layer of sandwich sheets can be modeled by cohesive elements in Abaqus. Forming simulation of fiber reinforced thermoplastics requires coupled thermo-mechanical analysis methods due to temperature dependence. For this, alternative modeling strategies for the inner layer of adhesive or polymer matrices will be tested in this paper that are able to transfer heat. The layer will be presented by solid elements with enriched property definitions or viscoplasticity. Furthermore the thickness of the layer will be neglected and replaced by contact formulations or spring elements.

Characteristics of Austenite Grain Refinement by High-Speed Large-Reduction Forging —Production Technology for Fine Grained Steel by Large Deformation Forging III—

To obtain fine and uniform microstructures, appropriate forging conditions were examined using high-speed large-reduction forging. Swing-type forging equipment was employed in hot-forging experiments using low-carbon steel (0.14%C­0.64%Mn). Also, a microstructure analytical system was developed by combining thermomechanical FE analysis with microstructural analysis to discuss the metallurgical phenomena occurring during forging. It was observed that coarse austenite grains can be refined to 20­30μm uniformly using the proposed forging technology in the case of 59% reduction in thickness at 1273K. In this case, dynamic recrystallization is a dominant factor for obtaining fine and uniform austenite grains. In the case of 43% reduction in thickness, the recrystallization is inhomogeneous, resulting in an inhomogeneous microstructure. Thus, about 60% reduction in thickness is necessary to obtain fine and uniform microstructures using the proposed technology when applied to the roughing of hot strip mills. [doi:10.2320/matertrans.P-M2014820]

3D coupled thermomechanical FE analysis of blank size effects on radial-axial ring rolling

Radial-axial ring rolling, which is widely used to manufacture large scale seamless rings, is an advanced but complicated plastic forming technique with multiprocess factors coupling with interactive effects. During the radial-axial ring rolling process, the blank size is a decisive parameter because it influences directly the degree of deformation of the ring and the rolling parameters of the process. In this paper, the blank size design method of the radial-axial ring rolling process is first proposed, then a valid three-dimensional (3D) coupled thermomechanical FE model of the process is explored under ABAQUS software environment. Based on the valid 3D FE model, the blank size effects on radial-axial ring rolling are investigated. The research results provide valuable guidelines for blank size design and optimisation in the actual radial-axial ring rolling production.

A Numerical Approach to Shape Correction of Stamped Products Using Laser Forming Techniques

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. In this paper, shape correction of stamped product using the laser forming technique is numerically invesitgaed. As a fundamental study, laser irradiated bending process has been analyzed through the thermo-mechanical FE analysis. Laser scanning experiments has been also conducted for varificaiton of numerical simulations. Finally, the laser forming technique is applied to the u-shaped channel member for springback compensation. It is observed that laser irradiation gives the desired bending angle to compensate the springback by controlling the process parameters such as the laser power, scanning speeds and the number of laser scanning.

3D Coupled Thermo-Mechanical FE Analysis of Surface Defects in Continuously Casting Slab

The behaviour of the surface defects on the continuous casting slab during hot rolling is investigated using the commercial FE-code LS-DYNA. The thermo-elastic-plastic material model is chosen in the simulation models, and the material implemented in the simulation is the austenitic stainless steel 304. The numerical results show the significant morphological changes of the surface defects during hot rolling and afford valuable indications for a deeper understanding of the underlying process. An accelerated crack growth and propagation are observed for the edge cracks, and the closure behaviour is found in the transverse and longitudinal cracks. The effect of temperature is significant on both the roll and the strip in hot rolling process. The developed models consider different types of mesh and element, thermal conditions, and rolling schedules. The predicted relationship between rolling conditions, the temperature distribution of crack, and the full history of temperature variation are discussed in this study.

鍛造型板厚大圧下によるオーステナイト組織の微細化機構

To obtain fine and uniform microstructures, appropriate forging conditions were examined using high-speed large-reduction forging. Swing-type forging equipment was employed in hot-forging experiments using low-carbon steel (0.14%C-0.64%Mn). Also, a microstructure analytical system was developed by combining thermomechanical FE analysis with microstructural analysis to discuss the metallurgical phenomena occurring during forging. It was observed that coarse austenite grains can be refined to 20-30 μm uniformly using the proposed forging technology in the case of 59% reduction in thickness at 1273 K. In this case, dynamic recrystallization is a dominant factor for obtaining fine and uniform austenite grains. In the case of 43% reduction in thickness, the recrystallization is inhomogeneous, resulting in an inhomogeneous microstructure. Thus, about 60% reduction in thickness is necessary to obtain fine and uniform microstructures using the proposed technology when applied to the roughing of hot strip mills.

Mathematical modelling and integration of micro-scale residual stresses into axisymmetric FE models of Ti6Al4V alloy in turning

The selection of process parameters during machining has a significant impact on the in-service life of the parts. This is particularly relevant in industries such as aerospace with product lifecycles extending beyond 20 years. The paper presents a model for prediction of turning induced residual stresses of Ti6Al4V alloy. The finite element method (FEM) is used in the current study. Dynamic thermo-mechanical FE analysis using explicit integration is performed. The workpiece is modelled as an isotropic thermal–elastic–plastic model using the Johnson–Cook constitutive equation. The near-surface residual stresses are predicted and compared with experimentally measured results. Mathematical algorithms and formulations for integrating micro-scale residual stresses into axisymmetric FE models are developed and successfully implemented in the ABAQUS FE code by a user-defined subroutine. As an example, the micro-scale residual stresses are integrated into an axisymmetric FE model of a shaft subjected to turning. The models are experimentally validated using face turning and the residual stress profile of a Ti6Al4V workpiece is generated and measured at two cutting depths (100 and 500 μm). The feed rate is kept constant at 100 μm/rev. Two residual stress measurement methods (X-ray diffraction and hole-drilling) are utilised in the current study. The X-ray diffraction method is used to measure the residual stress profiles on the surface of the machined workpiece. Compressive near the surface residual stresses are measured. The experimentally measured and the FE predicted residual stresses are in good agreement.

3D coupled thermo-mechanical FE analysis of roll size effects on the radial–axial ring rolling process

Radial–axial ring rolling is an advanced but complicated incremental metal forming technique with multi-factors coupling interactive effects. During the radial–axial ring rolling process, the deformation and thermal behaviors of the ring mainly occur in the roll passes which are constituted by rolls. So, the rolls sizes have enormous influence on the quality of the rolled ring as well as the stability of the process. In this paper, the ranges of rolls sizes and forming parameters are reasonably determined at first, then a 3D elastic–plastic and coupled thermo-mechanical FE model of radial–axial ring rolling is developed using the dynamic explicit code ABAQUS/Explicit, and its reliability is verified theoretically and experimentally. Based on the valid 3D FE model, the size effects of rolls on the radial–axial ring rolling process are investigated. The research results provide valuable guidelines for the design and optimization of the rolls sizes in the actual radial–axial ring rolling production.

유한요소해석을 이용한 다층 FCA 맞대기 용접부의 횡 방향 잔류응력 평가에 관한 연구

The purpose of this study is to evaluate the residual stresses at the multi-pass FCA weldment using the finite element analysis (FEA). In order to do it, an H-type specimen was selected as a test specimen. The variable used was in-plane restraint intensity. The temperature distribution at the multi-pass FCA butt weldment was evaluated in accordance with the relevant guidance recommended by the KWJS. The effective conductivity for the weld metal corresponding to each welding pass was introduced to control the maximum temperature below the vaporization temperature of weld metal. The heat flux caused by welding arc was assumed to be applied to the weld metal corresponding to welding pass. With heat transfer analysis results, the distribution of transverse residual stresses was evaluated using the thermo-mechanical analysis and compared with the measured results by XRD and uniaxial strain gage. In thermo-mechanical analysis, the plastic strain resetting at the temperature above melting temperature of <TEX>$1450^{\circ}C$</TEX> was considered and the weld metal and base metal was assumed to be bilinear kinematics hardening continuum. According to the comparison between FEA and experiment, transverse residual stresses at the multi-pass FCA butt weldment obtained by FEA had a good agreement with the measured results, regardless of in-plane rigidity. Based on the results, it was concluded that thermo-mechanical FE analysis based on temperature distribution calculated in accordance with the KWJS’s guidance could be used as a tool to predict the distribution of residual stress of the multi-pass FCA butt weldment.