Thermo-mechanical Coupling Model Research Articles

Delamination of sub-crustal lithosphere beneath the Isthmus of Tehuantepec, Mexico: Insights from numeric modelling

The Isthmus of Tehuantepec (IT) is a tectonically active and complex physiographic province in southern Mexico marked by an anomalous volcanism with unusual location and geochemical signature, an extensional stress regime and a well-imaged high seismic-velocity anomaly in form of a slab-like structure whose origin remains still not well understood. Here we use numeric modelling, tectonic information and composition of volcanic rocks from the Los Tuxtlas Volcanic Field (LTVF) to reconstruct the geodynamic evolution of the Isthmus of Tehuantepec from the Late Miocene to the present, and propose a model that reconciles the seismic observations with the tectonic evolution of the region. Using a high-resolution thermomechanical petrological coupled model, we show that rollback of delaminated continental lithosphere and associated asthenospheric upwelling provides a plausible mechanism for generating the observed high seismic-velocity anomalies beneath the Isthmus of Tehuantepec. Our model proposes that delamination of the entire lithospheric mantle initiated some 7 Myr ago by infiltration of hot and buoyant asthenospheric material into the base of the crust, when a slab gap appeared in the subducting Cocos slab. A geodynamic model involving sub-crustal lithosphere delamination reconciles the geological and geophysical observations and explains the complex oceanic-continental tectonics of the Isthmus of Tehuantepec.

Investigation of dynamic heat generation and transfer behavior and energy dissipation for nonlinear synchronous belt transmission

Study on energy dissipation and temperature distribution of synchronous belt transmission is of great importance in industrial engineering field, which is highly related to transmission efficiency estimation, thermal fatigue life prediction, and product design. However, the complex behaviors of viscoelastic hysteresis and meshing friction make it much more difficult to investigate heat generation and transfer mechanism of synchronous belt than other products. To accurately predict temperature and energy dissipation, a thermo-mechanical coupling model was developed through combining experiment and finite element analysis method, in which material nonlinearity of rubber hyper-viscoelasticity, and contact nonlinearity of meshing interference were comprehensively considered. Meanwhile, the friction heat flux partition coefficient and convective heat transfer coefficient were theoretically computed and corrected. As a result, the temperature distribution, hysteresis and friction energy dissipation of synchronous belt could be computed accurately, the transmission efficiency was estimated as well. The simulation temperatures of various operating conditions were confirmed by testing results. The presented methodology can completely predict energy dissipation and temperature distribution of synchronous belt transmission, which has far-reaching consequences in the engineering application filed.

Modeling of strain rate effect on the pseudoelastic behavior of NiTi SMA using a simple thermomechanical coupling model

NiTi SMA represents a popular group of metals with interesting properties like pseudoelasticity and a high energy dissipative capacity. Indeed, NiTi alloys, presents an interesting damping capacity due to solid-solid phase transformation. Such characteristics allow them to be used in many civil engineering fields mainly as actuators and damping devices. However, because of their complex behavior, the design process of these applications seems to be complicated and consequently, needs to build accuracy numerical models. One of these already existing models is the micromechanical Likhachev model. It seems to be very attractive thanks to its general formulation, numerical efficiency and model parameters relatively easy to determine. This paper concerns the numerical simulation of the pseudoelasticity behavior of NiTi wires dedicated to the application of damping devices, at different stress and strain rates. A thermomechanical coupling is introduced in the Likhachev formulation in order to simulate the thermomechanical behavior of NiTi under strain control. In this paper the model is adapted to a strain-controlled formulation, and 1D simulation is achieved using FORTRAN code. Parameters model are identified thanks to SiDoLo software and the corresponding results are presented and discussed. A good agreement with experimental data is found for the two formulations.

Thermo-Mechanical Coupling Analysis of the Actuating Mechanism in a High Speed Press

In order to ensure the manufacturing precision of an ultra-precision high speed press, an integrated thermo-mechanical coupling model of its actuating mechanism is proposed, which includes the mechanical models of the slider and crankshaft, the thermal models for calculating the heat generation powers at different bearings as well as the heat transfer and heat dissipation in the actuating mechanism. The validity of the proposed thermo-mechanical coupling model is verified by a thermal equilibrium experiment when the press operates under the full load of 3000kN at 300 rpm. A sensitivity analysis is conducted to investigate the simulation errors resulting from the variation of the ambient temperature, the results of which demonstrate that the average ambient temperature should be applied for improving simulation accuracy. Then the thermal stiffness of the actuating mechanism and the thermo-mechanical coupling characteristics of different parts are analyzed by the proposed model with the average ambient temperature applied. The influences of the thermally induced loads on the thermal stiffness are discussed in detail. It is concluded that the temperature rise of the actuating mechanism in the stamping process of a high speed press should be fully considered in the design phase for ensuring its manufacturing precision.

Numerical Simulation of the Electron Beam Welding and Post Welding Heat Treatment Coupling Process

AbstractIn this article, the electron beam welding and post welding heat treatment (PWHT) coupling process of nickel alloy GH80A is carried out using ABAQUS software. The thermo-mechanical coupling (TMC) model is considered in the simulation. The simulation results obtained from finite element method (FEM) including thermal history, heat source sharp, residual stress and stress relaxation. The simulation objectives are analysis of thermal field and heat source sharp which is compared with experimental results. These results also can determine the heat affected zone and residual stress during welding and stress relaxation which is produced by the post welding heat treatment process.

Finite element analysis and experimental validation of the thermomechanical behavior in laser solid forming of Ti-6Al-4V

A three-dimensional (3D) thermomechanical coupled model for Laser Solid Forming (LSF) of Ti-6Al-4V alloy has been calibrated through experiments of 40-layers metal deposition using different scanning strategies. The sensitivity analysis of the mechanical parameters shows that the thermal expansion coefficient as well as the elastic limit of Ti-6Al-4V have a great impact on the mechanical behavior. Using the validated model and optimal mechanical parameters, the evolution of thermo-mechanical fields in LSF has been analyzed. It has been found that the stresses and distortions develop in two stages, after the deposition of the first layer and during the cooling phase after the manufacturing of the component. The cooling phase is the responsible of 70% of the residual stresses and 60% of the total distortions. The analyses indicate that by controlling the initial substrate temperature (pre-heating phase) and the final cooling phase it is possible to mitigate both distortion and residual stresses. Hence, the influence of different pre-heating procedures on the mechanical fields has been analyzed. The results show that increasing the pre-heating temperature of the substrate is the most effective way to reduce the distortions and residual stresses in Additive Manufacturing.

Effects of Extrusion-Shear and Direct Extrusion on the Plastic Deformation of AZ31 Magnesium Alloy

Based on characteristics of direct extrusion for magnesium alloy seamless tube and continuous equal channel angular pressing (ECAP) of tubes, a new composite extrusion process of tubes including direct extrusion and many steps ECAP was invented firstly, which are shorten for TES process in this paper. A three-dimensional finite element thermo-mechanical coupled model and conditions for TES process were established. The extrusion process and cumulative strains evolution during TES process were simulated. The results show that TES process can improve the cumulative strains significantly. The microstructures observations of longitudinal sections for tubes fabricated by direct extrusion and TES process were carried out. It was found that when the extrusion temperature was 400°C, and extrusion ratio was 8.4 and the channel angle was 150°, TES process can refine the microstructures of tubes effectively.

Modeling temperature and residual stress fields in selective laser melting

The paper investigates the temperature and residual stress fields in the selective laser melting (SLM) process. A three-dimensional thermo-mechanical coupling model is developed to simulate a multi-track multi-layer SLM process using the finite element method. The model considers the temperature-dependent material properties which consist of thermal conductivity, density, enthalpy, yield stress, thermal expansion coefficient and Young's modulus. The simulated process includes the heating, melting, vaporization, solidification, shrinkage and cooling phenomena in the powder bed. The SLM scanning laser beam can be described as a moving volumetric heat source that is able to penetrate through the powder layers. The modeling results show that the residual stress component of the built part in the direction of the layer height increases with the number of the printed layers. It is found that at a given point, the residual stress component in the scanning direction is generally larger than the other two components, and the maximum von Mises stress occurs in the middle plane of the printed part. The temperature evolution and residual stress distribution predicted by the model can serve to provide guidance for SLM process parameter optimization.

A Fully Coupled Thermomechanical Model of Friction Stir Welding (FSW) and Numerical Studies on Process Parameters of Lightweight Aluminum Alloy Joints

This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding (FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson–Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules (i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.

Finite element simulation of bulge deformation for slab continuous casting

This paper aims to provide an investigation of the bulge deformation rules by using finite element analysis software, ABAQUS/Standard. A three-dimensional thermo-mechanical coupling model, considering the dynamic contact between the slab and rolls, has been established to study the temperature and bulge deformation distributions of the slab over the casting process. The simulated results of temperature profile were compared with the measured temperatures during the continuous casting process, the results of which showed a high agreement. Moreover, the bulge deformation rules of the slab were investigated systematically, especially at the thickness direction of the cross section which is the bulge deformation of the slab on the narrow side. A wave motion was found in the bulge deformation on the wide side of the slab cross section due to the joint effect of the ferrostatic pressure and the roller supporting force. The bulge deformation on the narrow side without the constraint from the roller support was cumulative, which was greater than the recovery count and compensated the bulge deformation on the wide side. In addition, the influences of various casting process parameters on bulge deformation were studied systematically in this paper. The results showed that bulge deformation on the narrow side and the wide side both increased with an increase in casting speeds and roll pitch. The method of fixed-gap and variable-diameter was suggested to be applied in the manufacture process in order to reduce the bulge deformation.

Two-Dimensional Finite Element Analysis of Turning Processes

Despite crucial efforts invested into computational methods, explicit dynamics simulation of cutting operations may still be unacceptably expensive. Therefore, in many cases a two-dimensional model is considered. Here an overview of the possibilities of two-dimensional simulations is given. For this, simulation and measurement of a straight turning process on AISI 1045 steel is presented. In the numerical analysis, material behavior and its failure was described by Johnson-Cook law, considering damage evolution. Coupled thermo-mechanical model with mass-scaling and adaptive remeshing was built. The numerically obtained cutting force was compared to the measured data. It was found that the forces obtained with simulation and the measured ones show good agreement. Sensitivity analyses were performed to examine the influence of specific parameters on the reaction force. The effect of these parameters is also shown.

Multi-scale numerical simulation analysis for influence of combined leaching and frost deteriorations on mechanical properties of concrete

Purpose The multi-scale numerical simulation method, able to represent the complexity of the random structures and capture phase degradation, is an effective way to investigate the long-term behavior of concrete in service and bridges the gap between research on the material and on the structural level. However, the combined chemical-physical deterioration mechanisms of concrete remain a challenging task. The purpose of this paper is to investigate the degradation mechanism of concrete at the waterline in cold regions induced by combined calcium leaching and frost damage. Design/methodology/approach With the help of the NIST’s three-dimensional (3D) hydration model and the random aggregate model, realistic 3D representative volume elements (RVEs) of concrete at the micro-, the meso-, and the macro-scales can be reconstructed. The boundary problem method is introduced to compute the homogenized mechanical properties for both sound and damaged RVEs. According to the damage characteristics, the staggering method including a random dissolution model and a thermo-mechanical coupling model is developed to simulate the synergy deterioration effects of interacted calcium leaching and frost attacks. The coupled damage procedure for the frost damage process is based on the hydraulic pressure theory and the ice lens growth theory considering the relationship between the frozen temperature and the radius of the capillary pore. Finally, regarding calcium leaching as the leading role in actual engineering, the numerical methodology for combined leaching and frost damage on concrete property is proposed using a successive multi-scale method. Findings On the basis of available experimental data, this methodology is employed to explore the deterioration process. The results agree with the experimental ones to some extent, chemical leaching leads to the nucleation of some micro-cracks (i.e. damage), and consequently, to the decrease of the frost resistance. Originality/value It is demonstrated that the multi-scale numerical methodology can capture potential aging and deterioration evolution processes, and can give an insight into the macroscopic property degradation of concrete under long-term aggressive conditions.

Study on thermal induced preload of ball bearing with temperature compensation based on state observer approach

The internal contact feature and thermal induced dynamic preload is essential for ball bearing, which is one of the key issues for thermal instability and stuck problems at high rotation speed. This paper presented a thermo-mechanical coupling model for angular contact ball bearing with preload and temperature compensation, for the purpose of dynamic preload monitoring. Based on the verified thermal balance equations, thermal deformation and thermal induced preload were achieved and feedback to the original local approach of heat generation calculation. Then, the nonlinearity and uncertainty heat transfer characteristic was considered via a state observer to verify the calculation process. The state variable of bearing’s temperature rise was defined and a state observer with proportional-integral term was designed. The difference between experimental data and calculation result was feedback by the observer to control the heat transfer and preload solving process. Thus, the real-time temperature rise, thermal deformation, and dynamic preload of bearing’s internal assemblies were obtained.

Second-order two-scale finite element algorithm for dynamic thermo–mechanical coupling problem in symmetric structure

The new second-order two-scale (SOTS) finite element algorithm is developed for the dynamic thermo-mechanical coupling problems in axisymmetric and spherical symmetric structures made of composite materials. The axisymmetric structure considered is periodic in both radial and axial directions and homogeneous in circumferential direction. The spherical symmetric structure is only periodic in radial direction. The dynamic thermo-mechanical coupling model is presented and the equivalent compact form is derived. Then, the cell problems, effective material coefficients and the homogenized thermo-mechanical coupling problem are obtained successively by the second-order asymptotic expansion of the temperature increment and displacement. The homogenized material obtained is manifested with the anisotropic property in the circumferential direction. The explicit expressions of the homogenized coefficients in the plane axisymmetric and spherical symmetric cases are given and both the derivation of the analytical solutions of the cell functions and the quasi-static thermoelasticity problems are discussed. Based on the SOTS method, the corresponding finite-element procedure is presented and the unconditionally stable implicit algorithm is established. Some numerical examples are solved and the mutual interaction between the temperature and displacement field is studied under the condition of structural vibration. The computational results demonstrate that the second-order asymptotic analysis finite-element algorithm is feasible and effective in simulating and predicting the dynamic thermo-mechanical behaviors of the composite materials with small periodic configurations in axisymmetric and spherical symmetric structures. This may provide a vital computational tool for analyzing composite material internal temperature distribution and structural deformation induced by the dynamic thermo-mechanical coupling response under strong aerothermodynamic environment. Second-order two-scale (SOTS) expansions for dynamic thermo-mechanical coupling problems in symmetric structure are obtained.SOTS finite element algorithm is proposed and unconditional stable implicit scheme is established.Anisotropic material is obtained by homogenization with enhanced strength and minor thermal expansion in circumferential direction.The mutual interaction and simultaneous vibration of the temperature and displacement field are simulated.A new computational tool is presented for analyzing thermo-mechanical response of composites under strong aerothermodynamic environment.

Numerical model for the cracking behavior of heterogeneous brittle solids subjected to thermal shock

• A thermo-mechanical coupling model is developed to study the cracking of heterogeneous brittle solids subjected to thermal shock. • The higher the initial temperature of the brittle solid, the larger the number of the initiated cracks is and the narrower the spacing between the cracks becomes. • The initiated cracks can be classified into different hierarchical levels according to their length. • The cracking pattern in the heterogeneous brittle solid depends on its thermal conductivity when quenching is applied. A finite element based numerical model is developed to simulate the thermal cracking behavior of brittle solids subjected to thermal shock. The heterogeneity of the brittle solids at mesoscopic level is taken into account using the Weibull distribution. Furthermore, the cracking behavior of meso-element is modeled using continuum damage mechanics. The finite element method (FEM) is used to obtain thermal stress distribution, and then damage threshold is determined by the maximum tensile stress criterion. In the present work, the cracking behavior, including the initiation and propagation of microcracks, and the formation of approximately equally spaced surface cracks, are well captured by the numerical model. Furthermore, the impact of thermal conductivity on the cracking pattern of the heterogeneous brittle solids is also discussed in this study. The numerical simulation results are found to be consistent with the experimental observations in the literature, which indicates that the proposed numerical model is a potentially powerful tool to study the cracking behavior of the heterogeneous brittle solids subjected to thermal shock.

Thermomechanical analysis of an elastoplastic rough body in sliding contact with flat surface and the effect of adjacent contact asperity

The study of the instantaneous frictional temperature, stress, and equivalent plastic strain generated when two surfaces are in frictional sliding process plays a significant role in understanding friction and wear mechanism. A thermomechanical coupling model between a rough body and a flat body is established. The model integrates the heat flux coupling between the sliding surfaces and considers the effects of the interaction among contact asperities and elastoplastic deformation of the rough body. The thermomechanical problem under this three-dimensional model is solved by the nonlinear finite element methods in ABAQUS software. The results show that the temperature, contact pressure, and stress are coupled. The results of the real contact area and the instantaneous frictional temperature, contact pressure, and VonMises equivalent stress on the local contact region fluctuate obviously due to the interaction among the adjacent contact asperities. The influence of asperity interaction is not constant but intermittent. Its time interval is related to the added interaction of a new adjacent contact asperity. The fluctuation of the VonMises equivalent stress makes the equivalent plastic strain of the frictional surface layer accumulate continually which might cause fatigue wear and plastic deformation wear of the material when the frictional rotating process was repeated.

Thermal Cycles and Residual Stresses in FSW of Aluminum Alloys: Experimental Measurements and Numerical Models

In the present work longitudinal residual stresses obtained by different methods, numerical and experimental, in Friction Stir Welding (FSW) process for AA7075 were analyzed. The experimental method employed for residual stresses measurements was sectioning, whereas the numerical is a finite element (FEM) thermomechanical coupled model which does not consider the stir in the material. The effect of travel speed during FSW was also analyzed, measuring with strain gages positioned in several points at different distances from weld centerline. From the obtained residual strains, the stress values, stress variation against weld centerline distance and null stress point were calculated. Numerical and experimental stress values agree in order of magnitude, being greater in numerical method inside stir zone's edge and even outside, and smaller at some point towards the end of plate. Stress variation against weld centerline distance and null stress position vary in different ways for each method. This phenomenon agrees with another works, and it could be related with no consideration of the stir process in the numerical method. Thus, it has been developed a simplified finite element model which averages in magnitude experimental residual stress in FSW.

Plane grind-hardening distortion analysis and the effect to grind-hardening layer

The high temperature and grinding force in grind hardening induce workpiece distortion that increases the magnitude of grinding to make the workpiece concave. The workpiece distortion also affects the grinding force, grinding heat flux, and grind-hardening depth distribution. The paper uses FE thermo-mechanical coupling model to simulate the thermal distortion in plane grind-hardening. Workpiece distortion, stress, and strain at different moments are calculated out and analyzed for different workpiece sizes. The calculated workpiece distortion is verified through the measured workpiece contour and the hardening layer distribution by experiment.

Coupled Thermomechanical Multiscale Modeling of Alumina Ceramics to Predict Thermally Induced Fractures Under Laser Heating

This study is concerned with thermally induced fractures and failure of high weight percentage alumina ceramics. A 3D coupled thermomechanical multiscale model has been developed to simulate thermally induced fractures. In laser heating of alumina ceramics, the temperature and stress distributions have been predominantly correlated with the interfacial glass phase within alumina microstructure. A coupled thermomechanical analysis with traction–separation law has been implemented in the finite element framework as a cohesive zone model (CZM). The alumina grains are modeled as thermomechanical continuum elements separated by CZM. A thermal and mechanical analysis has been conducted using Molecular Dynamics methods to obtain the thermal conductivities and parameterize traction–separation laws for the interface of alumina ceramics at different temperatures. The coupled thermal‐mechanical analysis achieved through a finite element model in Abaqus is compared with experimental results in laser‐heating tests. The model is successful in predicting temperature distributions and thermal fractures, which could help assist in selecting proper conditions in alumina applications and fabrication processes.

Effects of extrusion speeds on grains environment of magnesium by combined extrusion

In this paper, 3D computational models of extrusion-shear process of AZ31 magnesium alloy by compound extrusion die with different extrusion speeds have been studied. Simulations results are utilized to predict the evolutions of extrusion forces, temperatures and microstructures of magnesium alloy in rods. Coupled thermo-mechanical FEM model of extrusion process incorporating the material properties and simulation conditions (initial and boundary) have been applied. Theories of heat generation during extrusion have been discussed. A series of extrusion-shearing experiments and microstructure observations have been done to perform tests in order to validate the FEM simulation results with different ram speeds. The effects of ram speeds on the temperature distribution and extrusion environment have been researched. The temperature developed in extrusion increases with increase of ram speeds. Temperature rise is due to the fact that the strain rate is directly proportional to the ram speed, and the magnitude of the generated heat is proportional to the strain rate. Increasing the ram speed would produce a tendency to increase the extrusion forces. The strain rates caused by ES die increase with rise of ram speeds. The average grains size for magnesium alloy prepared by extrusion-shear decrease with the rise of ram speeds. The results of these simulations and experiments help to understand the mechanisms of extrusion-shear technology and assist in improving quality of wrought magnesium alloys.