Numerical simulation of a sheet metal extrusion process by using thermal-mechanical coupling EAS FEM

The thermal-mechanical coupling finite element method(FEM)was usedto simulate a non-isothermal sheet metal extrusion process. On thebasis of the finite plasticity consistent with multiplicativedecomposition of the deformation gradient, the enhanced as- sumedstrain(EAS)FEM was applied to carry out the numerical simulation. Inorder to make the computation reliable ad avoid hour- glass mode inthe EAS element under large compressive strains, an alterative formof the original enhanced deformation gradient was employed. Inaddition, reduced factors were used in the computation of the elementlocal internal parameters and the enhanced part of elementalstiffness.

ANALYSIS OF SHAKEDOWN OF FG BREE PLATE SUBJECTED TO COUPLED THERMAL-MECHANICAL LOADINGS

The static and kinematic shakedown of a functionally graded （FG） Bree plate is analyzed. The plate is subjected to coupled constant mechanical load and cyclically varying temperature. The material is assumed linearly elastic and nonlinear isotropic hardening with elastic modulus,yield strength and the thermal expansion coeffcient varying exponentially through the thickness of the plate. The boundaries between the shakedown area and the areas of elasticity,incremental collapse and reversed plasticity are determined,respectively. The shakedown of the counterpart made of homogeneous material with average material properties is also analyzed. The comparison between the results obtained in the two cases exhibits distinct qualitative and quantitative difference,indicating the importance of shakedown analysis for FG structures. Since FG structures are usually used in the cases where severe coupled cyclic thermal and mechanical loadings are applied,the approach developed and the results obtained are significant for the analysis and design of such kind of structures.

Analysis of thermal-mechanical coupled characteristics of vehicle twin-tube shock absorber

A comprehensive model that included mechanical dynamics of the shock absorber coupled with its thermal properties was proposed innovatively.Moreover a thermal-mechanical coupled model which reflected the closed-loop positive feedback system was established by using MATLAB/SIMULINK,and some curves of shock absorber temperature rising characteristic were obtained by simulation ＆computation under several operating modes and different parameters conditions.Research results show that：shock absorber design parameters,external excitations,and thermo-physical properties parameter,such as oil density have effect on the shock absorber temperature rising characteristic.However other thermo-physical properties parameters,such as oil specific heat,cylinder density,cylinder specific heat,and cylinder thermal conductivity,have no effect on it.The results may be used for studying reliability design of the shock absorber.

Thermal-Mechanical Coupled FE Analysis for Rotary Shaft Seals

The aim of this paper is to model the steady-state condition of a rotary shaft seal (RSS) system. For this, an iterative thermal-mechanical algorithm was developed based on incremental finite element analyzes. The behavior of the seal’s rubber material was taken into account by a large-strain viscoelastic, so called generalized Maxwell model, based on Dynamic Mechanical Thermal Analyses (DMTA) and tensile measurements. The pre-loaded garter spring was modelled with a bilinear material model and the shaft was assumed to be linear elastic. The density, coefficient of thermal expansion and the thermal conductance of the materials were taken into consideration during simulation. The friction between the rotary shaft seal and the shaft was simplified and modelled as a constant parameter. The iterative algorithm was evaluated at two different times, right after assembly and 1 h after assembly, so that rubber material’s stress relaxation effects are also incorporated. The results show good correlation with the literature data, which state that the permissible temperature for NBR70 (nitrile butadiene rubber) material contacting with ~80 mm shaft diameter, rotating at 2600/min is 100°C. The results show 107°C and 104°C for the two iterations. The effect of friction induced temperature, changes the width of the contact area between the seal and the shaft, and significantly reduces the contact pressure.

Topology Optimization of Geometrically Nonlinear Structures Under Thermal-Mechanical Coupling

A geometrically nonlinear topology optimization(GNTO)method with thermal–mechanical coupling is investigated.Firstly,the new expression of element coupling stress due to superimposed mechanical and thermal loading is obtained based on the geometrically nonlinear finite element analysis.The lightweight topology optimization(TO)model under stress constraints is established to satisfy the strength requirement.Secondly,the distortion energy theory is introduced to transform themodel into structural strain energy constraints in order to solve the implicit relationship between stress constraints and design variables.Thirdly,the sensitivity analysis of the optimization model is derived,and the model is solved by the method of moving asymptotes(MMA).Numerical examples show that temperature has a significant effect on the optimal configuration,and the TO method considering temperature load is closer to engineering design requirements.The proposed method can be extended to the GNTO design with multiple physical field coupling.

Thermal-mechanical coupled effect on fracture mechanism and plastic characteristics of sandstone

Scanning electronic microscopy (SEM) was employed to investigate fractographs of sandstone in mine roof strata under thermal-mechanical coupled effect. Based on the evolution of sandstone surface morphology in the failure process and frac- tography, the fracture mechanism was studied and classified under meso and mi- cro scales, respectively. The differences between fractographs under different tem- peratures were examined in detail. Under high temperature, fatigue fracture and plastic deformation occurred in the fracture surface. Therefore, the temperature was manifested by these phenomena to influence strongly on micro failure mechanism of sandstone. In addition, the failure mechanism would transit from brittle failure mechanism at low temperature to coupled brittle-ductile failure mechanism at high temperature. The variation of sandstone strength under differ- ent temperature can be attributed to the occurrence of plastic deformation, fatigue fracture, and microcracking. The fatigue striations in the fracture surfaces under high temperature may be interpreted as micro fold. And the coupled effect of tem- perature and tensile stress may be another formation mechanism of micro fold in geology.

An Innovative Finite Element Geometric Modeling of Single-Layer Multi-Bead WAAMed Part

Finite element (FE) coupled thermal-mechanical analysis is widely used to predict the deformation and residualstress of wire arc additive manufacturing (WAAM) parts. In this study, an innovative single-layermulti-bead profilegeometric modeling method through the isosceles trapezoid function is proposed to build the FE model of theWAAMprocess. Firstly, a straight-line model for overlapping beads based on the parabola function was establishedto calculate the optimal center distance. Then, the isosceles trapezoid-based profile was employed to replace theparabola profiles of the parabola-based overlapping model to establish an innovative isosceles trapezoid-basedmulti-bead overlapping geometric model. The rationality of the isosceles trapezoid-based overlapping model wasconfirmed by comparing the geometric deviation and the heat dissipation performance index of the two overlappingmodels. In addition, the FE-coupled thermal-mechanical analysis, as well as a comparative experiment of thesingle-layer eight-bead deposition process show that the simulation results of the above two models agree with theexperimental results. At the same time, the proposed isosceles trapezoid-based overlappingmodels are all straightlineprofiles, which can be divided into high-quality FE elements. It can improve the modeling efficiency andshorten the simulation calculation time. The innovative modeling method proposed in this study can provide anefficient and high-precision geometricmodelingmethod forWAAMpart FE coupled thermal-mechanical analysis.

Fluid-Thermal-Mechanical Coupled Analysis and Optimized Design of Printed Circuit Heat Exchanger with Airfoil Fins of S-CO_(2) Brayton Cycle

Printed Circuit Heat Exchanger(PCHE) with high-efficiency and compact structure has great application prospect in the supercritical carbon dioxide(S-CO_(2)) power systems for the next generation of high-temperature concentrated solar and advanced nuclear energy. However, the high operating temperature and pressure require PCHE to maintain good heat transfer performance, as well as reliable mechanical performance at the same time. It is necessary to carry out the fluid-thermal-mechanical coupled analysis of PCHE for the safe and efficient operation of the S-CO_(2) cycle. In this paper, a three-dimensional fluid-structure coupled numerical model was established to study the fluid-thermal-mechanical coupled characteristics of PCHE under different airfoil fin arrangements. The stress distribution of the single airfoil fin was studied, and a better airfoil arrangement that comprehensively considers heat transfer characteristics and stress distribution was obtained. Aiming at the high stress caused by the stress concentration at both ends of the airfoil fin, an optimized configuration combining straight channel and airfoil channel was proposed. The results show that the difference between the flow and heat transfer performance of the two optimized structures and the reference structure is only within 1.5%, but the maximum stresses of the two optimized structures are respectively reduced by 69.4% and 70.0% compared with that of the reference structure, which significantly reduces the stress intensity of PCHE. The result provides a new method to develop the airfoil PCHE with uniform stress distribution and good thermo-hydraulic performance.

Dynamic explicit FE modeling of hot ring rolling process

A new FE modeling method of hot ring rolling was presented by solving key technologies such as contact and heat boundary conditions,motion control over guide rolls,and mass scaling.The method has the following features:1)the elastic-plastic dynamic explicit approach instead of the static implicit approach is adopted to solve the process so as to greatly improve computational efficiency without sacrificing computational accuracy;2)the coupled thermal-mechanical effect is considered as opposed to the conventional isothermal assumption,which is more practical;3)in contrast to the simplified 2D or local 3D ring model,the full 3D ring is modeled to simulate the process.Based on the FE modeling method,two cases of hot plain ring rolling are simulated in the FEA software ABAQUS/Explicit.The simulation results are compared with the experimental measurements and the good agreement between them is observed regarding the material flow and the temperature distribution of the ring.

GURTIN-TYPE VARIATIONAL PRINCIPLES FOR DYNAMICS OF A NON-LOCAL THERMAL EQUILIBRIUM SATURATED POROUS MEDIUM

Based on the porous media theory and by taking into account the efects of the pore fuid viscidity, energy exchanges due to the additional thermal conduction and convection between solid and fuid phases, a mathematical model for the dynamic-thermo-hydro-mechanical coupling of a non-local thermal equilibrium fuid-saturated porous medium, in which the two constituents are assumed to be incompressible and immiscible, is established under the assumption of small de- formation of the solid phase, small velocity of the fuid phase and small temperature changes of the two constituents. The mathematical model of a local thermal equilibrium fuid-saturated porous medium can be obtained directly from the above one. Several Gurtin-type variational principles, especially Hu-Washizu type variational principles, for the initial boundary value problems of dy- namic and quasi-static responses are presented. It should be pointed out that these variational principles can be degenerated easily into the case of isothermal incompressible fuid-saturated elastic porous media, which have been discussed previously.

Microcrack-and microvoid-related impact damage and ignition responses for HMX-based polymer-bonded explosives at high temperature

Investigating the damage and ignition behaviors of polymer-bonded explosive(PBX) under a coupled impact and high-temperature loading condition is required for the safe use of charged PBXs. An improved combined microcrack and microvoid model(CMM) was developed for better describing the thermal effects of deformation, damage, and ignition responses of PBXs. The main features of the model under typical dynamic loadings(i.e. uniaxial tension and compression, and lateral confinement) at different initial temperature were first studied. And then the effects of temperature on impact-shear sensitivity of HMX-based PBXs were investigated. The results showed that the ignition threshold velocity of shear-crack hotspots exhibits an increase from 260 to 270 to 315-325 m/s when initial temperature increases from 301 to 348 K;and then the threshold velocity decreases to 290-300 m/s with the initial temperature continually increasing to 378 K. The predicted ignition threshold velocity level of the explosives under coupled impact and high temperature loading conditions were consistent with the experimental data.

FINITE ELEMENT ANALYSIS OF THERMOELASTIC BEHAVIOR OF PIEZOELECTRIC STRUCTURES UNDER FINITE DEFORMATION

It is noted that the behavior of most piezoelectric materials is temperaturedependent and such piezo-thermo-elastic coupling phenomenon has become even more pronounced in thecase of finite deformation. On the other hand, for the purpose of precise shape and vibrationcontrol of piezoelectric smart structures, their deformation under external excitation must beideally modeled. This demands a thorough study of the coupled piezo-thermo-elastic response underfinite deformation. In this study, the governing equations of piezoelectric structures areformulated through the theory of virtual displacement principle and a finite element method isdeveloped. It should be emphasized that in the finite element method the fully coupledpiezo-thermo-elastic behavior and the geometric non-linearity are considered. The method developedis then applied to simulate the dynamic and steady response of a clamped plate to heat flux actingon one side of the plate to mimic the behavior of a battery plate of satellite irradiated under thesun. The results obtained are compared against classical solutions, whereby the thermal conductivityis assumed to be independent of deformation. It is found that the full-coupled theory predicts lesstransient response of the temperature compared to the classic analysis. In the steady state limit,the predicted temperature distribution within the plate for small heat flux is almost the same forboth analyses. However, it is noted that increasing the heat flux will increase the deviationbetween the predictions of the temperature distribution by the full coupled theory and by theclassic analysis. It is concluded from the present study that, in order to precisely predict thedeformation of smart structures, the piezo-thermo-elastic coupling, geometric non-linearity and thedeformation dependent thermal conductivity should be taken into account.

Cu/WC功能梯度材料在热-机械耦合作用下的有限元分析

为了体现功能梯度材料的耐高温性,本文采用顺序耦合法,通过对Cu和WC组成的双材料和功能梯度材料在热-机耦合作用下进行了ANSYS有限元模拟,结果表明,功能梯度材料较双材料具有大大缓和热应力的作用,同时也证明了Cu/WC功能梯度材料较双材料更适合用作大电流滑动触头用耐磨材料。

Research Progress on Thermal Shock Behavior of Porous Ceramics

Thermal-mechanical coupling effect causes a large stress within porous ceramics at high temperatures,resulting in strength attenuation and product reliability decline.Thermal shock resistance is one of the key factors to characterize the reliability of ceramic materials under thermal-mechanical coupling effect.It is important to study the thermal shock resistance of the porous ceramics to evaluate their service performance and improve their service life.To better evaluate the effect of the thermal shock resistance on properties of the porous ceramics,the evaluation theories,experimental characterization methods and influencing factors about the thermal shock performance of the porous ceramics were reviewed in this paper,and some future research directions were prospected.

150 t钢水包扩容减重研究

针对某炼钢厂150 t精炼钢水包扩容到165 t后的初步设计超重问题,采用热机耦合有限元方法,考虑吊运、底部坐包和耳轴箱坐包3种工况,计算了初步设计钢包的温度场和热机耦合应力场。依据计算结果,进行了3轮减重优化分析。在每一轮分析中,根据耦合应力和温度分布分析结果,逐步优化钢包结构和尺寸。最终,使钢包外璧最高温度控制在340℃以下,最大耦合应力控制在265 MPa以下,耐火层最大耦合应力控制在20 MPa以下。通过选用高强度、抗热蠕变钢材制造钢包结构,使用减重优化设计降低钢包质量10.2 t,满足了不改造或更换吊运装置和钢水加盖机构的要求,现场运行良好。该研究为提高钢包扩容能力的相关技术水平提供了重要的依据。

Numerical analyses of coupled thermo-mechanical behaviors of cement sheath in geothermal wells

The stability of cement sheath under high temperature and high pressure is one of the most critical issues for the durability of geother-mal well systems.In this study,a two-dimensional plane-strain finite element code was developed to investigate the coupled thermo-mechanical behaviors of the casing-cement-formation system.Different from previous linear elastic analyses,a thermoelasto-plastic con-stitutive model based on the thermodynamic theory was adopted for the cement sheath.It is shown that the finite element simulations using the proposed model provide a more accurate and realistic prediction of stress–strain responses of the cement sheath under high temperature.The results demonstrate that the radial stress concentration and the tensile strain concentration occur at both the cement–casing interface and the cement–formation interface,where the cement sheath is most likely to fail.High strength and low stiff-ness in the cement sheath and the formation are preferred for the integrity of the system.Both large thermal cycles and large differences between the internal fluid pressure and the external pressure should be avoided during operation.The new code is an alternative tool for guiding the geothermal well design.The finite element framework described herein is universal for other thermo-mechanical applications,such as energy foundations and energy tunnels.

Multi-scale thermodynamic analysis method for 2D SiC/SiC composite turbine guide vanes

Ceramic Matrix Composite （CMC） turbine guide vanes possess multi-scale stress and strain with inhomogeneity at the microscopic scale. Given that the macroscopic distribution cannot reflect the microscopic stress fluctuation, the macroscopic method fails to meet the requirements of stress and strain analysis of CMC turbine guide vanes. Furthermore, the complete thermodynamic properties of 2D woven SiC/SiC-CMC cannot be obtained through experimentation, Accordingly, a method to calculate the thermodynamic properties of CMC and analyze multi-scale stress and strain of the turbine guide vanes should be established. In this study, the multi-scale thermodynamic analysis is investigated. The thermodynamic properties of Chemical Vapor Infiltration （CVI） pro- cessed SiC/SiC-CMC are predicted by a Representative Volume Element （RVE） model with porosity, leading to the result that the relative error between the calculated in-plane tensile modulus and the experimental value is 4.2%. The macroscopic response of a guide vane under given conditions is predicted. The relative error between the predicted strain on the trailing edge and the experimental value is 9.7%. The calculation of the stress distribution of micro-scale RVE shows that the maximum value of microscopic stress, which is located in the interlayer matrix, is more than 1.5 times that of macroscopic stress in the same direction and the microscopic stress distribution of the interlayer matrix is related to the pore distribution of the composite.

A thermo-viscoelastic model for particle-reinforced composites based on micromechanical modeling

Micromechanics-based constitutive models offer superior ability to estimate the effective mechanical properties for the composites,which greatly promote the computational efficiency in the multiscale analysis for composite structures.In this work,a thermo-viscoelastic model for particle-reinforced composites is proposed to estimate their thermal-mechanical coupling behaviors in terms of a micromechanics-based homogenization method in the time domain.The matrix and particles of the composites are modeled as“thermo-rheologically complex”viscoelastic materials.The temperature-dependent effective elastic strain energy ratios of particle to composite are proposed to evaluate the contributions of the matrix and particles.The thermo-viscoelastic model for the composites is then formulated by superposing the matrix and particle’s contributions.Finite element simulations based on the representative volume element models are employed to validate the constitutive model under various thermal-mechanical coupling loads.The effects of the loading rate,viscous parameter and particle content on the effective thermal-mechanical responses of the composites are also comprehensively discussed.The experimental data from literature are also employed to verify the constitutive model.The findings show that the proposed thermo-viscoelastic model can accurately predict the thermal-mechanical coupling behaviors for the particle-reinforced composites.

Dynamic thermo-mechanical behaviors of SME TiNi alloys subjected to shock loading

Dynamic thermo-mechanical coupling behaviors of shape memory TiNi alloy in the strain rate ranging from 300 s^−1 to 2000 s^−1 are investigated by the split Hopkinson pressure bar(SHPB)device with an infrared(IR)detection system.In stress–strain space,dynamic response shows a strong strain hardening property,however,in stress–temperature space,transformation path is particularly sensitive to the strain rate.The corresponding temperature evolution measured synchronously shows that local temperature increased associated with the forward phase transition,and it would keep the loading maximum value unchanged or decreased for unloading,depending on the strain rate.Besides,local temperature evolution was consistent with the transformation stress and its values at different points are the same.Temperature evolution and transformation deformation mechanism is then analyzed by a simple one-dimensional model.The results show that latent heat and dissipated energy are responsible for temperature variation.Furthermore,the temperature evolution with strain rate reveals that with the increase of strain rate,the phase transformation deformation mechanism undergoes a transformation from phase transition fronts propagation during lower strain rates to combination of local nucleation and front propagation during middle strain rate and to uniform nucleations during higher strain rates.The results are helpful for a passive shape memory alloy(SMA)micro-valve design.

Numerical Simulation of Dieless Drawing Process with Non-steady Processing Parameters

Since processing parameters have always been assumed to be stable in the current finite element numerical simulation of dieless drawing process, the simulation results for the product dimension tend to stabilize gradually. In fact, the dimension fluctuation exists in the forming process all the while. A mathematical model of Gauss distribution for processing parameters was employed and a finite element numerical model of dieless drawing process with non-steady processing parameters was established. Dieless drawing processing of Ni-Ti alloy wire was conducted for verifying the proposed model. The results indicated that the non-steady processing parameters model had higher simulation accuracy of the wire diameter than that given by the steady parameters model. Furthermore, the model could also be used to analyze the fluctuation characteristics in the whole dieless drawing process.