Thermomechanical Coupling Effects Research Articles

Numerical Simulation of Cutting Stress Deformation in Tungsten Carbide Turning Tools

With the aim of enhancing the precision and quality of turning processes, this study investigated cutting stress and thermal deformation induced by friction between the tool and chip of a Wolfram carbide (WC) tool cutting AISI-1045 carbon steel. Analysis of cutting stress and thermal deformation using COMSOL Multiphysics software is useful for evaluating the compensation for machining errors and reducing tool wear. Three cutting loads were adopted for the simulation of the thermal conduction, and changes in temperature and the stress field. Simulation results show that thermal deformation in the tool tip is proportional to cutting speed and time. As long as the temperature of the tool remains below the quasi-steady-state temperature, the amount of deformation does not change significantly. An understanding of the thermo-mechanical coupling effect during turning can help to improve the accuracy of compensation for thermal deformation in turning tools.

Effect of thermomechanical coupling on the scaling behavior of low-frequency hysteresis of PbZr0.52Ti0.48O3 ceramics

The dependence of the low-frequency hysteresis of Pb[Zr0.52Ti0.48]O3 ceramics upon coupled thermomechanical effect was experimentally examined based on the framework of power-law scaling. A new scaling relation was found to account for the observed hysteresis behavior under controlled temperature and mechanical compression while the strength and frequency of the electric field were kept constant. In the newly developed scaling relation, additional power functions of the stress are introduced and coupled with the electrical and thermal terms to describe the observed coupling effect. As a result, the difference in the hysteresis area between the stress-free state and the stressed state depends not only on the electromechanical coupling, but also on a newly introduced thermomechanical coupling term. This new scaling relation was confirmed by the experimental observations.

Non-classical dynamical equations of thick plateswith complete thermomechanical coupling

The dynamical governing equation of structures is the basis for solution of dynamics and control of distributed parameter systems. Until now, the refined dynamic equation of plates including the complete thermomechanical coupling has not been seen in the literature on structural dynamics. With the development of the modern aerospace technology, the refined dynamic equation of plates including the thermomechanical coupling effect is an urgent problem to be solved. But the traditional modeling method described in classical theory of plates and shells cannot be used to obtain the dynamic equation of thick plates under heating conditions because of the limitation of classical theory. In this paper, the coupled dynamical problem of plates with complete thermomechanical coupling is investigated based on the three-dimensional thermoelasticity and modern mathematics. The spectral composition method for modeling the structural dynamics is developed by combining the Vieta theorem of algebra with the classical method of operator spectra. In the time domain the refined dynamical equations of plates, which involve the bending and stretching vibrations under coupled thermomechanical conditions, are constructed by using the spectral decomposition of operators and proper gauge conditions to eliminate the non-uniqueness of unknown potential function without using the classical assumption in the theory of plates and shells. The dispersion relations from the refined equations of thermoelastic plates are presented graphically to test and verify the refined theory of thermoelastic plates. The space and time evolution of wave motion in heated plates and its dynamical stability are analyzed and discussed. We can see that the refined governing equations of thermoelastic plates are accurate, which would be used to solve the dynamics and control of thick plates with complete thermomechanical coupling, for instance, to investigate the coupling mechanism, coupled modes and dynamical response. And the modeling for the coupled dynamics of plates can be used in aerospace engineering for thermal protection system design.

Numerical study of thermo-mechanical coupling effects on crack tip fields of mixed-mode fracture in pseudoelastic shape memory alloys

The thermo-mechanical coupling effects on mixed-mode crack tip parameters in pseudoelastic shape memory alloys are studied by a finite element solution. Different loading rates are applied on the K-dominant part of the small scale transformation region. Both plane strain and plane stress analyses are carried out to study how the coupling between thermal and mechanical regimes alters the near tip fields in the martensitic region. The crack tip energy release rate and the J-integral remain history-dependent. The stress/strain response, the angular distributions of the stress and the released temperature, the shape of the transformation zone and the released temperature are selected as the crack tip fields of interest. Special attention is given to study of how the aforementioned crack tip fields are affected by the increase of applied loading rate. A comparison is also drawn between the crack tip fields in plane strain and plane stress states to complete the discussion.

Effect of solid body contact deformation on the real contact area under the thermo-mechanical coupling

To study the effect of solid body contact deformation on the real contact area, various models are established. These contact models include a contact model between an elastic rough solid and a rigid flat one (E-R model), an elasto-plastic rough solid and a rigid flat one (P-R model), an elasto-plastic rough solid and an elastic flat one (P-E model), an elasto-plastic rough solid and an elasto-plastic flat one (P-P model). The effects of thermo-mechanical coupling and the heat flux coupling are considered in the model which is solved by ABAQUS software. The results show that the real contact area is not only determined by the normal load, but also affected by the contact deformation mode of solid body. The real contact area from the purely elastic model (E-R model) is much smaller than that from the other elasto-plastic model. But the real contact area obtained from the P-R model is the largest. No matter what kind of the solid body contact deformation is, at the moment of the abrupt change of sliding speed and of the hot spotting coming into being, the real contact area increases noticeably, and then varies in a small range during the constant frictional sliding process.

Dynamic thermo-mechanical coupled simulation of statistically inhomogeneous materials by statistical second-order two-scale method

In this paper, a statistical second-order two-scale (SSOTS) method is developed to simulate the dynamic thermo-mechanical performances of the statistically inhomogeneous materials. For this kind of composite material, the random distribution characteristics of particles, including the shape, size, orientation, spatial location, and volume fractions, are all considered. Firstly, the representation for the microscopic configuration of the statistically inhomogeneous materials is described. Secondly, the SSOTS formulation for the dynamic thermo-mechanical coupled problem is proposed in a constructive way, including the cell problems, effective thermal and mechanical parameters, homogenized problems, and the SSOTS formulas of the temperatures, displacements, heat flux densities and stresses. And then the algorithm procedure corresponding to the SSOTS method is brought forward. The numerical results obtained by using the SSOTS algorithm are compared with those by classical methods. In addition, the thermo-mechanical coupling effect is studied by comparing the results of coupled case with those of uncoupled case. It demonstrates that the coupling effect on the temperatures, heat flux densities, displacements, and stresses is very distinct. The results show that the SSOTS method is valid to predict the dynamic thermo-mechanical coupled performances of statistically inhomogeneous materials.

Numerical analysis of crack tip fields in interface fracture of SMA/elastic bi-materials

The problem of an interface crack between a shape memory alloy and an elastic layer is numerically addressed. The shape memory alloy behavior is modeled with a continuum thermodynamics based constitutive model embedded within the finite element method. With the help of the boundary layer approach, and the assumption of small scale transformation zone, the K-dominated region in the tip of the interface crack is loaded under general mixed-mode condition. Both slow and fast loading rates are considered to study the effects of thermo-mechanical coupling on the interface crack tip fields, especially the crack tip energy release rate within a history-dependent J-integral framework, the stress/strain curve during the loading process, and the shape and size of the transformation zone and the heated zone. A special effort is made to investigate how changing the rate of applied loading, the mode-mixity, and the material properties of SMA and elastic layer modify the crack tip fields.

Prediction of cutting forces from an analytical model of oblique cutting, application to peripheral milling of Ti-6Al-4V alloy

In this work, a predictive machining theory, based on an analytical thermomechanical approach of oblique cutting (Moufki et al., Int J Mech Sci 42:1205–1232, 2000; Moufki et al., Int J Mach Tools Manuf 44:971–989, 2004), is applied to the peripheral milling process. The material characteristics such as strain rate sensitivity, strain hardening and thermal softening are considered. In the primary shear zone, thermomechanical coupling and inertia effects are accounted for. Due to the fact that the reference frame associated to the primary shear zone moves with the tool rotation, an analysis of the inertial effects has been performed. As the heat conductivity of Ti-6Al-4V is low, the thermomechanical process of chip formation is supposed to be adiabatic; thus, the problem equations are reduced to a system of two non-linear equations which are solved numerically by combining the Newton–Raphson method and Gaussian quadrature. The present analytical approach leads to a three-dimensional cutting force model for end milling operations. Calculated and experimental results extracted from the literature are compared for several operations: full immersion, up-milling and down-milling and for different cutting conditions. Although the present model was established for stationary conditions and for continuous chips, it gives acceptable predictions for machining titanium alloy for which the chips are usually segmented. The proposed model appears as an interesting alternative to the mechanistic approach which requires many experimental tests to determine the milling cutting force coefficients.

Thermomechanical properties of polyurethane shape memory polymer–experiment and modelling

In this paper extensive research on the polyurethane shape memory polymer (PU-SMP) is reported, including its structure analysis, our experimental investigation of its thermomechanical properties and its modelling. The influence of the effects of thermomechanical couplings on the SMP behaviour during tension at room temperature is studied using a fast and sensitive infrared camera. It is shown that the thermomechanical behaviour of the SMP significantly depends on the strain rate: at a higher strain rate higher stress and temperature values are obtained. This indicates that an increase of the strain rate leads to activation of different deformation mechanisms at the micro-scale, along with reorientation and alignment of the molecular chains. Furthermore, influence of temperature on the SMP’s mechanical behaviour is studied. It is observed during the loading in a thermal chamber that at the temperature 20 °C below the glass transition temperature (Tg) the PU-SMP strengthens about six times compared to the material above Tg but does not exhibit the shape recovery. A finite-strain constitutive model is formulated, where the SMP is described as a two-phase material composed of a hyperelastic rubbery phase and elastic-viscoplastic glassy phase. The volume content of phases is governed by the current temperature. Finally, model predictions are compared with the experimental results.

Thermoelastic interaction in a viscoelastic functionally graded half-space under three-phase-lag model

This paper aims at studying the thermo-viscoelastic interaction in a functionally graded, infinite, Kelvin–Voigt-type viscoelastic, thermally conducting medium due to the presence of periodically varying heat sources. Three-phase-lag thermoelastic model, Green–Naghdi model II (i.e. the model which predicts thermoelasticity without energy dissipation) and Green–Naghdi model III (i.e. the model which predicts thermoelasticity with energy dissipation) are employed to study thermomechanical coupling, thermal and mechanical relaxation effects. In the absence of mechanical relaxations (viscous effect), the results for various generalised theories of thermoelasticity may be obtained as particular cases. The governing equations are expressed in Laplace–Fourier double transform domain and are solved in that domain. The inversion of the Fourier transform is carried out using residual calculus, where the poles of the integrand are obtained numerically in the complex domain by using Laguerre’s method and the inversio...

Transverse Vibrations in Thermoelastic-Diffusive Thin Micro-Beam Resonators

This article deals with the transverse vibrations in a homogeneous isotropic, thermoelastic-diffusive thin beam based on the Euler–Bernoulli theory under clamped–clamped boundary conditions. The analytical expressions for deflection, thermal moment, mass moment, frequency shift, and damping due to thermoelastic-diffusion in the beam has been derived. The effects of mass diffusion, thermomechanical coupling, surface conditions, and beam dimensions on energy dissipation and other field quantities induced by thermoelastic-diffusion have been investigated. The analytical results have been numerically analyzed with the help of MATLAB software. The numerically computed results for deflection, temperature change, thermal moment, mass moment, damping factor, and frequency shift have been presented graphically. The computed values of effective flexural rigidity have been given in tabular form. The study may find applications in medical science, engineering, accelerometers, sensors, resonators, etc.

Investigate on distribution and scatter of surface residual stress in ultra-high speed grinding

The purpose of this study is to investigate the residual stress induced by ultra-high-speed grinding of difficult-to-machine materials considering the thermomechanical coupling effect that is generated due to the friction between diamond tool and workpiece’s surface. A three-dimensional finite element method taking the rotational motion of tool into account is proposed. The simulation consists of three operations including loading, unloading, and cooling. The influences of different grinding conditions (grinding speed and grinding depth) on the residual stress field are analyzed. Results show that the main grinding force comes from normal rather than tangential direction due to the tool’s negative rake angle and their ratio is in the range of 1.2 to 1.7. The residual stress state on the finished surface is either tensile or compressive depending on various grinding condition; even both states may exist simultaneously. Further study shows that the ultra-high speed grinding can obtain lower surface residual tensile stress comparing with the high-speed grinding. Besides, a larger grinding depth is not advantage for obtaining a better machined quality in subsurface layer as the tensile maximum principal stress is also larger. Finally, the effects of different grinding conditions on residual stress scatters are analyzed utilizing mathematical statistic method. Results show that both smaller grinding depth and higher grinding speed are beneficial to achieve a better consistency of residual stress.

Thermomechanical coupling effect of graphite electrodes upon the electric arc furnace dynamics

Prediction of the dynamic behavior of electrodes of the electric arc furnace (EAF) fed by AC current is rather difficult because of several phenomena superposed, particularly during the first step of the melting process, i.e. the so-called perforation, and in case of the melting of scrap. Unexpected ruptures of electrodes are often observed as a consequence of vibration. Dynamic excitation is applied by the vertical position control of the mast supporting the electrodes and by the Lorentz’s forces generated by the magnetic flux provided by each electric phase. Moreover, the irregular distribution of stiffness along the electrode, being due to the sensitivity of the material properties upon temperature, affects quite a lot the dynamic response of this structure. To identify the origin of the observed ruptures and to suitably predict the dynamic behavior of the whole system a modeling activity was performed. A numerical model of the EAF structures was built, by resorting to an integrated approach based on the finite element method and on the multi body dynamics, then it was preliminarily validated on an existing plant. It was demonstrated that stiffening effect upon the graphite electrode induced by the temperature distribution makes dangerous the action of the vertical position control, when it is applied too fast and excites the flexural modes of the electrode. Numerical model allowed refining the design of the electrode and improving the safety factor as well as finding some design requirement to suitably limit the operation of the position control system.

Control rules of surface integrity and formation of metamorphic layer in high-speed milling of 7055 aluminum alloy

Orthogonal experiments were conducted to investigate the effects of parameters on surface integrity in milling 7055 aluminum alloy. In order to correlate metamorphic layer with thermal and mechanical phenomena developed during milling, milling force and temperature fields of machined surface were obtained with finite element method, while milling speed and feed per tooth were paid particular attention to study formation of metamorphic layer. Experiment results show that when milling speed, feed per tooth, milling depth, and milling width are 1100 m/min, 0.02 mm/z, 0.7 mm, and 6 mm, respectively, obtained surface roughness, surface residual stress in X direction, surface residual stress in Y direction, and surface micro-hardness are Ra 0.258 µm, −123 MPa, −137 MPa, and 193.76 HV0.025, respectively. From precision machining to rough machining, depth of compressive residual stress layer increases from 35 to 45 µm, and the depth of plastic deformation layer increases from 5 to 20 µm. Finally, the formation of metamorphic layer can be explained by thermo-mechanical coupling effects.

Analysis of real contact area between an elasto-plastic rough body and an elasto-plastic flat body

A three-dimensional model of an elasto-plastic rough surface featured by fractal geometry sliding over an elasto-plastic flat body is developed. The three-dimensional model considers the thermo-mechanical coupling and the heat flux coupling between the sliding surfaces. To obtain the transient real contact area, the problem under this three-dimensional model is solved by the finite element method. The results show that the real contact area is a small fraction of the nominal contact area during the loading and sliding process, and increases with the increase in the applied normal load. In the initial stage of friction sliding, the real contact area increases and fluctuates noticeably for the abrupt change of sliding speed, and then varies in a small range under the constant normal load and sliding velocity. It is also shown that frictional heating increases the real contact area, the instantaneous maximum contact pressure by comparing the results with those obtained from the same model, however, in which the thermal effect of frictional heat is not considered. That is to say, the real contact area is larger when the thermo-mechanical coupling is considered. It is crucial to take the thermo-mechanical coupling effect into account especially for the micro frictional sliding analysis.

Mechanical and Infrared Thermography Analysis of Shape Memory Polyurethane

Multifunctional new material—polyurethane shape memory polymer (PU-SMP)—was subjected to tension carried out at room temperature at various strain rates. The influence of effects of thermomechanical couplings on the SMP mechanical properties was studied, based on the sample temperature changes, measured by a fast and sensitive infrared camera. It was found that the polymer deformation process strongly depends on the strain rate applied. The initial reversible strain is accompanied by a small drop in temperature, called thermoelastic effect. Its maximal value is related to the SMP yield point and increases upon increase of the strain rate. At higher strains, the stress and temperature significantly increase, caused by reorientation of the polymer molecular chains, followed by the stress drop and its subsequent increase accompanying the sample rupture. The higher strain rate, the higher stress, and temperature changes were obtained, since the deformation process was more dynamic and has occurred in almost adiabatic conditions. The constitutive model of SMP valid in finite strain regime was developed. In the proposed approach, SMP is described as a two-phase material composed of hyperelastic rubbery phase and elastic-viscoplastic glassy phase, while the volume content of phases is specified by the current temperature.

Thermoviscoelastic shape memory behavior for epoxy-shape memory polymer

There are various applications for shape memory polymer (SMP) in the smart materials and structures field due to its large recoverable strain and controllable driving method. The mechanical shape memory deformation mechanism is so obscure that many samples and test schemes have to be tried in order to verify a final design proposal for a smart structure system. This paper proposes a simple and very useful method to unambiguously analyze the thermoviscoelastic shape memory behavior of SMP smart structures. First, experiments under different temperature and loading conditions are performed to characterize the large deformation and thermoviscoelastic behavior of epoxy-SMP. Then, a rheological constitutive model, which is composed of a revised standard linear solid (SLS) element and a thermal expansion element, is proposed for epoxy-SMP. The thermomechanical coupling effect and nonlinear viscous flowing rules are considered in the model. Then, the model is used to predict the measured rubbery and time-dependent response of the material, and different thermomechanical loading histories are adopted to verify the shape memory behavior of the model. The results of the calculation agree with experiments satisfactorily. The proposed shape memory model is practical for the design of SMP smart structures.

Development of Stress-Induced Martensitic Transformation in TiNi Shape Memory Alloy

TiNi shape memory alloy (SMA) was subjected to tension at strain-controlled test on quasistatic testing machine. The nucleation, development, and saturation of the stress-induced martensitic transformation were investigated, taking into account the obtained dependency of mechanical parameters and the specimen temperature changes measured by an infrared camera (IR). Three kinds of data obtained by the IR system were analyzed: the temperature distribution on the SMA sample surface, the temperature changes derived as average from the chosen sample area, and the temperature profiles obtained along the sample length. The temperature distribution shows nucleation of the transformation process and a creation of the transformation bands. The average temperature reflects the effects of thermomechanical coupling, accompanying exothermic martensitic forward and endothermic reverse transformation. The temperature profiles revealed the temperature difference between the band and the rest of the sample. The experimental results were supported with finite element method numerical analysis (FEM). The FEM software components for structural and heat transfer problems, coupled in partitioned approach, were used for thermomechanical analysis.

Thermomechanical Investigation of TiNi Shape Memory Alloy and PU Shape Memory Polymer Subjected to Cyclic Loading

In applications to sensors, actuators, guide wires, special grips for handicapped people, a shape memory alloy (SMA) or shape memory polymer (SMP) are used as working elements that perform cyclic motions. In order to evaluate the reliability of the shape memory materials (SMM), cycling and fatigue deformation properties are investigated. Since the SMM are very sensitive to temperature, not only mechanical properties but also their related temperature changes accompanying the deformation process should be taken into account. The presented paper embraces experimental investigation of effects of thermomechanical couplings occurring in shape memory alloy and shape memory polymer subjected to various kinds of cycling loading. The deformation was carried out on MTS 858 Testing machine. The strain was measured by a mechanical extensometer, so the stress-strain characteristics were elaborated with high accuracy. Furthermore, a fast and sensitive FLIR Co Phoenix infrared (IR) measurement system was used in order to record infrared radiation from the sample surface. It enables obtaining temperature distribution of the sample as a function of the deformation parameters. For each strain cycle, an increase in temperature during the loading and the temperature decrease during the unloading processes was observed. It was found that the temperature increment recorded during the cyclic deformation depends on the strain rate, the kind of the material and the test conditions. The higher the strain rate the higher the stress and temperature changes were obtained, since the deformation process was more dynamic and has occurred in almost adiabatic conditions. It was shown that various deformation mechanisms are active during various loading stages.

Researches on the Mechanism of Thermo-Mechanical Coupling and Boundary Effects in Thick Wall Cylinders

The automatic weapons suffered the coupling load of in-bore pressure and temperature load during firing, which exerted a serious influence on the gun barrel life. Suppose the gun barrel was thick wall cylinders, the relations among the radial stress, tangential stress, longitudinal stress and equivalent stress in thick wall cylinders enduring interior pressure and temperature loads were analyzed by traditional analytic method, 2D finite element method (FEM) and 3D FEM respectively. Boundary effects of the stress field in thick wall cylinders were also analyzed. The obtained results showed that 3D FEM is suitable for the analysis on boundary effects, and the coupling stress could be designed and optimized by adjusting the interior pressure or temperature loads.