Thermal-mechanical Coupling Effect Research Articles

The chip generation and removal mechanisms of thermal-assisted polishing monocrystalline 4 H-SiC

The chip generation and removal characteristic of SiC in thermal-assisted nano-abrasion are investigated using molecular dynamics simulation. Varieties of minimum uncut chip thickness (MUCT) with different thermal-assisted conditions are inferred. Thermal-assisted extreme manufacturing is additional considered. The simulation results reveal that the atomic removal of 4 H-SiC substrates is easier with the thermal-mechanical coupling effect in nano-abrasion, however, not change significantly in compound thermal-assisted nano-abrasion. The removal efficiency witnesses a rise as the thickness of thermal affected region increases, while tends to be stable at a higher thickness. MUCT decreases with increasing the external temperature in coupling thermal-assisted processing, while keep stable in compound thermal-assisted processing. Chip generation and damage-free features of 4 H-SiC are observed in coupling thermal-assisted extreme manufacturing.

Investigation on damage-permeability model of dual-porosity coal under thermal-mechanical coupling effect

Understanding the permeability characteristics of coal under mining disturbance is crucial for ensuring coal mine safety and efficient gas extraction. Coal is a dual porosity medium consisting of matrix and fracture, and there are some differences in mechanics and permeability between matrix pores and fracture. However, research on the damage and gas seepage characteristics of dual-porosity coal is limited. In this paper, a coupled damage-permeability model considering matrix pores and fractures in coal is established, incorporating the influences of effective stress, gas adsorption, thermal expansion, and thermal cracking. And the reliability of the newly developed model was verified using experimental data of temperature and pressure variations under different stress boundary conditions. The results indicate that during the elastic stage, the total permeability and fracture permeability of coal exhibit a trend of decreasing and then increasing with pore pressure, while matrix permeability gradually increases. In the full stress-strain stage, the overall damage-permeability and fracture damage-permeability of coal exhibit an “S"-shaped variation trend with axial strain, while matrix damage-permeability shows a slow increasing trend. To accurately characterize the evolution of gas seepage in coal, contributions from matrix pores and fractures must be comprehensively considered, and the effects of gas adsorption, effective stress, thermal cracking, and thermal expansion on permeability cannot be ignored. Furthermore, through parameter sensitivity analysis, it is found that during the elastic stage, coal permeability decreases with an increase in the adsorption sensitivity coefficient and thermal expansion coefficient. In the full stress-strain process, coal permeability increases with an increase in the damage-permeability coefficient. The results of this study are of great significance for predicting the evolution of coal permeability in the working face ahead under mining disturbance.

Surface microstructural alterations and grain refinement mechanisms of tungsten heavy alloys by thermo-mechanical coupling: A laser-assisted milling case

Ultrafine-grained (UFG) tungsten heavy alloys possess potential applications in precision instruments and nuclear protection. In the present study, a comprehensive investigation of machined surface microstructural alterations and grain refinement mechanisms in laser-assisted milling (LAM) 95W-3.5Fe-1.5Ni alloy was demonstrated by recognizing its surface microstructures and mechanical properties under different combinations of the laser power and cutting depth. Graded microstructural characteristics along the surface degenerating layer and subsurface deformed layer of tungsten heavy alloy were identified for the first time, dramatically changing from workpiece bulk. Results showed that the adaptability between the thickness of the laser heat-affected layer and the depth of cut greatly influenced surface recrystallization layer microstructures regarding the thermal-mechanical coupling effect. An ordered, continuous, and equiaxed refined grains distribution layer was recognized when a particular machining condition was adopted, resulting in a substantial improvement of mechanical hardness. It could be indicated that a redundant heat-affected area would induce strain accumulation and promote recrystallization in LAM. Moreover, a dislocation density-based recrystallization model was applied to complement the experimental results considering the temporal transformation of grain refinement and recovery phenomena. Clarifying the above aspects is crucial to control the tungsten heavy alloys' surface microstructures and service performance during high-performance machining operations.

A new semi-analytic method for calculating the thermal–mechanical coupling stress intensity factor of interfacial crack

The interfacial crack thermal–mechanical coupling stress intensity factor (SIF) calculation plays an important role in anti-cracking design and safety assessment of compressed air energy storage (CAES) multi-layer cavern. In current SIF calculation method, there is no consideration of thermal–mechanical coupling effect caused by the difference between the singularity of stress field (λ) and temperature field (λT). In this study, a new semi-analytic method for calculating the thermal–mechanical coupling SIF of interfacial crack is established based on a new thermal–mechanical coupling Williams expansion for the cases of both insulated and constant temperature. The singularity index of temperature field at the crack-tip is dependent on the material parameters (heat conduction coefficient ki) for the crack perpendicular to and terminated at the interface, but independent on the material parameters (ki) for the crack located at the interface. The larger the difference of bi-material's heat conduction coefficient (ki), the larger the value of stress field when the crack is located on the side of larger Young's modulus (Ei) or on the side of lower ki. The semi-analytic method is degenerately verified by available literature results (without thermal–mechanical coupling term) and completely verified by finite element results (with thermal–mechanical coupling term), which can provide a theoretical basis for anti-cracking optimal design of CAES multi-layer caverns under thermal–mechanical loading condition.

Research on Multiscale Modeling and Experiment of CFRP Milling.

High-quality milling of carbon fiber reinforced polymer (CFRP) composites is of great importance for the high-performance manufacturing of structures made of this hard-to-machine material. In this paper, a multiscale finite element (FE) model, considering the thermal-mechanical coupling effect, was developed to simulate the milling process and reveal its material removal mechanism. The corresponding milling experiments were conducted to validate the simulated cutting forces and temperature, which were in good agreement with the experiment results. In the macroscale model, the Hashin failure criteria were used to estimate the failure of the composites. In the microscale model, the fibers, matrix, and the fiber-matrix interface were modeled separately, to investigate the mechanisms of material removal behavior during milling, among fiber breakage, matrix cracking, and fiber-matrix debonding. Based on the macroscale numerical and experimental results, the higher cutting speed was demonstrated to improve the surface quality of CFRP milling. According to the results from the microscale model, the material removal mechanism varies depending on the orientation of the fibers and can be divided into four stages. The outcome of this work provides guidelines to further investigate optimal manufacturing parameters for the milling of CFRP composites and their cutting mechanisms.

Deformation Characteristics of Mechanical Seal Face under Alternating Loads

Taking the mechanical seal of the submersible as the object, a transient coupled heat transfer model was established, and the deformation of the seal face under stable and alternating conditions was investigated by considering the thermal–mechanical coupling effect. The deformation characteristics of the seal face under two different alternative forms of amplitude and period were analyzed. The morphology and wear characteristics of the seal face were measured and discussed based on the pseudo-real test of the mechanical seal under alternating loads. The results showed that the seal face tended to be squeezed near the inner diameter and a tapered convergent gap appeared at the outer diameter of the seal face under alternating loads. The deformation of the seal face presented obvious alternating transient characteristics under alternating loads, and the deformation under alternating rotational speed was greater than that of alternating medium pressure. The deformation of the seal face increased with the amplitude of the alternating loads, while the period of the alternating loads had little influence on it. The wear mechanism of the seal face under alternating conditions was mainly abrasive wear, and the wear caused by alternating rotational speed is more significant.

Nonlinear unloading-reloading behavior and macro/micro models during multi-pass cyclic hot compression of aluminum alloys

Unloading-reloading behavior is of crucial importance in multi-pass forming of metal materials, the nonlinear of which creates challenges for the analysis of springback and residual stress of the precision manufacture components. Especially for the hot bulk-formed material at elevated temperature, the thermal-mechanical coupling effect makes the unloading-reloading process more complicated and thus more difficult to model and control, which remains to be solved. In this paper, the unloading-reloading behavior dependent on strain rate and deformation temperature and its model of hot compressive deformed aluminum alloys at elevated temperature were studied from the macroscopic and microscopic perspectives. The effect of deformation temperature, strain rate and strain on the unloading-reloading behavior of hot compressive deformed aluminum alloys were revealed, and corresponding micro-mechanism was elucidated and then discussed. Macroscopically, a strain-, strain rate- and temperature-dependent nonlinear macroscopic model describing unloading–reloading process was established, which can be used to describe the unloading stress relaxation and predict springback during multi-pass hot bulk forming. Microscopically, it is suggested that the relaxations of back stress and forest dislocation hardening stress collectively affect the unloading stress relaxation, due to the decrease of mobile and immobile (forest) dislocation density in unloading, while the dislocation-related behavior before yield, i.e. the dislocations’ bowing-out under pinning, affects the reloading behavior. Based on the micro-mechanism, a physically-based micro-model for describing unloading–reloading was constructed which further is used to clarify the physical mechanism of internal stress relaxation and inelastic strain recovery under multi-pass hot compression deformation. The comparison of the calculation results of the models with those of experiments indicated that the established unloading–reloading macroscopic and microscopic models are able to predict the stress–strain response upon the unloading–reloading loop of multi-pass cyclic hot compression deformation.

Impact of cooling rate on mechanical properties and failure mechanism of sandstone under thermal–mechanical coupling effect

High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction, space development, and energy utilization. One of the key issues is to understand the mechanical properties and failure mechanism of high-temperature rock disturbed by low-temperature airflow after excavation. Therefore, the experimental and numerical investigation were carried out to study the impact of cooling rate on mechanical properties and failure mechanism of high temperature sandstone. First, uniaxial compression experiments of high temperature sandstone at different real-time cooling rates were carried out to study the mechanical properties and failure modes. The experimental results indicate that the cooling rate has a significant effect on the mechanical properties and failure modes of sandstone. The peak strain, peak stress, and elastic modulus decrease with an increase in cooling rate, and the fragmentation degree after failure increases gradually. Moreover, the equivalent numerical model of heterogeneous sandstone was established using particle flow code (PFC) to reveal the failure mechanism. The results indicate that the sandstone is dominated by intragrain failure in the cooling stage, the number of microcracks is exponentially related to the cooling rate, and the higher the cooling rate, the more cracks are concentrated in the exterior region. Under axial loading, the tensile stress is mostly distributed along the radial direction, and the damage in the cooling stage is mostly due to the fracture of the radial bond. In addition, axial loading, temperature gradient and thermal stress mismatch between adjacent minerals are the main reasons for the damage of sandstone in the cooling stage. Moreover, the excessive temperature gradient in the exterior region of the sandstone is the main reason for the damage concentration in this region.

Breaking law of overlying strata in shallow coal seam fire area under thermal–mechanical coupling effect

AbstractThe cracks formed by the breaking and collapse of the overlying strata are the oxygen supply channels for the continuous combustion of coal fires. The development of cracks is of great significance for determining the scope of the fire area and controlling the fire efficiently and accurately. To study the development law of cracks, a breaking model of the overlying strata in the shallow coal seam fire area is established on the basis of beam theory considering the coupling effect of gravity load and temperature field. The physical model of the coal fire is established based on the similarity principle. The temperature data from rock strata in the model are monitored by the infrared thermal imager. The dynamic distribution function of the roof temperature field is obtained by fitting. According to the breaking model theory, the position of the maximum tensile stress on the roof of the shallow fire area is the middle of the lower surface. The theoretical calculation value of the first breaking distance of the roof is 0.575 m, which is consistent with the experimental results of the physical model. The maximum tensile stress of the roof under the thermal‐mechanical coupling is slightly less than that under the load only. For shallow coal seams, the thermal stress generated by the coal fire increases the first breaking distance of the roof.

Comprehensive study on fatigue degradation of road piezoelectric energy harvesters under thermal-mechanical coupling effect

Recent years have seen significant advancements in the field of road vibration energy harvesting using piezoelectric technology, including the watt-level road piezoelectric energy harvesters (RPEHs). However, research on the fatigue life of RPEH under thermal-mechanical coupling effect is lacking. In this study, six lead zirconate titanate (PZT) block piezoelectric transducers with distinct properties were fabricated, and five transducer structures were compared. The effects of piezoelectric material properties, pavement temperature, and transducer structure on RPEH fatigue degradation were investigated using approximately 23 million mechanical loads. The findings revealed that the output power of the soft PZT was significantly greater than that of the hard PZT under low-frequency cyclic loading. However, the Curie temperature decreased with an increasing piezoelectric constant of the soft PZT. Therefore, the stability of the output voltage worsened as the ambient temperature approached half the Curie temperature. Specifically, when the ambient temperature was 50 °C, the output failure phenomenon readily occurred during the initial stage of fatigue loading. By optimizing the transducer structure, the fatigue characteristics and high-temperature failure phenomenon of RPEH could be effectively improved. The coupling output modes of d 33 and d 31 were superior to that of the d 33 mode. Among these, the drum transducer exhibited the highest output performance and operational stability across different ambient temperatures, excitation frequencies, and displacements. After six million intermittent loads over 15 d (equivalent to two years of traffic load), the output power decreased from 6.51 to 6.02 mW with a degradation rate of merely 7.53%, indicating a promising application prospect. The results provide an crucial design foundation for the entire life cycle operation of RPEH in road engineering.

Heat Dissipation Behavior of a Low-Strength-Steel Welded Joint in Ultrasonic Fatigue

The coupled effects of heat and frequency in very-high-cycle fatigue are known under ultrasonic testing, while the heat dissipation behavior of welded joints is less investigated. In this work, the specimen surface temperature of a low-strength-steel welded joint and its base metal were monitored by infrared thermal imaging technique under ultrasonic fatigue loading. Results showed that the surface temperature distribution of both welded and base metal exhibited a parabola shape, and the temperature evolved with three stages. The location of the highest temperature within the weld metal correlated well with fatigue failure location. The inhomogeneity and asymmetry of temperature distribution implied a dominant role for heat transfer mode and insignificant influence of microstructure heterogeneity or specimen type. The nature of heat dissipation in low-strength steel in ultrasonic fatigue was thermal–mechanical coupling effect, which should be paid close attention in the standardization of ultrasonic fatigue testing.

Nanofabrication mechanism of [formula omitted]/20 features achieved by coupling field tip enhancement induced with nanosecond laser irradiating AFM probe tip

The nanofabrication mechanism of coupling field tip enhancement induced by laser-irradiated probe tip was investigated theoretically and experimentally. The coupling mechanisms and distribution characteristics of the enhanced electric, thermal, and stress fields were studied at wavelengths of 400–800 nm and tip-sample distances of 1–20 nm for 9 material combinations. The simulation results demonstrated that the electro-thermal coupling effect and thermal–mechanical coupling effect are the basic principles of this technique, independent of the materials. It was also demonstrated that probe damage due to mechanical scratching can be avoided through the estimation of probe displacement. The superposition of electromagnetic energy and thermal energy generates an extremely constrained total energy of up to 10–12 orders of magnitude near the tip end. The nano-line structures were processed at each tip-sample distance, and nanostructures with a feature size of approximately λ/20 were obtained. The experimental results and the total energy distribution demonstrated that the interaction of the coupling field tip enhancement with samples is in the form of total energy deposits on materials. The significance of this study will not only enable a refined understanding of the fundamental physics of surface nanostructuring but will also advance the scientific and industrial applications of the technology.

Surface deformation errors and self-adaptive compensation for microstructured surface generation of titanium alloys

In diamond servo cutting (DSC) of microstructured surfaces, the oscillated cutting motion inevitably cause non-uniform surface deformation errors. Although static and dynamic geometric errors for DSC have been studied, few studies focus on the prediction and compensation strategies of the surface deformation errors for microstructured surface generation. This study proposes an microstructured surface generation model of titanium alloys by considering the dynamic cutting forces, material microstructure evolution, thermal-mechanical coupling effect and subsurface stress-strain distribution. Harmonic microstructured surfaces are fabricated to characterize the non-uniform surface deformation errors as well as to validate the proposed model. The results show that the proposed model can accurately simulate the variation of surface plastic and elastic deformation errors as a function of undeformed chip thickness and cutting direction. Compared with the downslope cutting direction, the machined surface in upslope direction is subjected to greater plastic strain and plastic deformation errors even at the same depth of cut, due to cutting direction effect. To compensate surface deformation errors, a cooperative servo cutting (CSC) strategy is proposed by incorporating a self-adaptive fast tool servo into conventional servo cutting. The instantaneous compensation motion of CSC is jointly determined by the curvature radius deviation, instantaneous cutting depth and cutting direction. The experimental results show that CSC can make the error distribution more uniform, and greatly decrease the peak-to-valley surface deformation errors from 1.29 to 0.24 μm for different microstructured surfaces.

Complex unloading behavior of titanium alloy in cold and thermal-mechanical working

Unloading behavior is of crucial importance in metal forming, which particularly creates challenges for springback analysis and control of shape and dimensional accuracies of the manufactured components. For the working with hard-to-form materials at elevated temperatures, the thermal-mechanical coupling effect makes the unloading process more complicated and thus more difficult to model and control. Establishing an insight into the thermal-mechanical unloading behavior is crucial for ultimately improving the shape and dimensional accuracy of formed components. In this research, by using a near-alpha high-strength titanium alloy as a case study material, a series of continuous loading-unloading-reloading experiments within cold and warm forming domains were designed and conducted. Through the experiments, the complex unloading behavior, specially for the temperature-dependent degradation effect of elastic modulus and nonlinear stress-strain response, was investigated. A physically-based model was developed to reproduce the temperature-dependent nonlinear reduction effect of elastic modulus. In this model, the reversible mobile dislocation density is particularly included and represented to describe the evolving nonlinear elastic strain component upon unloading affected by both plastic strain and deformation temperature. Based on the model-based analysis, the mechanism accounting for the complex unloading nonlinearity in thermal-mechanical working was discussed and revealed from different evolutions of dislocation behaviors depending on plastic deformation and temperature.

Simulation and Analysis of the Thermal-Mechanical Response of an Energy Pile

Abstract An energy pile undertakes the functions of supporting the superstructure and controlling the indoor temperature of the building, and the thermal-mechanical coupling response of an energy pile makes its load transfer mechanism different from that of conventional engineering piles. Moreover, the thermal-mechanical coupling responses of the energy piles in summer and winter conditions are also different and need to be explored separately. Based on a ground source heat pump pile foundation workshop project in Kunshan city, Jiangsu Province, a multiphysics simulation study was carried out. The simulation results of the outlet water temperature and pile settlement are consistent with the real-world measurements, which verifies the reliability of the numerical simulation. The responses of the temperature distribution, axial stress, lateral shear stress, and settlement of the energy pile in summer and winter were analyzed, and the response laws of the energy pile in different seasons were obtained. Compared with the pure conventional load state, under the effect of thermal-mechanical coupling in winter conditions, the maximum compressive stress of the pile body is reduced by about 11.5%, but the settlement of the pile top increases by about 47.66%. Therefore, the winter conditions should be used as the design energy for the normal use of the pile. The control condition of the limit state: compared with the pure conventional load state, the maximum compressive stress of the pile increases by about 12% and the settlement of the pile top decreases by about 7.23% under the thermal-mechanical coupling effect of the summer condition. Therefore, the summer condition is the pile control conditions for the limit state of the body’s carrying capacity.

MXene/epoxy-based shape memory nanocomposites with highly stable thermal-mechanical coupling effect for constructing an effective information transmission medium

Information security is essential for any country, enterprise, and institution in the digital age. Shape memory polymers (SMP) and their composites provide attractive candidates for encrypted information transmission since they are an integral branch of intelligent materials. Herein, MXene/waterborne epoxy (WEP) shape memory nanocomposites were fabricated by a simple preparation process and employed as information transmission media. The results showed that the MXene/WEP nanocomposites noticeably improved mechanical properties, creep resistance, and thermal-mechanical coupling cycle stability while maintaining excellent shape memory properties compared to the pristine WEP which ensured nanocomposites’ stimulus-response signal are stable and reproducible. Furthermore, an information encryption transmission system was constructed by customizing the encoding correspondence among the information units, thermal-mechanical coupling stimulus conditions, and stimulus-response signals of the nanocomposites. Multiple security strategies to defend this system including information steganography, coded encryption, and the shape memory effect, which dramatically enhancing communication security. Finally, the application potential of the nanocomposites for encrypted transmission of text and image information were demonstrated. This work provides a new strategy for the application of SMP in information transmission and security.

Microstructure and Mechanical Properties of Aluminum Alloy/Stainless Steel Dissimilar Ring Joint Welded by Inertia Friction Welding

In recent years, studying the weldability of a dissimilar metal hybrid structure, with the potential to make full use of their unique benefits, has been a research hotspot. In this article, inertia friction welding was utilized to join Φ130 forged ring of 2219 aluminum alloy with 304 stainless steel. Optical observation (OM), electron back scattering diffraction (EBSD), and scanning electron microscopy (SEM) were utilized to examine the joint microstructure in depth. Depending on the research, a significant thermal–mechanical coupling effect occurs during welding, resulting in inadequate recrystallization on aluminum-side thermo-mechanically affected zone (TMAZ) and forming zonal features. The crystal orientation and grain size of each TMAZ region reflect distinct differences. On the joint faying surface, the growth of intermetallic compounds (IMCs) is inhibited by a fast cooling rate and metallurgical bonding characteristics were found depending on the discontinuous distribution of IMCs. The average joint tensile strength can reach 161.3 MPa achieving 92.2% of 2219-O; fracture occurs on aluminum-side base metal presenting ductile fracture characteristics.

Theoretical analysis for coupled thermal deformation behaviors of subassemblies in a single row in sodium-cooled fast reactors

Subassemblies in sodium-cooled fast reactor are different from pressurized water reactor in both geometry and assembly arrangement. In sodium-cooled fast reactor, assembly thermal deformation and narrow clearance between adjacent assemblies would cause them contact with each other, and reaction force between neighboring pads would occur. Under that circumstance, assembly deformation would be decided by both thermal load and mechanical load, which means significant coupling effect would lead to more complicated deformation behaviors. Therefore, so as to deeply study such thermal–mechanical coupling effect in reactor core, it is meaningful to conduct theoretical analysis and numerical simulation on such behaviors, which is indispensable for reactor safety analysis and structural design. In the present study, equilibrium equations and compatibility equations were conducted respectively for acquiring deformation parameters of assemblies in the row, which were already implemented into FADAC code and can perform calculation for row bowing. Furthermore, reaction forces and assembly deflections were analyzed in detail. Besides, sensitivity analysis were performed for row bowing calculation, in which wrapper tube thickness, distance across flat for wrapper tube, pad clearance and effects of core baffle were all taken into consideration. The present theoretical research for assembly deformation in SFR is essential for reactor safety and structural design, and will lay a solid foundation for assembly deformation analysis in the whole core.

Thermal network model and experimental validation for a motorized spindle including thermal–mechanical coupling effect

Thermal deformation caused by temperature rise affects the contact status of bearings in motorized spindles. In turn, the change in the contact status will affect the temperature rise and thermal deformation of the system. However, the latter has been rarely focused on in the previous literature. Therefore, a thermal network model of motorized spindle is enhanced by considering the thermal–mechanical coupling effect. Then, an iterative method is presented to solve the coupled equations, and a temperature test rig of the motorized spindle is set up to verify the proposed model. The predicted results by the proposed model are compared with the experimental results and the predicted results by the previous model. The relative error between the predicted and experimental results at two test points decreases by 9.56% and 3.44%, respectively, after considering the thermal–mechanical coupling effect. The temperature changes the contact angle and contact load of the bearings, thereby causing changes in frictional heat and temperature field. Such changes cause the difference between the proposed and previous models. The comparison with the experimental results shows that the proposed model with thermal–mechanical coupling effect can obtain a more accurate temperature field than the previous model.

Analysis on the removal mechanism of disc grinding based on dynamic thermal–mechanical coupling

Disc grinding is a commonly-utilized removal technology to generate the machining surface with higher precision. The material removal is caused by the force interaction between abrasives, which releases much heat during grinding. The dynamic thermal–mechanical coupling can be a crucial factor to influence the surface performance of the workpiece. However, previous studies on disc grinding are not enough for investigating the influence of the removal mechanism on the surface’s quality with dynamic thermal–mechanical coupling effect, which is caused by the double-side enclosed construction of grinding tool. To fill this gap, a novel coupled theoretical model is established based on effective abrasives dynamic removal. The moving trajectory of the discrete dynamic abrasives is deduced firstly. Meanwhile, the dynamic mechanical interaction is calculated by effective abrasives movements and height differences. Afterwards, the dynamic thermal relaxation is calculated by a finite difference method according to the effective abrasives moving trajectory and dynamic mechanical interactions, which is further validated by the finite element method. On account of the distribution of dynamic thermal–mechanical coupling, the uneven machining is found in disc grinding process. Furthermore, disc grinding experiments are performed to validate the analyzed regulations by the measurements of machining surface profile. The obtained findings are anticipated to be meaningful for improving disc grinding mechanism and optimization in wafer machining enterprises.