Thermo-mechanical Coupling Model Research Articles

Numerical investigation of deformation and residual stress in vacuum brazing of titanium alloy plate-fin structure

Various high-end equipment relies on titanium alloy plate-fin structure (PFS) as core components, owing to their remarkable advantages in terms of low density, superior mechanical strength and enhanced corrosion resistance. Brazing assumes a pivotal function in PFS connections, whereby the localized concentrated heat during the welding procedure can precipitate intricate structural deformation and generate residual stresses. A thermo-mechanical coupling model was developed, taking into account the service performance criteria of PFS. The effects of process parameters and clamping methods on the post-welding residual stress and deformation of PFS were investigated. The analytical expressions for the relationship between the process parameters and the stress/deformation were obtained by using the simulation outcomes. The constraint on the partition in the vacuum brazing process determines the extent of deformation and residual stress of PFS, with higher constraint leading to lower values. PFS generates z-directional displacement and y-directional warping deformation, and the weld seam between the fin and the partition is prone to stress concentration. As the brazing temperature and holding time increase, the PFS induces more deformation, while the residual stress value decreases. However, the deformation amount reaches a plateau when the holding time exceeds 30 min.

Study on thermo-mechanical coupling model in pantograph-catenary system of rail vehicle

Study on thermo-mechanical coupling model in pantograph-catenary system of rail vehicle

Fire resistance behavior and failure analysis of transmission tower exposed to wildfires

This paper deals with the fire resistance behavior and failure mode of transmission towers exposed to wildfires. A nonlinear thermo-mechanical coupling model of a latticed transmission tower was established by the finite element (FE) program ANSYS, which was validated from steel members’ perspectives. Wildfire analysis was conducted to determine the key parameters, including the number of legs in fire, fire intensity, and residence time, and the temperature–time curve was further proposed for parametric analysis. It reveals that the transmission tower may collapse under serviceability state loads in the wildfire, and the final failure mode was determined by the number of tower legs in the wildfire. A higher wildfire intensity will significantly reduce the wildfire resistance time of the transmission tower. Therefore, combustible materials around transmission towers need to be regularly cleaned to reduce the intensity and residence time of wildfires, which is an effective way to prevent wildfires. Moreover, a wildfire protection layer design process was proposed based on the environment surrounding the transmission tower, which proved reliable to provide valuable insights for the fire protection design of transmission towers in areas prone to wildfires.

Peridynamics thermomechanical coupling simulation of damage in engineered cementitious composite-concrete bonding specimens under high temperature

The current application of Peridynamics (PD) models in addressing thermally induced failures within Engineered Cementitious Composites (ECC) and concrete bonding specimens is relatively limited. This study introduces a novel semi-discrete PD model for ECC and a random heterogeneous PD model for concrete. These models are grounded in the microscopic constitutive relationships between ECC and concrete materials and incorporate the strain softening behavior of cement-based materials. The effectiveness of the interface model is evaluated through splitting tensile tests on ECC-concrete bonding specimens, employing a series model alongside PD surface effects for material interface correction. Considering the performance degradation of materials at elevated temperatures, a PD thermo-mechanical coupling model, which integrates PD thermal diffusion and motion equations, is proposed to analyze the failure of ECC and concrete under high thermal loads. The validity of both the thermo-mechanical coupling and concrete heterogeneity models is confirmed via thermal cracking tests on heated concrete columns subjected to drilling. Lastly, considering the dynamic response of fire, the Navier-Stokes equation are reformulated into a non-local form utilizing the Peridynamic differential operator (PDDO) to simulate fire environment. A thermo-fluid-mechanical coupling model is developed, and applied to analyze ECC and concrete bonding specimens’ failure behaviors under fire scenarios.

Thermal spalling failure mechanism of heterogeneous granite under moving heat source

The conventional mechanical methods employed for rock breaking encounter substantial challenges in deep, hard formation drilling, characterized by low penetration rates and exorbitant drilling costs. Consequently, there exists an urgent necessity to explore novel drilling methods and technologies. Thermal spallation drilling, as a non-contact rock breaking technique, offers high efficiency in rock fragmentation and substantially reduces drilling costs. However, the mechanism underlying rock fragmentation induced by thermal spallation remains unclear. Therefore, this study establishes a thermo-mechanical coupling model based on heterogeneous granite subjected to a high-temperature moving heat source. The model comprehensively considers the geometric shape, contact, and strength heterogeneity of rock minerals, and analyzes the effects of heating source speed, radius, mineral composition, heterogeneity index, and grain size on the thermal spallation mechanism of rock. The research findings indicate that lower heating source speeds and larger radii result in higher surface temperatures and greater damage volumes, whereas increasing speed and reducing radius enhance fragmentation efficiency, with speed exerting a more significant influence. Thermal spallation primarily results in tensile damage to rocks, with the surface damage and depth of damage being respectively influenced by the heating source speed and radius. Particle size exhibits minimal impact on thermal spallation, while increased quartz content enhances the rock's thermal properties, resulting in significant thermal spallation effects. Additionally, the location of rock damage is closely correlated with thermal parameters. These findings significantly contribute to a better understanding of the thermal spallation fracture mechanism in granite and facilitate the development of technical solutions for thermal spallation drilling methods.

Thermo-mechanical Stability Analysis of Hollow Cellular Concrete Block Air Convection Embankments for Cold Regions

Crushed-rock air convection embankment (ACE), as a highly open-graded porous medium, has been used to mitigate the thaw settlement of pavement structures in permafrost regions. Previous studies have revealed that cellular concrete has significant potential as a cost-effective material for ACE to solve the problem of crushed rock shortage in interior Alaska and improved the thermal stability of pavement structures in cold climates. The design configurations of the hollow cellular concrete block ACE were further designed to maximize the performance benefits and facilitate future implementation and field construction. However, the mechanical behaviors of the proposed structures and ice-rich subgrade were still unknown. In this study, a thermo-mechanical coupling model was developed to evaluate the thermal effect on the long-term mechanical stability of the selected pavement structures and subgrade soils. The results indicated that the thermal stability of the proposed hollow cellular concrete block ACEs was superior to that of the conventional crushed-rock ACE. The maximum thaw settlement of the proposed hollow cellular concrete block ACE was only 13.4% that of the conventional crushed-rock ACE. Thermal and mechanical analyses showed that the proposed cellular concrete ACEs have a significant advantage over conventional crushed-rock ACE.

Failure analysis and pin hole profile optimization design of combined piston for marine diesel engine based on Kriging model and NSGA-Ⅱ algorithm

Amidst the drive for enhanced performance and reliability in marine diesel engines, anti-fatigue design has emerged as a pivotal factor in ensuring safe operation. To investigate the cracking of a steel-topped aluminum-skirted combined piston in a marine diesel engine, thorough analyses were conducted on mechanical properties, chemical composition, and microscopic morphology. Subsequently, a piston thermo-mechanical coupling (TMC) model was established to simulate stress distribution and fatigue strength. Findings revealed that loose defects in the material and deformation mismatch in the pin hole bearing TMC were the primary factors contributing to cracking. Based on this, a multi-objective optimization (MOO) design method for piston pin hole profiles was proposed. Optimal pin hole profile design parameters were determined using the Kriging surrogate model and the second generation non-dominated sorting genetic algorithm (NSGA-II), and the nonlinear relationship between the design variables and the response objectives was obtained. Post-optimization, stress in the piston cracking source region decreased by 40.6%, peak contact pressure and stress in the pin hole decreased by 59.2% and 49.1%, respectively. Furthermore, the minimum fatigue safety coefficient improved from 0.86 to 1.18.

A multiscale thermo-mechanical coupling model for Fiber-Reinforced Cementitious Composite (FRCC)

This paper aims to develop a multiscale thermo-mechanical coupling model across from meso-scale to macro-scale to study the tensile thermos-mechanical behavior of fiber-reinforced cementitious composite (FRCC) on the base of thermodynamics. In meso-scale, the coupling process of thermal effect and the development law of a single crack were creatively presented and formulated in energy potential function. The effects of fiber dispersion on cracking behavior and crack strength of matrix were determined. In macro-scale, the multiple-fine-cracks and strain-hardening/softening behavior under tension were defined and studied. The bridging action stress of fibers is calculated by considering the bonding stress in the interface transition zone (ITZ). The model can be upgraded for FRCC materials ranges from strain-hardening cementitious composite (SHCC) and engineered cementitious composite (ECC). The numerical calculations of the proposed model were conducted based on the Fortran program for validation. The residual tensile strength, multiple-fine-cracks and strain-hardening/softening behaviors of FRCC were predicted. The behaviors of FRCC with different fiber types were accurately captured in a range of temperature from 20°C to 600°C through the comparative study with six groups test results in literatures. A sensibility study was carried out to analyze the impact of modelling parameters and thermal effect on the strain-hardening/softening behaviors of FRCC.

Finite element (FE) analysis of thermal stress in production process of multi-layer lining ladle

This paper presented the development of the thermo-mechanical coupling model and simulation analysis of a composite refractory layer ladle. The thermomechanical modeling of the ladle was carried out using the Finite Element Method (FEM), taking into account the joints between the slag line bricks as well as the contact between the composite refractory layers. The temperature and thermal stress characteristics of the overall ladle structure under different transit conditions were investigated using the finite element analysis software ANSYS. We also performed a comparative analysis on the improvement effect of thermal stresses by expansion joints of different sizes. The simulation results were validated with previous studies. The results showed that the installation of expansion joints within a suitable range did not significantly change the thermal expansion characteristics of the refractory lining, but it also reduced the thermal stress level of the lining to a large extent. A larger temperature gradient produced higher thermal stresses, and in the direction of the ladle height, the more downward the position of its maximum compressive stress was greater. Under different working conditions, compared with the axial and hoop stress, the radial stress was small in magnitude. Axial stress exhibited a greater degree of sensitivity to pressure variations than hoop stress. The developed thermodynamic model considering the full contact between the bricks and the refractory layer gave us a more complete view of the physical field laws inside the ladle.

Fractional derivative modelling for consolidation of multilayered saturated soils with interfacial thermal contact resistance subjected to time-dependent heating and loading

In this paper, the one-dimensional rheological consolidation characteristics of multilayered saturated soil foundations under time-dependent loading and heating are investigated by considering the semi-permeability and the interface thermal resistance. By introducing the fractional derivative model and the thermos-elastic theory, a thermo-mechanical coupling model is established to describe the rheological properties of saturated soils. Semi-analytical solutions for strain, temperature increment, pore water pressure and settlement were derived through the Laplace transform and its inverse. The accuracy of the solutions proposed in this paper has been verified by comparing with existing solutions. The effects of different thermal contact models of the interface on the rheological properties of saturated soils under semi-permeable boundary are discussed, and the effects of fractional derivative order, constitutive material parameters, and thermal conductivity of soil on the thermal consolidation process are investigated. The results show that: neglecting the thermal resistance effect can result in an overestimates of the impact of rheological properties on the thermal consolidation process of saturated soils under semi-permeable boundaries; As the thermal resistance coefficient increases, the influence of soil thermal conductivity on settlement decreases.

An implicit thermo-mechanical coupling model for heat conduction and thermal cracking in brittle materials

In this paper, an implicit thermo-mechanical coupling model is developed to simulate heat conduction and thermal cracking in brittle materials. In the thermal analysis, an implicit particle heat conduction model (PHCM) is proposed. A linear algebraic system of heat conduction equations is derived based on the temperatures of the particle system and the heat flux among adjacent particles. An analytical expression is introduced for the involved correction coefficient, with which the macroscopic thermal conductivity coefficient can be directly adopted without calibration. Furthermore, a thermal conductivity reduction coefficient is introduced to account for the thermal resistance of the cracks. In the mechanical analysis, particle discontinuous deformation analysis (PDDA), which is an implicit variant of the discrete element method, is employed. The PHCM is first verified against analytical and finite element solutions for transient heat conduction problems. The results show that the PHCM is an effective and accurate heat conduction model that readily reflects the thermal resistance of cracks. Then, the thermo-mechanical coupling model is verified by the expansion of heated specimens under different conditions. Finally, the successful application of the coupling model in the simulation of thermal shock tests demonstrates its effectiveness for thermal cracking problems.

Performance and evaluation theory of axial compression capacity for steel angle and tube members in wildfire

This paper deals with the performance of axial compression capacity for steel angle and tube members subjected to wildfire. An indirect thermo-mechanical coupling model of steel members, of which the accuracy was verified by the experimental results, was established to investigate the mechanical and wildfire resistance performance from different perspectives, such as bearing capacity, temperature distribution and critical temperature. Parametric analysis was conducted to further determine the key parameters including slenderness ratio, cross-sectional sizes and wildfire conditions that affect the change rule of axial compression capacity for steel angle and tube members. It reveals that the bearing capacity and critical temperature significantly decreased as the slenderness ratio increased, and the difference in wildfire resistance between steel angle and tube became enlarged with the increase of slenderness ratio. Comparatively, the critical temperature of steel angle was obviously lower than that of steel tube, since the additional bending deformation at mid-span induced by the non-uniform temperature distribution on cross-section was more evident for the angle member. Moreover, a calculation method for the ultimate capacity and critical temperature of steel members under wildfires was proposed, which turned out to be reliable to provide reference for wildfire resistance design of steel angle and tube members.

Thermo-mechanical stability analysis of thermosyphons for pipeline soil and their optimal layout in permafrost regions

In permafrost regions, warm-oil buried pipelines release vast amounts of heat energy to surrounding soils and lead to rapid permafrost degradation. Settlement disasters induced by permafrost degradation significantly increase the probability of pipeline failure. The two-phase closed thermosyphon (TPCT) can cool soil, inhibiting permafrost degradation, but its deployment is still at the experimental stages along the China–Russia Crude Oil Pipeline (CRCOP). Therefore, it is important to determine an optimal layout for TPCTs that can achieve both effective cooling and cost control. In this study, a strategy for a nonlinear thermo-mechanical coupled model is proposed through Python–Abaqus secondary development. Based on it, the thermal and mechanical effects of TPCTs under different spacings, as well as their optimal layout, are numerically investigated. Closer TPCT spacing leads to a lower degradation rate of frozen soil and a lower peak TPCT heat flux. In addition, the peak pipeline von Mises stress in the transition zone increases for greater TPCT axial distances over time. When the TPCT axial distance is ≤8 m, the minimum pipeline principal strains remain below the critical compression strain over 50 years. Finally, a backpropagation neural network is constructed to predict the maximum pipeline compressive strain, and most prediction results fall within the 95% confidence interval.

Coupled Thermo-Mechanical Phase-Field Modeling to Simulate the Crack Evolution of Defective Ceramic Materials under Flame Thermal Shock

Coupled Thermo-Mechanical Phase-Field Modeling to Simulate the Crack Evolution of Defective Ceramic Materials under Flame Thermal Shock

The Effect of Powder Temperature on Semi-Solid Powder Rolling AA2024 Based on Experiments and Numerical Simulation

Semi-solid powder rolling (SSPR) is widely used to produce alloy strips with fine grains and excellent performances in the automotive, aerospace and shipbuilding industries. During SSPR, powder temperature, as a very important parameter, greatly affects strips’ microstructures and mechanical properties, which have been investigated by many researchers, but its effect on the forming process and mechanism has rarely been studied. Therefore, based on online experimental detection and transient simulation, the microstructures, strip temperatures, relative densities and rolling forces at different conditions were, respectively, measured, calculated, compared and analyzed in order to study the deformation process and mechanism during SSPR. The result shows that with the increase in powder temperature, the strip temperature and relative density increase, while the rolling force decreases. The grains of the strips are refined after SSPR, and fine and dense microstructures are obtained at 600 °C, which is the optimum powder temperature. In the main deformation sections (II and III), when the contact normal force exists and reaches a maximum, the relative density and rolling force increase rapidly. At these sections, the strips rolled at 600 °C are mainly in a porous solid state, and powder crushing dominates the strip deformation. Therefore, SSPR at 600 °C and below can be considered porous or powder hot rolling, integrating powder crushing, solidification, deformation, densification and grain coarsening. Moreover, as the simulated values are basically consistent with experimental values, the thermomechanical coupling model based on the Fourier equation and its parameters are confirmed to be reasonable.

Thermo-mechanical analysis of functionally graded nickel/titanium alloys under different process parameters of directed energy deposition

The build-up of residual stress and porosity plays an important role in the mechanical properties of as-built parts during directed energy deposition (DED). However, the thermo-mechanical behavior of functionally graded nickel/titanium alloys (FGNTAs) in the DED process remains unclear. In this study, a computationally efficient thermo-mechanical coupled model of DED-printed FGNTAs with different porosities is developed. The temperature-dependent effective material properties of FGNTAs are first determined based on the rule of mixture. Subsequently, the temperature, residual stress, and deformation fields within as-built FGNTAs are predicted using the differential quadrature method. The predicted results show excellent agreement with the predictions and experimental data in the literature. Furthermore, the effect of key parameters on the thermo-mechanical responses of DED-printed FGNTAs is investigated, including energy density, porosity distributions, part dimensions, temperature settings, and structural modes. The results show that the residual stress and vertical deflection increase with the higher energy input, length-to-width ratio, and evener porosity distributions, while decreasing with larger porosity, preheating as well environment temperatures, external loads, and power index. These results can provide a useful guideline for the design and manufacturing of high-quality FGNTAs during DED.

A thermo-mechanical coupling model for concrete including damage evolution

In the current study, a coupled thermo-mechanical constitutive model of concrete was newly developed to characterize the mechanical responses of concrete at different temperatures within thermodynamics framework. The coupling thermo-mechanical contributions among thermal effect (up to 800°C), damage evolution and thermo-plastic hardening were creatively taken into account in energy potential function. The thermal damage evolution law and load induced plastic mechanical damage evolution law was developed respectively and were coupled in the dissipation function. The thermo-mechanical hardening rule was considered through adopting back stress and hardening parameters. A particular advantage of the proposed model is that fiber influence coefficients can be employed in potential functions to upgrade for modeling fiber reinforced concrete. The impact of types and volume fractions of fibers on the reinforcement mechanism was calculated in the fiber influence coefficients. Besides, an orthotropic triaxial compression model was developed for concrete and fiber reinforced concrete to predict multiaxial stress behavior at high temperature. The proposed model was coded and implemented into the Fortran program and the nonlinear behaviors of concrete and fiber reinforced concrete were predicted. Good effectiveness and accuracy have been validated through comparing the modelling results and six groups experimental results in literatures, which illustrates that the proposed model is robust and reliable. Finally, a discussed study was conducted to investigate the effect of hardening parameters and thermal effect on the yield surface.

Thermo-Mechanical Numerical Analysis of Stress and Damage Distribution within the Surrounding Rock of Underground Coal Gasification Panels

Underground coal gasification (UCG) is a promising technology for extracting synthesis gas from coal seams through in situ gasification. This study aims to investigate the thermo-mechanical behavior and integrity of the surrounding rock in the gasification vicinity to facilitate safe and efficient UCG operations. Rock property testing experiments are conducted under varying temperature conditions, revealing significant temperature dependencies for the thermal and mechanical parameters. A thermo-mechanical coupling model is developed to analyze the stress and damage distribution near the gasification chamber. The influence of the temperature dependency of stress states and failure risks during the gasification process is evaluated. In addition, the effects of panel orientation, chamber width, maintaining duration, operating temperature and operating pressure on the failure behavior of the gasification surrounding rocks are illustrated through parametric analysis. The findings have practical implications for the design and assessment of UCG processes, enhancing the safety and efficiency of coal gasification operations.

Coupled thermomechanical FE model of a railway disc brake for friction material wear calculations

The article presents a fully coupled 3D thermomechanical model of a railway vehicle disc brake for calculations of temperature, stress, contact pressure and wear distributions. Five specially designed composite organic friction materials associated with a cast-iron ventilated brake disc were analyzed. The performed computer simulations correspond to the operational parameters of braking carried out on a full scale dynamometer test stand at constant braking power and constant vehicle velocity. These conditions were obtained by correcting the clamping force in relation to changes in the coefficient of friction. In the finite element (FE) model of the disc brake, the pad wear depth distribution was determined on the basis of the Archard's law taking into account the specific wear rate, contact pressure and sliding velocity. To create the numerical model with the geometry deformation allowing for friction material loss due to wear, advanced techniques were adapted. The geometric model of the brake includes the complex shapes of the brake pad holder, brake pad and ventilated disc. The wear constants of the tested friction material were obtained by means of the FE simulation and the measurement of the pad weight loss before and after the test on a full scale dynamometer test stand. The distributions of temperature, stresses, contact pressure and accumulated wear depth, obtained from the finite element analysis, in combination with the measured changes in the clamping force and coefficient of friction during braking, enabled to establish relationships between the properties of materials, operational parameters of braking and geometrical features of the brake components.

Study on the Microstructure and Properties of Flash-Butt Welding Joints of High Nitrogen Steel

A thermomechanical coupling model for the solid-state flashing process of high nitrogen steel was established, based on finite element simulations and experiments. The effect of flash current on the microstructure and mechanical properties of the welded joint was investigated, and the temperature field of the flash-butt welding (FBW) process was simulated. The phase composition of the joint was determined according to the phase diagram and cooling curve. In addition, the joint with optimal parameters was subjected to full immersion corrosion tests. The results demonstrated that the interface structure was composed of austenite and δ-ferrite with a thyristor angle (flash current) of 45°. The microstructure of the overheated zone (OZ) was composed of austenite, ferrite and a small amount of the M2 phase, in which the heat-affected zone exhibited a single-phase austenite microstructure. The joint hardness displayed a “V” shaped distribution with the lowest interface hardness. As the flash current increased, the hardness and tensile strength of the interface area of the joint first increased and then decreased, with a maximum tensile strength of 902 MPa at 45°. During the full immersion corrosion tests, the joint exhibited the most serious corrosion in the interface center and gradually reduced corrosion on both sides.