Thermo-mechanical Coupling Model Research Articles

Analysis of residual stress distribution characteristics of laser surface hardening based on Voronoi model

The laser surface hardening’s parameters have a direct effect on the residual stress of the matrix. It is important to quantitatively reveal the influence degree of process parameters on the matrix residual stress for the formulation of optimal process. In this paper, a random polycrystalline model of the matrix is established based on the Voronoi method. The grain heterogeneity is introduced according to the nanoindentation results. The divided 7 different grain attributes are randomly assigned to each voronoi cell through a python script. A thermo-mechanical coupling model for the laser quenching process of SUS301L-HT stainless steel considering grain heterogeneity was established. The thermal stress field and temperature field distribution of the single laser surface hardening are calculated with different process parameters. On this basis, the BOX-Behnen Design method was used to establish a response surface model, and the response surface method was combined with the Monte Carlo sampling calculation method to calculate the sensitivity of the process parameters. The calculation results show that the analysis value D of the residual stress is a normally distributed. Laser power and laser scanning speed are the main factors affecting the average residual stress of the grain, and the effects of the two are opposite. The laser scanning speed has a greater influence on the residual stress of the matrix than the laser power.

Simulation-based parameter optimization of friction forge riveting for AA6061-T6 and TA2 with TA2 titanium rivet

Friction forge riveting (FFR) has been developed for connecting titanium alloy and aluminum alloy with titanium rivets, although the weak formation of rivet during this process is still a key issue that should be solved properly. In this study, a thermomechanical coupling model was established in DEFORM-3D based on the practical thermal cycle of rivet during FFR process. Furthermore, the temperature and stress fields were also revealed in detail. The results showed that by reducing the loading speed of friction tool in the first 1 mm stroke, the flash defects and root defects caused by insufficient filling of the driven rivet head can be effectively avoided, and the joint mechanical performance including strength and service life was also improved. With the optimized FFR parameters, perfect joints were obtained without surface flash, holes or tunnels.

Simulation Analysis and Verification of Temperature and Stress of Wheel-Mounted Brake Disc of a High-Speed Train

During the braking process, a large amount of heat energy is generated at the friction surfaces between the brake disc and pads and rapidly dissipates into the disc volume. In this paper, a three-dimensional thermo-mechanical coupling model of high-speed wheel-mounted brake discs containing bolted joints and contact relationships is established. The direct coupling method is used to analyze the temperature and stress of the brake discs during an emergency braking event with an initial speed of 300 km/h. A full-scale bench test is also conducted to monitor the temperatures of the friction ring and bolted joints. The simulation result shows that the surface temperature of the friction ring reaches its peak value of 414 °C after 102 s of braking, which agrees well with the bench test result. The maximum alternating thermal stress occurs in the bolt hole where the maximum circumferential compressive stress is − 658 MPa and the maximum circumferential tensile stress is 134 MPa. During the braking process, the out-of-plane deformation of the middle part of the friction ring is larger than that of the edge, which increases the axial tensile load of the connecting bolt. This work provides support for the design of brake discs and connecting bolts.

A new theoretical model of thermo-gas-mechanical (TGM) coupling field for underground multi-layered cavern of compressed air energy storage

Compressed air energy storage (CAES) is a promising method of large-scale energy storage. As the key components of the CAES, the underground cavern filled with compared air of the high-temperature and high-pressure would generate larger temperature, air seepage and stress fields to influence the safety of the CAES. Currently, coupling fields of CAES cavern are studied mainly by numerical method and little by theoretical method. The theoretical calculations of CAES cavern are almost by thermo-mechanical coupling model, where the air pressure is taken as a static pressure regardless of the gas seepage field. In this paper, a new theoretical model of thermo-gas-mechanical (TGM) coupling field with consideration of the gas seepage is established. Research results show the analytic solutions of the temperature, gas seepage and stress fields for single-, double- and three-layered caverns have almost the same changing trends with time but different with radius. The three-layered cavern has smaller heat/gas loss and better stability than the single- and double-layered cavern and therefore becomes a promising structure form. The new TGM coupling model is verified by the good agreement of our analytical solutions with available numerical results, and can provide theoretical basis for the safety assessment of the CAES multi-layered cavern.

An investigation on thermo-mechanical performance of graphene-oxide-reinforced shape memory polymer

Abstract Based on micro morphology, a thermo-mechanical coupling model of shape memory graphene oxide/epoxy resin (SMGO/EP) was proposed. The heat transfer capability, mechanical property and shape memory ability of shape memory polymer (SMP) were further investigated. The reliability of the modeling was verified by comparing the heat transfer and shape fixation rate of the experimental and simulation data. The results showed that the maximum error of heat transfer was 6.04%, and shape fixing rate error was 2.33%. When the volume fraction of GO was 1.50 vol%, the maximum stress can reach 158.39 MPa, 46.52% higher than that of pure shape memory EP. With the increase in the volume fraction of GO in the SMGO/EP composites, the heat transfer enhancement and recovery rate of SMGO/EP were directly affected by the doping content of GO. The surface temperature of the composites with GO doping content of 1.50 vol% was 20.26°C higher than that of pure SMEP after heating for 300 s. Under the coupling effect of heat transfer and stress characteristics, the mechanism of shape memory effect of SMGO/EP composites was revealed. The thermo-mechanical coupling modeling of SMGO/EP can effectively predict the shape memory characteristics of the SMGO/EP composites.

Thermal and mechanical analysis of the China–Russia Crude Oil Pipeline suffering settlement disaster in permafrost regions

In permafrost regions, the soil settlement disaster owing to permafrost degradation has become one of the important reasons for buried warm-oil pipelines failure. In this paper, the 3D sequential thermo-mechanical coupled model is carried out to investigate the interaction between buried warm-oil pipeline and surrounding permafrost. The effects of parameters, including thaw-settlement coefficient, length of transition zone, diameter-thickness ratio and internal pressure, on the pipeline mechanical behavior are numerically investigated. Among them, the thaw-settlement coefficient and length of transition zone present more significant effects on the peak strain of the pipeline. In addition, the effects of insulation layer and two-phase closed thermosyphon (TPCT) on pipeline–soil interaction are investigated in thermal and mechanical fields. With no protective measure, the permafrost layer under pipeline will completely degrade in about 20 years with 0.33m/a. The pipeline is considered to reach failure limitation even within 10 years. However, under the influence of combined measure, the permafrost degradation rate is only about 1/10 of that without protective measure. The peak compressive strain is significantly lower than the critical compressive strain, and the pipeline remains safe for 50 years. Therefore, the combined measure is an ideal method for ensuring pipeline safety in permafrost regions.

Stress sensitivity analysis of laser quenching based on regression model

In the laser quenching process, quantitative evaluation of the influence of different process parameters on quenching stress is the key to achieve quenching process optimization. A variety of different process parameters are selected as research objects, and a parameterized thermomechanical coupling model of the disk laser hardening process for 45 steel is established. Through the calculation of the model, the instantaneous change law of stress field and the phase change field under different process parameters are obtained, and the response surface equation between the multiphysics solution results and process parameters is established. The Monte Carlo method is used to randomly sample the response equation repeated times, and the sensitivity of quenching process parameters is calculated through sampling results. The calculation result shows that hollow teardroplike stress distribution is formed in the center of the spot during quenching, and the stress around the spot is larger. Thermal stress concentration appears in the reverse direction of quenching scanning, with a maximum value of 850 MPa, and a cometlike stress zone appears in the reverse direction of quenching scanning. The diameter of the laser spot is negatively correlated with quenching stress and has the greatest influence on it. The laser incidence angle has a great influence on the depth and width of the phase change layer and is positively correlated. This model can reveal the mechanism of multifield coupling changes in the material during quenching and provide technical and theoretical support for the reasonable selection of process parameters.

Numerical Simulation and Experimental Studies on Stationary Shoulder Friction Stir Welding of Aluminum Alloy T-Joint

The application of the corner stationary shoulder friction stir welding (CSSFSW) on T-shaped structures is exceptional, and adequate research is still required for the related theory. In this paper, taking 5,083 aluminum alloy as the workpiece, based on the Arbitrary Lagrangian Eulerian (ALE) method, a three-dimensional thermomechanical coupled model of the CSSFSW process was established. The temperature field and material flow were simulated and analyzed during the welding process. The friction heat formed an elliptical temperature gradient range, and expanded with the progress of the welding. The highest temperature of up to 575°C was recorded on the advanced side, which is higher than that on the retreating side (about 532°C). The forward and backward material flow directions were found to be opposite to each other. In the traverse direction, the material on both sides flowed upward along the pin and downward under the action of the stationary shoulder at the top. The difference between the simulated and the measured temperature lies within 7%, and the material flow also has good agreement with the experimental results.

All-optical laser ultrasonic technique for imaging of subsurface defects in carbon fiber reinforced polymer (CFRP) using an optical microphone

Defects, such as delamination and debonding, are critical to the performance of carbon fiber-reinforced polymer (CFRP) composites. In recent years, non-destructive testing techniques have been improved for the inspection of these defects among CFRPs. In this study, an all-optical and non-destructive laser ultrasonic technique with an optical microphone detection module has been presented to detect the artificial subsurface defects among the CFRP composites. A finite element simulation based on the thermo-mechanical coupling model was used to study the process of nanosecond pulsed laser excitation of the CFRP laminate to produce ultrasound and the propagation behavior of ultrasound among the CFRP laminate. A series of non-contact laser ultrasonic testing experiments were carried out to study the flat bottom holes of different sizes via a laser ultrasonic detection system. The artificial subsurface defects were reliably identified by the presented all-optical laser ultrasonic system imbedded in the optical microphone using four feature images.

Coupled thermomechanical modelling of shape memory alloy structures undergoing large deformation

Shape Memory Alloys (SMAs) exhibit strain recovery capabilities even after undergoing large deformation, out of underlying stress and temperature dependent diffusionless martensitic transformation. Modelling its behaviour accurately requires coupled thermomechanical analysis, considering absorption and emission of latent heat during phase transformation, thermoelastic effects, thermomechanical loading and boundary conditions. Moreover, the variation of material properties, e.g., modulus of elasticity and thermal expansion coefficient, during phase transformation, significantly affects the response of the system. In addition, appropriate stress and strain measures are required to model the large deformation of SMA-based components under practical thermomechanical loads. In this study, a nonlinear finite element formulation based on Total Lagrangian (TL) approach has been developed to address geometric as well as material non-linearity arising out of the SMA behaviour. Furthermore, considering all the above-mentioned effects, both the stress and thermal equilibrium equations are solved simultaneously in an incremental–iterative finite element (FE) framework, simulating the coupled SMA response. The SMA constitutive model, using Green–Lagrange strain and Second Piola–Kirchhoff stress measures, proposed by Qidwai and Lagoudas (2000), has been implemented. Using the developed FE model, the thermomechanical responses of SMA wire actuator, beam and biomedical staple are simulated to demonstrate the need for the coupled analysis while considering large deformation of the SMA structures.

Coupled thermo-mechanical modeling of drilling of multi-directional polymer matrix composite laminates

The influence of in-situ cutting temperature on machining induced damage and machining forces during drilling of multi-directional carbon fiber reinforced polymer (MD-CFRP) composites has been examined using a coupled thermo-mechanical finite element (FE) framework. The MD-CFRP laminate has been modeled ply-by-ply as an equivalent homogeneous anisotropic material (EHM) using temperature dependent laminate elastic and fracture properties. Stress-based criteria has been adopted for element deletion simulating the drilling process. The intralaminar damage model for simulating various composite machining induced damage modes was implemented in the FE framework via a user material subroutine. A new composite damage criterion is proposed that accounts for the out-of-plane drilling damage behavior along tool feed direction. Additionally, a fracture mechanics approach has been used to simulate interlaminar delamination onset using surface based cohesive elements at the drill exit plies. The current numerical model predictions show a good agreement with drilling experiments for thrust force, delamination damage, and in-situ cutting temperature.

Size effect in selective laser melting additive manufacturing of 700 mm large component

The complex structure with large size (e.g., >500 mm) in aerospace, mould, nuclear power industry, has been urgently required for production with selective laser melting additive manufacturing (AM). Revealing the effect of the component size on the distortion could contribute to better understanding of AM and suggest control strategy for distortion reduction. Here, a method combining elastic-plasticity theory and inherent strain theory is proposed to study the size effect in AM of large size component. Firstly, the traditional thermo-mechanical coupled model based on the thermo elastic-plasticity theory is used to calculate the inherent strain of AMed parts. And a single tracked experiment was performed to confirm the availability of thermo-mechanical coupled model. Secondly, the aircraft blade of 700 mm is used to verify the availability of simulating large component deformation based on the inherent strain. Finally, the size effect of distortion and effective stress of large-size components is briefly illustrated. This manuscript provides a powerful simulation framework for predicting the distortions of large structure produced by thousands and thousands of melts in selective laser melting, and this framework could also be extended to apply in the other AM technologies, e.g., laser metal deposition, wire-arc deposition, and so on.

Local strain release due to microcracking in laser melted tungsten

Residual stresses in laser powder bed fusion typically reach the yield stress of the material, leading to part deformations or even cracking. Previous work showed that there were no measureable residual stresses present in tungsten parts, but also that these parts were riddled with a microcrack network. In this work, the strain relaxation due to microcracking is directly measured by applying one-dimensional DIC-like techniques to high speed videos obtained of laser melting of tungsten single tracks. Coupled thermomechanical models match the measured strain release and confirm that the release is asymmetrical, with lower strains released on the side of the crack facing the melt pool. Finally, the distance between cracks correlates with the distance over which strains are released by the cracking event, showing that microcracks relax all residual stresses during laser powder bed fusion of tungsten.

Establishment and Verification of Thermo-Mechanical Coupled Model for Laser Direct Deposition of Titanium Alloy

Establishment and Verification of Thermo-Mechanical Coupled Model for Laser Direct Deposition of Titanium Alloy

Analysis and Evaluation on Residual Strength of Pipelines with Internal Corrosion Defects in Seasonal Frozen Soil Region

In order to study the residual strength of buried pipelines with internal corrosion defects in seasonally frozen soil regions, we established a thermo-mechanical coupling model of a buried pipeline under differential frost heave by using the finite element elastoplastic analysis method. The material nonlinearity and geometric nonlinearity were considered as the basis of analysis. Firstly, the location of the maximum Mises equivalent stress in the inner wall of the buried non-corroded pipeline was determined. Furthermore, the residual strength of the buried pipeline with corrosion defects and the stress state of internal corrosion area in the pipeline under different defect parameters was analyzed by the orthogonal design method. Based on the data results of the finite element simulation calculation, the prediction formula of residual strength of buried pipelines with internal corrosion defects was obtained by SPSS (Statistical Product and Service Solutions) fitting. The prediction results were analyzed in comparison with the evaluation results of B31G, DNV RP-F101 and the experimental data of hydraulic blasting. The rationality of the finite element model and the accuracy of the fitting formula were verified. The results show that the effect degree of main factors on residual strength was in order of corrosion depth, corrosion length, and corrosion width. when the corrosion length exceeds 600 mm, which affects the influence degree of residual strength will gradually decrease. the prediction error of the fitting formula is small and the distribution is uniform, it can meet the prediction requirements of failure pressure of buried pipelines with internal corrosion defects in seasonally frozen soil regions. This method may provide some useful theoretical reference for the simulation real-time monitoring and safety analysis in the pipeline operation stage.

Coupled thermomechanical analysis of fused deposition using the finite element method

A novel finite element-based simulation method is proposed for fused deposition modeling in two dimensions. The method assumes full coupling between the mechanical and thermal response under the assumptions of infinitesimal deformation and finite temperature variation. To account for continuous temperature-induced changes in the geometry, new elements are deposited on the current configuration, while the governing equations are solved on a reference configuration generated based on the desired shape. Representative simulations are conducted to assess the predictive capacity of the method, as well as the effect of thermomechanical coupling on the final shape of the printed solid. • Coupled thermomechanical modeling of fused deposition in two dimensions. • Under infinitesimal deformations and finite range of temperatures. • Continuous deposition on deformed geometry. • Algorithmic treatment of deposition in the presence of curved surfaces. • Computational comparison to (commonly used) uncoupled methods.

Thermo-mechanical coupling shock waves propagation with phase transition under impact loading

In the present study, a thermo-mechanical coupling model including constitutive relation and kinetics for phase transformation is developed to study stress wave propagation in shape memory TiNi rods. The front tracking/capturing method is adopted for numerical analysis and impact experiments are performed to verify theoretical model. It is demonstrated that, a phase transition shock wave will be induced during loading due to the mixed phase hardening effect originating from the temperature dependence of transformation stress, and for unloading, double wave profile (an elastic wave and a shock wave with reverse phase transition) will be excited since the change of unloading path caused by the transient temperature rise during loading. Furthermore, shock wave propagation speeds are increased with loading stress, while driving force acting on the shock wave is supplied by shock dissipation energy, in which the temperature gradient across the shock front plays an important role. SHPB experiments show that the phase change wavefront is also a moving temperature interface, which will have an important influence on the stress wave structure. Taylor impact experiments show that the proposed kinetic relation in this paper is in good agreement with the experimental results, which reflects the intrinsic characteristic of materials with strong nonlinear thermo-mechanical coupling behavior.

Study on the Compressive Stress Retention in Quenched Cam of 100Cr6 Steel Based on Coupled Thermomechanical and Metallurgical Modeling.

The assembled camshaft has obvious advantages in material optimization and flexible manufacturing. As the most important surface modification technique, the heat treatment process is utilized in this work to promote the desired compressive residual stress on the near-surface of the 100Cr6 steel assembled cam. The Johnson-Mehl-Avrami equation and Koistinen-Marbuger law are integrated into the ABAQUS software via user subroutines to simulate the evolution of diffusional transformation and diffusionless transformation, respectively. The linear mixture law is used for describing the coupled thermomechanical and metallurgical behaviors in the quenching of steel cam. The influences of various quenchants and the probable maximum phase volume fractions on surface residual stress or hardness are analyzed. Results show that a greater amount of martensite volume fraction and a slower martensitic transformation rate are beneficial for the compressive stress retention. Compared with the conventional quenching oil, the fast oil quenched cam surface has higher final compressive stress and hardness.

Fire resistance of T-shaped concrete-filled steel tubular columns under eccentric compression

In order to study the fire resistance of T-shaped concrete-filled steel tubular (CFST) columns subjected to eccentric loading, a series of fire tests were conducted along with a numerical study. Specifically, six half-scaled T-shaped CFST columns were tested under the ISO-834 standard fire; and the parameters of stiffener type, load eccentricity, and load angle were considered. The failure modes, thermal response, and structural response were investigated. The test results show that the fire resistance of T-shaped CFST columns decreases with the increase of load eccentricity, but at a lesser degree for relatively high eccentricity. The load angle also has a significant influence on the fire resistance of the columns. A finite element (FE) analysis was then conducted to establish the temperature field model and the thermo-mechanical coupling model which were both validated by the test results. Furthermore, an extensive parametric study including 2008 FE analyses was carried out to investigate the effects of key parameters on the fire resistance of T-shaped CFST columns, including load ratio (n), slenderness ratio (λ), column limb width (B), column limb depth-to-width ratio (D/B), load eccentricity ratio (e/r0), steel ratio (αs), material strength (fy and fck), and load angle (θ). The parametric study indicates that the load ratio n has a significant effect on the fire resistance of T-shaped CFST columns and the other parameters also have certain influences on the fire resistance when n < 0.5. Based on the numerical studies, a simplified method to calculate the fire resistance of T-shaped CFST columns is proposed.

High-speed tribology behaviors of aircraft tire tread rubber in contact with pavement

Aircraft tire suffers from high-speed friction due to harsh conditions in landing, which leads to high temperature and the short service life. So, the effect of different sliding speeds on the tribology behaviors of tread rubber was studied theoretically and experimentally. Firstly, high-speed friction and wear tests were carried out by using a self-developed high-speed friction testing apparatus. Then, a thermo-mechanical coupling model was developed to predict the friction temperature of rubber specimen by ABAQUS software. Finally, tribology behaviors of friction temperature, coefficient of friction (COF) and wear performance have been revealed. Results indicated that temperature and wear loss increased when sliding speed increased; however, COF decreased with increasement of sliding speed; ploughing was the main mechanism in rubber abrasion, and thermo-chemical degradation appeared at wear track; the predicted temperature rise was in good agreement with the experimental results.