Thermomechanical Coupling Effects Research Articles

Cyclic functional degradation of NiTi shape memory alloy wires in wide ranges of strain rate and ambient temperature

Shape memory alloy (SMA) dampers frequently experience cyclic loading over a broad spectrum of strain rates and ambient temperatures, resulting in a significant thermo-mechanical coupling effect during cyclic deformation. Nevertheless, the impact of this coupling effect on the functional degradation of SMAs has not been thoroughly examined, particularly in scenarios involving severe deformation. In this study, a series of strain-controlled cyclic loading–unloading tests were conducted on NiTi SMA wires utilizing various combinations of strain rates ranging from 5 × 10−4 6 × 10−2/s and different ambient temperatures (313–393 K). The functional degradation was exacerbated by increasing ambient temperature and loading rate due to the complex interactions among the inelastic deformation mechanisms and thermo-mechanical coupling effects. Furthermore, although the cyclic deformation behavior of NiTi SMA wires varied with the loading rate, this rate dependence diminished with increasing ambient temperature. The synergistic effect of elevated strain rates and high temperatures markedly accelerated the fatigue failure of NiTi SMA wires and substantially altered the underlying microstructural morphology. These findings can provide valuable support for evaluating the service performance of NiTi SMA dampers under various engineering conditions and contribute to developing a cyclic constitutive model for NiTi SMAs.

Theoretical and numerical study of the thermo-mechanical coupling effect on the fluid viscous damper

Theoretical and numerical study of the thermo-mechanical coupling effect on the fluid viscous damper

An Experimental Study on the Thermomechanical Coupling Effects of Carbon-Fiber-Reinforced Polyetheretherketone under Dynamic Impact.

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are widely utilized in aerospace, medical devices, and automotive industries, renowned for their superior mechanical properties and high-temperature resistance. Despite these advantages, the thermomechanical coupling behavior of CF/PEEK under dynamic loading conditions is not well understood. This study aims to explore the thermomechanical coupling effects of CF/PEEK at elevated strain rates, employing Hopkinson bar impact tests and scanning electron microscopy (SEM) for detailed characterization. Our findings indicate that an increase in temperature led to significant reductions in the yield strength, peak stress, and specific energy absorption of CF/PEEK, while fracture strain had no significant effect. For instance, at 200 °C, the yield strength, peak stress, and specific energy absorption decreased by 39%, 37%, and 38%, respectively, compared to their values at 20 °C. Furthermore, as the strain rate increased, the yield strength, peak stress, specific energy absorption, and fracture strain all exhibited strain-hardening effects. However, as the strain rate further increased, above 4000 s-1, the enhancing effect of the strain rate on the yield strength and peak stress gradually diminished. The interaction of the temperature and strain rate significantly affected the mechanical performance of CF/PEEK under high-speed impact conditions. While the strain rate generally enhanced these properties, the strain-hardening effect on the yield strength weakened as the temperature increased, and both the temperature and strain rate contributed to the increase in specific energy absorption. Microdamage mechanism analysis revealed that interface debonding and sliding between the fibers and the matrix were more pronounced under static compression than under dynamic compression, thereby diminishing the efficiency of stress transfer. Additionally, higher temperatures caused the PEEK matrix to soften and exhibit increased viscoelastic behavior, which in turn affected the material's toughness and the mechanisms of stress transfer. These insights hold substantial engineering significance, particularly for the optimization of CF/PEEK composite design and applications in extreme environments.

Laser-assisted Belt Grinding with Creep Feed for Enhanced Surface Integrity and Abrasive wear Reduction

Creep feed belt grinding (CFBG) is a vital machining technique used for intricate curved parts like aero-engine blades and flaps. CFBG effectively removes material by using larger depths of cut and lower feed rates, but high loads can lead to severe belt wear and thermal damage defects in the process. Laser-assisted processing technology can mitigate tool wear and enhance machining quality. This research compared and analyzed belt wear behavior and its impact on the surface integrity of titanium alloys in laser-assisted creep feed belt grinding (LCFBG) and CFBG processes. The following conclusions were drawn: The local thermal effect of the laser softened the material, reduced the grinding force. The wear pattern of the abrasive grains changed from abrasive fracture and stripping to steady abrasive wear. The effective life of the belt increased by about 33 %. In addition, due to reduction in grinding force, the thermo-mechanical coupling effect caused by material removal is reduced, and the grinding temperature is lowered. As a result of the reduction in grinding force and temperature, the mechanical and thermal stresses are reduced, the oxidation reaction on the surface of the titanium alloy is weakened, and the residual stress is lowered, leading to an improvement in surface quality.

A comprehensive transformation-thermomechanical model on deformation history in directed energy deposition of high-speed steel

ABSTRACT Phase transformation is a crucial factor that determines the quality and deformation of components in laser-directed energy deposition (L-DED). Owing to the limitations of in situ observation methods, there is a lack of effective means to study the complete phase transformation and their impacts on deformation during the deposition process. In this study, multilayer heterogeneous deposition was investigated with the high-carbon high-speed steel by modelling the coupled phase transformation-thermomechanical physics. The methodology was proposed to identify the specific phase transformations by iteratively comparing the whole deformation history between digital image correlation (DIC) measurements and simulations. Besides the thermo-mechanical coupling effect and basic volumetric phase transformation, carbon partitioning between precipitated carbides and matrix was manifested, which also resulted in a rise of the Ms point by 208.4 °C and a reduction of the transformation rate by 73.2%. Additionally, an increase of 13.8% in energy absorption could be attributed to the surface oxidation of the deposited layer. The model predictions exhibited good consistency with the DIC in-situ measurement data, indicating that the deformation history contained sufficient information on the phase transformations. Based on the proposed transformation-thermomechanical coupling model, it helps to understand the complete phase transformation during deposition.

Sliding wear-induced compositional lamination in a VCoNi alloy at elevated temperatures, and its implications for reduced friction and wear

During tribological loading of metallic alloys at elevated temperatures, the thermo-mechanical coupling effect can lead to the development of a distinct tribolayer, profoundly influencing their tribological behavior. This study reports on the compositional lamination in the tribolayer during dry sliding wear of a VCoNi multi-principal element alloy at elevated temperatures. As the temperature increases from 25 °C to 600 °C, the alloy exhibits a remarkable 40% reduction in the coefficient of friction and a notable two-order-of-magnitude decrease in wear rate. The compositional lamination at 600 °C reveals a distinct tribolayer comprising a nanocrystalline-amorphous oxide glaze layer, a Ni-rich dealloyed layer, and a plastic deformation layer. Within the oxide glaze layer, three sublayers are identified, each featuring a nanocrystalline-amorphous nanocomposite structure with unique equiaxed nanograins. Specifically, the outermost sublayer comprises Co3O4, the intermediate sublayer contains a mixture of Co3O4 and Ni2V2O7, and the inner sublayer consists of V2O5. This multilayered structure is attributed to significant differences in the chemical affinity for oxygen among the constituent elements and their respective diffusion rates in the oxide scale. Significantly, the tribolayer formed at 600 °C exhibits a remarkable 70% increase in yield strength compared to its formation at 25 °C, correlating with a substantial reduction in wear. These findings present a novel avenue for designing self-adaptive, high-temperature wear-resistant alloys through the in-situ formation of a protective compositionally-laminated tribolayer.

Warm Air Bending of AZ31B Sheets Based on an Online Local Contact Heating Method

Abstract Warm forming holds significant potential in shaping challenging materials due to its comprehensive advantages compared to cold and hot forming. Effective heating is crucial for precise warm forming processes. This study explored an innovative warm air bending technique employing an online local contact heating method. Heat transfer during the preheating stage and the air bending of AZ31B sheets were investigated through experiments and finite element analysis at temperatures ranging from room temperature (24 °C) to 250 °C, considering the thermomechanical coupling effect. The results indicate a significant increase in the bending center angle, advancing from 69.8 deg to more than 119 deg as the heating temperature rises from room temperature to 250 °C. Fractures were effectively eliminated when the sheet heating temperatures exceeded 150 °C. Simultaneously, as the localized heating temperature increases, a corresponding decrease in the rebound angle is observed, reducing from 10.6 deg to 2.3 deg. The findings validate the feasibility of warm air bending using online local contact heating in industrial applications, with regard to forming quality and production efficiency.

Effect of Ni4Ti3 precipitates on the functional properties of NiTi shape memory alloys: A phase field study

Ni4Ti3 precipitates, which generally exist in aged Ni-rich NiTi shape memory alloys (SMAs), can have a profound effect on material properties. However, the fundamental insights into the effects of Ni4Ti3 precipitates on the functional properties, including the superelasticity (SE), elastocaloric effect (eCE), and shape memory effects (SMEs), are not well understood yet, especially those originating from the B2-B19′ martensite transformation (MT). In this work, a phase field model coupling the precipitation of Ni4Ti3 and the B2-B19′ MT is proposed, where the thermo-mechanical coupling effect and grain size effect are considered. The precipitate-dependent SE, eCE, one-way SME (OWSME), and stress-assisted two-way SME (SATWSME) of single-crystal, polycrystalline, and gradient-nanograined NiTi SMAs are simulated. The effects of the precipitate density, grain orientation range (texture), and gradient-distributed precipitate are examined, and the underlying microscopic mechanisms are revealed. The simulation results and new findings not only contribute to a more comprehensive insight into the effect of Ni4Ti3 precipitates on the MT, martensite reorientation, and functional properties of NiTi SMAs but also provide a reference for the development of excellent SMA-based solid refrigerants or SMA smart materials with designable functional properties.

Localized Phonon Transport Study of GaN/SiO2 Core/shell Nanowires under Thermal-Stress Coupling.

In order to comprehensively explore the intricate mechanisms of thermo-mechanical interactions, this study employs the molecular dynamics method to investigate the influence of heat flux density, shell thickness and length, as well as stress on the radial interface phonon transport in GaN/SiO2 core/shell nanowire. Additionally, the surface eigenmode decomposition method is employed to analyze the interface phonon dispersion curves. The investigation reveals that with increasing heat flux density, internal thermal stresses intensify, leading to a complex distribution of thermal stresses within the system. Under the influence of thermal stress, the nonlinear acoustic properties interact with phonon scattering, resulting in the pronounced localization of interface phonons. Compressive stress causes an upshift in low-frequency phonons, while tensile stress induces a downward shift in the high-frequency optical branches at the interface. The localized phonon vibrations at the SiO2/GaN interface under nonuniform stress are identified as the primary cause for the abundant presence of nondispersive phonon modes at the radial interface. By elucidating the subtle interplay between lattice vibrations and stress fields, this study offers a novel and profound understanding of thermo-mechanical coupling effects, thereby providing innovative theoretical foundations for the design and performance management of thermoelectric devices.

A finite deformation formulation for amorphous glassy polymers under moderate and impact strain rates: Application to adhesive films

This work describes a novel finite strain hypo-elastic formulation for amorphous thermoset polymers working in the glassy regime. The constitutive formulation is able to describe time and pressure-dependent behaviour under loading rates ranging from quasi-static to impact-type loading conditions and to account for thermo-mechanical coupling effects. A non-linear pressure dependent potential function is introduced to capture the non-associative visco-plastic potential flow for volumetric plastic strain control. The formulation also incorporates an internal state or deformation resistance variable to enable the description of the polymer hardening — softening behaviour, as well as a novel relation for the dissipative fraction of the plastic work in terms of the equivalent accumulated plastic strain. The constitutive model is formulated within a finite strain kinematics framework, and full details of its numerical implementation into the finite element method using a fully implicit Euler Backward algorithm are given. Model calibration is carried out for three different thermosetting resins (PR520 and RTM6 Epoxies, and MMA adhesives).To illustrate the model capabilities, two case studies are investigated: (i) the de-formation behaviour of epoxy under moderate and impact-type loading conditions under isothermal and fully adiabatic conditions, and (ii) the fracture behaviour of adhesive layers used to bond stiff metallic substrates. Results on RTM6 epoxy show that at, e.g., 60% true strain, 48.5% of the rate of plastic work is dissipative, and that the corresponding predicted increase in temperature due to the locally dissipated heat is consistent with published calorimetry data on a similar thermoset polymer. It was also found that, by coupling the proposed constitutive model with a cohesive zone model, it was possible to predict accurately the effect of an MMA adhesive layer thickness and pressure-dependency on the growth of an interfacial crack between the MMA adhesive and the metallic substrates. The proposed model should constitute a generic phenomenological formulation for the mechanical behaviour prediction of a wide range of thermoset polymers under confined and quasi-adiabatic conditions such as in composites and adhesive joints.

Experimental and Simulation Investigation on Fatigue Performance of H13 Steel Tools in Friction Stir Welding of Aluminum Alloys.

As the central component in friction stir welding, the design and manufacture of welding tools for aluminum alloys have garnered substantial attention. However, the understanding of tool reliability during the welding process, especially in terms of fatigue performance, remains unclear. This paper focuses on the welding of AA2219-T4 as a case study to elucidate the predominant failure mode of the tool during the friction stir welding (FSW) of aluminum alloys. Experimental methods, including FSW welding and fracture morphology analysis of the failed tool, coupled with numerical simulation, confirm that high-cycle mechanical fatigue fracture is the primary mode of the tool failure. Failures predominantly occur at the tool pin's root and the shoulder end face with scroll concave grooves. The experimental and simulation results exhibit a noteworthy agreement, validating the reliability of the simulation model. The FSW Arbitrary Lagrangian-Eulerian (ALE) model developed in this study analyzes stress distribution and variation under the thermo-mechanical coupling effect of the tool. It reveals that stress concentration resulting from structural changes in the tool is the primary driver of fatigue crack initiation. This is attributed to exposure to alternating cyclic stresses such as bending, tension, and torsion at the tool pin's root, manifesting as multiaxial composite mechanical fatigue. Among these stresses, bending alternating cyclic stress exerts the most significant influence. The paper employs the Tool Life module in DEFORM software to predict the fatigue life of the tool. Results indicate that reducing welding speed or increasing rotation speed can enhance the tool's fatigue life to some extent. The methodology proposed in this paper serves as a valuable reference for optimizing FSW structures or processes to enhance the fatigue performance of welding tools.

Hot deformation behavior and microstructure evolution of TC11 dual-phase titanium alloy

Thermomechanical processing is one of the major steps in the fabrication of structural components used in various engineering applications. The thermomechanical coupling effect of temperature and strain rate has a significant impact on the stress-strain thermal deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy. Here, the hot deformation behavior of TC11 dual-phase alloy has been comprehensively investigated by the hot compression tests with deformation temperatures ranging from 870 °C to 960 °C and strain rates of 0.01 s−1 to 1 s−1. Based on the flow stress curves and Arrhenius-type constitutive equation, a strain compensated Arrhenius model for TC11 alloy was successfully developed, achieving rapid and accurate prediction of high-temperature flow stress. By studying the deformed microstructure characteristics of materials under various deformation conditions, the role of deformation temperatures and strain rates was fully discussed in microstructure evolution, including the primary α phase (αp) and lamellar (αs). The thin-long lamellar shape αs can be obtained at a higher strain rate and deformation temperature. The predominance of single-peaked stress features in most flow curves, along with EBSD characterization results, indicates that continuous dynamic recrystallization (DRX) is the primary softening mechanism under different deformation conditions. This work supports the rapid prediction of flow stress and the relationship between process parameters and microstructural evolution to expedite the design optimization of plastic deformation process parameters and the development of advanced TC11 titanium alloy with targeted microstructures.

Investigation on effects of thermo-mechanical coupling on residual stress in lithium niobate in surface acoustic wave device

Surface acoustic wave (SAW) devices are subject to thermomechanical coupling during operation, and when the temperature rises sharply to 180 °C, the surface of the lithium niobate crystal substrate generates nonuniform thermal stresses, thus leaving large residual stresses after complete cooling, which seriously influences its service performance and life. In this study, the thermal residual stresses of lithium niobate wafers were tested by nanoindentation tests, and the nanoindentation test process was simulated. The inverse calculation of the parameters of the lithium niobate constitutive model was carried out by comparing the load-displacement curves obtained from the finite element calculations with the experimental results. A multiscale model of the SAW device was established, its operation process was simulated, and then the generation law of residual stress was further discussed. The nanoindentation test results show that the thermal residual stress is positively correlated with the heating time under the effect of the same temperature; however, at the heating temperature up to about 180 °C, the lithium niobate crystal enters the high-temperature hyperelastic interval, and the yield stress of the crystal increases significantly at this stage. The constitutive model curves obtained by finite element calculations are in good agreement with the experimental results, and the thermal residual stress value of lithium niobate can reach 2/3 of its yield stress outside the high-temperature hyperelastic interval by comparison tests. The calculation results of the multi-scale model of the SAW device indicate that excessive thermal stress is the main cause of damage during the thermo-mechanical coupling of the SAW device. The polarization direction of lithium niobate crystals may cause the development of damage cracks, increasing the heat dissipation can effectively reduce the thermal stress to which it is subjected, and better extend the service life of the SAW device.

A strain rate and temperature dependent model for describing nonlinear unloading stress-strain response after warm and hot compression deformation

For an accurate numerical simulation of springback behavior and control of shape and dimensional accuracies of the manufacture component under warm and hot precision plastic forming, the use of an appropriate material model dependent with strain, strain rate and temperature describing the nonlinear unloading process is vital, which is remained to be developed. The thermo-mechanical coupling effect in difficult-to-form material deformed at elevated temperature makes the unloading process more complicated and thus more difficult to model. In this paper, by using face-centered cubic (FCC) aluminum alloys as case study materials, loading-unloading experiments with different strains and strain rates at warm and elevated temperatures of 300 – 500 °C were conducted, the effects and contributions of strain, strain rate and temperature on unloading chord modulus (elastic modulus) and nonlinear unloading stress-strain response were quantified. A unique strain-, strain rate- and temperature-dependent nonlinear unloading coupled model was established. By validating and applying the nonlinear unloading coupled model in the both monotonous loading-unloading and cyclic loading-unloading warm and hot compression deformation, the calculation results agree well with experimental results, indicating that the model can describe perfectly the nonlinear unloading stress-strain responds and springback behavior. From the discussion on calculated results and capabilities of model, it was found that the proposed unified equation incorporating strain rate and temperature is also able to be coupled with the existing strain-dependent chord modulus model such as modified Yoshida-Uemori (Y-U) model. The capability of predicting nonlinear unloading curves and springback strains of aluminum alloys deformed at various strains, strain rates, and temperatures demonstrates the potential applicability of the model to a wide range of warm and hot forming process conditions.

Linear permanent magnet electrodynamic suspension system: Dynamic characteristics, magnetic-mechanical coupling and filed test

This study investigates the dynamic electromagnetic characteristics and thermo-mechanical coupling effect of the linear permanent magnet electrodynamic suspension system (PMEDS) via high-speed test rig. Besides, a physical prototype weighing 1.5 tons along with a 50-m linear copper guideway is developed and tested. Firstly, the topology structure along with fundamental operation model is introduced, followed by establishing the analytical model. Subsequently, a multi-functional test rig is utilized to experimentally determine its speed characteristics, lateral stability, and vertical vibration, while also validating the simulation and analytical models. Additionally, thermo-mechanical coupling analysis is conducted through co-simulation, experimentation and calculation to determine the dependence of temperature on the levitation and drag forces. Finally, a prototype vehicle integrated with auxiliary components, is fabricated and tested on a copper guideway. The vehicle is suspended freely via levitation force in the air above 30 mm, with tested suspension height generally aligning with dynamic simulation results.

Numerical simulation on cavern support of compressed air energy storage(CAES)considering thermo-mechanical coupling effect

A reasonable support could ensure the stability and tightness of underground caverns for compressed air energy storage (CAES). In this study, ultra-high performance concrete (UHPC) and high-temperature resistant polyethylene were used for structural support and tightness of caverns excavated in hard rock. Laboratory experiments were conducted to investigate the fatigue tensile and compressive behavior of UHPC, and a fatigue damage constitutive model for UHPC was established. A two-dimensional precise thermal-mechanical coupled dynamic model of long-term CAES was developed by the finite element method. Stress and damage evolution of the UHPC lining for both short and long term have been stated, and the extent of crack propagation was evaluated. The numerical result proves that the qualities of rock have significant effect on stabilities of CAES. Finally, transient heat transfer equations and energy balance were used to analyze the heat transfer for CAES, which showed that the thermal stress caused by temperature variation would cause an increment of tensile stress in UHPC lining, and the energy loss rate would decrease to a certain level during CAES cycles. This creative cavern support provides a new method for the design of CAES in the future.

Investigating the strength of heat-sealed cast polypropylene film for lithium-ion pouch cells considering thermo-mechanical coupling effects

This study investigates the failure mechanism of the heat-sealed cast polypropylene (CPP) film of lithium-ion pouch cells (LIPC) under varying loads and temperatures. Firstly, an in-situ tensile test was conducted on strips cut from the sealing edge adhesive area (SEAA) to measure the maximum strength and peel displacement. Subsequently, an accelerated degradation test (ADT) under different constant loads and temperatures was performed to simulate strength degradation process of the SEAA. The stress-normalized displacement curves were measured, and residual strengths were obtained for each condition. Results of data analysis showed that the strength of the adhesive area decreased slowly over time for a given load and temperature. Moreover, the strength degradation rate was positively related to the level of load and temperature. A modified cohesive zone model (CZM) was established to describe the failure behavior and strength degradation of the SEAA. Finally, the proposed model is validated by experimental data.

Coupled Thermomechanical Dynamics of Phase Transitions in Shape Memory Alloys and Related Nonlinear Phenomena

The aim of this paper is to study the coupled non-linear dynamics of the behaviour of Shape Memory Alloys (SMA) under harmonic excitation. The thermomechanical model developed by Falk and based on Landau theory is used to describe the coupled thermomechanical behaviour of the SMA mass-damper-bar system. Fully coupled mechanical and thermal field equations are established to reveal the strong coupling phenomena arising from the phase transition. Then, the harmonic balance method is used to obtain the steady-state frequency responses. The effect of thermomechanical coupling on the frequency and time response curves is taken into account by modifying the heat transfer coefficient. The results show that deformation and temperature provide a stable sinusoidal response. The analysis of the results leads to different ways of controlling the nature and extent of the coupled and non-linear response of SMA-based oscillators. Comparison of the analytical results with experimental data from the literature validates the coupled thermomechanical nonlinear model. These results can be used effectively to control the external vibrations of various systems.

Experimental and thermal‐structure coupling analysis for oil and water‐swellable packer

AbstractIt has been widely acknowledged that traditional packers will lose their elastic performance in the context of long periods of operation due to plastic deformation. This paper will introduce a swellable packer that can reduce the failure cases of production effectively. The deformation of the packer rubber in different media and temperatures has been analyzed. The pressure test of several packer rubber under different media is carried out in this paper. The reasonable expansion clearance between the rubber tube and the well wall is obtained by strength calculation to ensure the sealing reliability of the packer. Finally, the thermomechanical coupling calculation of the packer with different structural sizes is carried out. Experiments at different temperatures show that the higher saline concentration is associated with a lower expansion rate and a larger expansion rate in clear water. At the same time, the expansion of volume in clear water increases. In addition, the higher the external temperature is, the larger the temperature gradient is. When the temperature of the outer ring is between 100°C and 140°C, the internal temperature rises to 37°C under the thermomechanical coupling effect.

Thermo-mechanical vibration and buckling analysis of porous FG sandwich plates with geometric discontinuity based on physical neutral surface

The effect of thermo-mechanical load coupling and porosity distributions on vibration and buckling characteristics of Functionally Graded Sandwich Plates (FGSPs) with cutouts is investigated by Finite Element (FE) formulation. Two sandwich configurations are considered and physical neutral surface is incorporated due to material asymmetry. Novel dynamic approach is proposed to evaluate buckling loads. Results obtained are compared with experimental, numerical solutions in literature and revealed that the FGSP buckling capacity under thermomechanical loads improves on using ceramic with lower thermal expansion coefficient. Also, at higher temperature rises, buckling capacity increases due to increasing porosity content, whereas capacity reduces at lower temperature rises.