Coupling Finite Element Model Research Articles

Numerical analysis and experimental investigation of residual stress and properties of T-joint by a novel in-situ laser shock forging and arc welding

A novel technique, referred to as Weld-LSF, has been proposed for the low-stress manufacturing of T-joints through in-situ synchronous assisted arc welding, employing laser shock forging. This innovative process introduces plastic deformation in the deposited weld seam at elevated temperatures, effectively reducing the tensile residual stresses (TRS) associated with welding. The thermal-mechanical coupling finite element model for Weld-LSF has been established, combining the classical bar-frame model and the inherent strain theory. The mechanism behind achieving low-stress welding of T-joints through in-situ LSF has been analyzed. Subsequently, experimental investigations were conducted using Q345 base metal and ER60–5 welding wire to study the influence of in-situ LSF on the microstructure and mechanical properties of the specimens. The results demonstrate that by introducing in-situ LSF at higher temperatures in the weld seam, tensile residual stresses are transformed from high to low levels, with the average TRS reduced from 342 MPa to 185 MPa, representing a significant reduction of 45.9 %. In-situ LSF forms a hardened layer with a depth of approximately 0.5 mm on the surface of the weld seam, albeit with certain depth limitations. Furthermore, the in-situ LSF treatment addresses the issue of poor ductility caused by stress concentration at the weld toe of T-joints, achieving a desirable combination of strength and ductility. The feasibility of in-situ LSF technology in welding fabrication has been established. In comparison to traditional welding techniques, the in-situ LSF treatment offers promising prospects for achieving low-stress welding, thereby enhancing the mechanical performance and fatigue life of the welding process.

Effects of different friction stir welding processes on residual stress and deformation of Ti62A alloy joints

Residual stress induced by welding easily causes deformation and even fracture failure in welded structures. In this paper, a three-dimensional thermal-mechanical coupling finite element model of friction stir welding (FSW) was developed. The effects of different welding processes, namely conventional friction stir welding (C-FSW), stationary shoulder friction stir welding (SS-FSW), and bobbin tool friction stir welding (BT-FSW), on the temperature, residual stress, and deformation of welded joints were investigated by employing a heat source model and a force model to the welding analysis. The results reveal that a discernible disparity in temperature gradient is observed in the region ahead of the tool and behind it among various welding processes. The peak values of longitudinal residual stress along the surface and bottom paths of SS-FSW are reduced by 35.7% and 34.1%, respectively. In addition, the deformation at the initial end of the weld is slightly larger than that at the final end along the welding direction in three welding processes. Compared with other FSW processes, SS-FSW exhibits the smallest deformation, which is advantageous for improving assembly accuracy and enhancing the load-bearing capacity of weldments. The above results provide an important theoretical reference for the FSW process optimization of Ti62A alloy.

Research on 750kV Reactor Vibration Based on Electromagnetic-mechanical Field Coupling Finite Element Model

The vibration signal characteristics of a 750kV shunt reactor with high voltage level and high vibration amplitude is one of the important indexes to evaluate the operating condition of the reactor. Since the high level of safe operation with Ultra-high voltage power equipment, it is challenging to collect long-term and extensive vibration signal data under safe operating conditions. This paper establishes the electromagnetic-mechanical field coupling finite element model (FEM) of a 750kV shunt reactor under a COMSOL open-source simulation environment. The resonance effect of magnetostriction of the iron core and the Maxwell forces between the iron core discs on the reactor structure is analyzed. The vibration distribution and typical frequency characteristics of each part of the 750kV shunt reactor are analyzed to provide a reference for the research of vibration fault diagnosis of Ultra-high shunt reactor.

Poroelastic response of inclined wellbore geometry in anisotropic dual-medium/media

Shale gas formations are typically characterized by anisotropic and fracture properties. Existing shale wellbore stability models have only considered the anisotropy of shale rocks and have ignored the effect of fractures. However, the mechanism of wellbore instability under the combined effects of shale anisotropy and dual-media (DM) remains unknown. Therefore, based on anisotropic poroelasticity, the DM theory, and the assumption of generalized plane strain, this study established a pseudo-3D hydraulic-mechanical coupling finite element model considering the DM and anisotropy of shale in wellbores. The effects of elastic anisotropy, fracture volume fraction, fracture permeability, mass transfer coefficient, and fluid pressure on wellbore stress were analyzed parametrically. The results showed that an anisotropic single-medium predicts that the wellbore will fail when the formation is drilled, whereas an anisotropic DM predicts periodic wellbore instability. The poroelastic effect of the matrix pore pressure is much greater than that of the fracture pore pressure. The matrix elastic anisotropy parameters control the distribution of mechanical parameters throughout the DM, further affecting the poroelastic response of the entire DM. When the drilling direction was mostly parallel to the bedding plane, the anisotropy of the matrix and fracture system of the elastic parameters were larger, and the wellbore was more stable. A larger fracture permeability leads to a larger fracture volume fraction and mass transfer coefficient, the matrix pore pressure and fracture pore pressure increase, and the instability of the wellbore also increases.

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.

A 3D Coupled Finite-Element Model for Simulating Mechanical Regain in Self-Healing Cementitious Materials

Interest in self-healing techniques that can enhance the performance of cementitious materials has been ever increasing over the past two decades. Alongside the experimental developments, a great deal of progress has been made on the development of numerical models for simulating the self-healing behavior. In spite of this, many models do not consider the coupled physical processes that govern the healing response. In addition, few are developed in a 3D setting that is necessary for many self-healing systems. This study aims to address this through the development of a new 3D coupled model for simulating self-healing cementitious materials. Key features of the model are a new embedded strong discontinuity hexahedral element that employs a damage-healing cohesive zone model to describe the mechanical behavior, a new approach for describing the dependence of the mechanical regain on healing agent transport based on a local crack filling function, and a generalized healing front model that is applicable to different healing agents. The performance of the model is demonstrated with a healing front study and experimental tests on self-healing cementitious specimens. The examples consider a vascular self-healing cementitious specimen that uses a sodium silicate solution as the healing agent and the autogenous healing of a cementitious specimen with and without crystalline admixtures. The results of the validations show that the model is able to reproduce the experimentally observed behavior with good accuracy.

Numerical simulations of fluid flow in trabecular–lacunar cavities under cyclic loading

BackgroundUnder external loading, the fluid shear stress (FSS) in the porous structures of bones, such as trabecular or lacunar–canalicular cavity, can influence the biological response of bone cells. However, few studies have considered both cavities. The present study investigated the characteristics of fluid flow at different scales in cancellous bone in rat femurs, as well as the effects of osteoporosis and loading frequency. MethodsSprague Dawley rats (3 months old) were divided into normal and osteoporotic groups. A multiscale 3D fluid–solid coupling finite element model considering trabecular system and lacunar–canalicular system was established. Cyclic displacement loadings with frequencies of 1, 2, and 4 Hz were applied. FindingsResults showed that the wall FSS around the adhesion complexes of osteocyte on the canaliculi was higher than that on the osteocyte body. Under the same loading conditions, the wall FSS of the osteoporotic group was smaller than that of the normal group. The fluid velocity and FSS in trabecular pores exhibited a linear relationship with loading frequency. Similarly, the FSS around osteocytes also showed the loading frequency-dependent phenomenon. InterpretationThe high cadence in movement can effectively increase the FSS level on osteocytes for osteoporotic bone, i.e., expand the space within the bone with physiological load. This study might help in understanding the process of bone remodeling under cyclic loading and provide the fundamental data for the development of strategies for osteoporosis treatment.

A rigid–flexible coupling finite element model of coupler for analyzing train instability behavior during collision

AbstractRail vehicles generate huge longitudinal impact loads in collisions. If unreasonable matching exists between the compressive strength of the intermediate coupler and the structural strength of the car body, the risk of car body structure damage and train derailment will increase. Herein, a four-stage rigid–flexible coupling finite element model of the coupler is established considering the coupler buckling load. The influence of the coupler buckling load on the train longitudinal–vertical–horizontal buckling behavior was studied, and the mechanism of the train horizontal buckling instability in train collisions was revealed. Analysis results show that an intermediate coupler should be designed to ensure that the actual buckling load is less than the compressive load when the car body structure begins to deform plastically. The actual buckling load of the coupler and the asymmetry of the structural strength of the car body in the lateral direction are two important influencing factors for the lateral buckling of a train collision. If the strength of the two sides of the car body structure in the lateral direction is asymmetrical, the deformation on the weaker side will be larger, and the end of the car body will begin to deflect under the action of the coupler force, which in turn causes the train to undergo sawtooth buckling.

Study of acoustic transmission losses in particle-reinforced rubber-based membrane-type acoustic metamaterials

In this work, the mechanical properties of particle reinforced ethylene propylene diene monomer (EPDM)/ethylene tetrafluoroethylene (ETFE) copolymer material were determined by molecular dynamics (MD) method, and the copolymer material was used in the structural design of acoustic metamaterials. Secondly, based on the discrete point matching method, the acoustic transmission loss characteristics of the material are predicted, and the accuracy and effectiveness of the theory are verified through the multi physical field coupling finite element model. Finally, seven key parameters that affect the material structure are studied, and their influencing rules and mechanisms are analyzed. The results show that the structure makes up for the sound insulation defect of traditional ETFE film materials at low frequencies. Through reasonable selection of key parameters, high sound insulation design can be carried out for specific frequency bands, which is of great significance to the potential application in the construction field (new building materials).

Experimental study and simulation analysis of thermal-vibratory stress relief treatment of Al-Cu-Mg alloy plate

The considerable uneven residual stress (RS) induced by the quenching process of aluminum (Al) alloys causes dimensional instability and deformation. RS relief is essential to enhance the performance of the Al alloys. Thermal vibration stress relief (TVSR), which integrates conventional thermal stress relief (TSR) and vibration stress relief (VSR), has been shown to effectively reduce and homogenize the RS of Al alloys. To date, the detailed processes and mechanisms of TVSR have yet to be studied. Therefore, TVSR experiments considering the coupling rules of TSR and VSR were conducted on the Al-Cu-Mg alloy. Coupled creep-mechanical finite element (FE) models considering the heat preservation time, vibration time, and vibration sequence was devised to predict the residual stress evolution during TVSR treatment. The TVSR simulation results are in good agreement with the experimental results. The results show that TVSR treatment with a heat preservation time of 110 min followed by vibration for 10 min had the optimal stress relief effect, with a stress relief rate 81.7 % higher than that of TSR. Different TVSR processes had little impact on the Vickers hardness and metallographic structure. The TVSR treatment mechanism was also analyzed.

Application of Pulse Compression Technique in High-Temperature Carbon Steel Forgings Crack Detection with Angled SV-Wave EMATs.

In order to solve the difficulty in localization and poor signal-to-noise ratio (SNR) of the angled shear vertical wave (SV wave) electromagnetic acoustic transducer (EMAT) in cracks detection of high-temperature carbon steel forgings, a finite element (FE) model of the angled SV wave EMAT detection process was established, and the influence of specimen temperature on the EMAT excitation, propagation, and reception processes was analyzed. A high-temperature resistant angled SV wave EMAT was designed to detect carbon steel from 20 °C to 500 °C, and the influence law of the angled SV wave at different temperatures was analyzed. Then a circuit-field coupled FE model of angled SV wave EMAT in the carbon steel detection process based on the Barker code pulse compression technique was established, and the effects of the Barker code element length, impedance matching method, and matching component parameters on the pulse compression effect were analyzed. In addition, the noise suppression effect and the SNR of the crack-reflected wave in the tone-burst excitation method and the Barker code pulse compression technique were compared. The results show that the amplitude of the block-corner reflected wave decreases from 556 mV to 195 mV, and the SNR decreases from 34.9 dB to 23.5 dB when the specimen temperature increases from 20 °C to 500 °C. When the temperature is 500 °C, the SNR of the crack-reflected wave obtained by the Barker code pulse compression technique can be improved by 9.2 dB compared to the tone-burst excitation method with 16 synchronous averages. The study can provide technical and theoretical guidance for online crack detection for high-temperature carbon steel forgings.

Head injury of two-wheeler cyclist based on fluid–solid coupling head model

Traumatic brain injury (TBI) is the main cause of driver death in electric two-wheeler accidents in China. Traumatic brain injury not only brings great threat to people's life safety, but also causes great economic losses in the process of national economic and social development. In this study, a head fluid–structure coupling finite element model was combined with a multi-rigid dummy body to form a finite element and multi-rigid body coupling model of an electric two-wheeler driver. Moreover, a human–vehicle-to-road combined system model was established that included a multi-rigid body two-wheeler model, a multi-rigid body vehicle model, and a road model, which is verified by an actual accident information. According to some simulation tests, moderate and severe nerve injuries may have happened to the driver although the HIC(Head Injury Criteria, common used in vehcile collision injury) is less than 1000. The result shows that the maximum pressure of the simulation result is 455.27 kPa, which exceeds the critical value of brain contusion. The overall relative error between simulation results and actual accident results is less than 10%. The driver model, especially the head model, can accurately simulate the bicyclist head injury and thereby provide a theoretical basis for the traffic injury assessment.

Analytical calculation method for predicting contact loads and structural strength of metallic gasket of subsea connectors under thermal loads

Identifying the effect of thermal loads that are caused by temperature differences of inner and outer fluids on the structural sealing performance and strength is a long-standing quest in the design of subsea connectors. However, the structural stress and sealing parameters of the gasket under thermal loads are difficult to analyze and calculate using the current theoretical method because the boundary conditions of the gasket’s geometry surface are contact constraints interacted by the gasket and hubs. This paper presents an analytical calculation method (ACM) that evaluates the thermal-structural coupling strength and sealing performance considering such special boundary conditions. The thermal load is converted into an equivalent compression load, that is, a concentrated force, and applied to the contact region of the gasket. Additionally, a thermal-structural coupling finite element model is proposed to verify the ACM and the results show good agreement. Taken together, this work contributes to the design of subsea connectors that more likely take thermal loads into account.

Deformation characteristics and inertial effect of complex aluminum alloy sheet part under impact hydroforming: experiments and numerical analysis

Impact hydroforming (IHF), as a novel sheet metal forming technology with the advantages of high strain rate forming and flexible liquid loading, is highly suitable for efficiently manufacturing aluminum complex-shaped sheet parts. In this paper, deformation characteristics of complex sheet parts under IHF are systematically investigated. The mechanical properties of 2024 aluminum alloy under a wide range of strain rates (10−3 s−1–3.3×103 s−1) were studied. It indicated that the elongation of 2024 aluminum alloy was improved by 116.01% under strain rates of 3.306 × 103 s−1, referring to 10−3 s−1. Further, a complex-shaped part with symmetrical and asymmetrical structures was selected. The deformation characteristics of sheet and role of inertial effect under IHF were investigated with well-developed solid–liquid coupling finite element (SLC-FE) model with high accuracy. Differentiating deformation tendency is found for symmetrical structure with notably prior deformation at central zone, showing a “bulging” profile at initial forming stage. Whereas, synchronous deformation is presented for asymmetrical structure with a “flat” profile. Additionally, distinctive inertial effect was observed at different positions change for both symmetrical and asymmetrical structures, in which lower values were resulted at their central regions. Meanwhile, the inertial effect evolved with the impacting speed. Specially, larger difference of inertial effect was observed with increasing impacting speed.

Tool Failure Analysis and Multi-Objective Optimization of a Cutting-Type Energy-Absorbing Structure for Subway Vehicles

This paper aims to provide essential guidance for the crashworthiness design of cutting energy-absorbing structures for subway vehicles. By investigating tool failure with experiment and numerical approaches, a new energy-absorbing tube structure was proposed and optimized to improve the crashworthiness and reliability of the cutting energy-absorption structure. The impact test results revealed that multiple failure modes occurred in the tool. Mechanical wear occurs mainly in the middle of the cutting edge, while the tool’s tip failure is primarily due to thermal wear. Impact forces were no longer stable due to tool failure. The simulation results of the established tool-tube thermal–structural coupling finite element model were consistent with the tests. The temperature distribution indirectly validated the failure modes in different tool areas. By eliminating the tearing-type fracture mode, the proposed new structure effectively reduced the high temperature of the tool’s tip, better maintained the uniform temperature of the cutting edge, and smoothed changing of the cutting force. Finally, the Kriging surrogate model and NSGA-II algorithm were utilized to obtain the tool’s minimum steady-state temperature (STT) and maximum mean average cutting force (MCF). The optimal solution determined by the minimum distance method is STT = 514 K, MCF = 131 kN.

Study of fatigue damage to the cochlea

In order to explore the hearing loss resulting from exposure to continuous or intermittent loud noise. A three-dimensional liquid-solid coupling finite element model of spiral cochlea was established. The reliability of the model was verified, and the stress and amplitude of the basilar membrane of the pivotal structure in cochlea were analyzed. The results show that under the action of the same high-pressure sound, the preferential fatigue area of the cochlear high-frequency area mainly causes fatigue in the cochlear. The safer area is a sound pressure level below 70 dB, while one above 90 dB accelerates damage to the ear.

Modelling of a shear-type piezoelectric actuator for AFM-based vibration-assisted nanomachining

Recent research investigations have reported the benefit of enhancing conventional AFM-based nanoscale machining operations by the introduction of high frequency vibrations between the AFM tip and the processed material. The technique relies on piezoelectric actuation and is relatively straight forward to implement in practice. However, the non-linearity of piezoelectric actuators when operated under high electric field and frequency conditions can affect the dimensional accuracy of the fabricated nanostructures. To address these issues, the paper reports a method based on coupled mechanical-electrical Finite Element (FE) modelling to predict the relative motion between an AFM tip and a workpiece for vibration-assisted AFM-based nanomachining applications. In particular, the novelty of the proposed method is that it combines two classical approaches for modelling the nonlinear behaviour of piezoelectric materials. More specifically, two sources of non-linearity are considered simultaneously by combining the field-dependant model from Muller and Zhang with the frequency-dependant model from Damjanovic. The resulting combined model is employed to establish the piezoelectric constitutive equations implemented in the developed coupled field FE model. A further distinguishing characteristic of the work is that the proposed approach was subsequently validated by comparing the predicted widths of nanoscale grooves against those machined with a custom AFM-based vibration-assisted nanomachining configuration.

Investigation on temperature uniformity control of titanium extrusion in hot stretch bending process

Regarding to the impact of temperature on springback in hot stretch bending (HSB) process, this work proposed an investigation on temperature uniformity control of titanium extrusion in HSB process based on the mould which can be elevated by resistance heating. Prior to the HSB test, mould structure was designed to fit for resistance heating. Coupled thermal electrical structural finite element model of HSB process was created in ABAQUS. Resistance heating and HSB tests were performed using displacement control electrically assisted stretch bending machine. The results of simulation indicate that the temperature uniformity of titanium extrusion and the forming accuracy of curved part can be effectively improved by increasing the initial temperature of mould. At last, the curved part of titanium extrusion with L-section was achieved, and the forming accuracy of which was measured and evaluated.

Modeling electron transport and multiplication in photomultiplier tubes using COMSOL Multiphysics®

Combining stochastic and finite element methods, a modeling approach was executed that will inform new photomultiplier tube and scintillation detector designs. Time-dependent signal formation within a commercially available photomultiplier tube was modeled including the release and transport of electrons from the photocathode through the dynode stages. An ET Enterprises 9214B photomultiplier tube was digitally reproduced using Computed Tomography, X-ray radiography, and SolidWorks solid-modeling software. Simulations were executed with COMSOL Multiphysics® finite element solving package. Stochastic models of electron emission from the photocathode and dynodes were integrated within the COMSOL framework. Photoelectron emission energy was modeled by combining NaI(Tl) spectral emission characteristics and K2CsSb photocathode quantum efficiency. Secondary electron emission yields were produced to follow nominal photomultiplier gain, while secondary electron energies were sampled from the Chung-Everhart distribution. Electron emission trajectories were sampled according to Lambert's cosine law. Coupling stochastic and finite element models, simulation reproduced signal formation for the commercial photomultiplier tube including timing characteristics within 9.5% and gain within 3% over a voltage range of 900–1250 V.

Springback prediction model of Ti-6Al-4V tube warm bending based on modified JC model considering variable temperature field

The plastic forming of titanium alloy tubes at room temperature exhibits strong anisotropy, low elongation, and large deformation resistance. Numerical control warm bending assisted forming technology can improve the stability of the titanium alloy tube bending process, increase the bending limit and reduce the springback angle. This technology promotes the wide application of high-precision titanium alloy bent tubes in many high-end fields such as aerospace, shipbuilding, chemical industry, and military industry. However, the titanium alloy tube bending at high temperatures involves complex material rheological behavior and microstructure characteristics. The coupling relationship between the stress-strain properties of the material and the temperature field makes it difficult to predict the springback behavior of titanium alloy tubes after warm bending. In this paper, based on the mechanical behavior of titanium alloy tubes at high temperatures, a constitutive model of titanium alloy suitable for local heating is improved. The theoretical model of springback for warm rotary draw bending of titanium alloy tube is established. The influence of warm bending strategies on the springback of bending is studied. The theoretical model is verified by establishing a thermal-mechanical coupling finite element model for the whole process of warm bending under the state of heat balance. The results show that the bending springback theory based on the modified John-Cook model can accurately simulate the temperature change of titanium alloy tube section, adapt to local heating strategies and provide high prediction accuracy of bending springback.