Numerical Simulation Technology Research Articles

Mistuning identification and model updating approach for bladed disks based on blade tip timing

To solve the problem of online mistuning identification of bladed disks, this paper proposes a novel mistuning identification method based on proper orthogonal modes (POM-ID) and the response data. Firstly, the proposed method is analyzed by numerical simulation technology, and the influence of related parameters on the identification results is discussed. Compared with the traditional method, the effectiveness of the proposed method is verified. Secondly, the POM-ID method is applied to identify the mistuning parameters of an actual bladed disk based on the blade tip timing test data. Finally, the identification results of the rotating bladed disk are verified by using static test results, and the dynamic model of the bladed disk is updated. The accuracy of the updated model is confirmed by the aspects of natural frequency and vibration coupling effect. The results indicate that the natural frequency error of the modified model is less than 1%, and the vibration coupling law between blades is consistent with the test results. The mistuning identification method proposed in this paper is especially suitable for test data of the rotating bladed disk and is expected to be applicable for online dynamic updating of the bladed disk model.

Prediction of Vortex-Induced Vibration Response of Open Bridge Girder Based on Machine Learning Method

The [Formula: see text]-shaped open section girder is a very common section, which has been widely used in the construction of modern bridges. However, compared with a streamlined box girder, it is easy to cause vortex-induced vibration (VIV) in bridges due to its bluff section shape and poor aerodynamic stability. In this paper, a typical open section with a height–width ratio of 10:1 is taken as the research object. Through wind tunnel tests and numerical simulation technology, the time-history data of VIV of the [Formula: see text]-shaped section are obtained. By selecting three different neural network models to establish the relationship between external parameters (wind attack angle, wind speed, turbulence) and structural response parameters (the onset wind speed of VIV, the length of the lock-in interval). After comparing different machine learning methods, the most suitable machine learning model is selected to predict the VIV response characteristics of the main girder. The research results show that the typical open section has a serious VIV phenomenon. The BP neural network model has the best performance in predicting the VIV performance of the open section in terms of calculation speed, prediction accuracy and solving nonlinear adaptability. At the same time, it is found that different characteristic parameters of the incoming wind field have different influences on the prediction results of the VIV response. Among them, the wind attack angle is the key parameter that affects the onset wind speed of VIV, but the turbulence intensity has a greater impact on the maximum amplitude of VIV. At the same time, the optimized BP model can predict the characteristic parameters of VIV response under unknown wind fields. This paper provides a new idea to study the effect of different incoming flow parameters on the performance of section VIV and further improves people’s understanding of VIV system.

Enhanced recovery of tight reservoirs after fracturing by natural gas huff-n-puff: Underlying mechanisms and influential factors

Tight oil resources are abundant in the world. It is very important to strengthen the research on the development theory and technology of tight oil reservoirs for ensuring national energy security. Natural gas huff-n-puff can effectively improve the oil recovery of tight oil reservoirs. However, the pore-scale oil production characteristics and the mechanisms of natural gas huff-n-puff in matrix-fracture cores are poorly understood. The influence degree of important factors on oil recovery is not clear and the interactions between factors are rarely considered. In this paper, the oil production characteristics and mechanisms of natural gas huff-n-puff in tight cores with different fracture lengths were quantitatively analyzed by combining nuclear magnetic resonance (NMR) with numerical simulation technology. The influencing factors and their interactions were evaluated by the response surface method (RSM). The results show that tight cores mainly consist of medium pores (0.1–1 μm) and small pores (0.01–0.1 μm). The fracture mainly increases the proportion of macro-pores (1–10 μm) and medium pores. In the natural gas huff-n-puff process, crude oil from macro-pores (1–10 μm) and medium pores is mainly developed, and the contribution percentage of crude oil in medium pores to oil recovery is the largest, up to 98.28%. The position of gas–oil contact (GOC) moves deeper as the number of huff-n-puff cycles increases. The contents of CH4 and CO2 in the oil phase remain at a high level within the GOC, while between the GOC and the component sweep front, the contents of CH4 and CO2 in the oil phase decrease with the increase in dimensionless distance. The gas component sweep volume is increasing with the increase in fracture length. Moreover, the injected natural gas mainly extracts C3–C10 components from crude oil. The reduction law of crude oil viscosity is consistent with the migration laws of CH4 components along the path. Compared with soaking time and gas diffusion coefficient, the injection pressure is the most significant factor underlying the recovery of natural gas huff-n-puff in tight cores. Besides the influence of single-factor, the interaction effects of gas injection pressure and diffusion also should be considered to determine the huff-n-puff parameters in the field implementation of natural gas huff-n-puff in tight reservoirs after fracturing.

Influence of clamping on out-of-plane deformation in thin-plate mild steel welded structures

Welding-induced deformation usually significantly degrade the dimensional accuracy of the fabricated structure, so it is crucial to mitigate welding distortion during the entire manufacturing process. Fixture is often used to control welding deformation for engineering welded structures. For thin-plate structures, if the welding procedure and conditions are not suitable, buckling distortion is prone to occur and its correction is very difficult. In order to clarify whether clamping can effectively prevent the occurrence of welding-induced buckling in thin-plate welded structures, both experimental method and numerical simulation technology were employed to investigate welding distortion in this study. Based on commercial software ABAQUS, a series of three-dimensional thermal-elastic-plastic finite element models were established to simulate welding distortions of mild-steel thin-plate structures with two different thicknesses (1.7 mm and 4.7 mm). Meanwhile, the corresponding experiments were carried out to verify the simulated results. Also, elastic buckling analyses were performed to evaluate the critical buckling stress for the thin-plate structures. Both simulated results and measured data indicate that clamping can effectively reduce the out-of-plane deformation in the weldment with 4.7 mm thickness, while it cannot prevent the occurrence of buckling distortion in the welded structure with 1.7 mm thickness.

Numerical Simulation and Experiment of Stress Relief and Processing Deformation of 2219 Aluminum Alloy Ring

Large aluminum alloy ring forgings are the core components of heavy-duty rocket fuel storage tanks, and the large residual stress inside the rings leads to poor shape accuracy of large thin-walled parts. The initial stress of the 2219 aluminum alloy ring blank was tested using the drilling method, and the creep constitutive coefficient of the 2219 aluminum alloy was determined through stress relaxation tests. The numerical simulation processes of thermal stress relief (TSR), vibration stress relief (VSR), and thermal–vibration stress relief (TVSR) were compared and established. Through the correlation analysis between the actual measurement results of residual stress and the simulation results, it can be seen that the strong correlation in three directions at each measurement point accounts for over 37.5%, and the moderate correlation accounts for over 62.5%. This indicates that the numerical simulation model of 2219 aluminum alloy ring containing initial residual stress can accurately reflect the size and distribution of residual stress inside the actual ring. The simulation results show that the derived constitutive model can describe the stress relaxation process of TVSR by combining a single thermal time effect stress relaxation constitutive theory with a VSR plastic deformation material model. The simulation models established above were used to calculate the residual stress homogenization ability of three types of aging. The results showed that VSR, TSR, and TVSR can homogenize and reduce the residual stress field inside the ring, improve the distribution of residual stress inside the ring, and have a better overall homogenization ability of TVSR. The VSR control has a certain effect on reducing and homogenizing residual stress, but compared with TSR and TVSR, the reduction and homogenization ability of residual stress control is limited. The homogenization control effect TVSR > TSR > VSR, and the maximum equivalent stress homogenization rates of VSR, TSR, and TVSR are 52.8%, 80.6%, and 82.2%, respectively. Then, numerical simulation technology was used to study how the initial residual stress in the blank causes the deformation of the ring during the thin-walled machining process. The roundness error theory of the minimum containment area method was applied to evaluate the deformation degree during the thin-walled numerical machining process, and the TVSR method was used for stress regulation. The deformation law of the thin-walled machining of the ring under different aging parameters was studied.

A Real-Time Calculation Method to Improve Boiler Safety in Deep Peak Shaving Cases

To tackle the overheating problem of the heating surface in deep peak shaving, it is urgent to develop working substance (steam) temperature regulation and heating surface safety control technologies that combine combustion and hydrodynamic instability evaluation. This work relies on a 1000 MW boiler involved in deep peak shaving, and adopts CFD numerical simulation technology to obtain reasonable holographic heat load data of the boiler. The heat load data and the working substance side data are coupled to develop a real-time performance calculation model that combines combustion and hydrodynamic steam temperature. Real-time monitoring of the local position of the boiler water wall and the convection heating surface can be achieved through the three steps: heat load screening, heat exchange process calculation, and result display. The results show that through the corresponding expression of on-site industrial parameters and CFD simulation data, the effective analysis, extraction, modeling and optimization of the operation data can be realized for real-time online monitoring and intelligent early warning of the entire working condition. The model error is less than 2 °C and the model can realize early warnings at 5 min, so as to ensure the safety and stability of boiler operation and save the operating cost of the power plant to a certain extent.

Equivalent Circuit Models of a Bifunctional Optical Metasurface for Beam Splitting and Refractive Index Sensing

Metasurfaces have attracted extensive attention in the micro/nano-optics field depending on their significant ability to modulate optical parameters. However, the current numerical simulation technology cannot meet the demand of the design and analysis of metasurfaces efficiently due to consuming substantial calculating time and memory. Besides, they cannot illustrate the physical mechanism straightforwardly behind the optical responses. Herein, we propose and demonstrate two equivalent circuit models systematically for a bifunctional metasurface with metal–dielectric–metal structural meta-atoms based on polarization multiplexing in the visible band. In the y-polarization state, the equivalent circuit model is established to interpret the phase shift exactly with a high goodness of fit of 0.931, resulting in the beam splitting function from the anomalous reflection phenomenon. The polychromatic light splits from 34 to 69° to produce the grating-type high-saturation structural colors with a large gamut of about 170.07% of the DCI-P3 standard. In the x-polarization state, the metasurface produces the surface lattice resonance that is suitable for the refractive index sensing function due to the high sensitivity to environmental changes. The second equivalent circuit model simulates the linewidth narrowing and red-shift phenomenon with a sensitivity relative error of 7.00%. We introduce a branch with a narrow-band-pass filter and a capacitor in series into the model to mimic the characteristic of Rayleigh anomalies. Both models extend the application of equivalent circuit theory in optics further and provide a crucial approach to enhance the insights into the mechanism of metasurfaces.

Development of Fatigue Life Model for Rubber Materials Based on Fracture Mechanics.

In this paper, the research on the fatigue damage mechanism of tire rubber materials is the core, from designing fatigue experimental methods and building a visual fatigue analysis and testing platform with variable temperature to fatigue experimental research and theoretical modeling. Finally, the fatigue life of tire rubber materials is accurately predicted by using numerical simulation technology, forming a relatively complete set of rubber fatigue evaluation means. The main research is as follows: (1) Mullins effect experiment and tensile speed experiment are carried out to explore the standard of the static tensile test, and the tensile speed of 50 mm/min is determined as the speed standard of plane tensile, and the appearance of 1 mm visible crack is regarded as the standard of fatigue failure. (2) The crack propagation experiments were carried out on rubber specimens, and the crack propagation equations under different conditions were constructed, and the relationship between temperature and tearing energy was found out from the perspective of functional relations and images, and the analytical relationship between fatigue life and temperature and tearing energy was established. Thomas model and thermo-mechanical coupling model were used to predict the life of plane tensile specimens at 50 °C, and the predicted results were 8.315 × 105 and 6.588 × 105, respectively, and the experimental results were 6.42 × 105, with errors of 29.5% and 2.6%, thus verifying the accuracy of thermo-mechanical coupling model.

Numerical and Experimental Investigation of Slope Deformation under Stepped Excavation Equipped with Fiber Optic Sensors

The real-time evaluation of slope stability is a crucial technical issue in foundation excavation and slope construction. However, conventional monitoring methods often fall short of achieving real-time and accurate measurements, which poses challenges to the timely assessment of slope stability. To address this problem, laboratory tests and numerical simulations were jointly used to evaluate slope stability in this paper. In numerical simulations, the finite element method (FEM) results clearly illustrate the distribution and evolution of internal strain during slope excavation, and the limit equilibrium method (LEM) calculates changes in the safety factor. In laboratory tests, the fiber Bragg grating (FBG) sensing technology was employed to monitor the internal strain of the slope in real time. The distribution characteristics of the slope internal strain field under the condition of stepped excavation were analyzed, and the feasibility of strain-based evaluation of slope stability was discussed. The measurements with FBG sensing technology agree well with the numerical simulation results, indicating that FBG can effectively monitor soil strain information. Of great significance is that the maximum horizontal strain of the slope is closely related to the safety factor and can be used to evaluate slope stability. Notably, the horizontal soil strain of the slope provides insight into both the formation and evolution of the critical sliding surface during excavation. The combination of numerical simulation and intelligent monitoring technology based on FBG proposed in this paper provides a reference for capturing strain information inside the slope and realizing real-time assessment and critical warning of slope stability.

Pore-Scale Oil-Water Flow Behaviors in Different Development Adjustment Schemes for Enhancing Oil Recovery in Waterflooding

Development mode adjustment is an important measure to further enhance oil recovery after primary waterflooding. Investigating the oil-water flow behaviors in the pores is significant to deepening the understanding of the macrobehavior of waterflooding and the designation of the reservoir development plan. Previous studies mainly focused on the change in recovery factor and macroflow characteristics, while less attention was paid to the causes of the change in recovery factor and the difference in macrocharacteristics. In this paper, the numerical simulation technology by coupling the Navier-Stokes equation with the method of volume of fluid is employed to investigate the dynamic formation mechanism of the remaining oil at pore-scale in the primary waterflooding, and then the pore-scale oil-water two-phase behaviors under three waterflooding development adjustment schemes: changing flooding direction, turning extraction well to injection well, and increasing injection rate are studied. The research shows that when the viscous resistance of the water-bearing channel is less than the sum of the capillary barrier and drainage capillary resistance (the resistance in the displacement of wetting phase displacement using the nonwetting phase), the remaining oil is formed. Water➔oil➔water➔oil displacement mode is formed in the process of changing flow direction, which makes the force of the phase interface tend to balance, reduces the capillary effect in waterflooding, and improves oil recovery. In the process of developing the scheme of turning extraction into an injection well, through multipoint injection, it advances from the central water-bearing area to the oil-bearing area on both sides in multiple paths, forming a larger spatial spread range than that in the change of flooding direction. Under the influence of the capillary barrier effect and drainage capillary resistance, when the injection rate is increased, the remaining oil can restart to move only when the flowing rate exceeds a certain value. The small viscous resistance in the water-bearing channel and the lateral resistance from the capillary barrier limiting the lateral sweep of water are the primary reasons for the insignificant improvement of oil recovery under the condition of a low liquid injection rate. The findings of this study can help for better understanding of pore-scale flow mechanism behaviors and their influences on the macroscopic development features in the waterflooding process.

Digital Integration of Temperature Field of Cable-Stayed Bridge Based on Finite Element Model Updating and Health Monitoring

A health monitoring system typically collects and processes data to observe the health status of a bridge. The cost limitations imply that only the measurement point data of a few key points can be obtained; however, the entire bridge monitoring information cannot be established, which significantly interferes with the data integrity of the structural monitoring system. In this study, a solution is proposed for reconstructing the monitoring data of the entire bridge. By updating the finite element (FE) model based on structural thermal analysis, numerical simulation technology, and other methods, the temperature field integration model of a cable-stayed bridge is realized. The temperature spatial expansion method of deep learning is established by using the complete simulated temperature field of the entire bridge based on limited measured temperature data; this data is verified and applied to the main beam and bridge tower, thereby establishing the complete measured temperature field of the whole bridge. This is of great significance in supplementing health monitoring information, allowing for the accurate monitoring and evaluation of the structural safety and service performance of long bridges.

Study on the Convergence of Surrounding Rock in Shallow Buried Unsymmetrical Pressure Tunnel Construction

In order to study the evolution law of tunnel convergence deformation during the construction of shallow buried unsymmetrical pressure tunnel, the deformation characteristics and evolution law of shallow buried unsymmetrical pressure tunnel during the three-step construction method are studied based on the background of Qingshui No. 2 tunnel project and numerical simulation. The results show that: with the tunneling, when the tunneling depth is less than 40m, the settlement deformation gradually decreases, and the maximum settlement is at the entrance; When the tunnel footage is greater than 40m, the settlement deformation first increases and then decreases. The maximum settlement of the arch crown is 15m in front of the tunnel face, while the maximum settlement of the arch shoulder is 20m in front of the tunnel face; The maximum value of arch waist convergence appears at 10m in front of the tunnel; The effective combination of numerical simulation and monitoring technology can provide guidance for engineering practice.

Key theoretical and technical issues and countermeasures for effective development of Gulong shale oil, Daqing Oilfield, NE China

Aiming at the four issues of underground storage state, exploitation mechanism, crude oil flow and efficient recovery, the key theoretical and technical issues and countermeasures for effective development of Gulong shale oil are put forward. Through key exploration and research on fluid occurrence, fluid phase change, exploitation mechanism, oil start-up mechanism, flow regime/pattern, exploitation mode and enhanced oil recovery (EOR) of shale reservoirs with different storage spaces, multi-scale occurrence states of shale oil and phase behavior of fluid in nano confined space were provided, the multi-phase, multi-scale flow mode and production mechanism with hydraulic fracture-shale bedding fracture-matrix infiltration as the core was clarified, and a multi-scale flow mathematical model and recoverable reserves evaluation method were preliminarily established. The feasibility of development mode with early energy replenishment and recovery factor of 30% was discussed. Based on these, the researches of key theories and technologies for effective development of Gulong shale oil are proposed to focus on: (1) in-situ sampling and non-destructive testing of core and fluid; (2) high-temperature, high-pressure, nano-scale laboratory simulation experiment; (3) fusion of multi-scale multi-flow regime numerical simulation technology and large-scale application software; (4) waterless (CO2) fracturing technique and the fracturing technique for increasing the vertical fracture height; (5) early energy replenishment to enhance oil recovery; (6) lifecycle technical and economic evaluation. Moreover, a series of exploitation tests should be performed on site as soon as possible to verify the theoretical understanding, optimize the exploitation mode, form supporting technologies, and provide a generalizable development model, thereby supporting and guiding the effective development and production of Gulong shale oil.

Research on ballistic performance and numerical simulation technology of Si3N4 ceramic materials

Ceramic materials are widely used in the field of armor protection because of high hardness and low-density. In order to research the ballistic performance of Si3N4 ceramic and evaluate the penetration effect, the DOP test against the 12.7 mm API was carried out. The results show that the protection coefficient is in the range of 1.85-4.26, and thickness coefficient is in the range of 1.85-4.26. On this basis, the numerical simulation technology of Si3N4 ceramic composite armor is studied by using LS-Dyna software. The accuracy of the finite element model is verified by comparing the test result. It can guide significance for the use of Si3N4 ceramic in the field of armor protection.

A Review on Process-Based Groundwater Vulnerability Assessment Methods

The unreasonable development and pollution of groundwater have caused damage to the groundwater system and environmental problems. To prevent this, the concept of “groundwater vulnerability” was proposed, and various evaluation methods were developed for groundwater protection. However, with changing climatic conditions and human activities, groundwater vulnerability is now emphasizing physical processes. This study aims to review and analyze the principles and applications of process-based groundwater vulnerability methods to achieve the source protection of groundwater resources. It introduces the assessment method and elaborates on pollutant migration processes and numerical simulation technology. Relevant articles from the past 30 years are reviewed to show the evolution of process-based groundwater vulnerability assessment. The study also discusses current research trends and proposes future development paths. It concludes that process-based groundwater vulnerability assessment will become the mainstream method, and modern technologies such as artificial intelligence will be necessary to solve challenges and achieve sustainable development.

Simulation of SLM manufactured aluminum process and optimization of the parameters by computational fluid dynamics method

The additive manufacturing technology of metal components is an advanced technology in the field of mechanical engineering and material science. Laser selective melting (SLM) is one of the most widely used methods in additive manufacturing. The temperature field of SLM process is the key factor to determine the quality of additive, so it has important research value. In this paper, the influence of laser power and additive speed on the temperature field of aluminum alloy additive manufacturing is studied by CFD numerical simulation technology. The results show that the CFD model can well simulate the SLM process. The additive temperature decreases with the increase of additive speed and increases with the increase of laser power. By adjusting the additive manufacturing parameters, the quality of additive manufacturing can be corrected and improved.

Dynamic Cutting Performance Test and Parameter Optimization of Longicorn Bionic Blade for Industrial Hemp Harvester

In response to the unclear issue of whether the dynamic cutting performance and structural parameters of an industrial hemp blade, which was developed earlier based on the bionic prototype of the batocera horsfieldi, can be optimized in actual working conditions, this paper analyzes the effective clamping conditions of a reciprocating double-acting cutting blade for stalks and the cutting motion. To investigate the effect of different structural and motion parameters, as well as their interactions, of the bionic blade on cutting energy consumption, bionic blades with different combinations of tooth pitch and tooth angle were designed. A Box–Behnken response surface method with three factors and three levels was used to design an experimental scheme. Utilizing rigid-flexible coupling numerical simulation technology, numerical simulation experiments were conducted to investigate the cutting performance of industrial hemp stalks using the blade. A regression model for cutting energy consumption was established, and variance analysis indicated that tooth angle, speed ratio, and the interaction between tooth angle and speed ratio had an extremely significant effect on the regression model. The primary and secondary orders of factors affecting cutting energy consumption were determined to be: speed ratio > tooth angle > tooth pitch. Through optimization, the optimal parameter combination was found to be a blade tooth pitch of 6.61 mm, a tooth angle of 30°, and a speed ratio of 1.62. Under these conditions, the cutting energy consumption was 3947.99 mJ. The optimized parameters were verified through numerical simulation cutting experiments, and the results showed that the error compared with the optimization results was only 8.16%. This indicates that the optimization results have high credibility and further verifies the reliability of the model. This study can provide a reference for the development of cutting devices for industrial hemp harvesters and the selection of motion parameters.

Failure time of reinforced concrete column under blast load

To explore the damage and the failure time of the reinforced concrete column in an adjacent physical field of explosion, a comprehensive finite element model of TNT-air-column in the software LS-DYNA is set up in consideration of the advanced numerical simulation technologies (i.e., element birth and death technology, large deformation technology, contact technology, etc) and the strain rate effects of the concrete and steel materials. First of all, an explosion test is conducted on two scale models of the reinforced concrete column, and the finite element model is validated by comparing the numerical simulation results with the experimental data. The failure process, failure mode, and failure criterion of the reinforced concrete column under blast load are further investigated. Thereafter, a series of parameter studies are conducted to investigate the damage and the failure time of the reinforced concrete column. Finally, a new method is proposed to estimate the failure time of the reinforced concrete column and the corresponding basic steps are given in this study. Through the researches and analyses of the typical cases, the results show that the failure modes change from punching failure to compression-flexure failure via compression-shear failure with the increase in the scaled distance. The medium damage and the high damage occur mostly on the reinforced concrete column in an adjacent physical field of explosion. The damage index of the reinforced concrete column varies significantly with the compressive strength of concrete, column height, column depth, longitudinal reinforcement ratio, transverse reinforcement ratio, and axial compression ratio, especially the column depth and the axial compression ratio; however it has little relation with the column width. The failure time of the reinforced concrete column is up to tens of milliseconds or even more than one hundred milliseconds. The calculation formulas used in the proposed method are based on previous research and simulation results. The proposed method is rigorous and thorough and the predicted results are highly accurate and effective. Besides, this method can provide a good prediction of the failure time of the reinforced concrete columns with different axial compression ratios.

Three-Dimensional Simulation of Corona Discharge in a Double-Needle System during a Thunderstorm

The effect of corona discharge from buildings or structures on the surrounding atmospheric electric field is very important in the measurement of urban atmospheric electric fields and the early warning of lightning. However, most previous studies were focused on independent buildings, with little research on three-dimensional building groups. Therefore, based on three-dimensional numerical simulation technology, this paper uses a double-needle system to simulate the characteristics of thunderstorm corona discharge from two equal-height buildings separated by a variable distance. The shielding effect of the double-needle system on the ground electric field is evaluated both with and without corona discharge, and the main conclusions are as follows: (1) The larger the distance between the two needles, the closer the peak corona current from each tip of the double-needle system is to that from an independent lightning rod at the same height. When the peak corona current from each tip of the double-needle system equals the peak corona current from an independent lightning rod at the same height to some level of approximation, the distance between the two needle systems is determined by the needle height at this time. (2) If the distance between the two needles is 0.1 m, the corona charge released by the double-needle system is almost equal to that released by an independent lightning rod. The corona charge released by the double-needle system is approximately twice as much as that released by an independent lightning rod when the distance between the two needles is increased to a certain value that increases with the needle height and the time of corona discharge. (3) The greater the value of the time of corona discharge, the stronger the shielding effect of the corona discharge on the ground electric field and the larger the shielding range, but the greater the value of the needle height, the smaller the shielding range. (4) Compared with the shielding effect with no corona discharge, that with corona discharge is greater, but the greater the value of the needle height, the less the enhancement. For example, for corona discharge with a time of 10 s, the needle height is 20 m, and the shielding range is ca. 70 m, which is 8.8 times that without corona discharge; however, for the needle height of 100 m, the shielding range is ca. 150 m, which is only 1.5 times that without corona discharge.

Unified modeling of the microstructure and densification of TC4 powder titanium alloy during hot deformation

An accurate material constitutive model is very important to apply numerical simulation technology to predict, establish and optimize the thermoplastic forming process parameters of powder titanium alloy. To achieve this goal, the microstructure evolution and densification of TC4 powder titanium alloy were investigated during compression at temperatures from 860 °C to 960 °C, strain rates from 0.05 s−1 to 20 s−1 and strains from 0.357 to 1.204. The results show that the microstructure undergoes dynamic recrystallization under different conditions. High temperature, large deformation degree and low strain rate are helpful to reduce porosity, pore size and pore colony. Plastic deformation and diffusion are two main mechanisms of densification. The microstructure evolution and densification model were established, combining the power constitutive law, a unified constitutive model was proposed to predict flow stress, microstructure and relative density of TC4 powder titanium alloy. The model constants were determined through a genetic algorithm. The predicted values of flow stress and relative density agreed well with the experimental values. The variations in relative density with temperature, strain rate and strain were analyzed based on the prediction results.