最新刊期
期 4 ， 2022
- 摘要：In order to predict remaining useful life（RUL） of bearings, the wavelet-spectral kurtosis analysis method is used. Firstly, the bearing vibration sequence signal is decomposed by wavelet packet, the spectral kurtosis is chosen to determine the fault characteristic frequency band and reconstructed the signal. Then, determine whether the bearing is faulty according to its spectral characteristics. Lastly, the incipient fault point（IFT） of the bearing vibration sequence signal is determined. On this basis, the one-dimensional deep separable convolutional neural network with attention mechanism is used for the extraction of bearing vibration signal features. Compared with traditional convolutional neural networks, deep separable convolutional layers can reduce the number of network training parameters and speed up network training. The experimental results show that the introduction of the attention mechanism enables the network to focus on the key features in the signal, assign greater weight to important features, avoid the shortage of manual processing features, and facilitate effective feature extraction. The final prediction results are better than common data-driven methods such as SVR, CNN, and RNN.关键词：Deep separable convolution;Attention mechanism;Neural network;Incipient fault point（IFP）;Remaining useful life（RUL） prediction
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发布时间：2022-09-22 - 摘要：The uncertainty analysis of test results of nonlinear system shows the dispersion of test results. In this paper, an evaluation method of test uncertainty of nonlinear system based on polynomial chaos expansion is suggested. The evaluation method is compared with the method specified in the national standard Monte Carlo Method for Evaluation of Measurement Uncertainty through Ishigami test model. The results show that the suggested method has higher accuracy and efficiency. Taking the seat belt anchorages test as an example, the surrogate model of the test is established by polynomial chaos expansion method, and the uncertainty evaluation of the test is realized. To solve the problem of insufficient sample size, the improved hyperbolic truncation technique and Sobol sensitivity analysis based on polynomial chaos expansion model are used to simplify the model. The results show that the two simplified methods can significantly reduce the demand for samples size. The results show that polynomial chaos expansion and its simplification can be widely applied to the uncertainty analysis for various product tests.关键词：Measurement uncertainty;Polynomial chaos expansion;Safety-belt anchorages test;Nonlinear system test
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发布时间：2022-09-22 - 摘要：The airborne fuel pump is a key component of the fuel system. In view of the phenomena of mode aliasing and excessive residual component in the process of signal decomposition and reconstruction, a fault diagnosis method for airborne fuel pump based on CEEMD Shannon entropy and improved SVM is proposed. The signals of shell vibration and outlet pressure under various working conditions are obtained on the fault diagnosis test bench of airborne fuel pump. Then in the simulation I decomposed the vibration signals by using CEEMD method and calculated the Shannon entropy of IMF. Based on the above results, I selected the energy value and the mean value of pressure signal as the input eigenvectors of SVM, and used the SVM optimized by Gapso the to diagnose the fault types of fuel pump. Compared with BP neural network, SVM optimized by particle swarm optimization（PSO） and SVM optimized by genetic algorithm（GA）, the results showed that the model of SVM diagnosis optimized by GA has the advantages of fast training, high accuracy and short time-effect, and it has good engineering application value.关键词：Aircraft fuel pump;CEEMD;Shannon entropy;Support vector machine;Fault diagnosis
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发布时间：2022-09-22 - 摘要：The energy dissipation characteristics of the non-linear normal vibration contact system of the interface have important theoretical and engineering significance for describing the dynamic mechanism of the interface.Based on Hertz contact theory, the dynamic model of nonlinear normal vibration contact of damping joint interface is established, and the dynamic response of damped free vibration and simple harmonic forced vibration and the calculation method of vibration contact energy dissipation are proposed; the non-linearity is established The dynamic equation of the normal vibration contact system, the energy dissipation rate and cumulative energy dissipation rate of damped free vibration, and the input energy and damping loss energy of simple harmonic forced vibration are calculated; the nonlinear normal vibration contact interface is studied The relationship between energy dissipation characteristics and energy transfer provides a theoretical basis for describing the dynamics of the vibrating contact interface.关键词：Non-linear;Normal;Vibration contact;Energy dissipation;Damping joint interface
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发布时间：2022-09-22 - 摘要：Two kinds of aluminum alloy sheets, AL5052 and AL6061, and basalt fiber cloth are selected to be laid as symmetrical and alternate layers to manufacture fiber-metal laminates with different structures. The bending and low-speed impact performance of the laminate structure are tested and compared; the laminate low-speed impact simulation model is established to study the influence of laminates fiber layup methods on the low-speed impact resistance; the thickness of aluminum alloy plates were optimized with multiple objectives to obtain the best thickness values of each layer of aluminum alloy plates; the optimal laminate structure is applied to the external panel of a car door for column collision simulation analysis. The results show: compared with the original door, the energy absorption characteristics and weight reduction effect of the fiber metal laminate door have been improved obviously.关键词：Basalt fiber;Fiber-metal laminate;Low-speed impact performance;Multi-objective optimization;Crashworthiness of automotive door
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发布时间：2022-09-22 - 摘要：The encapsulation test of 0.1 mm thick SUS304 stainless steel with BNi-2 as the intermediate layer was carried out by using resistance spot brazing technology. The influence of technological parameters on the microstructure and mechanical properties of resistance spot brazing joint was analyzed, the element distribution and phase composition in the joint area were determined, and the air tightness of the joint was verified. The results show that the resistance spot brazing joint is composed of the brazing zone, the thermomechanical affected zone and the base material; With the increase of welding current and electrode pressure, the thickness of the brazing zone decreases and the dynamic recrystallization degree of the thermomechanical affected zone increases; The high cooling rate inhibits the element diffusion between the brazing joint and the base metal, the phases of the brazing joint are nickel based solid solution and dispersively distributed fine Cr2B and Ni3B particles, the maximum shear resistance of the joint is 118.3 N; The maximum load pressure of the package element reaches 0.53 MPa, which indicates that the resistance spot brazing joint of ultra-thin austenitic stainless steel has excellent air tightness.关键词：Resistance spot brazing technology;SUS304 stainless steel;Microstructure;Mechanical properties;Air tightness
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发布时间：2022-09-22 - 摘要：The residual compressive stress of shot peening can effectively improve the fatigue resistance of the material, but the residual compressive stress is unstable during service and will relax. In order to further study the relaxation rule of the residual compressive stress, the fatigue test of the standard tensile specimen of the shot peening 2024 aluminum alloy under two kinds of load was carried out. μ-X360 n X-ray diffractometer based on cosα method was used to analyze the variation law of residual stress during fatigue test. The results show that when the load is 10 kN the residual compressive stress shows regular relaxation, that is, the residual compressive stress drops significantly after the first cycle loading and the residual compressive stress basically remains unchanged or slowly decreased. At the load of 15 kN, the residual compressive stress appears to relax in reverse, that is, the residual compressive stress becomes a residual tensile stress after the first cyclic loading, and gradually decreases with the number of fatigue cycles and the residual stress distribution changed from the initial “√”-shaped distribution to an approximate linear distribution, gradually decreasing from the inside to the outside. In order to describe the relaxation behavior and process of residual compressive stress of shot peening, based on the existing experimental models, a new residual stress relaxation model considering the surface state of shot peening was proposed.关键词：2024 aluminum alloy;Shot peening;Residual compressive stress;Relaxation;Fatigue test
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发布时间：2022-09-22 - 摘要：According to the common structure characteristics of the plug-in fillet weld, a new weld defect detecting method was presented in this paper. The flexible phased array probe was inserted into the internal surface of the tube under water immersion during the detection process. The beam focusing model of convex flexible phased array was theoretically analyzed. Meanwhile, the acoustic focus beam with CIVA software were simulated. The typical flaws were added to the model of plug-in fillet weld, and defect response were obtained. The sample of the plug-in fillet weld with artificial flaws is manufactured, the system was calibrated in the laboratory. The experiment results indicated that this technique can successfully detect the typical flaws of crack, slag and porosity. Finally, the technique was applied to the manufacture quality inspection of the products, one incomplete penetration and one porosity were detected. The detecting system can effectively ensure the general welding flaws of the product were detected.关键词：Plug-in fillet weld;Flaw;Flexible phased array probe;CIVA software;Test
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发布时间：2022-09-22 - 摘要：Based on the shear load case, the bearing capacity and failure mode of composite laminates with circular and diamond holes were studied by test and numerical simulation. The results show: under the premise of the same laminate weight, the same hole accessibility and the same stacking angle information, the load-carrying capacity of the laminate with diamond hole is greater than that of the laminate with circular hole; based on the nonlinear continuum damage mechanics（CDM）, the fiber damage is predicted by using the maximum strain failure criterion, and the matrix damage is predicted by using the three-dimensional nonlinear puck failure criterion A three-dimensional finite element model of laminate is established and numerical simulation is carried out. The comparison with the experimental results shows that the model can effectively predict the bearing capacity and failure mode of laminate with hole.关键词：Composite;Laminate;Hole;Continuum damage mechanics;Failure mode
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发布时间：2022-09-22 - 摘要：This paper, based on theory of critical distance（TCD）, carried out a research on the fatigue strength prediction of axle specimens with surface notch. The fatigue limit of smooth specimens, specimens with V-shaped surface notch, and specimens with hole-shaped surface notch were tested by axial loading. Meanwhile, the crack growth threshold value when stress ratio R=-1 was tested. The fatigue limit of railway axle specimens with surface notch were predicted by the point method and line method of TCD with the aid of finite element calculation. Calculation results show that, when TCD is used to predict fatigue limit of axle specimens with surface notch, the relative error of point method is larger, and line method has higher prediction accuracy. Line method is able to meet engineering needs and has important guiding significance in predicting the fatigue strength of axles with surface notches.关键词：Notch;Railway axle;Fatigue test;Fatigue limit;Theory of critical distance TCD
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发布时间：2022-09-22 - 摘要：Large deformation and fracture processes of materials are often involved in the finite element simulation of high-speed collision. Based on the Johnson-Cook fracture failure model, TC4 titanium alloy samples with different notch sizes were designed, and the fracture strain and stress triaxiality of the samples were studied by combining test and finite element simulation. Speckle was produced during the experiment. The fracture strain of the sample under quasi-static tensile condition was obtained by using two-dimensional digital image correlation（DIC） technique at room temperature. The software Abaqus was used to simulate the quasi-static tensile process and obtain the average stress triaxiality of each sample. The parameters of Johnson-Cook fracture failure model were obtained by fitting the fracture strain with average stress triaxiality. The parameters of the fracture failure model were brought into the Pamcrash software for simulation, the fracture morphology and load-displacement curves of the test and Pamcrash simulation showed good consistency, which verified the correctness of the parameters of the failure model.关键词：TC4 titanium alloy;Stress triaxiality;Johnson-Cook fracture failure model;Fracture strain;DIC measurement technique
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发布时间：2022-09-22 - 摘要：The quasi-static(Strain rate of 0.001 s-1～0.01 s-1) and dynamic(Strain rate of 1000 s-1 ～ 5 000 s-1) compression tests of TA17 titanium alloy were conducted on at 25℃. The strain hardening characteristics and the mechanism of strain rate on its rheological behavior were studied, and the rheological characteristics under high strain rates were quantitatively studied by means of strain hardening index（n） and strain rate sensitivity index（m）. Based on the dynamic rheological characteristics of TA17 titanium alloy and considering the influence of the coupling between strain and strain rate on its flow stress, a new J-C constitutive model is constructed. based on the obtained experimental data, the model parameters are identified, the predicted values of the model are compared with the experimental data, and the two parameters of correlation coefficient（R） and average absolute relative error are introduced to evaluate the prediction accuracy of the constructed constitutive model.The results show that TA17 titanium alloy exhibits obvious strain hardening, strain rate strengthening and strain rate plasticizing effects, and its rheological behavior is dominated by strain, strain rate and the coupling between them. The strain hardening index decreases with the increase of strain and strain rate, while the strain rate sensitivity index increases with the increase of strain rate, and decreases with the increase of strain. The correlation coefficient（R） of constructed constitutive model is 0.997 7 and the average absolute relative error is 0.27%.关键词：Strain hardening characteristics;Strain rate sensitivity index;Constitutive model
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发布时间：2022-09-22 - 摘要：The variable density method has become an effective method to solve the topology optimization problem of continuum structure due to its advantages such as few design variables and high efficiency. Aiming at the problem of the gray unit and sawtooth boundary in the optimization process of the variable density method, a post-processing method of variable density method for continuum topology optimization is proposed in this paper. The topology optimization model is binarized and the sawtooth shape boundary line is extracted, and the target discrete corner point set is obtained, used as the sample point for curve fitting to obtain the optimized structure with smooth boundary. Experimental results show that this method effectively avoids the zigzag boundary and intermediate density of the optimization result, and improves the manufacturability of the optimization result under the premise of ensuring that the structural performance is within the allowable range.关键词：Continuum;Variable density method;Post-processing;Curve fitting
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发布时间：2022-09-22 - 摘要：Reliability is one of important index in the analysis and evaluation of mechanical structure. Aiming at the problems of various failure modes and low efficiency of reliability evaluation for complex mechanical structures, the reliability analysis method based on polynomial chaos expansions is applied to the reliability analysis of mechanical structures by combining Monte Carlo random sampling and polynomial chaos expansions. In addition, considering the correlation of parameters and various failure modes in the limit state function, the reliability evaluation method of mechanical structure considering failure correlation is given. Finally, a worm gear two-stage reducer is taken as an example to verify the proposed method according to analyzes the various limit state function of different failure form. The computational results show that the reliability evaluation method based on polynomial chaos expansions is efficient and accurate in mechanical structure reliability analysis. And when failure correlation is considered, it is also simple because of avoiding the complex transformation calculation problem.关键词：Structural reliability;Polynomial chaos expansions;Failure correlation;Two-stage reducer;Monte Carlo simulation
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发布时间：2022-09-22 - 摘要：In order to accurate reflect the highly non-linear relationship between structural parameter uncertainty of frame and its responses, and promote reliability design level of frame. A multi-objective reliability optimization design method based on GA weighted network is proposed. Firstly, establish the parametric analysis model of the frame and carry out the experimental design. After that, the sample data of frame responses and uncertain parameters are obtained. Secondly, the initial BP neural network between responses and uncertain parameters is established. Furthermore, using mathematical model to express BP neural network. On this basis, four kinds of weight coefficients are introduced. Then the GA method is used to find optimal combination mode of weight coefficients, so as to improve the accuracy of the initial BP neural network model. Moreover, make the internal relationship between frame responses and uncertain parameters more accurate. Finally, taking the multi index failure probability of the frame as the objective function, the optimization model is constructed. And the multi-objective reliability optimization design of frame is carried out. The results show that there is a better uniformity of prediction results between improved model and test sample. The absolute error of maximum stress response is less than 1 MPa of them under standard working condition. The new frame parameter combination which is obtained by this method not only improve the frame comprehensive reliability, but also provides a reference for the adjustment and optimization of its design parameters.关键词：Bogie frame;Multi-objective optimization;Reliability;Genetic algorithm;BP neural network
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发布时间：2022-09-22 - 摘要：The application field of longitudinally welded pipe is expanding day by day, and its quality requirements are increasing.The inner burr removal device, as a key equipment to improve the quality of the inner surface of the longitudinally welded pipe, has gradually attracted the attention of manufacturers.Taking the high frequency longitudinally welded pipe with constant bottom surface as the research object, an inner burr removal device was proposed based on the cantilever arbor to improve the burr scraping quality of the welded pipe.According to the working principle and functional requirements of the inner burr removal device, the structure of the inner burr removal device was designed and the three-dimensional model was established; According to the actual production conditions, using the ANSYS software, the finite element model of the inner burr removal device under different extreme working conditions was established and simulation analysis was performed to ensure the rationality of the structural design.The inner burr removal device, which integrates lifting, rotating, knife lifting and other auxiliary movements, also has the function of online breaking the inner burr, avoiding falling off inner burrs to block the welded pipe, enriching the functions of the inner burr removal device and laying a foundation for product development.关键词：High frequency longitudinally welded pipe;Inner burr removing device;Structural design;Simulation analysis
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发布时间：2022-09-22 - 摘要：In order to achieve accurate prediction and optimization of milling surface residual stress. In this paper, Al7075-T6 aluminum alloy was taken as the research object. Firstly, a surface residual stress prediction model was proposed by analyzing the forces of orthogonal milling model and considering the machining parameters, milling force and heat. Compared with the traditional exponential empirical model, the superiority of the improved prediction model was proved. Taguchi algorithm and average signal-to-noise ratio were used to analyze the significant effect of process parameters on residual stress on workpiece surface, and the optimal process parameters for residual compressive stress generation were obtained. The optimized process parameters were verified by experiment and prediction model. The results show that compared with the traditional exponential model, the prediction accuracy of surface residual stress in X direction and Y direction is improved by 18.5% and 8.2%, respectively. After parameter optimization, the residual compressive stress in X and Y direction increases by 16.0% and 6.3%. The surface roughness value did not decrease obviously, which provides a theoretical basis for active control of residual stress of aerospace thin-walled parts.关键词：Al7075-T6;Residual compressive stress;Prediction model of surface residual stress;Taguchi algorithm;Parameter optimization
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发布时间：2022-09-22 - 摘要：The loads applied on the driving hydraulic cylinders, attack angle joint bearings and sideslip angle joint bearings in the tail support device of the FL-17 wind tunnel were deduced using a coordinate transformation approach. The load vectors applied on these components were obtained in closed form. A load assessment program with graphical user interface was developed using MATLAB. The safety coefficients of the driving hydraulic cylinders and the bearings can be readily calculated by importing the structural parameters and inputting the load parameters. The shortages of high computational cost and low assessment efficiency of the multi body dynamics simulation is overcame. Taking the example of a wind tunnel test, the developed method and program is applied to verify the strength of the tail support device and the results indicate that the tail support device is sufficient to perform the wind tunnel test. The present work provides a method with high accuracy and efficiency for the preparation and argument for wind tunnel tests and has significant practical value.关键词：Wind tunnel;Tail support;Strength verification;Serial mechanism;Coordinate transformation
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发布时间：2022-09-22 - 摘要：In order to study the mechanical properties of the ballastless track structure under the load of the train, this paper simplified the ballastless track structure to an infinite double-layer elastic beam. The double-layer elastic beam model and its theoretical expression formula was established using the elastic foundation beam concept. When the train was at a certain position on the rail, the differential balance equation between the rail and the concrete slab was established under the action of the vehicle load. Combined with the generalized “initial parameter method” and its boundary conditions, the analytical solution of the double-layer beam displacement and stress were obtained under the vehicle load. Through calculation examples, the displacement and stress of the rail and concrete slab were analyzed, and the analytical results were compared with the results of ANSYS, which proved the reliability of the analytical solution. Therefore, simplifying the slab ballastless track into infinite double-layer elastic beam is closer to the actual working conditions. The results can provide a reliable basis for the theoretical study of the ballastless track of high-speed railways and design reference for related projects.关键词：High-speed railway;Slab ballastless track;Two layered elastic beam;ANSYS;Mechanical analysis;Initial parameter method
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发布时间：2022-09-22 - 摘要：Aiming at the bearing capacity of TBM hydraulic propulsion mechanism under the conditions of large sudden load and extreme heavy load, the stiffness performance performance and sensitivity of TBM hydraulic propulsion mechanism are studied. The method regards the cylinder block, piston and hydraulic oil of each hydraulic propulsion cylinder branch chain connected in parallel as a multi-flexible body connected in series. The static stiffness model of the propulsion cylinder is established and its effectiveness is verified by the finite element method. Then, the mechanism kinematics model was established using the principle of differential motion of the parallel mechanism, the deformation coordination equation and the dynamic compatibility equation were established, and the relationship equation of the static stiffness of the mechanism was obtained, and its effectiveness was verified by the finite element method. The relationship between the stiffness of the mechanism and the structure size and pose was obtained with the sensitivity analysis method. The results show that the wedge angle of the mechanism and the size of the movable platform have a greater influence on the stiffness of the transverse x-axis, vertical y-axis and the longitudinal z-axis rotation stiffness. The lateral x-axis stiffness, the vertical y-axis stiffness and the steering stiffness are equal respectively, the distribution law of the stiffness deviation in all directions of the mechanism is the same and gradually decreases with the increase of the longitudinal displacement, the calculation deviation does not exceed 2%.关键词：TBM propulsion mechanism;Hydraulic cylinder static stiffness;Mechanism static stiffness;Mechanism sensitivity;Finite element method
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发布时间：2022-09-22 - 摘要：Composite multi-pin connection is a common connection form in engineering structure. In this paper, numerical analysis and experimental study on the failure and damage of composite multi-pin connection structure under tensile load are carried out. Firstly, different failure criteria are established for fiber, matrix and delamination. Based on fracture mechanics, the strength parameters of single-layer plate considering in-situ effect are derived. Combined with the method of stiffness exponential decay, the continuous damage mechanical constitutive model of composite single-layer plate is compiled by using finite element subroutine. In order to improve the calculation efficiency, this paper proposes to use the partition Newton method, which is different from the traditional Puck method and the partition golden section method, to calculate the angle of matrix failure fracture surface in Puck failure criterion. Secondly, the tensile properties of composite laminate plate and perforated plate are analyzed by using the above mechanical model, and the feasibility of the model is verified by comparing the test results. Finally, the failure and damage evolution process of the composite multi pin connection structure is analyzed by using the above mechanical model, and the results are compared with the experimental results. The results show that the mechanical model proposed in this paper can predict and calculate the mechanical response and damage mode of carbon fiber composite multi-pin connection structure under tensile load.关键词：In-situ effect;Failure criterion;Zonal Newton method;Mechanical test;Composite materials
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发布时间：2022-09-22 - 摘要：Based on the research of worm gear pair and double roller enveloping hourglass worm without backlash, a new type of worm drive with end roller enveloping is proposed. Based on the principle of gear meshing, the coordinate system of end roller enveloping hourglass worm is established. The equations of worm gear meshing function, meshing equation, lubrication angle, self rotation angle, induced normal curvature and relative entrainment velocity are derived. Matlab is used to analyze the influence of its own parameters on the transmission performance. The results show that: The worm lubrication angle, relative entrainment speed and induced normal curvature can obtain good data, and the self rotation angle of worm gear needs to be optimized.关键词：Face roller;Hourglass worm drive;Meshing performance analysis
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发布时间：2022-09-22 - 摘要：Aiming at the minimum cutting thickness existing in mesoscopic cutting process, the formation mechanism of the minimum cutting thickness was described, and the theoretical model of minimum cutting thickness based on tool edge radius and friction coefficient between workpiece and tool was proposed, and the cutting parameters were substituted into the theoretical model, and the minimum cutting thickness is calculated to be 2.3 μm. Taking Ti6 Al4 V titanium alloy as the research object, the 2 D cutting model of titanium alloy was established by using ABAQUS finite element software, and the simulation results show that the minimum cutting thickness is between 2 μm～3 μm, which verifies the correctness of the theoretical model of minimum cutting thickness. The influence of cutting edge radius and friction coefficient between workpiece and tool on minimum cutting thickness is analyzed, and the results show that the minimum cutting thickness is directly proportional to the tool edge radius and inversely proportional to the friction coefficient between the workpiece and the tool.关键词：Mesoscopic scale;Cutting mechanism;Minimum cutting thickness;Cutting simulation
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发布时间：2022-09-22 - 摘要：In the paper, the suction device of linear compressor is taken as the research object, and aiming at the transverse bending problem of suction valve plate of linear compressor, the structural control equation of suction valve plate is constructed according to elastic mechanics and plate and shell mechanics. Based on the basic theory of fluid-solid coupling, the fluid control equation, structural control equation and fluid-solid coupling equation are established. Based on 3 D dynamic mesh and UDF（User Defined Function） technology, the bidirectional fluid-solid coupling simulation model of suction device of linear compressor is established, and the performance test experiment of linear compressor is carried out. The flow field characteristics and mechanical behavior of suction device under unidirectional and bidirectional fluid-solid coupling are studied by taking the optimal inlet temperature and inlet pressure obtained from the experiment result as the simulation boundary conditions. The simulation results show that unidirectional and bidirectional fluid-solid coupling are essentially different. In the simulation of unidirectional fluid-solid coupling flow field, the valve plate will not open, but in the bidirectional, a pressure gradient exists between the valve channel and the piston cavity in the bidirectional fluid-solid coupling, while the unidirectional it doesn’t, and the bidirectional fluid-solid coupling simulation is closer to the actual situation, The results can provide theoretical guidance for the structural design and topology optimization of valve plate and suction device.关键词：Two-way fluid-structure interaction;UDF technology;Dynamic response;Suction device
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发布时间：2022-09-22 - 摘要：In this paper, a typical component in parallel manipulator--the parallelogram mechanism, is studied and the terminal position error that results from the change in length of each connecting rod is analyzed. Taking a two-degree-of-freedom manipulator as the research object, the Modified D-H method is used to solve the forward kinematics, and the prediction model of terminal position in consideration of the inaccuracy by parallelogram mechanism is established. The corresponding simulation experiment of error distribution is carried out by using the Monte-Carlo method in Matlab, and the distribution characteristics of the manipulator’s terminal position error under different machining tolerance are obtained, then the accuracy of the prediction model is verified by the prototype experiment. The research shows that the joint angles of parallel manipulators calculated using this method are more accurate, which improves the accuracy of terminal position modeling.关键词：Parallel manipulator;Parallelogram mechanism;Position error;Modified D-H method
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发布时间：2022-09-22 - 摘要：During the crack propagation process, the crack branching behavior makes fracture more unpredictable. In this work, three kinds of crack branching models were selected, and the FEM simulations based on GTN（Gurson-Tvergaard-Needleman） damage model were used to further investigate the influence of constraint on the crack branching behavior during crack propagation. The results show that the constraint has a great influence on crack branching behavior. Compared with low constraint, the crack branching phenomenon is more obvious under high constraint. The matching between strength mismatch induced by both the mechanical properties and dimensions of different regions and constraint is the key of crack branching. When the crack propagation trends induced by strength mismatch and constraint different in direction, similar in size and large enough, crack branching occurs.关键词：Constraint;Crack branching behavior;Crack propagation path;Strength mismatch
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发布时间：2022-09-22 - 摘要：The traditional quasi-static K＆C characteristic test can not reflect the hysteresis effect caused by shock absorber damping and bushing viscoelasticity comprehensively and effectively, but the suspension dynamic K＆C characteristic test can make up the deficiency of the quasi-static characteristic test.Development of dynamic K＆C test involves two aspects of excitation spectrum and performance evaluation of the research content, in this paper, A class A sedan for the study of the carrier, through A skid pad road load spectrum sampling test and simulation analysis, through the bench test iterations, designed the suspension K＆C dynamic characteristic test of typical excitation spectrum, and its validity is verified by bench test and virtual test.The results show that the dynamic characteristics of the suspension can be reflected effectively by using the typical excitation spectrum designed in this paper, which provides some support for the research of wheel positioning parameters and the development of K＆C test technology.
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发布时间：2022-09-22 - 摘要：To ensure the safe operation of mechanical transmission equipment, it is necessary to predict gears′ fatigue life accurately. Based on the cumulative damage theory and the flexural fatigue test results under two-stage loads, the relationship between the ratio of two-stage stress amplitudes and the bending fatigue damage is established in this paper. The relationship is used to improve the original model. The improved bending fatigue life prediction model can accurately predict the bending fatigue life of gears. Compared with the bending fatigue test results under multi-stage loading under various modes, the prediction result has a small deviation from the average test life.关键词：Spur gear;Endurance bending test;Fatigue damage;Life prediction
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发布时间：2022-09-22 - 摘要：As the core component of high-speed EMU bogie, gearbox should meet the requirements of lightweight and high reliability in order to ensure the safety and comfort of vehicle operation. Taking the gearbox of a domestic high-speed EMU as the research object, the existing problems of the gearbox are analyzed by finite element method, then using the topology optimization technology to improve the design of the box structure. The results of finite element analysis show that the stiffness and strength of the gearbox meet the requirements under various working conditions. But it’s natural frequency is close to the main vibration frequency of wheel shaft system, which may cause resonance that leading to noise and box cracks. According to this characteristic, a topology optimization scheme is proposed to increase the natural frequency of the box. Verified by calculation and modal test, the natural frequency of the gearbox after topology optimization is raised to an interval that avoiding the main vibration frequency of wheel shaft system and reducing the possibility of resonance. The research in this paper provides theoretical and data support for the design of high-speed EMU gearbox with good static and dynamic characteristics.关键词：High-speed EMU gearbox;FEM;Topology optimization;Natural frequency;Modal test
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发布时间：2022-09-22 - 摘要：The space unlocking device is a key component to realize the connection and separation between spacecraft and its accessories. In order to solve the problem that the non-self-locking thread connection space unlocking device is affected by impact, vibration and other loads during launch and lift-off, which leads to the risk of loosening failure of the main power source（loading nut）, the unlocking mechanism of the non-self-locking thread connection space unlocking device was analyzed. The redundant power source of the redundant drive mechanism was designed by multi-objective optimization algorithm. At the same time, the overrunning clutch was selected as the transmission main body of the redundant driving mechanism, which can ensure the smooth unlocking of the device in the case of failure of the main power source, and effectively avoid the interference between the redundant power source and the main power source in the normal operation of the device. Finally, the dynamic simulation analysis and experimental verification of the space unlocking device driven by the redundant mechanism have been carried out. The results show that the redundant mechanism can complete the unlocking task of the device quickly and reliably.关键词：Space unlocking device;Redundant design;Multi-objective optimization algorithm;Dynamic simulation
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发布时间：2022-09-22 - 摘要：To improve the bending formability of Q960 structural steel plate, the internal structure of the steel plate was enhanced by pulse current assisted method. The bending resilience difference of Q960 structural steel plate was measured when it is subjected to pulse current. The alloy was subjected to different pulse current densities for bending test, and the change of microstructure morphology was observed. Results show that the deviation coefficients of neutral layer are above 0.5 after 90°V bending test. When the current density increases, the specimen changes from elastic deformation to plastic deformation, and the temperature of the specimen increases continuously. When electrically assisted treatment is applied to the sample, the bending rebound Angle decreases with the increase of current density. When the current density reaches 2.5 A/mm~2, no rebound phenomenon can be observed. Few twin crystals will appear with gradual increase of the current density in the bending process. A large number of equiaxed crystal structures are formed on the outer side, showing the characteristics of slip plastic deformation, resulting in a slightly asymmetric tension and compression state. With a grain size of 13 μm or so, the microstructure of the base plane slips due to electroplastic action, which realizes the plastic transformation of the material without twin coordination. The research is of great significance to improve the mechanical properties of building structural steel, especially for high-rise buildings.关键词：Pulse current assist;Q960 steel plate;Bending forming;Microstructure;Springback;Twin;Plastic deformation
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发布时间：2022-09-22 - 摘要：In view of high-speed working characteristics of four-bar beating-up system, the simulation study was carried out under the influence of joint clearance and beating-up resistance. The discontinuous contact model with two-state was applied to clearance modeling of crank bearing. A rigid flexible coupling model of double side four-bar beating-up system was set up by ADAMS/View which on the basis of mechanism design and analysis of beating-up principle. The beating-up resistance from sley was transformed into an equivalent torque on rocking shaft by use of step function. The results of contact dynamics simulation with different clearance states show that there are obvious differences between flexible body simulation and rigid body simulation, and the former can better reflect the real situation of beating-up; The clearance of 0.03 mm and 0.06 mm has a great influence on sley vibration which is not conducive to reduce vibration and noise for loom system; 0.09 mm clearance will not only cause high-frequency reaction force on main shaft bearing, but also aggravate contact and collision between crank and connecting rod; There are many overlaps between centroid trajectory of flexible main shaft with clearance and ideal trajectory, because of that, multi-point contact collision occurs in the crank bearing. The study is helpful to explore mechanical characteristics and working mechanism of the four-bar beating-up system with clearance.关键词：Joint clearance;Sley;Beating-up resistance;Loom;Rigid flexible coupling
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发布时间：2022-09-22 - 摘要：In order to investigate the formation mechanism of fishhook shaped spalling defect on rail surface, the fatigue calculation model of wheel/rail rolling contact was established and the prediction method of crack propagation path was proposed based on the contact element method and maximum circumferential tensile stress criterion. And the influence of wheel/rail contact state and multiple cracks on crack propagation path were analyzed. The results show that, the initial rail surface microcrack is an I-Ⅱ mixed crack, and gradually tends to propagate in the 90° direction. When the crack grows to a certain depth, the driving force of crack propagation changes from KI to KⅡ. At this point, the crack tip will turn about 70° under the drive of KⅡ, and tends to propagate upward and leads to fishhook shaped spalling defect. The characteristics of wheel/rail tangential loads have a great influence on the spalling path, and the maximum depth of spalling defect can be up to 1.76 mm under the traction condition. When there are multiple cracks on the rail surface, the sliding driving effect of the middle crack will be strengthened. Finally, the intersection between adjacent cracks will form, and accelerates the formation of spalling defect.关键词：Rail;Spalling defect;Maximum circumferential tensile stress criterion;Propagation path
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发布时间：2022-09-22 - 摘要：The cutter wear of TBM significantly reduce the tunneling ability. For overcoming the defects of current testing method, the detection based on magnetostatic effect is proposed in this work. The proposed method greatly loosens the limitation of the protective shell material and has the advantage of high linearity. At first, the principle of detection method is presented, and the feasibility is investigated by finite element method. Secondly, the experimental equipment and signal processing circuit were built. The test results verify the linear variation feature between static magnetic force and wear loss. The gradient of static magnetic force is always about-592 mN/mm, which is much higher than the 25 mN accuracy of pressure sensor, so high accuracy was ensured.关键词：Wear detection;TBM;Cutter;Magnetic force;Pressure sensor
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发布时间：2022-09-22 - 摘要：In view of the problem that the gas turbine blades rely more on the long-term test of the whole machine in the later stage to expose the insufficient design, this paper takes the gas turbine blades of an engine as an example to study the low cycle fatigue life of gas turbine blades. Firstly, the stress-strain analysis of gas turbine blade is carried out under typical cycles. It is determined that the main failure mode of gas turbine blade is low cycle fatigue failure controlled by strain fatigue. According to the principle of linear damage accumulation, the low cycle fatigue life of gas turbine blade is predicted. Then, a design method of low cycle fatigue test of turbine blade on rotating test-bed is innovatively proposed. The method uses open-loop electromagnetic induction coil to heat the blade, realizes the temperature field of gas turbine rotor with temperature gradient through heat conduction, and determines the test speed of gas turbine rotor according to the principle of strain equivalence. The test results show that the predicted service life of gas turbine blade is within 5 times of service life dispersion zone, and the crack position of component test blade is consistent with the test results of the whole machine.关键词：Aero-engine;Turbine blade;Low cycle fatigue;Fatigue life;Test design method
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发布时间：2022-09-22
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