China Mechanical Engineering

Research Progresses for Machining Characteristics and Field-assisted Techniques of γ-TiAl Alloys

FAN Tao1, 2, YAO Changfeng1, 2, TAN Liang1, 2

2025, 36(04): 636-645. DOI: 10.3969/j.issn.1004-132X.2025.04.001

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γ-TiAl alloys, due to their low density, high specific strength and excellent high-temperature oxidation resistance had broad application potentials in the aerospace fields. However, due to their high brittleness and low room-temperature plasticity, they were considered typical difficult-to-machine materials, with challenges such as high cutting forces, rapid tool wear and surface defects during the machining processes. In recent years, field-assisted machining technologies provided new solutions to these issues. The material properties, machining characteristics, and surface integrity of γ-TiAl alloys were systematically analyzed, with a focus on the research progresses of field-assisted machining technologies, including their applications in reducing cutting forces, extending tool life and improving surface quality. Additionally, the current research limitations and future development trends were sorted out, aiming to provide theoretical and technical references for the efficient machining of γ-TiAl alloys.

Effects of Forced Positioning&Clamping on Geometric and Physical Assembly Performances for Composite Structures and Collaborative Guarantee Strategies

GUO Feiyan1, ZHANG Yongliang2, LIU Jialiang1, ZHANG Hui2

2025, 36(04): 655-670. DOI: 10.3969/j.issn.1004-132X.2025.04.002

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The large-size & thin-walled aviation composite structures had low forming accuracy and huge in-plane warping deformation. The accumulation of assembly errors, unexpected geometric gaps and shape deviations were prone to occur at the joining areas. In engineering, passive reduction actions, such as applying local clamping forces was usually applied, but uneven internal stress distribution and even internal damages would be occurred, which affected the mechanical performances of the structures in service directly. Firstly, the principle of forced positioning clamping was explained, and the affection on geometric accuracy and mechanical properties of weak rigid composite parts was analyzed. Secondly, starting from the analysis of two main aspects, i.e. optimization on forced clamping process parameters before assembly, and flexible positioning force&position adjustment of fixtures during assembly, five key technologies were solved with detailed technical solutions, i.e. setting forced assembly force limits, reduction of geometric gaps, prediction of stress/damage evolution, reverse optimization of forced clamping process parameters, and precise measurement of assembly stress&damage. Then the active control of shape&force coupling and macro & micro collaborative guarantee in the clamping processes for assembly performance, could be achieved. Finally, for the composite assembly structures, from the perspective of practical engineering applications, the future working focus towards high assembly quality and efficient, and low-cost assembly goals were proposed.

Depth of Cut Control for Thin-walled Parts in Robotic Milling Based on FLADRC

SHI Long, ZHOU Hexiang, LI Zhoulong

2025, 36(04): 671-680. DOI: 10.3969/j.issn.1004-132X.2025.04.003

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Weakly rigid large thin-walled parts had large deformations and vibrations during robotic thinning machining, which led to a degradation of the surface quality of the workpieces and difficulties in ensuring the accuracy of the remaining wall thickness. To this end, a VCM-driven follower support head was used for vibration and deformation suppression, and a FLADRC based control strategy was proposed for depth of cut of robotic milling thin-walled parts. In order to verify the effectiveness of the control strategy, the system control models were firstly established based on the MATLAB/Simulink simulation and experimental platform, and the simulation analysis was carried out, then experimental verification was carried out on the thin-walled parts robotic milling experiment platform. Both of the simulation and experimental results show that the depth-of-cut control strategy based on the follower support head may significantly suppress the vibrations and deformations during the machining processes of thin-walled parts and effectively ensure the accuracy of the remaining wall thickness. In addition, compared with the traditional fuzzy PID control, the FLADRC has a better control effectiveness and exhibits higher robustness in the presence of external disturbances.

Instantaneous Milling Force Modeling and Coefficient Calibration Method of Variable Helical Circular-arc End Mills with Unequal Rake Angle

QI Shutao, LI Jiaqi, ZHENG Shucai, XU Jinting, SUN Yuwen

2025, 36(04): 681-687,696. DOI: 10.3969/j.issn.1004-132X.2025.04.004

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Variable helical end mills with unequal rake angle maight effectively suppress milling chatters, which significantly improved the machined surface quality and simultaneously reduced the risk of tool breakages, however, due to the unequal geometric parameters of each cutting edge, the existing models had difficulty to accurately predict the cutting forces, hence, a new instantaneous milling force modeling and coefficient calibration method were proposed. Firstly, the geometry and position relational expression of the cutting edges for variable helical circular-arc end mills were given, then considering the tool runout and variation of geometrical parameters of cutting edges, an instantaneous uncut chip thickness calculation and element cutting force prediction model was established; Subsequently, a nonlinear optimization method to simultaneously calibrate the cutting force coefficients and tool runout parameters was proposed, and an efficient algorithm for solving the model parameter initial values was also given based on linear least squares and oblique cutting theory. The experimental results show that the amplitude and waveform of predicted cutting forces are consistent with the measured ones with errors of less than 15%, verifying the effectiveness of the proposed model.

Generation Method of Milling Paths of Open Blisk Channels Based on Parameter Mapping

HAN Jiang1, 2, ZHANG Wenqiang1, 2, TIAN Xiaoqing1, 2, XIA Lian1, 2

2025, 36(04): 688-696. DOI: 10.3969/j.issn.1004-132X.2025.04.005

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A machining strategy for variable layer thickness with layered surfaces was proposed to address the rough machining issues of the channels across the entire blisk components. Considering the characteristics of the variation in the width of the channels across the entire blisk components, the geodesic offset was used to determine the toolpath boundaries on both sides of the channels, and the step size and the number of paths were determined. A planning method for the longitudinal milling path along the channels was proposed, and then the tool axis vector of the channel boundaries is calculated, and the tool axis vector of the middle cutter positions of the channel boundaries is calculated by quaternion interpolation. The calculation results show that, compared with the conventional uniform layering method using the blisk hub rotary surface offset or the blisk covering rotary surface offset, the variable layer thickness surface delamination may better adapt to the surface changes from the covered rotary surface to the hub rotary surface, the surface quality of the blades is ensured, with the advantage of a uniform machined blade surface allowance, and the feasibility of the algorithm was verified through machining examples.

Spiral Machining Trajectory Planning Method Based on Discrete Point Cloud Construction of Radial Lines

WU Jiangsheng, CHAI Xingliang, BO Qile, LIU Haibo, WANG Yongqing

2025, 36(04): 697-702,714. DOI: 10.3969/j.issn.1004-132X.2025.04.006

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Aiming at the problems that it was difficult to directly generate efficient and accurate continuous smooth tool path trajectories based on discrete point clouds, a method to directly construct radial lines on point cloud and generate spiral machining trajectories through radial line interpolation was proposed herein. For the construction of radial lines, a boundary recognition method was proposed based on feature descriptors to extract boundary points as two end points of the radial lines. Taking the optimal discrete geodesics between two end points on the point cloud as the radial point set, the curvature minimization problems of discrete geodesics were proposed and solved by Newton iteration method. The B-spline curves were used to fit and resampling according to the residual height based on the radial point sets. The radial line interpolation algorithm was proposed to generate the spiral machining trajectory with equal residual height. Finally, an example was given to demonstrate the spiral machining trajectories directly generated by the point cloud data, which fully verified the effectiveness of the proposed method.

Design of Jig and Fixture for Machining Precision Forged Blade Tenons of Aeroengine

ZHANG Shen1, LIANG Jiawei2, WU Dongbo3, WANG Hui4, ZHAO Bing1, XU Lijun5, ZHOU Fen5

2025, 36(04): 703-714. DOI: 10.3969/j.issn.1004-132X.2025.04.007

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Precision forged blades of aeroengine were a typical thin-walled parts with complex curved surface. When milling the blade tenons, it was difficult to locate and easy to produce deformations and vibrations. Aiming at the above problems, a design method of multi-point clamping fixture for precision forged blades was proposed, and a low stress hard clamping fixture was designed. Static analysis was used to optimize the clamping position, select the coping element materials and optimize the clamping method. The effectiveness of the fixture was tested by modal tests and vibration tests. The results show that the low-band amplitude of the system is reduced by 50%, the high-band amplitude by 75%, the first-order resonance frequency is increased from 210 Hz to 402 Hz, the damping ratio under the peak value is increased from 17.4% to 25.9%, the effective value of vibration displacement signals is reduced by 35%, and the machining error margin is reduced by 59%.

Study on Lubricating Performances and Mechanism of Nano-carbon Balls Cutting Fluids

SUN Hao1, LAN Qixin2, YAO Bin2, LU Jingjing1, ZHANG Jinhui2, PAN Zhirong2, ZHAO Kexin2

2025, 36(04): 715-723. DOI: 10.3969/j.issn.1004-132X.2025.04.008

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Nano-carbon balls cutting fluid was applied to the cutting processes of difficult-to-machine aerospace gear steels(15Cr14Co12Mo5Ni2W), and the lubrication enhancement effects of nano-carbon particles on the cutting fluid were investigated. Firstly, a cutting force model for metal cutting was established to analyze the relationship between cutting lubrication and cutting forces. Furthermore, through combined friction-wear tests and milling experiments, the lubrication performance of nano-carbon balls cutting fluid was evaluated in terms of friction coefficient, wear volume, friction surface quality, and cutting forces. Compared with the base cutting fluid, when the mass fraction of nano-carbon is reached 0.02%, the milling forces for the gear steels are decreased by over 10%, and surface roughness is reduced by more than 15%. Experimental observations reveal that nano-carbon particles on the friction contact surfaces preferentially are adsorbed onto micro-peak regions with higher surface free energy, forming a nano-carbon adsorption film. Lubrication mechanism analysis indicates that this adsorption film may exert a friction-reducing “micro-bearing” effects.

Thread Defects Control and Tensile Property Analysis of C/SiC Composites by L-UHM

XU Haoran1, 2, WANG Jiaqi1, 2, YU Zhanjiang1, 2, XU Jinkai1, 2

2025, 36(04): 724-731,742. DOI: 10.3969/j.issn.1004-132X.2025.04.009

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C/SiC composites were often used to make high-temperature composite fasteners. However, in conventional machining（CM）, the integrity of thread features was low, and there were micro-defects such as fiber pull-out and matrix broken on the surfaces, which made it difficult to meet the requirements of a high-performance connection. L-UHM was used to carry out C/SiC composites thread feature machining herein. The variation of micro-defects on the surfaces of thread features and tensile test results in different machining methods were studied. The defects of thread features in CM, LAM(laser-assisted machining) and L-UHM and the relationship between surface micro-defects and tensile properties were revealed. The advantages of L-UHM in C/SiC composites thread feature micro-defects controlling were proved. The results show that compared with CM and LAM, the fiber pull-out, fiber debonding and matrix broken of the teeth tops, teeth sidewalls and teeth bottoms are inhibited, the micro defects on the surfaces of thread features are reduced, and thread feature integrity is improved in L-UHM. In addition, in the tensile tests, L-UHM achieves the highest tensile strength, which is increased by 29% compare to CM and by 10% compare to LAM.

New Process and Mechanism of Squeeze-machining for Preparing Bilateral Gradient Structure Sheets with Controllable Thickness

PANG Xueqin1, 2, ZHAO Junyu1, DENG Wenjun2, ZENG Yuning2, ZHONG Peixuan2

2025, 36(04): 732-742. DOI: 10.3969/j.issn.1004-132X.2025.04.010

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To address the issues of high strength but low ductility in ultrafine-grained materials, a unique squeeze tool and extrusion channel design was developed. This design enabled the one-step fabrication of ultrafine-grained sheets with a controllable thickness and a bilateral gradient structure through the combined effects of squeeze, friction and cutting. The numerical simulation and experimental methods were combined to analyze the forming processes of bilateral gradient structured pure copper sheets. The mechanism of squeeze-machining machining and the influences of processing parameters on the formations of the bilateral gradient microstructure were explored. The results show that, compared to the original pure copper samples, the maximum hardness of the pure copper sheets prepared using the squeeze-cutting method is increased by approximately threefold. Additionally, the sheets exhibit an excellent strength-ductility synergy: while some ductility is sacrificed, the yield strength nearly is of doubles, and the ultimate tensile strength increases by a factor of four.

Experimental Study of Ultrasonic Vibration Assisted Turning Titanium Alloys with Nanofluid MQL

ZHENG Jintao, MA Haoran, WANG Jin, LIU Guoliang

2025, 36(04): 743-752,759. DOI: 10.3969/j.issn.1004-132X.2025.04.011

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By combining the ultrasonic vibration assisted cutting with nanofluid MQL, ultrasonic vibration assisted turning experiments were conducted for titanium alloys with different vibration directions and cutting speeds. The synergistic mechanism among diamond, graphene, diamond/graphene composite nanofluids and ultrasonic vibration was analysed. The results show that all modes of ultrasonic vibration may reduce the main cutting force and increase the compressive residual stress, but the ultrasonic vibration in depth of cut direction may enlarge surface roughness. During the ultrasonic vibration assisted cutting, graphene nanosheets may generate interlayer shear effect and enhance heat transfer, thus reducing the cutting forces, decreasing the values of surface roughness, and increasing the compressive residual stresses. The dominant effects of diamond nanoparticles are scratching and polishing under the conditions of high-speed cutting and vibrations in feed direction, which may reduce the values of surface roughness of Ra to 50%. Diamond/graphene composite nanofluid exhibites balanced performances and reduces the main cutting force and surface roughness than that of palm oil in all three cutting modes, namely the speed-depth of cut direction elliptical ultrasonic vibration-assisted low-speed cutting, the speed-depth of cut direction elliptical ultrasonic vibration-assisted high-speed cutting and the speed-feed direction elliptical ultrasonic vibration-assisted cutting. The maximum reductions of main cutting force and Ra were both larger than 20%.

Study on Low Wear Machining Method of High Volume Fraction SiCp/Al Composite Materials by ECM-mechanical Combined Machining Processes Method

HE Bin, ZHOU Xingyu, LU Hongyu, ZHANG Junfei, DING Kai, LI Qilin, LEI Weining

2025, 36(04): 753-759. DOI: 10.3969/j.issn.1004-132X.2025.04.012

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To improve the problems of tool wear, poor surface quality and low machining efficiency of aluminum-based silicon carbide（SiCp/Al) composites with high volume fraction under conventional machining, an ECM-mechanical combined machining method was proposed, and the ECM-mechanical combined machining experiments of 60% volume fraction SiCp/Al composites were carried out. The results show that SiC particles are exposed on the surfaces with the removal of aluminum matrix. There is a certain depth of transition zone between the surface of the workpiece and the matrix after ECM, the aluminum matrix in the transition zone is locally removed, and the binding force of SiC particles is reduced. When the diamond grinding rod is used for machining the transition zone, the aluminum matrix adhesion phenomenon is not observed, the diamond grinding rod has almost no wear, and the surface damages are obviously reduced. The machinability of high volume fraction SiCp/Al composites may be improved by ECM-mechanical machining processes.

Material Removal Mechanism of CFRP in Longitudinal-torsional Ultrasonic Milling Based on Mesoscopic Simulation Model

ZHANG Chao1, REN Yinghui1, 2, YU Xiaolin1, LI Maojun2, YU Chengyang2, DU Xinliang1

2025, 36(04): 760-769,779. DOI: 10.3969/j.issn.1004-132X.2025.04.013

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In order to reveal the material removal mechanism of CFRPs in longitudinal-torsional ultrasonic vibration milling, a simulation study of CFRP mesoscopic-cutting was carried out. The kinematic characteristics of longitudinal-torsional ultrasonic vibration milling were analyzed, and a 3D mesoscopic-cutting model of CFRPs was established. The fiber removal mechanism, matrix damage, chip morphology and cutting force of conventional cutting and longitudinal-torsional ultrasonic vibration cutting were compared under different fiber orientation angles. The results show that when the fiber orientation angle is 0°, the longitudinal-torsional ultrasonic vibration cutting impact characteristics accelerate the fiber bending processes, and the fiber removal mechanism at the cutting-edge changes from conventional rolling to scratching. When the fiber orientation angle is 45° and 90°, the impact characteristics enhance the shear effects of the cutting-edge on the fiber, especially when the fiber orientation angle is 90°. When the fiber orientation angle is 135°, the fiber removal mechanism changes from large area bending to local fracture. Longitudinal-torsional ultrasonic vibration milling is beneficial to restrain matrix damage, improve chip morphology and reduce heat accumulation in the cutting areas and decrease the average cutting forces. The experiments verify the accuracy of the simulation analysis.

Inverse Solution for TC4 Residual Stress Gradient Distribution in Four-axis Milling with Tapered Ball-end Cutters

ZHOU Jinhua1, 2, QI Qi1, 2, REN Junxue1, 2, ZHAN Mei1, 2

2025, 36(04): 770-779. DOI: 10.3969/j.issn.1004-132X.2025.04.014

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The internal and external profile finishing of the metal reinforcing edges of the leading edge of large composite fan blades for commercial aero-engines was accomplished by four-axis milling with a customized taper ball-end cutter, and the machining residual stresses introduced at this stage often caused excessive bending and torsional deformations leading to dimensional overshoots of the parts. For the four-axis milling of titanium alloy TC4 with taper ball-end cutter, an inverse identification method of milling residual stress gradient distribution was proposed based on the deformation tests of thin plate machining herein. The hyperbolic tangent models were used to parametrically characterize the milling residual stress gradient distribution, and the solution of the residual stress gradient distribution was converted into the inverse solution of two pending coefficients k and ω. The model coefficient k was determined by testing the residual stress on the machined surfaces of the titanium alloy specimen blocks, and the model coefficient ω was inversely solved by testing the bending deformation deflection of milled titanium alloy thin plates, then the residual stress gradient distribution curve was determined. Four groups of titanium alloy TC4 test block milling validation experiments were carried out, and the test results show that the average prediction accuracy of the milling residual stress gradient distribution is as high as 99.35%. Compared with the traditional X-ray test method, the proposed method avoids the use of electrolytic corrosion stripping to test the subsurface residual stresses, and also takes into full consideration the non-uniformity of the distribution of milling residual stresses on the machined surfaces, namely the problem of the dispersion of milling residual stresses.

Evolution Mechanism of Surface Integrity of GH4169G Turning-shot Peening under Thermal and Mechanical Loads

HE Zhe1, LI Jiale1, SHI Kaining1, FAN Yuchang3, HUANG Xinchun2

2025, 36(04): 780-789. DOI: 10.3969/j.issn.1004-132X.2025.04.015

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A study of the evolution mechanism of surface integrity of turning-shot peening composite machining under service load conditions was carried out for the nickel-based superalloys GH4169G for aero-engines. The forms of thermal, mechanical, and thermo-mechanical loads on surface integrity were analyzed by simulating thermo-mechanical load tests under service environments. The thermo-mechanical loading model for surface integrity control and the residual stress and microhardness evolution model with cosine function control factor were established. The laws of residual stress relaxation under thermo-mechanical loading and the laws of microhardness changes and surface microstructure changes were mastered. The results provide basic data for mastering the evolution of surface integrity of nickel-based superalloys processed under service environments. The surface integrity control processes were further optimized.

Investigation on Evolution Laws for Surface States of TC17 Alloy Induced by UIT during High-cycle Fatigue at 400 ℃

TAN Liang1, 2, FAN Yi3, YAO Changfeng1, 2

2025, 36(04): 790-801. DOI: 10.3969/j.issn.1004-132X.2025.04.016

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Based on UIT experiments, surface state measurement and tension-tension high cycle fatigue tests at 400 ℃, the evolution laws of surface roughness, surface morphology, residual stress, microhardness, and microstructure of TC17 alloy were investigated. Results show that, compared with the surface states of the UIT processed specimen, after 1h heating treatment at 400 ℃, the value of surface roughness Ra increases from 0.46 μm to 0.67 μm, the surface microhardness decreases from 630 HV0.025 to 450 HV0.025, the surface compressive residual stress decreases from -640 MPa to -525 MPa, the maximum value of compressive residual stress decreases from -1088 MPa to -776 MPa, and the depth of plastic deformation layer decreases from 20 μm to 13 μm. After fatigue failure of the specimen at 400 ℃, the value of surface roughness Ra is as 1.22 μm, the depth of compressive residual stress layer is as 70 μm, the depth of plastic deformation layer is as 9 μm, and the subsurface equiaxed α phase transforms into elongated strips, the average grain area increases from 11.8 μm2 to 34 μm2.

Simulation and Experimental Study of Temperature for Polishing Aero-engine Blades with Abrasive Cloth Wheel#br#

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XIAN Chao1, 3, XIN Hongmin2, 3, DAI Hui2, CHENG Qingsi2

2025, 36(04): 802-810. DOI: 10.3969/j.issn.1004-132X.2025.04.017

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ANSYS software was used to simulate the instantaneous temperature fields in the polishing processes with abrasive cloth wheel using a rectangular heat source loading method. The temperature distribution on the blade surfaces and along the blade thickness direction in the polishing processes was studied, and the influences of processing parameters on the polishing temperature was explored. The results show that as the polishing process progresses, the polishing temperature distribution gradually stabilizes. When the polishing temperature stabilizes, the temperature values of the machined parts of the blade at different depths tend to be consistent, while the temperature of the machining parts decreases continuously along the depth direction; the polishing temperature gradient gradually decreases from the contact area being machined to the machined area; the polishing temperature increases with the increase of spindle speed, the effects of feed speed on the polishing temperature are not significant and the polishing temperature is positively correlated with the tangential polishing forces; the deviation rates between the measured and the simulated temperature values are not more than 10%, indicating that the good consistency and high accuracy of the simulation.

Kinematics and Dynamics Modeling and Experiments of OmnilLegs

XU Yuze, LU Zhongyue, ZHU Yiming, LUO Zirong

2025, 36(04): 811-820. DOI: 10.3969/j.issn.1004-132X.2025.04.018

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A 3-DOF serial-parallel leg mechanism was introduced and mathematically modelled. Based on the special configuration and motion form of the OmnilLeg, a multi-method combined kinematics modeling method was proposed by applying the rotational and geometrical methods for individual kinematics modeling according to the characteristics of different parts and then combining them with the influence coefficient method to obtain the kinematics model of the whole machine. The proposed method reduces the modeling difficulties. The dynamic models of the OmnilLeg were established by Lagrangian method. The correctness of the theoretical models of the OmnilLeg was verified by simulation and prototype experiments.

Lightweight Design of Concrete Pump Truck Boom Pins Based on Multi-fidelity Surrogate Model

LI Peng1, 2, 3, 4, LI Mengcong1, 4, XIAO Libo2, 3, WANG Yitang1, 4, SONG Xueguan1, 4, YANG Ling5

2025, 36(04): 821-829. DOI: 10.3969/j.issn.1004-132X.2025.04.019

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As a key connecting and supporting component in a concrete pump truck boom system, how to reduce the mass of the pin shafts was a noteworthy issue in boom design. A parameterized finite element model of the hollow dumbbell pin shafts was constructed based on control parameters. Then, a more accurate feature mapping based MFS(FM-MFS) model was established through the mutual disturbance of high and low fidelity models and the reasonable allocation of high and low fidelity data. Genetic algorithm was used for optimization to obtain the optimal design scheme for the hollow dumbbell pins based on this surrogate model, achieving a weight reduction of 36%. Through theoretical, simulation, and experimental verification, it is shown that the hollow dumbbell pin shafts constructed based on the optimal parameters of the surrogate model may achieve lightweight and material consumption savings while still ensuring the physical and mechanical properties, which provides data support and reference for further applications in the future.

Reconstruction of Magnetic Field Responses Caused by Rail Surface Cracks with Alternative Current Excitation

WANG Chi1, 2, ZHOU Yu1, 2, WENG Zhiyi1, 2

2025, 36(04): 830-839. DOI: 10.3969/j.issn.1004-132X.2025.04.020

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As the response laws of the perturbed magnetic field in ACFM to rail RCF crack morphology parameters remained unclear, a novel method was proposed for functional reconstruction between the ACFM perturbed magnetic field and rail RCF crack parameters. The ACFM calculation models were established based on multiple field tests of surface length, ellipse ratio, and internal angle of RCF cracks in heavy-haul railway rails throughout their full life cycle. The perturbed magnetic field above RCF cracks with different parameters was numerically calculated using the ACFM model. The relationship between RCF crack parameters and the perturbed magnetic field was systematically analyzed. Through fitting and evaluation of the perturbed magnetic field's response to the spatial morphology parameters of RCF cracks, the functional expression of the response laws was reconstructed. The results demonstrate that the ACFM response to rail RCF crack parameters is synthetically characterized. The peak value of magnetic field x-component is observed to increase linearly with the surface length and nonlinearly with the internal angle of RCF cracks. Conversely, a nonlinear decrease may be identified as the ellipse ratio of RCF cracks increases. These variations are effectively described by polynomial functions. The change rules between the perturbed magnetic field and RCF crack parameters may be functional reconstructed. The determination coefficient between the reconstructed results and the perturbed magnetic field is found to exceed 0.99, while the sum of squared errors(SSE) and root mean squared errors(RMSE) are constrained to less than 0.001 15 and 0.003, respectively.

Fatigue Failure Study and Topology Optimization of Metro Vehicle Cowcatchers Based on Virtual Excitation Method

LIU Yang1, WEN Zefeng1, WU Xingwen2, ZHOU Yabo1, TAO Gongquan1, ZHANG Zhenxian3, HOU Jianwen3, YI Zhi4

2025, 36(04): 840-849. DOI: 10.3969/j.issn.1004-132X.2025.04.021

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The cowcatchers were an important safety guarantee device for metro vehicles. The causes of the cowcatcher failure were investigated by field test and theoretical research. The results indicate that the resonance of the cowcatcher contributes to the premature fatigue failure due to the first-order eigenmode frequency (95.7 Hz) which is close to the passing frequency(95 Hz) of the rail corrugation in small-radius curves. Topology optimization design of the cowcatchers was carried out according to the causes of failure based on the mistuning modal design method. The first-order eigenmode frequency was raised to 160 Hz, and the resonance problems of the cowcatchers were solved. A sub-structure analysis technique was proposed based on the virtual excitation method. A random vibration model was established to reproduce the vibration environment of the cowcatchers under real conditions. And the dynamic stresses at key positions was calculated and the results show that the maximum dynamic stress error between simulation and measurement as 1.8%. Finally, the excitation loading method was optimized, and the fatigue life of the cowcatchers was verified based on field test data. The fatigue life of the optimized cowcatchers was calculated by using the Dirlik and the Zhao-Baker method, and the results show that the optimized structure meets the design life requirements of 30 years and 3.6 million kilometers at both of the weld and base material locations.

Simulation and Experimental Analysis for Active Vehicle Interior Noise Control Based on FFxLMS

WANG Jian1, ZHANG Ming1, LIU Song1, QUAN He1, FENG Chao1, ZHANG Zhe2

2025, 36(04): 850-856. DOI: 10.3969/j.issn.1004-132X.2025.04.022

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In view of the problems such as huge computational counts, low convergence speed and poor stability of the widely-used time-domain feedforward adaptive algorithm(TFxLMS) for active vehicle interior noise control, a FFxLMS was proposed based on fast Fourier transform(FFT) and block computation. The strengths and weaknesses of the FFxLMS algorithm and the TFxLMS algorithm were compared in terms of the noise reduction, computational count, convergence speed, and stability. Furthermore, the numerical findings were experimentally validated. The results show that the FFxLMS algorithm has advantages in noise reduction, computational count, convergence speed and stability.

Continuous Multi-stable Gear Cell Mechanical Metastructures and Mechanics Properties

MO Shuai1, 2, 3, HUANG Xuan1, 2, HUANG Zurui1, 2, ZHANG Wei1

2025, 36(04): 857-863，887. DOI: 10.3969/j.issn.1004-132X.2025.04.023

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In order to expand the forms of mechanical metastructures and optimize the dynamic adjustment ability of mechanical metastructures, a micro gear unit structure was designed, which was periodically arranged in a two-dimensional plane to form a metastructure. The structural design principle and stability of the metastructure were analyzed. It is demonstrated that continuous and stable tunable of mechanics properties may be achieved by the designed metastructure. The extensive mechanics properties of this metastructure, including statics and dynamics, were analyzed through finite element simulation method. The results indicate that the elastic modulus of the externally meshed gear cells has a tuning range exceeding 10 times, while that of the internally meshed planetary gear cells exceeds 200 times. A considerable tunable range is also observed in the shear modulus. Additionally, the continuous change of the natural frequency and frequency amplitude curve may be realized by this gear unit-based metastructure, providing a new idea for the design of materials aimed at vibration reduction. Finally, a variety of metastructure vibration reduction devices were designed based on this micro gear unit, demonstrating the unique advantages and broad application prospects in vibration reduction and dynamic control.

Fast Focusing Method for Precision Vision Detection System Based on YOLOv5s

HU Xinyu, LIU Xiyang, ZHANG Junwei, YAN Shuang, LI Yunxiang, YE Xuhui

2025, 36(04): 864-872. DOI: 10.3969/j.issn.1004-132X.2025.04.024

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During measurement, the visual inspection system was influenced by factors such as production accuracy and assembly errors, leading to defocused and blurred images. Consequently, a rapid focusing method for the precision visual inspection system was developed based on YOLOv5s. This method employed a combination of coarse and fine focusing strategies. Initially, the trained YOLOv5s models were utilized to search for clear imaging depth ranges with an accuracy of 97.6%, completed the coarse focusing processes within 900ms. Subsequently, the clarity evaluation function and an improved search algorithm were applied for precise focusing, swiftly identified the optimal imaging plane within the depth range. Experimental results indicate that within a defocus range of ±4 mm, the focusing accuracy reaches 0.04 mm, with an average time not exceeding 1600 ms, which reaches a 47.6% reduction compared to existing methods. This method offers rapid speed, high accuracy, and strong adaptability, making it ideally suited for online precision measurements in visual inspection systems.

Topology Optimization of Single Material Flexible Mechanisms Based on Informed Tectonics Theory

SU Ke1, WANG Ying1, LIANG Tengteng1, WEI Yili2, ZHANG Nannan2

2025, 36(04): 873-881. DOI: 10.3969/j.issn.1004-132X.2025.04.025

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In the topology optimization proceses, the number of subdomains would increase, so that the material distribution would occur at the junctions between the outer diameter and the inner diameter, and the too little optimization spaces in the subdomain of topology design would affect the overall performance of the structures. Therefore, the topological optimization models of single material flexible mechanisms were proposed based on the ITT. Through the description of material properties and attribute parameter calculation, the models made the value of the design subdomain number on the basis of adapting to the material characteristics and distribution of materials, so as to ensure that the structures had enough optimization spaces. Aiming at the maximum geometric gain of the mechanisms, the topological optimization models of single material flexible mechanisms were established based on the element-free Galerkin(EFG). In the topology optimization processes, the grid-fess Galerkin method was introduced to construct the EFG relative density field, and the EFG nodes in the design domain were used to construct the deformation function. Under the conditions that the material properties were effectively described in advance, the nodes might be flexibly arranged, so as to avoid the phenomenon of numerical instability, which might affect the performance optimization effectiveness. The typical analysis examples demonstrate the effectiveness of the proposed method.

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