Abstract:When the gear system starts or stops in non-stationary working conditions,a sharp change of the speed can cause it to exhibit complex vibration characteristics which has a significant impact on the performance and lifespan of the gear.Considering the influence of time-varying meshing stiffness,backlash and gear meshing error,a dynamics model of spur gear system was established.The influence of external load and angular acceleration on the vibration characteristics of the start-stop process was studied.At the same time,the time-frequency analysis of the non-stationary vibration signal of the gear system was carried out by using the short-time Fourier transform.The results show that increasing the load and angular acceleration during the start and stop processes will exacerbate the degree of vibration and impact of the gear pair,and both will make the unstable motion process in the early start period end earlier,and the unstable motion process in the late stop period appear later,but the impact components in the late start period(the early stop period)will increase(decrease).In the frequency domain,increasing the external load will enhance the energy of the harmonic component of the gear system's meshing frequency,but it has no effect on the fundamental energy of the meshing frequency.However,increasing the angular acceleration will enhance the energy of both the fundamental and harmonic components of the meshing frequency.

Abstract:To address the issue of damage caused by low-speed impacts on composite material laminates coated with polyurethane coating,a numerical analysis method based on three-dimensional progressive cumulative damage in composite laminates and a yield damage criterion for polyurethane coatings was proposed.Firstly,a damage numerical model of polyurethane coating-carbon fiber reinforced composite laminates under erosion was established,and a Vumat subroutine was written.Subsequently,referring to the ASTM D7136 test standard,impact tests with various energy levels were conducted on samples coated with 1 mm and 2 mm polyurethane coatings and uncoated samples.Simultaneously,the proposed damage model was employed to study the formation reasons and propagation patterns of primary damages such as fiber damage,matrix damage,and delamination,thereby revealing the mechanism of polyurethane coating in absorbing impact energy.The results indicated that the mechanical response results calculated by the proposed damage model showed a high degree of agreement with the test results,validating the correctness of the proposed model.Additionally,comparative tests demonstrated the enhancement effect of polyurethane coating on the impact damage resistance of carbon fiber composite laminates.The findings of this study can provide a reference for the design of protective coatings for aircraft.

Abstract:High-temperature mechanical strength is a key performance determinant for the long term,stable operation of advanced energy systems and components in high-temperature service and has been a disciplinary branch in the mechanical strength theory.Its research and development have accompanied major industrial technological advances.The research paradigm has shifted from early empirical formulas and single damage model to a structural integrity assessment framework characterized by mechanistic interpretability,prediction orientation,and evidential reproducibility.Building on the historical trajectory of the field together with bibliometric analysis and keyword clustering,the phase specific migration of research hotspots and the evolving knowledge structure were delineated.Recent progress was synthesized along three complementary themes,namely multiscale modeling,multiple damage coupling,and multidisciplinary integration.The synthesis covered material deformation and damage mechanism,damage evaluation and life assessment,and in-service monitoring and reliability assessment,thereby establishing a traceable mapping from microstructural mechanisms to engineering applications.Looking ahead,advances are expected to deepen in multiphysics coupling,intelligent decision-making algorithms,and standards system development.Critical challenges include bridging high-fidelity models and real-time prediction,establishing robust mappings from microstructure to service life,and translating theoretical modeling into engineering codes.

Abstract:Abnormal yaw positioning during yaw operations induces progressive deviation in yaw alignment accuracy,thereby compromising wind-tracking precision and risking excessive cable twisting that threatens operational safety.Concurrently,frequent position oscillations or repetitive short-duration position holding generate transient control errors,destabilizing the yaw control system.These coupled mechanisms collectively escalate yaw system failure frequency and operational maintenance costs.To proactively mitigate these risks,a data-driven fault diagnosis methodology is proposed for early detection of anomalous yaw positioning in wind turbines.Firstly,a large amount of data in a supervisory control and data acquisition(SCADA)system was processed using a standardized interaction gain and Relief-F(SIG-Relief-F)feature selection algorithm to identify multiple feature parameters with the strongest correlation with the target variable(which in this case may be yaw system failure).The advantage of this method lied in its ability to consider effectively the correlation between features,thus maximizing the retention of relevant features related to yaw system failures and interaction features.Secondly,a back propagation neural network(BPNN)yaw position prediction model was established,and the distribution of residuals was statistically analyzed using a sliding window method to determine the fault threshold.Finally,through empirical verification,the effectiveness and accuracy of the proposed method were demonstrated,and compared with multivariate state estimation technique(MSET)and support vector machine(SVM)algorithms,it was shown to have superior abnormal warning performance.The conclusions drawn can serve as a reference for the fault diagnosis of a practical yaw system.

Abstract:In the screening of optimization design regions for subway car body structures,the sensitivity method is often used;however,its operation process is complex and cumbersome,and it cannot be quickly applied to the design of car body structures.To address this issue,based on the stiffness contribution theory and on the premise that the accuracy of the finite element model was verified through experiments,the local stiffness and global stiffness of the aluminum alloy subway car body were combined to quickly determine the main optimization regions of the car body.A method integrating topology optimization and size optimization was adopted to conduct a secondary optimization design study on the car body structure.The structural performance of the optimized car body fully complied with the EN 12663 standard:the mass of the optimized car body was reduced by 5.34%,the 1st-order vertical bending frequency was increased by 16%,and other modal frequencies were also significantly improved.This optimization provides a technical reference for the optimization design of other subway car body structures.

Abstract:During the operation of inclined elevators,their safety braking systems were identified as key factors affecting the safety and reliability of the equipment.To address the characteristics of dynamic fault occurrence and uncertain fault rate in the safety braking systems of inclined elevators,a reliability analysis method for such safety braking systems based on the fuzzy dynamic fault tree(FDFT)was proposed.The fault rates of the bottom events in the safety braking systems were expressed based on fuzzy mathematics theory.Combined with the dynamic fault tree analysis(DFTA)method,the dynamic fault tree of the inclined elevator safety braking system was divided into static subtrees and dynamic subtrees.For the static subtrees,static OR logic gates were used to solve the fuzzy fault probabilities of events;for the dynamic subtrees,the fuzzy transition rates of different states in the Markov model were adopted to obtain the time-varying failure rate function of the safety braking system.Subsequently,the membership functions of the fault failure probability of the safety braking system at different operation times were derived,realizing the dynamic reliability analysis of inclined elevator systems under the condition of uncertain fault rates.Based on the calculation principle of fuzzy probability importance,the probability importance ranking analysis of the bottom events in the safety braking system was conducted,provided a basis for the regular inspection and maintenance of the safety braking systems of inclined elevators is provided by this research.

Abstract:The high-speed circuit breaker is an important device to ensure the safety of train circuits,which controls the connection and disconnection of the circuit via opening or closing the moving and static contact terminal.It is an important basis to study the remaining life of the contact terminal for the operation and maintenance of circuit breakers.However,there is no systematic work being reported yet.Therefore,test scenarios were built that matched the operation and maintenance conditions of circuit breakers,and established a residual life model of circuit breakers based on test data.The contact terminal of high-speed circuit breakers in Chengdu Metro subway vehicles was taken as the research target,and then its evolution law of the remaining life in daily service conditions was studied by using a combination approach that comprises finite element simulation and test investigation,which was to study the variation rule of the thickness of the silver-plated layer thickness of the contact terminal with the number of uses.The numerical simulation results show that the stresses in moving and static contact terminals are less than the material fatigue limit,and the fatigue service life of both types of contact terminals is considered to be an infinite life level in the safety life assessment.Moreover,the test results show that the coating thickness of the moving contact terminal decreases with the increase of test cycles,yet the reducing thickness is mainly due to the wear caused by the grinding process such as bias grinding.Based on the linear prediction model,the remaining life of the moving contact terminal was evaluated,and the calculation results show that when the coating thickness of the moving contact terminal reduced from the initial 3.003 mm to the limit of 1.5 mm,the circuit breaker contact can be used for 19 313 cycles,corresponding to the natural year about 36.2,which is about 2.4 times of design service life.The predicted value has been verified by hypothesis testing,and the calculated result is within the predicted interval.The above research results are expected to provide relevant support for the development of maintenance intervals and maintenance strategies for contact terminals.

Abstract:[Objective]In order to enhance the load-bearing performance of face gear transmission and reduce its sensitivity to installation misalignment,a high-order segmented topological modification method based on a predefined contact path was proposed.[Methods]Firstly,2nd-order and 4th-order segmented modification functions were designed along the predefined contact path of the pinion and the instantaneous contact line direction,respectively.Based on the surface superposition method,the equation of the modified tooth surface was established.Subsequently,the tooth contact analysis(TCA)equation incorporating installation errors was derived.The influence of parameters such as predefined contact path angle,modification length,modification curve order,and maximum modification amount on the contact characteristics of face gear pair under different installation error conditions was investigated.Finally,a comparative analysis of the load-bearing contact characteristics of the face gear pair under different modification functions and modification amounts was conducted using the finite element method.[Results]The calculation results show that compared to 2nd-order modification,the 4th-order modification method reduces the contact stresses of the tooth surface and the error amplitude of load-bearing transmission.Furthermore,the contact trace extends from the root of the inner diameter tooth of the face gear to the tip of the outer diameter tooth.The high-order segmented modification method can reduce the sensitivity of the face gear pair to installation errors,optimize the load distribution of the tooth surface,and enhance meshing performance.

Abstract:[Objective]Significant stress and deformation characteristics are exhibited by power batteries during charging and discharging,and higher requirements are imposed on battery management and pack design accordingly.To accurately evaluate the structural strength state of power battery packs and the safety and health state of single cells in bottom impact tests,the critical intrusion amount that triggers fire and explosion of single cells under specific scenarios or working conditions shall be clearly defined.Accurate predictions of the structural strength state of power battery packs and the safety state of single cells in bottom impact tests were performed by means of simulation methods.Based on the numerical test model,the dynamic response characteristics and energy distribution laws during the impact process were thoroughly analyzed.[Methods]Firstly,a refined explicit dynamic finite element model for the bottom crash test of a power battery pack was established using Abaqus software.Secondly,the displacement,equivalent plastic strain,and energy distribution of the structures were calculated and evaluated.[Results]Simulation results show that the deformation shapes,intrusion amounts,and strength statuses of the impacted components are highly consistent with the test data.The simulation accuracies for the intrusion amounts of the bottom guard plate,liquid-cooled plate,and battery cell housing are 94.36％,98.80％,and 96.78％,respectively.The maximum impact force of the ball head reaches 27 299 N.Concurrently,80.96％of the total impact energy is converted into the strain energy of the main impacted components,and their energy absorption proportions correlate positively with the corresponding intrusion depths.These findings provide a valuable theoretical reference for the underbody safety protection design of battery packs.

Abstract:[Objective]To address the challenge of single materials struggling to simultaneously satisfy anti-penetration performance and lightweight design requirements,the quasi-static penetration mechanical behavior and energy absorption characteristics of fiber-metal laminates with crochet core structures were investigated.[Methods]Firstly,laminate samples featuring different fiber crochet core layers were fabricated using short-needle crocheting and bonding methods,followed by quasi-static penetration tests on an electronic universal testing machine.Then,equivalent idealized numerical models were established using SolidWorks and imported into Abaqus finite element analysis software for simulations,with evaluation metrics introduced to process the test and numerical data.[Results]The numerical simulation results exhibit excellent agreement with the test curves.Single-layer cores exert a negligible effect on the peak load of the laminates,whereas double-layer or hybrid crochet structures display a pronounced buffering effect.Compared with the reference un-cored plates(40.08 kN),the peak loads of PSP and PKP laminates increase by 0.52 kN and 0.54 kN,while those of PSSP,PKKP,PSKP,and PMP laminates decrease by 13.17,0.87,10.48,and 8.12 kN,respectively.Due to reduced stiffness and expanded deformation,their energy absorption capacities significantly increase by 95.12％,80.93％,95.59％,153.2％,65.95％,and 30.70％,respectively,with the double-layer stainless steel crochet laminate(PSSP)demonstrating the optimal energy dissipation capability.

Abstract:[Objective]Deep learning-based remaining useful life(RUL)prediction of aeroengine provides a foundation for guaranteeing the reliability of the aeroengine.However,most researches are devoted to the acquisition of degenerate information in Euclidean space,while topological relations in non-Euclidean space can provide additional degenerate information.Thus,a novel RUL prediction method named parallel graph node embedding learning-gated recurrent unit(Parallel-GraphSAGE-GRU)was proposed in this work.[Methods]Firstly,the maximum mutual information method was used to describe the relationships among monitoring parameters of aeroengine.Then,a series of graph inputs was constructed using a fixed time window to obtain topological relations in the non-Euclidean space of the aeroengine.Besides,GRU was used for the acquisition the temporal degradation relations of the monitoring parameters for aeroengine in the Euclidean space.The implicit vectors of GraphSAGE and GRU at each moment were concatenated and mapped to the RUL values of the input degradation information by fully connected neural network.The C-MAPSS dataset was used to validate the effectiveness and advancement of the proposed method,and the best R2 of the proposed method reached 0.988 6.[Results]The results indicate that this method is feasible in ensuring prediction accuracy and computational efficiency.

Abstract:[Objective]A hierarchical optimization design method for impact resistance of isosceles triangular honeycomb structures was established to provide a reference for lightweight design of spacecraft impact buffering devices.[Methods]Firstly,a numerical simulation model was built using Abaqus software,and the mechanical properties including relative density and plateau stress of isosceles triangular honeycomb structures under in-plane impact were analyzed,with the model reliability verified by comparison with literature results.Secondly,based on the Isight software platform,a multi-objective genetic algorithm was adopted to optimize macroscopic size parameters including cell base length,cell height,and wall thicknesses in different regions,with the objectives of minimizing structural mass and peak load.Then,for the optimal configuration obtained from macroscopic optimization,a symmetric cross-section was selected to establish a plane-strain model,and detailed optimization of the fillet radius at cell junctions was further carried out.Finally,the effectiveness of the hierarchical optimization strategy was evaluated by comparing the reaction force-time histories and deformation modes of honeycomb structures before and after optimization.[Results]The results show that after macroscopic optimization,the structural mass is reduced by 73％(at 5 m/s)and 83％(at 35 m/s)under different impact velocities;after detailed fillet optimization,the peak reaction force is reduced by 31％.

Abstract:[Objective]To address the problems of insufficient consideration of uncertain factors and low design accuracy in the traditional design of gantry crane main girders,research on lightweight design and multi-objective reliability optimization of main girder webs was conducted to improve the rationality and safety of structural design for heavy lifting equipment.[Methods]Firstly,a parametric finite element model of web thickness was established with SolidWorks software and Ansys software for a gantry crane main girder with a span of 10 m and a load capacity of 800 t,which provided numerical support for optimization analysis.Secondly,an implicit limit state function of the structure was constructed by combining the Latin hypercube sampling method and back propagation(BP)neural network technology,and the structural reliability index was calculated using the Monte Carlo simulation method.Thirdly,multi-objective reliability design optimization was carried out with the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ),taking the minimum main girder mass,minimum maximum total deformation and maximum reliability index as optimization objectives.Finally,the simulation accuracy of the finite element model was verified through a scaled model lifting test and acoustic emission sensing detection.[Results]The results show that 70 groups of Pareto optimal solution sets are obtained through multi-objective optimization.For the comprehensively selected optimal scheme,the mass of the main girder structure is reduced by 24.56％and the structural reliability is improved by 9.7％under the premise that deformation and stress meet safety requirements.An efficient reliability optimization system for main girders can be constructed with the proposed method,and reference can be provided for the structural safety design of heavy lifting equipment.

Abstract:[Objective]Corrosive environments significantly degrade the load-bearing capacity of honeycomb structures and may even induce structural instability.Investigating this influence is of great importance for engineering applications.[Methods]Firstly,quasi-static compression tests were conducted to compare and analyze the variation patterns of load-bearing capacity for regular hexagonal and square honeycomb structures before and after corrosion,aiming to clarify the differential effects of corrosion on the performance degradation of the two cellular configurations.Secondly,finite element models of both structures were established,and the accuracy of the numerical models was validated through comparison of load-displacement curves.Then,based on the validated numerical models,simulation calculations were performed on regular hexagonal honeycomb structures with different porosities to analyze the effect of porosity on structural strength.Finally,different corrosion degrees were simulated by varying local wall thicknesses,and the degradation patterns of the load-bearing capacity of honeycomb structures in corrosive environments were systematically investigated.[Results]The results show that regular hexagonal honeycomb structures exhibit better stability than square ones.Corrosion has a relatively minor effect on the load-bearing capacity of hexagonal honeycombs,with reductions of 4.58％and 20.53％after 5 and 20 corrosion cycles,respectively,while the corresponding reductions for square honeycombs reach 13.29％and 25.88％.As porosity increases from 70％to 80％,the stress concentration at the structural bottom intensifies and the structural strength decreases.

Abstract:[Objective]The contact stress and frictional heat generation between the cycloidal gear and pin teeth critically influence the transmission performance and service life.Current research on profile modification optimization mostly focuses on a single objective,lacking comprehensive consideration of thermo-mechanical coupling effects.To address this issue,a multi-objective optimization method for cycloidal gear tooth profile modification was proposed considering frictional heat conditions,aiming to simultaneously reduce the maximum contact stress and frictional heat flux density on the tooth surface,and to improve the temperature distribution.[Methods]Firstly,a theoretical load contact analysis model was established according to the meshing characteristics of cycloidal planetary transmission,providing a mechanical calculation foundation for subsequent optimization.Secondly,the tooth surface was discretized and the frictional heat flux density calculation was introduced,and an optimization function was constructed with the objectives of minimizing the maximum contact stress and the sum of heat flux density.Then,a genetic algorithm program was coded using Matlab software,the range of modification parameters and constraint conditions were set,and a multi-objective optimization model for tooth profile modification was established,with feasibility judgment and penalty mechanisms added to address iteration non-convergence and abnormal results.Finally,the temperature fields of the tooth surface before and after optimization were compared through finite element simulation,and the optimization effect was evaluated in combination with theoretical calculation of meshing efficiency.[Results]The results show that after multi-objective optimization,the maximum contact stress on the tooth surface is slightly reduced,and the total heat flux density on the tooth surface is significantly decreased.The simulation results show that the maximum tooth surface temperature is reduced by 5.346℃and the area of temperature concentration is notably diminished.Meanwhile,the meshing power loss is decreased,and the meshing efficiency is improved by 1.5 percentage points.

Abstract:[Objective]At present,there is no targeted static stiffness calculation method for bushing-type rubber suspensions of tracked vehicles under combined deformation conditions.A static stiffness calculation method applicable to multiple bushing configurations was proposed to provide reference for the initial design and stiffness matching of rubber suspensions.[Methods]Firstly,based on the linear elastic mechanical analysis method,the effects of radial,tilting and torsional deformations of axisymmetric rubber bushings on suspension travel were analyzed,and calculation formulas for the balance elbow rotation angle and road wheel vertical displacement were derived to support stiffness calculation.Secondly,combined with the cross-sectional characteristics of axisymmetric and non-axisymmetric rubber bushings,vertical deformation compensation and rotation angle correction coefficient were introduced,and calculation methods for the static vertical stiffness and static torsional stiffness of the suspension under combined deformation were established.Then,finite element models of the bushings were established using Ansys/Workbench software,and static mechanical simulation analysis was performed to verify the accuracy of deformation calculation.Finally,a loading test bench for rubber suspensions was constructed,and the engineering applicability of the stiffness calculation method was verified through quasi-static loading tests.[Results]The results show that the force and deformation law of the rubber bushing is consistent with the simulation and test results.The errors between the calculated values and test values of the static vertical stiffness and static torsional stiffness are 9.43％and 5.71％respectively,both within the 10％allowable engineering error range,which can satisfy the engineering requirements of preliminary suspension design.

Abstract:Aiming at the problem of the weld fatigue test of the new energy vehicle subframe,a program load spectrum compilation method based on the failure dominant load was proposed.Firstly,the finite element model of the rear subframe was established,and the stress distribution under unit load was coupled with the load of each connection point.The structural stress method was used to evaluate the fatigue life of the subframe welds,and six dangerous points that were easy to fail were selected.Secondly,by comparing the load damage of each connection point,the failure dominant connection point corresponding to the weld dangerous unit was determined.Then,the failure dominant load was determined by the principal stress analysis,time domain correlation and uniaxial damage contribution at the weld,so as to reduce the dimension of the multi-axial load and reduce the difficulty of the bench test loading.Finally,a pseudo-damage matrix was output based on the failure dominant load,the characteristic working conditions and their proportions were selected to obtain the load spectrum of the fatigue accelerated test program,and the minimum number of cycles was determined according to the principle of the damage equivalence.The numerical simulation results show that the program load spectrum can reproduce the damage of dangerous points and has a high acceleration coefficient,which verifies the effectiveness of the accelerated test spectrum.

Abstract:To study the response characteristics of the hollow extruded profile of the vehicle after the collision,the generalized incremental stress state-damage model(GISSMO)was introduced and the finite element simulation was carried out.Firstly,based on the test results of 6082-T6 aluminum alloy,the dynamic and static mechanical properties and fracture behavior under different stress states were characterized by the modified Johnson-Cook(MJC)model and DF2016 model respectively.Secondly,the parameter calibration of GISSMO was carried out based on the combination of LS-OPT soft ware and manual optimization.Then,according to the mesh size effect,the mesh size dependence correction was carried out,and the effectiveness of the model and correction were verified by comparison between the experiment and simulation.Finally,the impact simulation analysis of a hollow extruded profile on the side wall of a vehicle body was carried out,and the impact of material damage and fracture on the simulation results was compared.The results show that GISSMO can more accurately reflect the response of profiles under longitudinal impact than without considering the damage and fracture of materials.

Abstract:In order to achieve simulation prediction of the isolation performance of rubber isolators,simulation and testing comparative research on the vibration transmissibility of standard specimens were conducted.Firstly,a compression test was conducted on the standard specimen to obtain pressure deformation data.Based on the theory of the large deformation,the data was processed to obtain the true stress-strain curve.The Mooney-Rivlin model was chosen to define the material properties.Secondly,a vibration transmissibility testing system was established,an exciter to excite the standard sample was used,and the measured vibration transmissibility curve was obtained.Then,a simulation model based on the testing system was built,and the simulation transmissibility curve based on the transient dynamic analysis was obtained.Finally,the test results were compared with the simulation results to achieve the simulation prediction of the rubber isolation performance.The results show that the simulated isolation rate curve is highly consistent with the test results,with a peak frequency error of only 4.8%,which can achieve the simulation prediction and provide a simulation guidance for the optimization design and performance improvement of isolators.

Abstract:The gap between the rotor and the ball bearing in a wide temperature range increases with the increase in temperature.At the same time,the internal clearance of the bearing changes with the temperature.The inner ring of the bearing is subject to increased friction torque,which reduces its speed.This results in the deviation of the characteristic frequency of the outer ring defect,which is not conducive to the fault diagnosis of the ball bearing and the stable operation of the equipment.Considering the temperature-variable gap between the rotor and the bearing,a dynamic model of the bearing with an outer ring defect in a wide temperature range was established.The time-domain waveform and frequency of the model were analyzed.The simulation and test results show that the bearing vibration increases with the temperature,and the characteristic frequency of the outer ring defect decreases with the increasing temperature.Properly increasing the interference between the rotor and the bearing according to process requirements is beneficial for reducing the bearing system vibration in a wide temperature range and improving the accuracy of bearing defect frequency identification.The results provide reference for the use and health monitoring of ball bearings in a wide temperature range.