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:During the operation of the BV500 type controlled seismic source vibrator in Sichuan and Chongqing areas,due to the improper plate design,the vibration energy down-transfer rate is low and the excitation signal distortion is serious.Therefore,the continuum topology optimization method was introduced,and a variable density method of the solid isotropic material with penalization(SIMP)model was used to optimize the design of BV500 controlled seismic source vibrator plate from two aspects—reducing mass and increasing stiffness,and an"octagonal I-steel-20a"plate was innovatively developed.After optimization,the mass of the plate was reduced by 45.29%,and the stiffness of the plate was increased by 79.92%,the vibration performance of the plate before and after optimization is studied.The simulation results show that compared with the original aluminum alloy plate,the energy down-transfer rate of the"octagonal I-steel-20a"plate increases by 15.11%,the displacement amplitude of the ground surface contact center point increases by 43.74%,and the amplitude of the interaction force increases by 40.56%.The field experiment shows that when the"octagonal I-beam-20a"plate is excited,the effective value of the average vibration velocity of the near-field signal of the detector is increased by 22.23%,and the effective value of the average vibration velocity of the far-field signal of the detector is increased by 39%,the law is consistent with the numerical simulation conclusion of controlled seismic source road excitation.The excitation performance of the"octagonal I-beam-20a"plate is better than that of the original aluminum alloy integral plate,which effectively improves the road excitation effect of BV500 type controlled seismic source in Sichuan and Chongqing areas.

Abstract:In order to eliminate the restriction of the return spring stiffness on the power generation and system reliability of the energy harvesting speed bump with the full wave mechanical rectifier,a dual-speed bump energy harvester(DBEH)based on the half-wave mechanical rectifier was proposed.The device utilized a mechanical transmission module to convert the downward linear movement of two speed bumps,driven by wheels,into the one-way rotary movement of a single generator shaft,thereby converting mechanical energy into electrical energy.The unidirectional motion conversion reduced the demand for the load of the return spring.The theoretical model of the wheel excitation and speed bump dynamics was established and verified by road tests.Based on the theoretical model,the power generation performance of DBEH was studied by numerical simulation.The research results indicate that the root mean square(RMS)power and output electrical energy of the system increase with the increase of external excitation amplitude and the decrease of the spring stiffness.When the load resistance value is 7-9 Ω,the output performance of the system is optimal.Compared to reducing the gear radius,increasing the speed of the gearbox has a more significant impact on the improvement of system output.A small inertia flywheel can effectively improve the system's capture of the mechanical energy and the conversion rate from the mechanical energy to the electrical energy.

Abstract:Taking multicellular square tubes as the research object,the influence of the evolution of cross section shape on the energy absorption of the structure of multicellular square tubes was studied by using the verified finite element model.The results show that,under the same mass conditions,the multicellular tubes with the best energy absorption k=0.25 increased by 26.34% compared with those with the worst energy absorption k=0.40.Under the same wall thickness,the energy absorption with k=0.25 and the specific energy absorption of the multicellular tubes were 311.69% and 73.80% higher respectively than that of the ones with k=0,and the crushing force efficiency was increased by 52.51% .Finally,the parametric study of shape coefficient and wall thickness on the structural crashworthiness was carried out systematically.The research results can provide a reference for innovative design of multicellular square tubes.

Abstract:To investigate the vibration performance of RV reducers and analyze the fault identification,the torsional vibration test bench for RV reducers was built.Based on the mechanical structure and transmission principles of RV reducers,the vibration frequencies under different operating conditions were calculated.The vibration signal of RV reducers of superior and inferior products was collected,and the acceleration signal of the torsional vibration under different speeds and swerves was collected.The torsional vibration signals were decomposed using the variational mode decomposition(VMD)to obtain the intrinsic mode function(IMF).The results demonstrate a high correlation between the extracted IMF features obtained through VMD and the vibration frequencies observed during the operation of RV reducers.Furthermore,by comparing the spectrum of IMF,the reasons behind the abnormal vibration in inferior RV reducers were identified.Ultimately,it is determined that the abnormal vibration in inferior RV reducers were caused by the excitation from the interaction between the auto rotation of the planetary gear and the crankshaft or the revolution of the cycloid gear.This study provides valuable insights for enterprises aiming to improve the transmission accuracy and product quality of RV reducers.

Abstract:In order to study the dynamic behavior of stiffened cylindrical shells with composite material sandwiched by co-cured damping films under the clamped boundary condition,the specimens of stiffened cylindrical shell with composite material sandwiched by co-cured damping films were prepared,and the dynamic modal test platform was set up.The fundamental frequency,damping ratio and modal shapes of stiffened cylindrical shell specimens were solved,and the accuracy of finite element model was verified.The influence of geometric parameters on structural vibration characteristics was further discussed by the numerical simulation method.The results show that,the fundamental frequency,damping ratio and modal shape of the structure will change abruptly when the height of stiffeners changes,and there is a suitable height value before the abrupt change to make the whole structure consider both damping and stiffness requirements;when the thickness of composite materials is constant,the fundamental frequency of the whole structure decreases gradually and the damping ratio increases gradually with the increase of the damping thickness or damping layer number of single layer;for the stiffened cylindrical shell of single layer damping composite materials,the closer the damping layer is to the inner skin,the higher the stiffness is,and vice versa,the damping capacity is better.

Abstract:The slat of aircraft is subjected to the combined action of thermal load and aerodynamic force during its service,which has an impact on the safety of the structure.The typical aluminum alloy structure widely used in slat structure is taken as the main research object,and the stress distribution and structural strength under the combined action of heat and force were studied by experiment and finite element method.Firstly,in order to explore the influence of temperature on material properties,the linear tensile test of 2024-T62 rectangular thin plate and the high temperature tensile failure test of perforated thin plate were carried out under four different temperature conditions.The test shows that the high temperature environment has a reduction effect on the elastic modulus of the material,and at 190 °C,the bearing strength of the test piece decreased by 15%.Therefore,considering the reduction effect of temperature on material parameters can establish a more accurate model for predicting structural strength.Secondly,aiming at the thermal stress problem of aluminum alloy parts and structures,the test and simulation of aluminum alloy sheet and simplified slat structure under the combined action of heat and force were carried out respectively.A set of modeling method and thermal stress measurement test technology under the combined action of heat and force were established.The maximum error between the simulation and test results of aluminum alloy sheet is 10%.The thermal stress simulation of the simplified slat structure has a good trend compared with the experimental results,and the maximum error is 20%.In addition,through the experiment,it is also found that the thermal stress is particularly sensitive to the setting of boundary conditions.For the model with complex constraints,it is necessary to expand the modeling range to the stable boundary conditions to simulate the actual thermal stress.

Abstract:The mechanical response of external rotor direct drive generator under time-varying loads is analyzed theoretically,calculated by simulation and verified by test.Firstly,the source of magnetic pull of the rotor core of the external rotor generator and its variation with load were analyzed.The expression of magnetic pull of the rotor and the characteristics of time and space order were determined.The basic vibration model of the external rotor core was analyzed,and the basic vibration equation of the external rotor core was determined.Then the simulation model of the external rotor generator was established,and the spatiotemporal order characteristics of the magnetic pull and the typical daily variation rule with time were obtained.The magnetic pull density obtained from the electromagnetic field was used as the input load to guide the structure field.The magnetic-solid coupling simulation was carried out,and the deformation and stress distribution and noise response of the external rotor core were calculated and analyzed.Finally,a simulation example of a 13 kW external rotor direct-drive generator proved the correctness of the analysis and simulation.The results of the study determined the time-varying load on the outer rotor core and its mechanical response distribution.It is found that the time and position of the rotor core should be tested emphatically when the generator is running.Noise characteristics under time-varying loads are also analyzed.The analysis provides reference for the maintenance and design of the generator.

Abstract:The gearbox of wind turbine is in the complex environment such as random wind load for a long time,and the gear contact fatigue becomes a key factor limiting the stability and reliability of wind turbine equipment.The research on the gear contact damage evolution mechanism is faced with difficulties such as complex stress states,damage anisotropy and failure modeling.Material configurational force theory can describe the effect of defect configurational change on the free energy of materials and can be used to predict the damage and failure behavior of materials.A wind turbine gear contact damage model was constructed based on this theory.The gear contact interface stress field simulation analysis was carried out for the key bearing area of gear contact,and the gear contact damage evolution process under contact load was simulated.The results show that the configurational force theory damage model can effectively simulate the contact damage phenomenon of gear and explain the pitting and spalling of gear surfaces.It has significance to predict contact fatigue life of gears accurately.

Abstract:The traditional Paris formula ignores the influence of various uncertain factors in the crack growth process,which leads to a big difference between the predicted crack growth process and the real crack growth process.In order to improve the prediction accuracy of fatigue crack growth,a fatigue crack growth prediction method based on the improved particle swarm optimization particle filtering(IPSO-PF)algorithm was proposed.Firstly,based on the framework of the particle filtering(PF)algorithm,the particle swarm optimization(PSO)algorithm was used to optimize some particles based on the updated observation information,keeping the state of particles with large weights unchanged,and particles with small weights tend to high likelihood region,and IPSO-PF algorithm was designed.Then,combining IPSO-PF algorithm with Paris formula,a fatigue crack growth prediction model based on Paris formula and IPSO-PF algorithm was constructed.Finally,the validity of the model was verified by using the open 2024-T351 aluminum alloy data set.The results show that compared with the traditional PF algorithm,IPSO-PF algorithm can improve the diversity of particles.The prediction error of the crack growth prediction model based on IPSO-PF algorithm is 2.6%,which is better than 9.2%based on PF algorithm.

Abstract:In order to simulate the crack propagation by corrosion fatigue,a coupled peridynamics corrosion-fatigue fracture model was proposed and applied to the simulation and analysis of crack propagation in A7N01P-T4 aluminum alloy.In this model,the interaction of hydrogen and stress was used to reflect the synergy between the two mechanisms of anodic dissolution and hydrogen cracking in corrosion,and the corrosion solution step and the mechanical solution step were coupled when quantifying the fracture behavior of the material due to corrosion.Since hydrogen reduces the plasticity of the material and brittle fracture occurs,a bonded peridynamics theory suitable for simulating isotropic brittle damage was used,and the relation between near-field force and elongation was described using an intrinsic force function for quasi-brittle materials that incorporates both linear and nonlinear mechanical behavior.The feasibility of the model is verified by comparing the simulation results with the test results of A7N01P-T4 aluminum alloy in 3.5%NaCl solution,and it is found that the results are in good agreement between them.

Abstract:The relative curvature of the spur gear mesh point is one of the key geometric parameters of the tooth profile,which has a significant impact on the stress distribution and mesh stiffness of the gear.Starting from the relevant research on constant relative curvature(CRC)gears,three types of non-involute spur gear tooth profiles were constructed based on the relative curvature control strategy considering the time-varying mesh characteristics of gears,and the mesh simulation of gear pairs was implemented.The influence of relative curvature control on the maximum contact stress,maximum bending stress,and mesh stiffness of gears was analyzed.The effectiveness of the control strategy was verified.This work provides some reference for the design of spur gears based on the relative curvature control.

Abstract:A theoretical model of composite metal rubber(C-MR)was established on the basis of static mechanical test.A novel preparation process was used to prepare C-MR,which was subjected to static mechanical tests.The mechanical model of C-MR was established by combining the static mechanical models of wove-metal rubber(W-MR)and tangled-metal rubber(T-MR),and the effects of different knitting and winding ratios on the mechanical properties of C-MR were investigated.The comparison between the test data and the theoretical model shows that the theoretical model can predict the mechanical properties of C-MR effectively.The results show that the knitting and winding ratio has a significant effect on the mechanical properties of C-MR,and the larger the knitting and winding ratio is,the larger the stiffness and damping properties of C-MR are.The conclusion can provide a theoretical support for the preparation and application of C-MR.