Abstract:The eccentric installation of high-lock titanium alloy bolts(an assembly angle between the bolt head and the fastening plate)leads to premature failure,which seriously affects the safe operation of aerospace aircraft.Currently,the test research is difficult to obtain the bolt fracture process,which in turn limits the revealing of fracture mechanism.Meanwhile,test research cannot obtain the fracture strength variation value of bolts with different assembly angles.Therefore,in response to the problem of premature fracture of high-lock bolts in the eccentric installation,finite element analysis method was employed and the model was verified by test.The verified finite element model was used to visualize the fracture process of eccentric installation bolts and predict the tensile strength of eccentric installation bolts with different angles.The research results indicate that the tensile strength and fracture position of bolts with installation angles of 0° and 3° obtained from finite element analysis are consistent with the test results,which show that the finite element model has good accuracy.As the installation angle increases,both the bolt head and thread are subjected to eccentric loads,and the bending moment generated aggravates the stress concentration in these two areas.When the assembly angle is less than 3°,the stress at the thread is larger,and when the angle is over 3°,the stress on the head is greater.The finite element model successfully predicts the tensile strength of bolts with an assembly angle of 1°,2°,and 4°.The research results effectively reveal the fracture mechanism of high-lock titanium alloy bolts under the eccentric load.Meanwhile,the simulation model can predict the tensile strength of bolts under different installation angles,and provide technical specifications for the service of eccentric bolts.

Abstract:Aiming at the inaccuracy of the finite element analysis(FEA)of heavy-duty engineering wheels under the radial loading condition,a new simulation analysis model based on the results of wheel-tire contact pressure test was established.Firstly,a stress data corresponding to the wheel under inflation pressure condition alone undergo testing,and a loading model for inflation pressure was formulated using a Gaussian function of 4th order.Secondly,a stress data collected while the wheel experiences combined inflation pressure and radial load were analyzed.The influence of inflation pressure was isolated,allowing for the development of a circumferential loading model and an axial loading model for the radial load,using a Fourier function of 4th order and a sinusoidal function of 4th order,respectively.Finally,the validation of the loading model was conducted through Ansys simulation.The outcomes demonstrate the calculation error of mere-approximately 1.943%in relation to the measured data for the key calibration points.Additionally,the observed stress distribution manifests a remarkable degree of consistency.This substantiates the accuracy and reliability inherent in the proposed radial contact pressure distribution model.

Abstract:Metro gearbox is a key component for torque transmission in vehicles,and its failure will directly affect the safety of train operation.The vibration characteristics of tooth breakage faults in metro gearbox were studied by combining dynamic simulation and vibration test.Firstly,based on the dynamic relationships and constraint characteristics between various components of metro gearbox,a rigid-flexible coupling dynamic model of metro gearbox with tooth breakage faults was established through the impact function method,Coulomb friction model,bearing modeling,flexible body of the housing and gear system dynamics theory.The dynamic response of the gearbox under different types of tooth breakage faults was studied,and the influence of operating parameters on the vibration characteristics of tooth breakage was analyzed.Then,through vibration test,the dynamic response of metro gearbox under normal state and broken tooth fault was obtained,verifying the accuracy of the dynamic simulation model.The results indicate that the rigid-flexible coupling dynamic model can effectively calculate the acceleration response of gearbox in different operating states,provide diagnostic basis for the prediction and identification of tooth breakage faults in the gearbox.

Abstract:The calculation of bending strength for spiral bevel gears is complex,making accurate evaluation extremely challenging.Focusing on the two distinct calculation methods,B1 and B2,as outlined in the ISO 10300 standard,this study begins with the computational principles of both approaches.It compares the selection methods and numerical application principles for parameters involved in calculating root bending stress and allowable bending stress under both methods.The influence of parameter values on root bending stress calculations is analyzed for each method.Through computations on multiple design samples,the root bending stress values derived from both methods are compared.Finite element analysis is employed to validate the computational results.The findings indicate that due to differences in the types and values of correction coefficients used,there are certain discrepancies in the bending strength evaluation results obtained by the two methods.Method B1 yields a more conservative evaluation of root bending strength,with root bending stress approximately 5%lower than that calculated by Method B2.Although the ISO calculation standard accounts for load sharing among multiple teeth,it overlooks the combined effects on root bending stress,leading to deviations from finite element analysis results.Method B1 shows closer agreement with finite element results,with an error margin of about 6%.

Abstract:The rapid assessment method for metal fatigue performance based on the infrared thermography presents advantages such as short testing cycles,low costs,and high efficiency.However,accurately quantifying factors influencing the dissipation of energy,such as convective heat transfer and thermal radiation,proves challenging.The difficulty leads to complications in achieving the precision necessary to meet test standards in the final assessment results.A mixed-hardening constitutive model for 304 stainless steel was established and coupled with the low-cycle fatigue thermomechanical mechanism,to analyze the evolution pattern of dissipated energy caused by convective heat transfer and thermal radiation during the loading process.Furthermore,the impact of low-cycle fatigue loading frequency on the rapid assessment results of fatigue performance was explored based on the critical threshold of dissipated energy.The research indicates that during the low-cycle fatigue process of 304 stainless steel,the dissipated energy from convective heat transfer and thermal radiation constitutes over 54%of the total dissipated energy.Moreover,this proportion continuously increases with the augmentation of the convective heat transfer coefficient.Therefore,it is crucial not to neglect these factors in dissipated energy assessment calculations.With an increase in loading frequency,the peak load narrows within the region of action time.Consequently,the dissipated energy of each load cycle decreases,leading to a rapid assessment result of fatigue performance that tends to be larger than the test value.

Abstract:Negative Poisson ratio structures are widely applied in various engineering fields due to their excellent mechanical properties.By combining the star-shaped honeycomb structure with the re-entrant structure,a novel re-entrant angle-type negative Poisson ratio honeycomb structure is proposed.Firstly,the unit cell structure was simplified and analyzed based on symmetry,and the analytical expressions for the Poisson ratio and equivalent elasticity modulus of the structure were derived using the energy method.Secondly,the vertical compressive mechanical properties of the structure were investigated using Abaqus finite element software,and the numerical simulation results were compared with the theoretical calculations to validate the accuracy of the analytical expressions.Finally,the influence of different geometric parameters of the unit cell structure on the equivalent Poisson ratio and equivalent elasticity modulus was discussed,and the equivalent mechanical properties of the structure were compared with those of conventional star-shaped honeycomb structures.The results demonstrate that the proposed structure exhibits favorable negative Poisson ratio characteristics,and its equivalent mechanical properties can be adjusted by modifying the geometric parameters.The findings provide valuable insights for the design of novel negative Poisson ratio metamaterials.

Abstract:Aiming at optimizing the gear surface modification process,the influence of ion nitrogen implantation on the bending fatigue strength of carburized and quenched gears was studied.Using low-carbon alloy steel 18CrNiMo7-6 carburized and quenched gears as the matrix,nitrogen ion implantation treatment was carried out through a radio-frequency plasma-assisted ion implantation system.The root metallography,hardness gradient,residual stress distribution,and bending fatigue properties of ion-implanted gears and unimplanted gears were systematically compared.The results show that the ion nitrogen implantation process increases the root hardness from 695 HV0.1 to 780 HV0.1,an increase of 12.2%;the hardened layer depth decreases from 1.50 mm to 1.41 mm,a reduction of 6.0%;and the surface residual stress decreases from-400 MPa to-286 MPa,a reduction of 28.5%.Based on the R-S-N equation fitted by bending fatigue tests,under 99%reliability,the fatigue life of ion-implanted gears is only 12.3%-19.3%of that of the control gears,with the failure mode dominated by brittle fracture and accelerated crack propagation rate.The study indicates that although ion nitrogen implantation can delay crack initiation through surface strengthening,the excessively shallow hardened layer and reduced residual stress lead to insufficient crack propagation resistance,ultimately weakening the bending fatigue life of gears.

Abstract:The subsurface damage depth of grinding WC-10Co-4Cr coating with a cup wheel was investigated in an effort to address the issue that the subsurface damage will cause the coating·s performance to deteriorate.The theoretical formula of single particle grinding force was obtained based on the principles of indentation fracture mechanics and grinding material removal theory.A theoretical subsurface damage depth prediction model was developed based on the cup wheel·s surface grinding properties.The design of the single factor surface grinding test and the single point polishing test was to confirm the model·s accuracy.Analysis was done on how various grinding parameters affected the workpiece·s surface roughness and depth of subsurface damage.The maximum relative error is 15.8%,and the predicted subsurface damage depth agrees with the measured value,according to the results.Surface roughness and subsurface damage depth rise with feed speed and grind-ing depth,but fall with spindle speed.The study has some theoretical significance for directing the process parameter optimization of cup wheel grinding of WC-10Co-4Cr coatings.

Abstract:Gear's Circular plot is a result presentation method which needs to be combine with time synchronous averaging(TSA),which can clearly display gear meshing vibration waveform extracted by TSA.Aiming at the problem of parameter setting of gear's Circular plot and lack of the quantitative index,Fi index for waveform edge recognition and Yi index based on Hu-moments were proposed.Firstly,TSA algorithm was used to extract the gear meshing vibration signal,and the upper and lower edges of the vibration signal waveform were determined by calculating the minimum Fi index.Secondly,Circular plot of gears were drawn by the upper and lower edge parameters.Then,the Circular plot of the gear was divided into four parts,and Yi index of the Circular plot was obtained by calculating Hu-moments of the picture after segmentation.Finally,based on the Yi and Fi indices extracted from the gear Circular plot,a K-nearest neighbors(KNN)classifier was utilized to classify the gear vibration signals.The results show that there is a significant difference between the Yi and Fi indices of the vibration signals of normal gears and those of abnormal gears.By combining with the KNN classifier,it is possible to distinguish between normal and abnormal gear signals,which proves the effectiveness of this method.

Abstract:To address the problem that it is difficult to label variable working condition gearbox fault samples and the significant data distribution discrepancies in practical engineering,which result in reduced accuracy of fault diagnosis models,a semi-supervised gearbox fault diagnosis method based on masked contrastive learning is proposed.Firstly,a random mask was used to hide part of the information in the unlabeled dataset,generating two different masked instances for each unlabeled sample.Secondly,a dynamic convolutional neural network was employed to dynamically weight and aggregate the masked instances,enabling discriminative feature modeling of different masked instances.Then,a contrastive learning framework was constructed with the optimization goal of maximizing the similarity between features of different masked instances.By enhancing the consistency of feature representations of masked instance pairs,the model's dependency on labels was reduced.Finally,during the fine-tuning phase,a domain-conditioned feature correction strategy was introduced to generate target domain feature corrections.By aligning source domain features and target domain corrected features according to the metric of minimizing domain feature distribution discrepancies,the method explicitly reduces the domain distribution differences caused by varying working conditions.Validation on a variable working condition gearbox fault dataset demonstrates the effectiveness of the proposed method.

Abstract:Based on Reddy's layerwise theory(RLWT)and O(1)homogenization method,a three-scale layerwise multiscale analysis method(LMAM)for composite honeycomb sandwich structures was established.The macroscopic model of composite laminates was discretized by RLWT,and the microscopic unit cell model composed of fibers and matrix was established by three-dimensional finite element method.In the numerical example,the numerical simulation of the cubic block with inclusions was carried out,and the simulation results were compared with those of the direct numerical simulation(DNS)method,which verified the correctness of the LMAM.LMAM is also used to calculate and analyze the macroscopic,mesoscopic and microscopic stress distribution of composite honeycomb sandwich structures.

Abstract:Surface texture design is an effective way to achieve small leakage,long life and highly reliable operation of mechanical end seals.To investigate the characteristics of the interface film of guide groove texture,through the design and preparation of semi-circular,herringbone and E-shaped guide groove textures,experiments and theoretical research under high-speed operation conditions were carried out,the influence of different guide groove textures on the tribological properties of end face seals was explored.The results show that the existence of the guide groove can effectively improve the bearing capacity of the interface film and improve the tribological performance.In numerical calculations,the results show that the frictional performances of face seals varied with the configuration of guide groove.The herringbone textures and E-type ones show an obvious guide-aggregation effect.When the lubricant in E-type texture after being guide-aggregation through the groove,the pressure accumulates at the textured tail barrier,and fluid in the face seal clearance cannot escape from the guide groove boundary.As a result,the low energy loss in system,and an optimal liquid film bearing capacity achieves.Under different depths,the existence of guide groove promotes the hydrodynamic pressure.With the increase in depth,the bearing capacity of the liquid film increases first and then decreases.For the E-shape texture,the optimum bearing capacity of liquid film Pav=0.527 5 MPa is obtained at h1=10 μm.The bearing capacity of fluid film of E-shape texture has a 51.2%increase in comparison to the common grooved texture,the value of frictional torque has a 53.5%decrease.The analysis show that,the configuration of guide groove results in an accumulation of lubricant on the top of texture,which enhances the pressure convergence,thereby improving the bearing capacity of the lubricating fluid film and reducing friction('guide-aggregation effect').The geometric parameters of the guide groove have a significant impact on the fluid dynamic pressure in the end face sealing pair,which will influence the tribological performances of face seal.The research result provides theoretical support for the design of non-contact end face seal material surface texture in future.

Abstract:Elbows are an important component of oil and gas pipelines.The force state and the medium flow state are more complex than that of the straight pipe.Once the defect occurs at the elbow,the elbow pipe is more prone to fail.The high steel grade pipeline is the development trend of the long distance oil and gas pipeline construction,and it is urgent to evaluate the residual strength of the high steel grade bending pipe.Through the establishment of the finite element model,the defect size,relative position,bending radius,pipe parameters and pipe performance influence were studied on the ultimate internal pressure of the elbow,and finally the prediction formula of the bending was established.The results show that with the increase of defect length and defect depth,the ultimate internal pressure of the elbow is significantly reduced.The trench defect affects the ultimate internal pressure when the trench defect is located in the inner arch of the elbow.The bending radius,the wall thickness and the pipe material will affect the ultimate internal pressure.The error analysis shows that the prediction formula is more accurate,which can provide the basis for the residual strength evaluation of high steel grade elbows with trench defects.

Abstract:In order to ensure the industrial robot realizes the reliability goal,reliability allocation is a task to be accomplished in its manufacturing design stage.According to the characteristics of industrial robots,such as complex structure,high uncertainty,few samples,and failure correlation between component parts,a reliability allocation method for industrial robot systems based on BP neural network and Pythagorean fuzzy numbers was proposed.Using Copula function to establish a system reliability model,the failures of industrial robots were classified into three levels,the system level,the subsystem level,and the component level.By using the back propagation(BP)neural network,the system reliability,subsystem structure importance and subsystem complexity were taken as the input variables to complete the system-to-subsystem reliability allocation.The Pythagoras fuzzy number was introduced to score the influence factors of importance,environmental condition,technical level,maintainability,cost sensitivity and complexity,complete the reliability allocation from the subsystem level to the component level.The results show that the methodology achieves reliability goals and ensures reliability growth.

Abstract:Due to the needs of transportation,installation,grid connection,and maintenance,the construction of offshore wind farms in inshore areas often cannot be far from busy surrounding waterways,which significantly increases the probability of offshore wind turbines being impacted by ships.To analyze the performance and damage of different hollow ratios of protective devices when offshore wind turbines are hit by ships,the collision process of a 5000-ton bow-downward ship with an offshore wind turbine at a speed of 2.0 m/s was simulated using Ansys/Ls-Dyna.The influence of the hollow ratio on the anti-collision performance of Ogden rubber,Mooney-Rivlin rubber and Aluminum foam aluminum constitutive protective devices was studied and compared.The results show that with the increase of hollow ratio,the impact duration of aluminum foam protective devices increases,and the contact force decreases accordingly,while rubber materials show the opposite trend.As the hollow ratio decreases,the protective device is more similar to a solid tube,with a relatively smaller maximum indentation depth.Under the influence of hyperelastic properties,the indentation depth of rubber materials is smaller than that of aluminum foam after the collision is completed,and the material damage of the protective device is smaller.However,the proportion of internal energy in the support area gradually increases,so the influence of hollow ratio on the leg support needs to be considered in the design and research of protective devices.

Abstract:In order to study the strain softening phenomenon of ultra-fine grain(UFG)metal materials under uniaxial tensile loading,a modified model considering the effect of residual internal stress was proposed based on the classical crystal plasticity constitutive model,and the specific form of residual internal stress and its evolution were programmed into the user subroutine.The uniaxial tensile test data were fitted to verify the validity of the model,and the finite element simulation results of crystal plasticity were compared with and without the residual internal stress.The results show that the simulation results obtained by using the modified crystal plasticity constitutive model are in good agreement with the experimental results,indicating that the modified crystal plasticity constitutive model can effectively capture the strain-softening phenomenon of UFG metal materials,and the simulation results show different properties under the two conditions whether the residual internal stress is taken into account.It is reasonable to explain the strain softening phenomenon of UFG metal materials from the perspective of the formation and action of residual internal stress.

Abstract:In order to improve the high temperature wear resistance and extend its service life of 304 stainless steel,the high temperature wear-resistant NiCrAlY/Co coating was prepared on the surface of 304 stainless steel by the laser cladding.The morphology,phase composition and microhardness of the coating were analyzed.The tribological properties of 304 stainless steel and NiCrAlY/Co coating at different temperatures(the room temperature to 800℃)were studied,and the wear mechanism was analyzed.The results show that the coating is metallurgically bonded to the 304 stainless steel substrate;the coating is mainly composed of γ-Co,(Cr,Ni)and AlNi3 phases;the average microhardness of the coating(303 HV)is about 1.6 times that of the substrate(194 HV);Compared with the substrate,the coating has a smaller friction coefficient at 200-600℃,the friction coefficient is comparable at 800℃,and the lowest friction coefficient of the coating is 0.5 at 600℃.The wear rate of the coating from the room temperature to 800℃is lower than that of the substrate,and the lowest wear rate is 1.91×10-5 mm3/(N·m)at 400℃,which is about 1/3 of the substrate,indicating that the NiCrAlY/Co coating improves the high temperature wear resistance of 304 stainless steel.At medium and low temperatures,the wear mechanism of the substrate is mainly abrasive wear and adhesive wear,and the wear mechanism of the NiCrAlY/Co coating is mainly abrasive wear and gradually slight adhesive wear.At 800℃,the wear mechanism of the substrate is plastic deformation,and the wear mechanism of the coating is oxidation wear.

Abstract:Aiming at the issues of fracture and weight reduction in the wheel hub motor housing of an off-road vehicle,a structural strength finite element simulation analysis and structural topology optimization design were conducted.Firstly,a multi-body dynamics model of the entire vehicle was established,and a simulation analysis was performed to determine the load boundary conditions of the hub motor housing.Secondly,based on the spatial position relation between the housing and interconnected structures,a finite element model of the motor housing and suspension system was constructed for dynamic simulation analysis.Subsequently,using the OptiStruct software platform,with the objective of minimizing structural compliance and constraints on volume ratio before and after optimization as well as the maximum stress,a mathematical topology optimization model for the motor housing under various typical operating conditions was established and solved to obtain the optimal material distribution scheme.Finally,the optimization results were verified by simulation.The results indicate that compared to the existing design,the optimized hub motor housing structure experiences a stress reduction of over 40%and a weight reduction of 2.6%.It addresses the original fracture issue and eliminates the phenomenon stress concentration,thus providing the valuable reference for the design of similar hub motor housing structures.

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.