Abstract:The disc spring will bear the cyclic displacement load during using,resulting in the fatigue damage and the stiffness degradation of the disc spring,which causes irreversible influence on the compensation function when accumulated sufficiently to cause fracture.Therefore,the disc spring material which occurred internal fatigue and structural stiffness degradation was studied under the cyclic load.By considering characteristics of the geometric nonlinearity and the action of the cyclic load,based on the traditional stiffness degradation model,a stiffness degradation model fitting for disc springs was established.The force change of the structural system,the law of stiffness degradation of the disc spring,and the stiffness degradation model were analyzed and verified with the finite element software.The model was modified based on the test data to obtain the model that can be used to calculate the degradation of the disc spring stiffness.This model can predict the deformation of disc springs'structure in service,and determine the fatigue damage and performance degradation degree,which can provide some basis and reference for the application of disc springs.

Abstract:The fatigue limit of 7085 aluminum alloy was tested by four-point bending fatigue test for samples of different sizes and roughness.The results show that the greater the thickness of the specimen,the greater the ultimate fatigue strength of the material.The higher the surface roughness of the sample,the lower the ultimate fatigue strength of the material.The stress analysis and calculation of the specimen show that the dangerous cross section occurs at the position where the indenter contacts the specimen,where the specimen is subjected to the combined action of bending normal stress and shear force.With the increase of the thickness of the specimen,the shear force on the specimen decreases,and the bending normal stress on the specimen increases under the same fatigue limit.And vice versa.The relation between the surface roughness and the radius of curvature of the sample is shown by establishing a simplified model,and then the relationship between the surface roughness and the fatigue ultimate strength of the material is obtained.

Abstract:This article took the folding section cam linkage mechanism of a carton folding machine as an example.Firstly,a preliminary design of the cam was carried out based on actual working conditions.Then,combined with the analytical method designing the cam mechanism based on the allowable pressure angle of the cam,a mathematical model was established with the swing rod angle and the center distance between the cam and the swing rod as design variables.Using the NSGA-Ⅱ optimization algorithm,perform multi-objective optimization design on the cam linkage mechanism and select the optimal solution from the generated Pareto solution set.Based on the optimization results,the preliminary design of the cam linkage combination mechanism was adjusted,and the contour of the cam was obtained through Matlab programming,verifying that the optimized cam pressure angle met the allowable pressure angle.Finally,simulation analysis was conducted on the optimized cam linkage mechanism using Adams software.It is found that the displacement,velocity,and acceleration of the blade movement meet the design requirements,verifying the correctness and feasibility of the optimization results.At the same time,it also provides a reference method for the optimization design of other cam linkage mechanisms.

Abstract:The harsh operational environment of helicopters renders their structures highly susceptible to the initiation and propagation of hole-edge cracks around bolt holes,thereby compromising structural integrity and load-bearing capacity.To monitor hole-edge cracks in helicopter attachment lug structures,piezoelectric guided wave-based structural health monitoring(SHM)techniques are commonly employed.However,due to the difficulty in detecting small cracks at the early stages of propagation and the presence of large through-hole configurations in attachment lug structures,the accuracy of guided wave monitoring remains suboptimal.Therefore,addressing the accuracy issues in crack monitoring of attachment lug structures,this study proposes a piezoelectric guided wave array-based method for hole-edge crack detection.Firstly,damage feature information was extracted from acquired piezoelectric guided wave array signals encompassing the entire sensor network.Subsequently,a damage alarm threshold was established using a mean-value method to facilitate damage detection.Furthermore,an improved delay-and-sum imaging algorithm was developed based on the specific configuration of the attachment lug structure to optimize probability distribution and achieve precise crack localization.Finally,validation was conducted through test monitoring of crack propagation in attachment lug structures.Test outcomes demonstrate that the proposed method enables accurate alarm triggering and localization of hole-edge cracks around bolt holes,with localization errors confined within 2.01 mm,thereby confirming the efficacy and precision of the proposed approach.

Abstract:Aiming at the problems of traditional impact load identification methods,such as the requirement for a large number of sensors,high sampling frequency,and low identification accuracy,a new impact load identification method based on empirical mode decomposition(EMD)technology was proposed.The EMD technology was used to decompose the complete impact response to obtain the modal acceleration response.The impact location was quickly realized by measuring the collinearity between the uncorrected mode shape vector and the column vector of the mode shape matrix in the modal acceleration response.According to the positioning results,an optimization objective function was constructed.The time history of the impact load was fitted by using the Gaussian basis function,and the optimal fitting parameters were quickly solved by using the two-dimensional gradient descent method.Tests conducted on a cantilever plate with dimensions of 600 mm×200 mm×3 mm show that with only one accelerometer,the success rate of 36 impact positioning tests is 91.67%.The peak relative error and relative error index of the reconstruction results are less than 10%and 40%,respectively.

Abstract:To explore the penetration resistance of aluminum alloy tubes under spherical steel projectile impact,focusing on the effects of varying tube radii and wall thicknesses on ballistic limit velocity,providing a foundation for tube protection design.A finite element model of spherical steel projectile penetration into 2024-T42 aluminum alloy targets was established using Ansys/Workbench software and the Johnson-Cook material model,which was then verified.Simulations of the response characteristics of aluminum alloy tubes with different radii and wall thicknesses under normal impact of spherical steel projectiles were conducted,along with an analysis of tube deformation and damage.The study found that the penetration resistance of the upper and lower walls of aluminum alloy tubes differs,with the upper convex structure outperforming the lower concave structure.A smaller tube radius enhances the penetration resistance of the upper wall,while for tubes of the same radius,increasing the wall thickness leads to a roughly linear increase in the ballistic limit velocity of both upper and lower walls.

Abstract:In pressurized-water reactor nuclear power plants,the vessel nozzles of large carbon steel equipment such as reactor pressure vessel(RPV),steam generator(SG),and main pumps are connected to austenitic steel pipes through dissimilar metal welds(DMWs).The thick-walled DMW has material inhomogeneity and complex weld residual stress(WRS),which easily leads to the generation of fatigue or stress corrosion cracks.Firstly,the WRS of DMW in nuclear power plants obtained through international measurements and numerical analyses was investigated.Then,based on a rapid WRS simulation method for volume uniform heating of unit cells,the WRS of DMW in the hot leg of the primary loop(the connecting pipe section from RPV outlet to SG inlet,which is the pipe section with the highest operating parameters in the primary loop pressure boundary)was obtained.The numerical simulation results are consistent with the trend of the fitting envelope curve recommended by the United States,and the overall results can be enveloped by the fitting curve recommended by the United States,indicating that the described rapid WRS simulation method is feasible.The WRS of thick-walled DMW is relatively high,and the stress values at the inner and outer surfaces of the pipe are more conservative than the recommended values of the United States,suggesting that more safety margins can be obtained in actual structural analyses.

Abstract:In order to investigate the nature and causes of the cracked passage hole of the low-pressure turbine shaft of aero-engine during the high and low circumference compound fatigue test,the low-pressure turbine shaft crack location was examined in appearance,fracture analysis,surface inspection,metallographic organization,finite element analysis and crack expansion simulation.The results show that the low-pressure turbine shaft passage hole crack failure is a fatigue crack,which is caused by the incomplete removal of the remelting layer after the passage hole is cut by electrical discharge machining,resulting in the existence of part of the unremoved remelting layer and visible microcracks on the internal surface,and the fatigue crack sprouted and crack expansion occurred under the action of large high and low circumferential composite load,thus leading to the passage hole crack failure.The initial crack length is estimated to be between 0.2-0.3 mm by the crack expansion simulation analysis.In order to ensure the processing quality of the through oil hole,considering the poor processing accessibility of this location,it is suggested that special tooling can be designed and the machining technology can be used for processing,on the basis of ensuring the processing,fundamental eliminate the influence of the remelting layer.

Abstract:Aiming at the issues of under-maintenance or over-maintenance in preventive maintenance of DSA200 type pantograph,a method was proposed to optimize inspection and maintenance parameters by using pantograph failure data.Firstly,the failure datas of the pantograph components were analyzed by using graph parameter method,which failure time distribution models were fitted.The failure datas were preliminarily determined to obey the exponential distribution,and the Bartlett value method was further used to verify the validity of the failure data obey exponential distribution.Secondly,based on the structure and working characteristics of pantographs,a reliability block diagram model with pantograph components in series was constructed.According to the characteristics of constant failure rate of pantograph components,the failure rate of pantographs was obtained.Thirdly,the minimum cost model of preventive maintenance and replacement of pantographs was established,and the optimal preventive maintenance interval and the optimal number of spare parts were obtained.Finally,the structure importance,probability importance and critical importance of pantograph components were analyzed by using fault tree analysis method,and the failure probability of pantograph and the key components in inspection and maintenance were obtained.The optimized pantograph inspection and maintenance parameters can provide scientific reference for maintenance personnel to improve their maintenance level and reduce maintenance costs.

Abstract:Octet-truss lattice structure is one of the preferred materials in engineering field with light,high strength and high toughness properties.Three-point bending experiments were carried out on Ti6Al4V Octet-truss lattice structure with shallow pre-crack,and the fracture process was observed by digital image correlation(DIC)technique.To further study the fracture toughness of Octet-truss lattice structure,the fracture behavior of the structure under three-point bending load was analyzed by finite element method.The mechanical response of the truss member for the structure was characterized by the isotropic elastoplastic mechanical model.The validity of the finite element model was verified by experiments.Based on the elastic-plastic fracture behavior of the structure,the J-integral method was used to calculate the fracture toughness of the Octet-truss lattice structures.The results show that the fracture toughness of the Octet-truss lattice structure increases linearly with the relative density and the square root of the truss length.For the truss member at the crack tip,truss in different planes have different stress states and deformation modes with the same cross-sectional size.According to the failure mode of the structure,the stress state of truss from different planes is balanced by optimizing the proportion of the cross-section size,which can optimize toughness of the lattice structure with same relative density.

Abstract:High-speed machining technology by improving the cutting speed and feed rate to improve the material cutting rate,machining accuracy and machining quality,is one of the main ways of modern processing.Therefore,to ensure the stability of high-speed machining is the basis of application of high-speed machining.Firstly,based on the traditional stability analysis,the influence of feed rate on the static cutting thickness was further considered,the stability model related to feed rate and radial cutting depth ratio of tool was established,and the stability of high-speed milling was analyzed by combining stability variance ratio.Secondly,based on the single factor variable feed rate test,a filter was designed to filter the frequency component of the spindle speed.The variance ratio between the filtered signal sequence and the original signal sequence was used to analyze the milling stability changes of the continuous variable axial depth test,and the validity of the analysis method considering the feed rate to affect the stability of high-speed milling was verified.The results show that the proposed method can determine milling stability more accurately for high-speed machining with small radial cutting depth.And the axial cutting depth of unstable cutting limit changes slightly with the increase of feed rate,and the feed rate will aggravate the instability of milling system.

Abstract:In order to solve the problem of the accuracy of the random vibration transmissibility calculation of airborne electronic equipment,the basic STEINBERG sinusoidal vibration transmissibility model and the IRVINE random vibration transmissibility model were firstly verified through tests,and it was found that there was room for improvement in the accuracy of the IRVINE random vibration transmissibility model.Therefore,on the basis of the"Three-interval method",the effects of 4σ and 5σ transient acceleration of random vibration were taken into consideration,and a more comprehensive"Five-interval method"was proposed;then,the structural fatigue coefficients of the model were corrected by combining with the characteristics of the airborne electronic equipments.The results show that the error between the proposed random vibration transmissibility calculation model and the measured value is less than 5%,which is closer to the measured value,proving that the proposed model is more accurate.

Abstract:Metal structures are widely used in industry.Metal structures in service are prone to crack defects under tensile and compressive fatigue load.In order to realize quantitative detection of metal structures'crack defects,a quantitative analysis method of metal structures'weak magnetic detection based on back propagation(BP)neural network was studied.In view of the poor effect and low efficiency of BP neural network in parameter adjustment,the improved whale optimization algorithm(IWOA)based on Sine chaotic mapping was adopted to optimize the BP neural network parameter adjustment mode,giving consideration to global optimization while improving the local optimization ability,and then the optimal parameters searched by IWOA were assigned to BP neural network,improving the quality of initial network parameters.The length,width and depth of the artificial rectangular slot were quantified by inversion.The results show that the average prediction accuracy of IWOA-BP neural network is above 80%,and the prediction accuracy of depth,length and width is improved respectively by 106.72%,9.68% and 6.86% .

Abstract:Since the fault vibration data collected in the real engineering may be accompanied by noise,traditional diagnostic models are difficult to identify fault categories.To address this problem,a rolling bearing fault diagnosis research method based on channel and spatial reconstruction and progressive convolutional neural networks(CSRP-CNN)was proposed.The model utilized channel and spatial reconstruction convolution(CSConv)to reduce the redundant information of channels and space in fault features,and reduced the complexity and computation to improve the performance;using the convolutional block attention module(CBAM),attention enhancement operation was carried out in the channel and spatial dimensions to make the model pay attention to the important fault feature information;and the progressive convolutional network structure was used in the shallow layer of the network,which would fuse the previous fault feature information with the current input to obtain the richer feature information.The performance of CSRP-CNN was evaluated by two different datasets of Case Western Reserve University(CWRU)and machinery fault simulator magnum(MFS-MG).After the noise and ablation tests,it is verified that CSRP-CNN has strong robustness and the effects of CSConv,CBAM and progressive convolutional neural network(PCNN)on the model noise immunity performance.

Abstract:The noise of automotive electronic water pump(EWP)is an important indicator of the performance of EWP,and its active control is conducive to improve the sound quality of the car.In order to achieve the active control of the noise of EWP,a hybrid random carrier space vector pulse width modulation(HRCSVPWM)strategy was proposed.Firstly,the Xorshift algorithm was used to design a random sequence generator to generate random numbers with good randomness to disperse a large number of harmonics concentrated in the carrier frequency and its integer multiples.Secondly,the sawtooth wave period function was combined to increase the weakening effect on the pulse width modulation(PWM)harmonic amplitude.Then,the simulation model of the EWP was constructed to investigate the harmonic suppression effects of control strategies of space vector pulse width modulation(SVPWM),random carrier space vector pulse width modulation(RCSVPWM)and HRCSVPWM,to verify the ability of HRCSVPWM to suppress PWM harmonics.Finally,EWP noise test platform was constructed to analyses the noise of EWP under three types of control strategies.The results show that the noise suppression effect of HRCSVPWM is remarkable,which can make the noise's sound pressure level of EWP decrease significantly,with an average decrease of about 3 dB.

Abstract:The bearing section of the work roll neck often suffers burnout failure due to bearing seizure,and additive manufacturing is usually used in the field to repair it.Life prediction of the repaired roll neck is the key to predict the safe service of the work roll in the field production and carry out overhaul,but there is a lack of research on the related issues.In view of the above problems,the stress analysis and multi-axis life prediction of the working roll neck bearing section of the four-high mill were carried out.Based on the SIMS model and the influence function method,the rolling force and the stress between the rolls were calculated.The moment balance equation of the roll neck end was established in the bearing section,and the bending stress model of the roll neck bearing section was established.The deformation resistance was regarded as the plastic deformation energy per unit volume to calculate the rolling torque in the deformation zone,and the torsional shear stress model of the roll neck bearing section was established.Using the first strength theory,the equivalent stress was obtained by combining the bending stress and the torsional shear stress.On the basis of proving the calculation accuracy of the model,the multi-axis fatigue model was used to predict the fatigue life of the roll neck bearing section,and compared with the service life of the actual roll in the production line.The results show that the stress calculation model of the working roll neck bearing section of the four-high mill is in line with the actual stress state of the roll neck.The error between the expected service life predicted by the theoretical model and the actual service life is less than 20%,which meets the actual engineering error requirements.

Abstract:In view of the difficulty of obtaining durability test specifications for axle components,a method of constructing driving load of the front axle dynamic model was proposed to provide the input for system-level bench test and life verification of front axle components.The life of front axle was obtained based on the whole vehicle dynamics model and the measured road load,and the useful information and life prediction results in the above process were employed to guide the construction of driving load applied on front axle.Firstly,the frequency band of the measured six-component forces at the wheel center was adjusted.Then,with the goal of minimizing the difference between the damage/life of the front axle and the reference value under each working condition,the adjustment coefficient of the amplitude of the three-way forces at the wheel center was optimized by combining the response surface method and genetic algorithm.The optimized three-way forces at the wheel center and the other three-way torques constituted the driving signal of the front axle model.The results show that the constructed wheel center drive signal is used to simulate the dynamic load of the front axle model.The life of the front axle,the failure sequence of risk points and the damage contribution ratio of various road conditions to dangerous points are obtained and in good agreement with the reference results,which verified the effectiveness of the proposed method and provided reference for the drive signal construction and component life evaluation of system-level bench durability test.Finally,the damage distribution of the front axle can be consistent with the reference results by modifying the main damage load of the shaft tube.

Abstract:Taking a 1.5 MW wind turbine tower with different initial crack lengths as the research object,vertical and horizontal earthquake loads with four earthquake intensities and three actual earthquakes were applied,respectively.The influence of vertical and horizontal earthquake loads on the strain field at the crack tip of the wind turbine tower was studied and compared.The results indicate that both under vertical and horizontal earthquake loads,the equivalen plastic strain area at the crack tip increases with the increase of earthquake intensity,but under horizontal earthquake loads,the equivalent plastic strain area at the crack tip increases more rapidly.Under earthquake intensities of Ⅵ and Ⅶ,the impact of vertical earthquake loads is greater than that of horizontal earthquake loads.As the earthquake intensity increases,the impact of horizontal earthquake loads increases sharply under earthquake intensities of Ⅷ and Ⅸ,and far exceeding the impact of vertical earthquake loads.The impact of vertical actual earthquake load on the crack tip equivalent plastic strain area is related to the magnitude and earthquake acceleration time-history curve,while the impact of horizontal actual earthquake load on the crack tip equivalent plastic strain area is related to the earthquake acceleration time-history curve.

Abstract:Impulse current under short-circuit condition is the key factor for the structural reliability of the testing transformer.Therefore,the structural reliability analysis model of transformers was proposed based on the probability density evolution theory.Firstly,the basic principle of probability density evolution theory was introduced,and the analysis method of electromagnetic force field for windings was given considering the coupling effects of magnetic and electric fields.On the basis,the numerical analysis model of transformers structure was constructed by using the Abaqus software finite element analysis method.Taking an AGF 20 kV testing transformer as an example,the above model was validated.The longitudinal Mises stress of windings was chosen as the control variable,and the stress distribution and probability density evolution characteristics were given.Then,the structural reliability index was calculated,and the extreme mechanical response and the corresponding distribution zones of windings and iron cores were discussed.The results show that the stress of windings increases significantly under the action of short-circuit impulse current.The maximum value of windings'stress reaches 82%of the threshold,and plays the key role in structural reliability,the increase of impedance has obvious influence on the reliability of transformers.

Abstract:Constitutive analysis of steel wire rope conveyor belt is a key problem for conveyor belt design optimization and energy conservation.Maxwell model and Burgers model based on viscoelastic theory and transient dynamics were constructed.Considering the fretting friction damping between steel wires and the mutual damping between steel wire rope and conveyor belt,a mixed constitutive model was constructed.Under the condition of 0-30℃,the relationship between the parameters of the constitutive model was established,the simulation curve was fitted and solved by Matlab,and the accuracy of the mixed constitutive model was verified by taking 40℃as the control group.The verification results show that the maximum error between the conveyor belt represented by this constitutive model and the experiment is 5.88%,demonstrating that this constitutive model can better characterize the rubber conveyor belt with steel wire rope core.The universality of this model is verified by the method of simulation and prediction.It provides a theoretical basis for the structural optimization and energy-saving analysis of conveyor belt.