最新刊期
卷 46 ， 期 2 ， 2024
- 摘要：Feature selection and classifier design are often studied separately in rolling bearing fault diagnosis, so it is difficult to obtain satisfactory classification accuracy. An adaptive feature selection k-sub convex hull (AFSKCH) classificationmodel was proposed by combining feature selection and classifier optimization, which realized the integration of adaptive featureselection and classification. Firstly, the convex hull distance function was used to maintain the local neighborhood structure on the data manifold, and the feature weight matrix was obtained by alternately constructing k-sub convex hulls. Secondly, thedistance was solved by the method of linear programming proximity, and the adaptive feature space was obtained by using the multiplier alternating direction method. Finally, the classification was carried out according to the minimum reconstruction distance from the test point to the k-sub convex hull. The analysis results of rolling bearing fault vibration signals show that the feature selection performance of this method is better than other feature selection methods, and the classification accuracy is higher.
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发布时间：2024-07-05 - 摘要：A single degree-of-freedom plastic impacting oscillator was considered under the conditions of grazing and codimension-1 bifurcations. Based on the two-and one-dimensional parameters bifurcation analysis、 the bifurcation characteristics of single-impact periodie motions was studied. The non-smooth bifurcations such as Crossing-sliding. Switching-sliding anc codimension-2 sliding bifurcations as well as the discontinuous bifureations such as grazing bifureation and uous boundary crisis were revealed. The non-sticking periodic motion and sticking periodic motion transit into each other via a crossing-sliding bifurcation. In the two-dimensional parameter region of the low frequency and small clearance, the periodic motions (1, 1, 1) and (1, 2, 1) are distributed alternately. The boundary between the two types of periodic motions is a switching-sliding bifurcation curve. The boundary crisis of chaos occurs leading the chaotic attractor and its basin to vanish.关键词：Non-smooth system;Plastic impact;Sliding bifurcation;Grazing bifurcation;Boundary crisis
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发布时间：2024-07-05 - 摘要：In allusion to the difficulty to obtain fault samples of multi-stage centrifugal pumps in practical engineering, three typical faults containing rubbing, misalignment and unbalance were simulated through the fault simulation test-bed of multi-stage centrifugal pumps. And a fault diagnosis model based on support vector machine (SVM) was established to realize the classification of three types of faults. High dimensional feature samples were constructed by extracting time-frequeney domain characteristies of vibration signal with ensemble empirical mode decomposition(EEMD). combined with characteristies of time domain, frequeney domain and information entropy. The efficient fault classification was achieved by optimizing the quality of input samples with principal component analysis (PCA). In addition, by comparing the classification effects of SVM and back propagation (BP) neural network, it shows that the SVM model has better classification effect and high applicability in fault diagnosis of multi-stage centrifugal pump.关键词：Multi-stage centrifugal pump;SVM;BP neural network;EEMD;PCA
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发布时间：2024-07-05 - 摘要：In response to the difficulty in extracting early fault feature signals of rolling bearings, a joint fault diagnosis method based on Improved Complete Ensemble Empirical Mode Decomposition (ICEEMD) and Independent Component Analysis(ICA) was proposed. This method utilized the kurtosis criterion to reconstruct the Intrinsic Mode Function (IMF) obtained from ICEEMD and combined it with Fast Independent Component Analysis (FastICA) for noise reduction and unmixing, significantly reducing the noise in the measured signals. The maximum energy amplitude was obtained at the fault feature frequency, making it easy to identify fault features. Through experimental research and analysis, it is shown that this method can significantly reduce noise interference and highlight fault frequency components. Compared with the method combining ICEEMD and envelope spectrum, the signal-to-noise ratio is inereased by 29.54%, which can more accurately identify fault features and meet the discrimination requirements for rolling bearing faults, thus providing a new approach for bearing fault feature extraction.关键词：Improved complete ensemble empirical mode decomposition;Blind source separation;Independent component analysis;Fault diagnosis;Noise reduction
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发布时间：2024-07-05 - 摘要：Through the application of ultrasonic impact treatment technology to the surface of S355 steel, this research aimed to investigate the influence of different treatment durations on the material's microstructure, surface residual stresses, and tensile properties. The results show that ultrasonic impact treatment effectively mitigates residual tensile stresses in S355 steel while inducing compressive residual stresses. With an increase in ultrasonic impact treatment duration, the elimination of residual stresses along the x-axis and y-axis reaches values of 194.81 MPa and 200.46 MPa, respectively, at a treatment duration of 10 minutes. Furthermore, ultrasonic impact treatment prominently elevates the material's tensile strength and yield strength. Specifically, at a treatment duration of 10 minutes, the tensile strength and yield strength experience increments of 16 MPa and 13 MPa. respectivelv. By ultrasonie impact treatment, refinement of grain structure on the sample's surface is observed alongside distinct manifestations of work hardening layers. A comprehensive analysis suggests that post ultrasonic impact treatment, the material's internal dislocation density increases, and grain refinement occurs, serving as pivotal factors in the release of residual tensile stresses and the enhancement of tensile performance. These outcomes provide an experimental foundation for a deeper comprehension of the mechanisms by which ultrasonic impact treatment contributes to the improvement of metallic material properties.关键词：Ultrasonic impact treatment;Residual stress;Tensile properties;Microstructure
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发布时间：2024-07-05 - 摘要：In order to study the energy absorption characteristies of circular tubes with rectangular groove, a method based on regression analysis of fitting the relationship between structural parameters and energy absorption characteristics was proposed. Firstly, Cowper-Symonds constitutive model of 6005A-T6 was established, which was used as input to verify the accuracy of the simulation model of circular tubes. Secondly, an orthogonal experiment on energy absorption characteristies and structural parameters was designed, and a nonlinear calculation model between the two was established. Then. the mult tiple linear anc nonlinear regression analysis methods were used to solve the calculation model parameters, and the empirical formulas of peak force and energy absorption were obtained by comparing the two fitting results. By comparing the calculated value of the empirical formula with the finite element numerical value, the empiricalformula has higher accuracy within the research range, and the error is within 8%. Finally, the energy absorption performance index was introduced and the structure of the circular tube was optimized by genetic algorithm. The optimization results show that when the diameter and the groove end distance are the smallest. the wall ess and the groove width are the largest, and the groove depth is the shallowest, the circular tube has the best energy absorption performance in the range of research.关键词：Rectangular groove;Thin-walled circular tube;Multiple regression analysis;Empirical formula;Structural optimization
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发布时间：2024-07-05 - 摘要：Based on theoretical modeling, finite element simulation and experiment, the shear deformation and failure characteristies of two-dimensional cellular structure were studied, along with the influence of geometric parameters on overall anti-shear property. Through finite element simulation, the shear deformation rule was obtained. A frame shear fixture was used in shear test, whose results were compared with the finite element simulation results. The results show that the failure can attribute to tensile failure and shear failure near the nodes of cell walls, and the damage extends gradually from the edge to the inside. The cell size and cell-wall thickness have significant impact on the shear properties of the material, while the thickness and arrangement angles have little impact on shear properties. The anti-shear property of the hexagonal cellular structure is the largest among hexagonal, re-entrant and semi re-entrant cellular structures.关键词：Two-dimensional cellular structure;Anti-shear property;Geometric parameters;Failure characteristics
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发布时间：2024-07-05 - 摘要：An improved calculation method for the time-varying mesh stiffness of helical gear was proposed based on the potential energy method and the slice integration principle, taking into account the transition curve equation of tooth root. This method considered the parameter equation of the transition curve of the real tooth root, corrected the integral interval of the involute tooth profile, and compared with the finite element method to verify the validity of the algorithm and reduce the calculation error of the time-varying mesh stiffness. The influence of tooth width, helix angle, tooth number and modulus on the time-varying mesh stiffness was analyzed based on this method. The results show that the average time-varying mesh stiffness is greatly affected by the tooth width, exhibiting an approximate linear relation. In contrast, it is less influenced by the helix angle and number of teeth. As the helix angle increases, the average value fluctuates in a small range. When the center distance is fixed, as the number of teeth increases, the time-varying mesh stiffness slowly increases. Moreover, changes in gear parameters affect the contact ratio. Notably .when the axial contact ratio is an integer, the fluctuation of time-varying mesh stiffness is relatively small.关键词：Helical gear;Contact ratio;Improved potential energy method;Time varying meshing stiffness
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发布时间：2024-07-05 - 摘要：Aiming at the system non-linearity caused by the change of load mass of seat suspension and the effective control of seat vibration, an active control system of variable mass seat suspension based on the proportional-derivative (PD) control was proposed. The proposed control system structure was based on several different controllers. The primary controller was used to evaluate the actual value of the main force that should be generated in the suspension system, and the secondary controller was used to calculate the instantaneous value of the signal that controled the active element through its reverse model. The active seat suspension system model was established, and the active seat suspension control system was designed. The robustness of seat suspension system with different load mass was verified by simulation. The controller parameters were optimized to realize the fine control of adaptive quality identification of active seat suspension. The optimized design results were compared and verifed, and the results show that the influence of mass change on the dynamic performance of active seat suspension system is significantly reduced. Under 100 kg mass load and EM3、 EM5 and EM6 excitation signals, the SEAT factor of the active system is reduced respectively by 49.81%, 20.96% and 29.85%. At the same time, the suspension stroke is reduced respectively by 4.76%, 33.87% and 18.18%. The active control system established in this paper significantly improves the performance of the seat suspension, and has better robustness to the varying load mass, which provides a reference for the research on the vibration isolation performance of the active seat suspension.关键词：Active seat suspension;Load excitation;Adaptive control;Vibration reduction performance;Optimal design
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发布时间：2024-07-05 - 摘要：In recent years, ultrasonic guided waves technology has been widely used in nondestructive pipeline detection. However, the weak and insignificant defect echoes caused by the different types of tiny defects such as cracks, void, and dent deformation makes it difficult to identify and classify different types of miero defects. In order to identify the types of different tiny defects, the sensitivity of Duffing system to weak periodie signals was exploited and a signal feature classification method based on the dynamic index fractal dimension of the Duffing system and the back propagation (BP) neural network was proposed. By extracting the fractal dimension、 wavelet cocfficient and time domain signal parameters of the Duffing oscillator after inputting the defect signal to be tested as the characteristic parameters of the echo signal, inputting the BP neural network to complete the construction of the BP neural network, realizing the learning of the weak ultrasonie guided wave signal, classification. The numerical simulation and experimental verification show that the recognition accuracy is significantly improved by taking the fractal dimension of chaos index of three Duffing oscillators into consideration. The accuracy of numerical simulation is increased from 86.35% to 91.85%、 and the accuracy of experimental verification is increased from 83.16% to 86.06%. The numerical simulation and experiment verify that the combination of fractal dimension and BP neural network can effectively improve the identification of pipeline features and defects. The innovative use of fractal as the feature input of BP neural network effectivel y improves the accuracy of classification, facilitating identification and accurate classification, particularly in cases of insufficient experimental data or difficult detection scenarios invol ving small defects in the pipeline. The novel classification method that has been proposed has important significance for the pipeline defects classification and accidents prevention.关键词：Pipeline;Ultrasonic guided wave;Fractal dimension;BP neural network
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发布时间：2024-07-05 - 摘要：In view of the brake squeal suppression problem of automotive disc brakes during braking, the effects of brake imbalance and uncertainty in brake parameters, a stability and reliability analysis method of disc brake with the hybrid parameters was proposed by combining response surface methodology, finite element method, and reliability analysis theory. In this method . random, uncertain interval and fuzzy parameters were used to describe the dynamie characteristies of the brake system, and an unstable order response surface agent model of the disc brake system was established including random parameters, uncertain interval parameters and fuzzy parameters. Then, the remarkable affecting factors were obtained through sensitivity analysis of stability and reliability on brake system. Therefore, the influence laws of the second-order interaction of each factor were analyzed deeply based on stability and reliability analysis in Design Expert software. This method was used to verify the caliper disc brake of a certain type of automobile, and the results show that when the stability of the brake system with mixed parameters is not ideal, it can improve the stability of brake system effectively by increasing the thickness and elastie modulus of back plate of brake system.关键词：Brake squeal;Hybrid parameters;Reliability;Global sensitivity;Stability
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发布时间：2024-07-05 - 摘要：In order to solve the problem of unreliable bandwidth caused by fuzzy variables in the design of phononic crystals, a new two-dimensional multi-component local resonance phononic crystal is established. The band gap curve is obtained by numerical calculation and the mechanism of band gap generation is explored. Based on the analysis of the influence of the geometric parameters and material parameters of the cladding layer on the band gap, the ring cladding layer material parametersare considered as fuzzy variables and the geometric parameters are used as design variables. The experimental design is carried out by Latin hypercube sampling. The optimization model of the band gap of the phononic crystal based on Kriging model is established. The global optimization of the Kriging model is carried out by the sparrow search algorithm(SSA), and the optimal design solution of the phononic crystal is obtained. The results show that the optimized band gap width increases by 121. 5% from 101. 17 Hz to 224. 164 Hz, and the band width boundary is within the design target range. The Kriging band gap optimization model avoids a large number of numerical calculations and considers the influence of fuzzy variables. It has high prediction accuracy and reliability, which provides a new research idea for the design of phononic crystals.关键词：Phononic crystal;Fuzzy variable;Band gap;Kriging model;Sparrow search algorithm
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发布时间：2024-07-05 - 摘要：In order to improve the manufacturing difficulty of the complex helical-shape magnetic pole (HSMP) in permanent magnetic serew, the structure of HSMP is improved and replaced. The static characteristies of thrust and torque were simulated with the finite element method (FEM). It is proved that the two kinds of permanent magnetic screws, whose screw is oblique ring magnetic poles (ORMP), nut is HSMP, and screw is HSMP, nut is ORMP, can realize smooth transmission. Two practical improvements were carried out, because there were still some HSMP in the structures. Scheme one was to combine andarrange several circular arc-shaped magnetic poles (CASMP) blocks in step. Scheme two was a semi-oblique ring magnetic poles(SORMP) composite strueture. The results show that the number of combined pole blocks required for the latter is less, it can ensure the smooth transmission of the motion system, at the same time, with greater thrust and torque. Compared with LRMG which screw and nut are HSMP, the thrust and torque errors are 3.981% and 0.583% respectively, so it is an ideal scheme to replace HSMP. In addition, the concept of pole pitch ratio K was proposed, and it is concluded that when K=0. 3, the thrust and torque of unit volume pole have the largest value, and the utilization rate of magnetic pole is the highest. On this basis, SORMP composite structure is optimized by Halbach array. The peak thrust and torque can be increased by 42.3% and 36.3% respectively, and the optimal auxiliary ratio λ =0.4.关键词：Permanent magnetic screw;Magnetic pole;Semi-oblique ring;Halbach
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发布时间：2024-07-05 - 摘要：To estimate the structural failure risk of column disconnector subjected to typhoon, the efficient solution model of stochastic reliability was established considering the uncertainties of wind field and material resistance. First, the typhoon random field model was given based on the power spectral density, in which the uncertainties of ground roughness, average wind speed, and boundary wave number were incorporated. Then, the three-dimensional structural mechanies analysis model of disconnector was proposed based on the Abaqus software. Third, the calculation method of probability density function of structure target variable was obtained using the probability density evolution model (PDЕM). Finally, the efficient solution strategy was realized by the joint simulation of Matlab and Abaqus. Results indicated that the extreme stress of the bottom section of insulating pillar was the mainly dominated parameter. The uncertainties of wind field and material resistance have great influence on fragility curve. The uncertainty of material aspect should be controlled in structure design.关键词：Typhoon;Reliability;Column disconnector;Failure risk;Probability density evolution model
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发布时间：2024-07-05 - 摘要：The structure design of traditional energy absorbing box has some shorteomings, such as failure to realize stable and orderly folding and collapsing during collision and poor energy-absorbing ability in unit mass, which limits the improvement of automobile safety performanee. The aluminum alloy was added into the traditional 316L stainless steel composition to form afunetionally graded material (FCM) structure of the energy obsorbing box, and the cross section was optimized to be a stick insect tibia cross-sectional structure. The cross section of the energy absorbing box is then optimized by multiple objectives based on the optimized Latin hypercube experimental design and response surface model. The results show that the optimized bionic funetionally graded energy absorbing box can be folded and collapsed stably from head to tail. In addition, the energy-absorbing effect in unit mass was also improved as compared to the traditional energy absorbing box. The results indieate that the damage of the car body in collision can be effectively weakened by the FGM and bionie designed energy absorbing box.关键词：Energy absorbing box;FGM structure;Bionic cross section;Geometry design;Multi-objective optimization
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发布时间：2024-07-05 - 摘要：In order to comprehensively improve the commercial vehiele collision performance and protect the personal safety, at the time of standards change, a certain type of truck that passed GB 26512—2011 was taken as the research object, the frontal A-pillar pendulum impact test and top strength test added by GB 26512—2021 standard were taken as the object of investigation. The cab collision simulation model was established in Hypermesh, and the accuracy of the finite element model was verified through the real vehicle frontal collision test. In view of the intrusion in the top strength test, the structural sensitivity and foree transmission path were combined to optimize, and the corresponding structural optimization scheme was pгорosеd. The results show that the optimized cab structure has enough living space and meets the collision requirements of the new national standard.关键词：Commercial vehicle;Collision safety;Finite element analysis;Structure optimization
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发布时间：2024-07-05 - 摘要：A new falling object protective structures (FOPS) was designed by a topology optimization method based on the equivalent static load method to improve the safety of the operator of an electric excavator. Firstly, the dynamic and nonlinear crush process is simplified into multiple static and nonlinear deformation processes based on equivalent displacement. Secondly, the dynamic and nonlinear topology optimization was transformed into static and nonlinear topology optimization involving multiple load cases by the weighting coefficient method. The computational cost was saved and the convergence was improved. Finally, a new FOPS based on the topology optimization result was numerically validated based on the GB/T 17771—2010. The results show that the new FOPS can meet the safety regulation without additional protective grill and the total mass of the FOPS is reduced by 49.8 kg which are positive to save the costs of procurement and operating and reduce the fuel consumption.关键词：Topology optimization design;Equivalent static load method;Electric excavator;Falling object protective structures
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发布时间：2024-07-05 - 摘要：In order to export the vehicles to ASEAN smoothly, according to the needs of new vehicle research and development, aiming at meeting the limit value of leg protection under ASEAN-NCAP, a flexible leg (Flex-PLI) collision finite element model is built and calculated. Aiming at the problems in the vehicle design, an improved scheme was proposed and verified by simulation to be feasible. Finally, a full score was obtained through the actual vehicle test. The test results verified the reliability of the simulation, accumulated experience for the development of pedestrian calf protection.关键词：ASEAN-NCAP;Pedestrian protection;Flex-PLI;Simulation analysis;Test
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发布时间：2024-07-05 - 摘要：In order to overcome the disadvantage that it is inconvenient to introduce stress boundary conditions when solving the stress of element nodes in displacement finite element method, firstly, according to the generalized minimum potential energyprinciple of piezoelectric materials, a practical 8-node hexahedral nonconforming displacement element is proposed for the static analysis of piezoelectric structures. Then, based on the generalized H-R variational principle, a linear equations method for calculating the generalized stress of composite structures with piezoelectric layers is proposed. This method provides conditions for the introduction of generalized stress boundary conditions, and ensures the continuity of stress on the same node of adjacent elements, which lays a theoretical foundation for high-precision numerical results. Numerical results show that the accuracy of generalized stress results obtained by linear equations method is higher than that by Gauss-point stress extrapolation method(GSEM).关键词：Piezoelectric materials;Laminated structure;Nonconforming displacement element;Generalized stress
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发布时间：2024-07-05 - 摘要：Aiming at the damage of a Iow-range micro-electro-mechanical system(MEMS) acceleration sensor under tens of thousands of gn overload during the measurement of outer ballistic information of conventional weapons and ammunition, a kind of shrimp claw anti-impact micro-acceleration sensor was proposed, which could realize the index requirements of anti-overload 30 000gn and range 50gn. The finite element simulation results show that the displacement of the sensor is 0. 99 μm and the sensitivity is 0.124 pF/gn under 50gn load. The maximum equivalent stress of the acceleration sensor under 30 000gn overload is reduced from 1 022.5 MPa to 84.326 MPa, which effectively improved the reliability of the sensor.关键词：Accelerometer;Impact resistance;Capacitive;Low range;Bionic cushioning structure;Micro-electro-mechanical system
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发布时间：2024-07-05 - 摘要：Aiming at the high-speed impact problem of laminates, a three-dimensional finite element impact model consisting of 8 node cohesive element and 8 node solid element is established based on continuous damage mechanies. Based on the Hashin criterion, fiber damage can be well predicted, and puck criterion can well predict matrix damage, therefore. the criterion formed by the mixture of Hashin and puck is compared with the single Hashin failure criterion. It is found that the prediction result of the mixed criterion is closer to the test value. On this basis, the effects of ply angle and impact angle on the impact resistance of laminates are analyzed. The results show that the greater the angle difference between adjacent plies, the greater the incident angle, the stronger the impact resistance of laminates.关键词：Composite laminates;Puck criteria;Hashin criteria;Impact resistance;Numerical simulation
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发布时间：2024-07-05 - 摘要：The double cycloid tooth profile was applied to the NN type planetary gear transmission with small tooth difference. By analyzing the concavity, curvature and radius of curvature of the inner and outer cycloid tooth profile, the characteristics of the inner and outer cycloid tooth profile were obtained. Through the graphic method, the calculation formula ofthe pressure angle of the inner and outer cycloid gears in the double cycloid pin gear transmission was derived, and the variation law of the pressure angle in the meshing process and the influence of the main parameters of the double cycloid pin gear on the pressure angle of the inner and outer cycloid gears were obtained. Through the study of equidistant modification and shift modification, it is shown that the tooth profile modification has a significant impact on the tooth profile.关键词：Double cycloid pin gear transmission;Tooth profile characteristics;Profile modification;Pressure angle
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发布时间：2024-07-05 - 摘要：Based on D' Alembert's principle, the differential equation of the motion about the system was deduced, and the transfer function of the system was obtained by the basis of estabishing virtual equilibrium state of a seat suspension system. The mechanical properties of main components of seat suspension and seat transfer characteristies were obtained by means of experimental measurement. The accuracy of theoretical model was verified by the experimental results. On this basis, the influence of each parameter on resonance frequency and amplitude of the suspension system was discussed. The suspension system was partially improved according to structural parameters. The ideas and methods of this thesis can provide ideas and solutions for seat structure design.关键词：D'Alembert's principle;Seat suspension system;Virtual equilibrium state;Transfer function;Structure design
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发布时间：2024-07-05 - 摘要：Due to the high stress concentration of spot welding joints, it is very easy to initiate fatigue cracks at the edge of the nugget, and the residual stress produced by spot welding will affect its propagation. To explore the influence of spot welding residual stress on fatigue crack propagation, a three-dimensional finite element simulation model of DP600 high strength steel spot welding joint was established. Based on the thermal-elastic-plastic theory, the residual stress field of spot welding was solved. On this basis, the local stress intensitv factor (SIF) solution of the kinked crack with and without residual stress was calculated. By analvzing the variation curve of the local stress intensity factor at the deepest point of the crack with the crack depth ratio under the two conditions, the influence of residual stress of spot welding on the propagation of kinked crack was studied. Based on the fracture mechanics theory, the improved two-parameter model is used to predict the fatigue life wit th and without residual stress. The results show that the residual stress of spot welding significantly increases the local stress intensity factor, and the influence of residual stress on it increases with the increase of crack depth ratio. Considering the residual stress, the overall crack propagation trend remains unchanged but the propagation rate increases significantly, and the fatigue life decreases from 35 616 times to 12 564 times.关键词：Spot welding residual stress;Kinked crack;Stress intensity factor;Fatigue life
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发布时间：2024-07-05 - 摘要：In this study, the effect of average stress on the fatigue properties of 7075-T651 aluminum alloy was studied, and four stress ratios of R = 0.5, 0.3, 0.1 and -0.1 were selected for fatigue experiments. The results show that under the same stress ratio, with the increase of the peak stress level, the fatigue life gradually decreases, under the same peak stress level, with the increase of the stress ratio, the fatigue life shows a trend of increasing gradually. At the same time, using the scanning electron microscopy (SEM) to observe the fatigue fracture morphology, it is found that under the same peak stress, the sector area of the crack initiation and propagation zone increases with the inerease of the average stress. Finally, based on the fatigue test results of 7075-T651 aluminum alloy, an improved prediction model considering S-N-R is proposed in this paper. The comparison results show that this model has better prediction effect to a certain extent than other models.关键词：7075-T651 aluminum alloy;Average stress;Fatigue life;Fracture morphology;Prediction model
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发布时间：2024-07-05 - 摘要：In order to solve the problem that the traditional involute worm helical gear is prone to root fracture when the transmission ratio is too large, a new involute worm pair based on unequal modulus and pressure angle is put forward, which can increase the modulus and pressure angle of the helical gear at the sartime and greatly improve the root strength of the helica gear. By analyzing the transmission characteristics of this kind of worm pair, a special calculating method of meshing angle and center distance is obtained. In addition, through the modeling and finite element analysis of ZI worm helical gear pair and traditional Zl worm helical gear pair designed based on unequal modulus in the same transmission ratio and worm. it is found that the root strength of helical gear in the case of large modulus ratio is about 2.956 times that of traditional helical gear, which increases the application range of involute worm. The sum of squared errors (SSE) minimum model is compared with grey predictionto verify the accuracy of prediction. The maximum stress σ1max of helical gear meshing teeth under different torques is predicted, which provides a basis for corresponding engineering analysis and necessary checking design.关键词：Cylindrical worm helical gear drive;Unequal modulus;Unequal pressure angle;Finite element analysis;Grey prediction
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发布时间：2024-07-05 -
ANALYSIS OF THE CONSTRAINT EFFECT AND CREEP CRACK INITIATION TIME FOR STRUCTURE WITH ЕMBEDDED CRACKS
摘要：The specimen structure with embedded cracks served at elevated temperature was studied. The constraint effect and creep crack initiation time were analysed using the ductility exhaustion approach by 3D finite element method. The results revealed that the max value of constraint parameter was located at the end of major axis of elliptical crack, and the constraint levels enlarge with increasing the crack length or the crack depth, which meant that embedded cracks with a larger a/t or a/c would suffer from worse condition of stress concentration and there would be more dangerous. Besides, for the creep crack initiation times, the structure with a larger a/t or a/c or loadings would accompany high crack driving force under creep condition, which could cause a shorter period to creep cracking initiation, as well as a smaller creep crack initiation time. Additionally, a prediction equation and engineering method of the constraint parameters and creep crack initiation time for embedded cracks was proposed, and the prediction method of creep crack initiation time was validated.关键词：Embedded crack;Creep crack initiation time;Ductility exhaustion model;Creep damage;Constraint effect- 12
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发布时间：2024-07-05 - 摘要：In response to pipeline corrosion surplus intensity, a surplus intensity prediction method based on the Improved Whale Optimization Algorithm (IWOA ) -Least Square Support Vector Machine (LSSVM) combination algorithm model. Firstly the influencing factors of the surplus intensity of pipeline corrosion. On this basis, the theoretical introduction of the LSSVM and IWOA were analyzed was introduced to propose a combination method of the model. Taking the L245N material pipeline of a certain oil field in our country as an example, the use of some pipes to corrode the remaining strength and its influencing factors to train the combination model, and predict another part of the data. Essence studies have shown that the IWOA-LSSVM model proposed at the institute was in the process of conducting pipeline corrosion surplus intensity predictions. Its average root error is 0.323 5%, the average relative error is 2. 17%, and the fitting superiority is 0.988. The three evaluation indicators are better than the PSO-LSSVM model and the WOA-LSSVM model. Therefore, using the IWOA-LSSVM model can accurately predict the remaining intensity of pipeline corrosion, and then provide data support for the maintenance and replacement of pipelines.关键词：Pipe corrosion;Residual strength;Improved whale optimization algorithm;Least square support vector machine;L245N material
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发布时间：2024-07-05 - 摘要：Due to the low fatigue life of the air hammer bit in the drilling process, the drilling efficieney is greatly reduced and the drilling cost is increased. Therefore, the fatigue life of the air hammer bit is studied and its structure is optimized to improve the service life of the air hammer bit. On the basis of the 12.25 in (1 in = 2.54 cm) air hammer bit. the overall structure of the air hammer bit was designed considering the anti-drop structure. The concept of micro bit was proposed and the fatigue life experiment of miero bit samples was completed, using Ansys/Ls-Dyna and nCode DesignLife software, the dynamics and fatigue life of the micro drill bit are analyzed and verified with the experimental results, and the basie structure and material of the drill bit are determined. The simulation process is applied to the drill bit body, considering the size of the drill bit body and the impact velocity of the piston, etc. The influence of the problem on the fatigue life of the drill bit, the structure of the drill bit is optimized. The research shows that the drill bit with 40CrMnSiMoV has the best fatigue life. Among the basic dimensions of the drill bit body, the diameter has the greatest impact on the fatigue life of the drill bit. When the impact energy changes, the fatigue life of the drill bit decreases with the increase of the end speed. When the impact energy is constant, when the square of the end speed of the drill bit is close to the quality of the drill bit, the fatigue life of the drill bit is the best.关键词：Air hammer bit;Structural optimization;Dynamics;Fatigue life
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发布时间：2024-07-05 - 摘要：With the development of high speed, high precision and high reliability of rotating machinery systems, rolling bearings as basic components are a very important part of rotating machinery systems. Since the bearing slippage behavior seriously affects the stability, running accuracy and service life of the rotating machinery system, the research on the sliding characteristies and motion mechanism of rolling bearings has become a hot topic discussed by scholars at home and abroad. The mechanism of slipping motion of rolling bearings in the form of slip damage is introduced, and the research methods of rolling bearing slip and the slip factors of rolling bearings are summarize in detail. Finally, the research status, deficiencies and future development directions of the research methods (experimentation, dynamic simulation) and the slippage factors (working conditions, structures, assembly parameters and faulty bearings) of rolling bearings are discussed.关键词：Rolling bearing;Sliding characteristics;Experimentation;Dynamics;Slippage factor
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发布时间：2024-07-05 - 摘要：Aiming at the cracking problem of the catalyst of an extended-range three cylinder engine in the durability test, the fracture form and the cracking reason were analyzed, the optimization and verification were carried out. The fracture and material were analyzed by means of chemical composition detection, metallographic structure analysis and fracture electron microscope scanning. The vibration characteristics of the three cylinder engine were discussed, and the heat transfer analysis and thermal modal analysis of the catalyst were carried out. The cracking reason was determined by modal interferogram and strain energy density. An improved scheme was proposed based on the modal frequency and mode shape, and the analysis and verification were taken. The results show that the surface of the engine catalyst will form intergranular cracks under high temperature oxidation. When the stiffness of the support is insufficient, the thermal modal frequency of the catalyst is too low, it will resonate with the third-order combustion excitation of the three cylinder engine under high temperature, leading to the propagation of surface cracks and the formation of fracture. By analyzing the thermal modal frequency, vibration mode and strain energy density of the catalyst, the catalyst support can be effectively improved, which provides a reference for the design of the catalyst of the three cylinder engine.关键词：Three cylinder engine;Catalyst;Cracking;Analysis and optimization
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发布时间：2024-07-05 - 摘要：In order to improve the accuracy of structural damage localization, a method to locate structural damages is proposed by combining the cross-model modal strain energy and the wavelet analysis(WA). Firstly, indices based on cross-modelmodal strain energy of all elements have been calculated. Secondly, the wavelet analysis is conducted on the sequence composed of the calculated indices of all elements, with high-frequency detail coefficients extracted to form the improved damage index. Finally, damage locations are judged according to the improved index. A planar truss is taken as the numerical example, with the Monte Carlo analysis carried out in consideration of 5% noise level. The result shows that the improved index is more robust to resist noise interference and can better indicate damage locations.关键词：Damage localization;Modal strain energy;Wavelet analysis;Structural health monitoring;Modal identification
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发布时间：2024-07-05
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