Abstract:Addressing the rotational vibration issues encountered during the operation of seawater pumps,and integrating measured vibration characteristics,a quasi-zero stiffness ring meta-structure isolator was designed for vibration control based on the principles of quasi-zero stiffness isolation and the bandgap features of meta-structure.First of all,taking a typical seawater pump as the research object and based on an integrated quasi-zero stiffness structure,a structural design scheme of the ring meta-structure isolator was proposed.Then,models of quasi-zero stiffness unit cell,one-dimensional quasi-zero stiffness meta-structure and quasi-zero structure ring meta-structure isolator were established using finite element method and theoretical method,respectively.Their static and dynamic mechanical characteristics were calculated and analyzed,and their isolation effect on the output vibration of seawater pumps was evaluated.The calculation and test results show that the quasi-zero stiffness ring meta-structure isolator provides multiple bandgaps at low frequencies,and exhibits significant vibration suppression effects on typical frequencies of seawater pumps.

Abstract:In response to the problems of reduced surface quality and severe twist drill wear in HR-2 hydrogen resistant steel deep small holes drilling,integrated thermal coupling finite element simulation with experimental investigations of deep small holes drilling to analyze the variations in tool wear,drilling temperature,and the quality of the machined surface during the process of machining deep small holes.The improvement effect of introducing ultrasonic vibration on poor surface quality and severe tool drilling wear was analyzed by comparing ultrasonic vibration assisted drilling(UVAD)and conventional drilling(CD).The results show that as the drilling depth increases,the heat accumulation of the tool's transverse and cutting edges significantly increases,gradually leading to problems such as coating peeling,edge passivation and chipping.Concurrently,the accumulation of cutting heat on the surface of the machined hole causes temperature rise,resulting in material coating,debris adhesion,oblique scratching and other problems on the machined surface,resulting in a deterioration of surface quality and an elevation in surface roughness.Compared to CD,the UVAD effectively reduces drilling temperature,helps to reduce tool wear and maintain cutting edge integrity,while suppressing the increase in surface roughness during machining,ultimately improving surface quality.

Abstract:To address the issue of characterizing static and dynamic mechanical behaviors of the surface-modified layer(SML)in 18CrNiMo7-6 alloy steel,a layered inversion method for the Johnson-Cook(J-C)constitutive model of SML was proposed.The SML was subjected to layered processing,and dynamic compression tests were conducted on cylindrical specimens with different SML thicknesses.Through progressive parameter inversion,the strain rate sensitivity coefficient C at each depth of the SML was determined.Combined with quasi-static thin plate tensile tests at different temperatures for each depth of the SML,the corresponding yield strength A,strain hardening coefficient B,strain hardening index n,and thermal softening exponent m were determined.Test results show that the SML of 18CrNiMo7-6 alloy steel exhibits significant strain hardening,strain rate strengthening,and temperature softening effects.Additionally,a correlation model between J-C constitutive parameters and dimensionless depth h/hb(distance to SML surface/SML effective depth)was established,providing support for subsequent composite strengthening simulations.

Abstract:Different parts of high-speed train bogies are usually designed with aluminum alloy materials of varying strengths,and welding is adopted to connect these different parts.When high-speed trains operate under complex road conditions,the bogies will be subjected to tensile overload,which will produce a coupled superposition effect with the strength difference of welded joints.Therefore,tensile overload tests were carried out on the welded structural components of bogies to study the fatigue crack growth behavior and intrinsic mechanism of aluminum alloy welded joints with different strengths under the action of tensile overload.The compliance method was used to measure the crack growth rate under tensile overload;the digital image correlation(DIC)technology was applied to analyze the change in the size of the plastic zone at the crack tip before and after the application of tensile overload;the scanning electron microscope(SEM)was employed to observe the fracture morphology characteristics of different aluminum alloys in the region affected by tensile overload.The crack growth behavior and intrinsic mechanism under tensile overload were explained based on the change in the size of the plastic zone at the crack tip and the corresponding fracture morphology characteristics.The results show that a single tensile overload can reduce the fatigue crack growth rate and extend the fatigue life.Further analysis indicates that during the tensile overload process,the plastic zone at the crack tip expands and the crack tip is blunted,which together lead to the reduction of the fatigue crack growth rate.The lower the material strength,the more severe the deformation at the crack tip and the more obvious the hysteresis effect under the same tensile overload.The test results of welded joints under tensile overload are consistent with those of the base metal,suggesting that the strength of the hysteresis effect depends only on the inherent strength of the material itself.

Abstract:Blind bolted rivets with large flange are widely used as standard fasteners for single-side connection in the aerospace industry,and their minimum tensile load is one of the clearly specified mechanical properties.However,the current method for calculating the tensile strength of blind bolted rivets with large flanges is not yet fully developed.In order to improve the forward design process of blind bolted rivets with large flanges and predict their tensile strength,the failure modes during the tensile process were investigated.First,mechanical analysis reveals three failure modes due to stress concentration:the breakage of the forming sleeve,breakage of the head,and indentation of the nut sleeve.Then,a finite element simulation was used to propose a prediction method for the tensile strength of blind rivet nuts with large flanges,which helps obtain the failure modes and predict the tensile strength.Finally,a hydraulic testing system was used to conduct tensile tests on a specific model of blind bolted rivets with a large flange,the specific failure modes and force-displacement curves are obtained.The accuracy of the proposed prediction method is verified by the test result.This study provides a reference for improving the connection strength of blind bolted rivets with large flanges and enables the prediction of tensile strength in the forward design process.

Abstract:Taking cast iron material of cylinder head as the research object,a series of thermo-mechanical fatigue experiments under different temperature ranges were conducted through bulk sampling.The results show that the fatigue test of cast iron materials exhibits three stages:cyclic softening,cyclic stability and rapid failure.Additionally,the fatigue life of materials under inverse phase loading is significantly shorter than that under positive phase loading.Six typical supervised learning models,including artificial neural networks(ANN)and random forest(RF),were used to predict the fatigue life of the experimental data.However,the results indicate that these models failed to learn the fatigue life distribution trend of the materials.For this problem,the prediction of the thermal mechanical fatigue life of cast iron materials for cylinder heads was achieved by using the self-supervised algorithm based on the generative adversarial network(GAN),and it showed a good prediction effect under the condition of small samples.This research has strong guiding significance and reference value for cylinder head design and fatigue analysis.

Abstract:In order to improve the comprehensive mechanical properties of 960 MPa high strength steel weld metal,the optimum content of Ti element in 960 MPa high strength steel weld metal was revealed.Firstly,four kinds of weld metals with different Ti contents(0.01%-0.08%)were designed and welded.The effects of Ti content on the microstructure and mechanical properties of welds were systematically studied by scanning electron microscopy,energy dispersive spectroscopy,tensile and impact tests.The effect of Ti content on the initiation energy and propagation energy was evaluated by fracture observation and fracture morphology.The results show that when the Ti content is less than 0.06%,the microstructure of the weld metal changes from granular bainite to granular bainite+acicular ferrite.With the increase of Ti content,the content of acicular ferrite increases significantly.When the Ti content reaches 0.06%,the tensile strength reaches 939 MPa,the elongation reaches 23.5%,the elongation increases by 27%compared with Ti0.01,and the impact absorption energy at-40℃reaches 104 J;when the Ti content increases to 0.08%,the formation of coarse lath bainite and the precipitation of TiN lead to a sharp decrease in plasticity and toughness,the elongation decreases to 18.2%,and the impact energy at-40℃is only 25 J.Ti promotes the nucleation of acicular ferrite and improves the comprehensive mechanical properties by forming TiO2 inclusions.However,excessive Ti will induce the precipitation of brittle phase and the formation of coarse lath bainite,which significantly deteriorates the plasticity and toughness.

Abstract:At present,the deterministic design and evaluation of high-temperature structural strength have been fully developed and formed a relatively complete system framework,laying the theoretical foundation for the design and manufacturing of numerous mechanical equipment under harsh service conditions.Considering the randomness of high-temperature structural failure and the small-sample characteristics of failure data,safety factors are usually adopted for conservative design in engineering.However,this often leads to structural redundancy and cost waste,so there is an urgent need to conduct research on design methods from determinism to uncertainty.Nevertheless,no universal and mature theoretical methods for high-temperature structural reliability or national/industrial standards have been established so far,making it difficult to effectively predict and guarantee the reliability of high-end equipment such as China's aero-engines during operation.Based on this,firstly,uncertainty analysis was elaborated.The damage-threshold interference criterion was introduced in detail,and its differences from and connections with the stress-strength interference criterion was explained.Finally,taking a certain steam turbine rotor as an example,it illustrates the engineering application of the damage-threshold interference criterion in the reliability analysis of high-temperature structures.

Abstract:As a typical self-excited vibration phenomenon in metal cutting processes,chatter leads to deteriorated machining surface quality,manifested by texture fluctuations,increased dimensional errors,and compromised surface integrity.Effective detection and suppression of chatter is crucial for ensuring machining efficiency and enhancing component performance.Current research has established a multi-dimensional technical framework encompassing physics-model-based offline prediction methods,multi-sensor signal-dependent experimental detection schemes,and intelligent algorithm-integrated online monitoring frameworks.However,existing review literature lacks in-depth dissection of this domain.Addressing this gap,this study conducts a systematic technical review and analysis focusing on chatter detection and suppression technologies.For chatter detection,an analytical-experimental dual methodological framework is established,emphasizing the dissection of applicability scenarios and performance boundaries of various techniques.In terms of chatter suppression,a triple control strategy classification system integrating active-passive-parameter adjustment is constructed,comparing implementation costs and vibration attenuation effects of different solutions.Based on multi-dimensional technical comparisons and cross-disciplinary method integration,existing challenges and potential solutions in this field are explored,providing comprehensive theoretical support and technical references for subsequent research.

Abstract:Sandwich structures are widely used in aerospace,national defense and other fields due to their lightweight and energy-absorbing properties,and it is of great significance to improve their anti-explosion performance under internal explosion loads.Three structures were designed,including ring sandwich tube(R),polyurethane foam sandwich tube(F),and ring-polyurethane foam hybrid sandwich tube(RF),with the non-filled sandwich tube(A)as the control group.Through internal explosion load tests and finite element simulations,the deformation modes and energy absorption capacities of the four structures under different explosive amounts were compared and analyzed,and the influence of foam filling methods on the mechanical properties of sandwich tubes was explored.The results showed that,compared with the control group,the non-dimensional deflection of structures F,R and RF was reduced to varying degrees under TNT equivalents of 24 g,36 g and 48 g.At a TNT equivalent of 48 g,the specific energy absorption of RF structure was 5%higher than that of R structure,exhibiting the best anti-explosion performance.In addition,when the TNT equivalent was greater than 37.39 g,the foam-filled ring structure(FR)showed the strongest deformation resistance;when it was less than this value,the foam-filled structure in the gap between the ring and the tube wall(RF)had the optimal anti-explosion performance.

Abstract:To address the insufficient stability of high-altitude line inspection robots under wind loads,this study proposes optimization strategies involving a novel elastic pressing mechanism and an improved wheel groove,which can effectively enhance their walking stability.A power transmission and distribution line inspection robot with dual-mode switching(flight and walking)capabilities was developed.Firstly,a dynamic model of the robot under wind loads was established,and the relationship between the swing decay time and clamping force,contact area,and friction coefficient was derived.Secondly,dynamic simulations were conducted to verify the performance advantages of the two optimization strategies in suppressing swings.Finally,outdoor wind swing tests were performed to validate the effect of structural improvements.The results show that the elastic pressing mechanism can effectively increase the contact area between the pressing wheel and the line,and the improved wheel groove can enhance the friction coefficient of the walking wheel;both significantly shorten the robot's swing decay time and improve its inspection stability in wind load disturbance environments.The effective technical support and engineering practice basis for the stable operation of high-altitude line inspection robots in complex environments were provided.

Abstract:Under the background of automotive lightweighting,the use of resistance spot welding to achieve effective connection of aluminum to steel structures is an unremitting pursuit.However,in actual welding production,fluctuation of working conditions occur frequently,seriously affecting the quality of weld points.Firstly,the resistance spot welding process was adopted to connect aluminum alloy and low-carbon steel plates.The influences of different inclination angles,plate gaps,and fluctuations in cooling water flow conditions on the resistance spot welding of aluminum-steel were investigated.Then,the quality of the weld points was evaluated by comparing the diameter and thickness of the nugget,the thickness of the intermetallic compound,the coach peel performance,as well as the fracture mode.The research results show that an increase in the inclination angle and the gap between the plates within a certain range,as well as a decrease in the cooling water flow within a certain range,will both reduce the quality of the weld points.Therefore,they should be avoided as much as possible in actual production.The results of this study provide a theoretical basis and practical guidance for optimizing the resistance spot welding process of aluminum to steel.

Abstract:To compensate for the intermittency of renewable energy generation,coal-fired power units are required to operate under low-load conditions over a long time,which causes the last stage blades of steam turbine low-pressure cylinders under small flow conditions persistently,leading to increased dynamic stresses and fatigue damage in the blades.To evaluate the safety of these last-stage blades,the fluid-structure interaction analysis of the last two-stage flow path and last stage rotating blades were conducted for a 660 MW air-cooled steam turbine under typical operating conditions.The results demonstrate that as the load decreases,both the maximum equivalent stress and deformation of the last stage rotating blades gradually diminish first,then slightly increasing.The maximum equivalent stress of the last stage rotating blades remains consistently below the material's yield strength,indicating that the blades are in the stage of elastic deformation and no plastic deformation has occurred.Using the Goodman curve analysis method for the high-cycle fatigue life assessment of the last stage rotating blades,the dynamic stress levels of the last stage rotating blades fall within the safe zone of the Goodman curve,indicating that there is no risk of fatigue damage to the blades.

Abstract:To investigate the influence of structural parameters on the yield strength and deformation behavior of truss lattice structures,face-centered cubic(FCC)porous lattices were fabricated and the mechanical responses were systematically studied.A finite element model was developed to evaluate the yield strength and failure modes of structures with varying geometric parameters.The analysis revealed a correlation between the member slenderness ratio and the transition from progressive collapse to global yielding under different loading orientations.Structures with lower slenderness ratios tend to exhibit global yielding,while those with higher slenderness ratios are prone to layer-by-layer compression failure.Furthermore,lattices supported along the face diagonals demonstrate more uniform global deformation,whereas those supported along the body diagonals are characterized by localized deformation.

Abstract:Reaction bonded silicon carbide(RB-SiC)is widely used for manufacturing core components in nuclear energy and optics due to its excellent thermal stability,radiation resistance and chemical inertness.However,RB-SiC is highly hard and brittle,making it difficult to ensure processing quality and efficiency with traditional methods.Ultrasonic diamond wire saw cutting technology,as an efficient machining method for hard brittle materials,has been successfully applied in the processing of single crystal Si,single crystal SiC,and other hard brittle materials.However,the cutting test and process research of this technology in RB-SiC materials need to be carried out.To this end,the ultrasonic sawing test of RB-SiC was carried out for the first time.The ultrasonic wire saw cutting RB-SiC platform was built.The surface quality of parallel and vertical ultrasonic vibration directions was compared and analyzed.The effects of ultrasonic amplitude,line speed and feed speed parameters on surface roughness and surface micro-morphology were studied.Results demonstrate ultrasonic sawing has significant advantages in improving surface quality.Increasing the amplitude from 3 μm to 7 μm reduces surface roughness value by 17.4%and decreases the number of surface scratches and pits.Compared to the vertical feed direction,ultrasonic vibration sawing in the parallel feed direction is more effective in improving the surface quality of RB-SiC materials.This study can provide guidance for the research of ultrasonic sawing process of RB-SiC materials.

Abstract:Aiming at the problem of the low fault diagnosis accuracy caused by the lack of fault samples for the rolling bearings of doubly fed wind turbines under normal conditions for a long time,an improved generative adversarial network fault diagnosis method based on expanding high-quality fault samples and using dual feature extraction was proposed.Firstly,a finite number of rolling bearing fault samples were expanded through a Wasserstein type generative adversarial network with maximum mean discrepancy and penalty constraints.Secondly,based on the dual feature extraction model,the time-frequency converted temporal features and local features were extracted separately.Finally,the fault diagnosis of the rolling bearing balance data was completed through a classifier.The standard dataset and test results show that the proposed method improves the fault diagnosis performance while lacking fault samples.

Abstract:To enhance the computational efficiency of structural lightweight design for complex structures,a structural lightweight design method based on the Kriging surrogate model is proposed.The proposed method incorporates a hybrid addition strategy and a sample deletion strategy considering a distance threshold,aiming to rapidly improve the fitting accuracy of the Kriging surrogate model.This model was then applied to a multi-objective lightweight design model of the truck frame,with the optimization objectives of minimizing frame mass and maximum stress.Subsequently,the multi-objective lightweight model was solved using the non-dominated sorting genetic algorithm-II(NSGA-II).The results demonstrate that the proposed hybrid addition strategy and sample deletion strategy considering the distance threshold effectively enhance the update process of the Kriging surrogate model.The structural lightweight design method based on the Kriging surrogate model exhibits significant advantages in both computational efficiency and lightweight performance.

Abstract:A set of anti-impact protection device was designed for the test fracture accident of 30 MN tension sensor calibration device.Firstly,based on the kinematic theory,the kinematic model of each component in the fracture process of test fixture was established.Then,different protective device structures at three impact locations were designed.Finally,the finite element models of three buffer structures were established and verified,calculated and optimized.The results show that the egg-box structure protection device at the top plate of the upper reaction rack and the upper ball joints can effectively solve the problems of small protection space and large impact value.The whole device dissipates 59.5%impact kinetic energy of the upper reaction rack,60.7%impact kinetic energy of the lower reaction rack and 100%impact kinetic energy of the lower ball joints.After the improvement,the initial peak load of the protective device at the lower ball joints is reduced by 62.7%.

Abstract:To evaluate the performance of various equivalent stress intensity factor models in predicting mixed-mode fatigue crack growth and to address the challenge of parameter estimation under limited sample conditions.A crack growth parameter estimation method based on the Bootstrap method resampling technique was proposed firstly.Mode Ⅰ fatigue crack growth tests were conducted on CT specimens to obtain the material parameters,and the proposed method was employed to expand the sample set and mitigate the issue of data scarcity.Then,using the statistically augmented material parameters,mixed-mode Ⅰ+Ⅱ fatigue crack growth experiments were performed on 6005A-T6 aluminum alloy CTS specimens under loading angles of 0°,30°,45° and 60°,employing a Richard-type loading fixture,to validate the accuracy of various equivalent stress intensity factor models.The results indicate that the Irwin model achieved the highest goodness-of-fit,with a value of 0.942 1,demonstrating the best crack growth prediction performance.Increasing the loading angle was found to reduce the initial crack growth rate,highlighting the need for angle-specific experiments to obtain appropriate Paris law parameters.This study confirms the applicability of multiple ΔKeq models and provides theoretical support for fatigue life prediction in mixed-mode crack growth scenarios.

Abstract:The acceleration of the reciprocating parts of the compressor with the crosshead settlement fluctuates violently,and the comprehensive piston force becomes larger,which leads to the increase of the vibration amplitude of the crankshaft and the instability of the vibration.Therefore,this paper firstly studied the kinematic law of the crosshead settlement on the crank-connecting rod structure,and established the differential equation of the torsional vibration of the crankshaft.Subsequently,the vibration response characteristics of the crankshaft were solved by the mean filtering-Runge-Kutta method.Finally,the influence of the crosshead settlement,motor speed and reciprocating mass of the piston assembly on the crankshaft vibration amplitude,phase trajectory and amplitude-frequency diagram was discussed.The results show that with the increase of the crosshead settlement,the"serrated"fluctuation of the crankshaft phase space trajectory line is intensified,and the torsional angular velocity shows an upward trend.When d=0.25 mm,the torsional angular velocity amplitude increases by 23.6%compared with that without the settlement,and the crankshaft vibration state changes from frequency doubling period to chaos.As the motor speed decreases,the torsional angle and vibration state fluctuation of the crankshaft are controlled.As the reciprocating mass of the piston assembly decreases,the peak frequency response decreases,which helps to control the crankshaft torsion angle.The research can provide a theoretical guidance for predicting the vibration state of the crankshaft and the torsional vibration control of the crankshaft under the condition of the crosshead settlement,and ensure the stable operation of the crankshaft.