Aseries of [(Fe_(0.6)Co_(0.2)Ni_(0.2))_(0.75-0.03x)B_(0.2)Si_(0.05+0.03x)]_(96)Nb_(4) amorphous alloy composite coatings were prepared by adjusting the silicon content(x=0,1,2,3,4,5,and 6)and their microstructures and...Aseries of [(Fe_(0.6)Co_(0.2)Ni_(0.2))_(0.75-0.03x)B_(0.2)Si_(0.05+0.03x)]_(96)Nb_(4) amorphous alloy composite coatings were prepared by adjusting the silicon content(x=0,1,2,3,4,5,and 6)and their microstructures and tribological properties were investigated by laser cladding technique.Additionally,the effect of Si on the glass forming ability(GFA)of the layers was understood.Results show that an appropriate Si content can refine the microstructure of the FeCoNiBSiNb laser cladding layers and improve the mechanical and tribological properties.The hardness of the coating layer increases monotonically with the Si content.At the Si content of 4.8at%(x=0),the coating layer exhibits a relatively low hardness(734.2HV 0.1).Conversely,at the silicon content of 13.44at%(x=3),the coating layer exhibits the highest hardness(1106HV 0.1).The non-crystalline content and tensile strength exhibit an initial increase,followed by a subsequent decrease.At x=2,the coating exhibits its maximum fracture strength(2880 MPa).However,when x>2,the fracture strength of the coating decreases with an increase in x.Conversely,with an increase in Si content,the wear volume loss initially decreases and then increases.At a Si content of 10.56at%(x=2),the coating exhibits the highest non-crystalline content(42%),the highest tensile strength(2880 MPa),and the most favorable dry friction performance.展开更多
In this work,the effect of ultrasonic vibration modes on the mechanical properties and relaxation of residual stress in 6061-T6 aluminum alloy was studied.A new ultrasonic vibration Johnson-Cook model was proposed,and...In this work,the effect of ultrasonic vibration modes on the mechanical properties and relaxation of residual stress in 6061-T6 aluminum alloy was studied.A new ultrasonic vibration Johnson-Cook model was proposed,and the relaxation and distribution of residual stress under ultrasonic vibration were predicted and analyzed using the finite element method(FEM).The mechanical properties of 6061-T6 aluminum alloy under different ultrasonic vibration modes were analyzed through experiments involving notched specimen tensile testing and scanning electron microscopy(SEM)analysis.The findings indicate that ultrasonic vibration treatment during deformation,unloading,and load-holding,as well as treatment with its natural ultrasonic frequency,can effectively release residual stress;however,treatment with its natural frequency has the highest rate of release up to 65.4%.Ultrasonic vibration treatment during deformation better inhibits fracture under the same conditions.The FEM results are in good agreement with the experimental results,and it can be used as a valid tool for predicting residual stress release under ultrasonic vibration.展开更多
Fault diagnosis occupies a pivotal position within the domain of machine and equipment management.Existing methods,however,often exhibit limitations in their scope of application,typically focusing on specific types o...Fault diagnosis occupies a pivotal position within the domain of machine and equipment management.Existing methods,however,often exhibit limitations in their scope of application,typically focusing on specific types of signals or faults in individual mechanical components while being constrained by data types and inherent characteristics.To address the limitations of existing methods,we propose a fault diagnosis method based on graph neural networks(GNNs)embedded with multirelationships of intrinsic mode functions(MIMF).The approach introduces a novel graph topological structure constructed from the features of intrinsic mode functions(IMFs)of monitored signals and their multirelationships.Additionally,a graph-level based fault diagnosis network model is designed to enhance feature learning capabilities for graph samples and enable flexible application across diverse signal sources and devices.Experimental validation with datasets including independent vibration signals for gear fault detection,mixed vibration signals for concurrent gear and bearing faults,and pressure signals for hydraulic cylinder leakage characterization demonstrates the model's adaptability and superior diagnostic accuracy across various types of signals and mechanical systems.展开更多
This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode ...This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.展开更多
Trace amounts of Zr and V can increase the recrystallization temperature of Al-Mg-Si wrought aluminum alloys,which is expected to regulate the recrystallization grain.In this paper,trace amounts of V and Zr were added...Trace amounts of Zr and V can increase the recrystallization temperature of Al-Mg-Si wrought aluminum alloys,which is expected to regulate the recrystallization grain.In this paper,trace amounts of V and Zr were added to recycled Al-Mg-Si alloys,and their e ffects on the microstructure and mechanical properties of the cast alloys were studied by scanning electron microscopy(SEM)and synchrotron radiation X-ray tomography(SRXT).The results show that the addition of Zr significantly increases the grain sizes due to the“Zr poisoning”;V addition has no significant effect on the grain size.The morphology of Fe-rich phase gradually changes from the large Chinese-script shape to the fine short rod and curved long strip shape,and the distribution uniformity is improved with the combined addition of V and Zr.The three-dimensional(3 D)morphology of Fe-rich phase includes granular,short rod-like,simple branch and multi-branch structures.The individual addition of V and Zr has no significant effect on the morphology of Fe-rich phase;but the combined addition of V and Zr significantly increases the number and volume fraction of Fe-rich phase with small size(diameter£15μm),the number of branches in the largest Fe-rich phase is significantly reduced,resulting in the improvement of elongation.This work provides a theoretical basis for the development of new recycled Al-Mg-Si alloys in industrial application.展开更多
The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sand...The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.展开更多
The influences of hot stamping parameters such as heating temperature,soaking time,deformation temperature and cooling medium on the phase transformation,microstructure and mechanical properties of 30MnB5 and 22MnB5 a...The influences of hot stamping parameters such as heating temperature,soaking time,deformation temperature and cooling medium on the phase transformation,microstructure and mechanical properties of 30MnB5 and 22MnB5 are investigated and analyzed in this work.The quenching experiment,tensile testing,hardness measurement and microstructure observation were conducted to obtain the mechanical and microstructural data.The results indicate that 30MnB5 possesses a higher tensile strength but a lower elongation than 22MnB5,if hot stamped at the same process parameter.The tensile strength and hardness of the hot stamped specimens decrease under inappropriate heating conditions for two reasons,insufficient austenitization or coarse austenite grains.The austenitic forming rate of 30MnB5 is higher than that of 22MnB5,because more cementite leads to higher nucleation rate and diffusion coefficient of carbon atom.More amount of fine martensite forms under the higher deformation temperature or the quicker cooling rate.展开更多
Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufactu...Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufacturing highlights the capability in manufacturing FGMs with a high geometrical complexity and manufacture flexibility.In this work,the 316L/CuSn10/18Ni300/CoCr four-type materials FGMs were fabricated using SLM.The microstructure and properties of the FGMs were investigated to reveal the effects of SLM processing parameters on the defects.A large number of microcracks were found at the 316L/CuSn10 interface,which initiated from the fusion boundary of 316L region and extended along the building direction.The elastic modulus and nano-hardness in the 18Ni300/CoCr fusion zone decreased significantly,less than those in the 18Ni300 region or the CoCr region.The iron and copper elements were well diffused in the 316L/CuSn10 fusion zone,while elements in the CuSn10/18Ni300 and the 18Ni300/CoCr fusion zones showed significantly gradient transitions.Compared with other regions,the width of the CuSn10/18Ni300 interface and the CuSn10 region expand significantly.The mechanisms of materials fusion and crack generation at the 316L/CuSn10 interface were discussed.In addition,FGM structures without macro-crack were built by only altering the deposition subsequence of 316L and CuSn10,which provides a guide for the additive manufacturing of FGM structures.展开更多
In this paper,the indirect thermal tensile experiments of 7075 aluminum alloy including the pre-deformation process at room temperature and the final heat tensile process were carried out,the plastic deformation behav...In this paper,the indirect thermal tensile experiments of 7075 aluminum alloy including the pre-deformation process at room temperature and the final heat tensile process were carried out,the plastic deformation behavior and forming limit of the material in the compound forming process were investigated considering three pre-deformation amounts 4%,9%,14%,two strain rates 0.001 s^(-1),0.01 s^(-1) and four forming temperatures 300℃,350℃,400℃,450℃.In the indirect hot forming process,the material is sensitive to the pre-deformation,strain rate,and forming temperature,when the strain rate is 0.01 s^(-1),the pre-deformation amount is 4%,and the forming temperature is 400℃,respectively,the maximum tensile deformation is 50 mm.Finally,taking the process in which the forming temperature is 450℃ as an example,according to the observation of the microstructure appearance of fracture,the fracture type in the hot forming process was judged as the ductile fracture.By analyzing the microstructure of the specimen treated with the quenching and artificial aging process,the eutectic T(AlZnMgCu)phase and α(Al)matrix formed a network of non-equilibrium alpha binary eutectic.展开更多
This paper puts forward an unprecedented avoidance-striking-arrival problem aiming to address the need for tank's uncertain mechanical systems on the intelligent battlefield.The associated system uncertainties(pos...This paper puts forward an unprecedented avoidance-striking-arrival problem aiming to address the need for tank's uncertain mechanical systems on the intelligent battlefield.The associated system uncertainties(possibly rapid)are time-varying but bounded(possibly unknown).The goal is to design a controller that enables the tank to aim at and attack the enemy tank while keeping itself(out of the enemy fire zone).The tank maintains this condition until reaching the predefined region.In this paper,an approximate constraint following control method is adopted to solve this problem,and the original constraints are creatively divided into two categories:the avoidance-tracking constraint and the striking-arrival constraint.An adaptive robust control method is proposed and consequently verified through simulation experiments.It is proved that the system fully obeys the avoidance-tracking-constraint and strictly obeys the striking-arrival constraint under the control input.Besides,the control of the tank vehicle running system and tank gun bidirectional stabilization system are unified to deal with the control signal delay caused by complex uncertainties on the battlefield.Overall,this paper reduced the delay of signal transmission in the system while solved the avoidance-striking-arrival problem.展开更多
Focused on the dynamics problems of a lunar lander during landing process, the whole process was analysed in detail, and the linear elastic model of the moon soil was established by means of experiments-analogic metho...Focused on the dynamics problems of a lunar lander during landing process, the whole process was analysed in detail, and the linear elastic model of the moon soil was established by means of experiments-analogic method. Combining the way of elastic impact with the way of velocity replacement, the dynamics model of damping free vibration dynamics model with 3-degree of freedom(DOF) for lunar lander is obtained according to the vibration mechanics elementary theory. Based on Lagrange equations and the energy principle, the damping free vibration differential equations for the lunar lander with 3-DOF are derived and the equations are solved in simulation ways by means of ADAMS software. The conclusions obtained can be used for the design and manufacture of lunar lander.展开更多
Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show tha...Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show that vanadium enriches around the boundary ofαphases with increasing annealing temperature to 973 K,andα′phases transform intoα+βat 973 K.The typicalα′martensite microstructure transforms to fine-scale equiaxed microstructure at 973 K and the equiaxed microstructure significantly coarsens with increasing annealing temperature to 1273 K.The SLM Ti-6Al-4V alloy annealed at 973 K exhibits a well-balanced combination of strength and ductility((1305±25)MPa and(37±3)%,respectively).展开更多
For non-quenchable dual-phase(DP)steel sheet,the warm forming process can effectively reduce the amount of springback,and the mechanical parameters that influence its elastic and inelastic recovery to decrease exhibit...For non-quenchable dual-phase(DP)steel sheet,the warm forming process can effectively reduce the amount of springback,and the mechanical parameters that influence its elastic and inelastic recovery to decrease exhibit a strong temperature dependence,especially under cyclic loading conditions.In this paper,the monotonic and cyclic loading tests of DP980 steel sheets are conducted at the temperatures ranging from 25℃ to 500℃.The temperature-dependent flow stress,nonlinear elastic recovery,and Bauschinger effect are investigated.The results demonstrate that both the elastic modulus and Bauschinger effect show an exponential law with pre-strain,and decrease with the increase of forming temperature,while there will be an abnormal phenomenon of rebound due to the influence of dynamic strain aging effect.Meanwhile,a linear relationship between the Bauschinger effect and inelastic strain is observed at various temperatures,and the weight of the Bauschinger effect in the total strain reduces with temperature increasing,which indicates that the springback is dominated by linear elastic recovery.Furthermore,the U-draw bending tests are carried out to clarify the influence of Vickers hardness distribution and martensite size effect on the springback behavior.展开更多
With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electr...With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electromagnetic braking technology to recoil mechanism.In this paper,prototype tests of a certain artillery were carried out to verify the feasibility of the electromagnetic brake(EMB)and obtain the electromagnetic braking force.Due to the brittleness of Nd Fe B,in order to eliminate the worry about the safety of EMB,SHPB experiments of Nd Fe B were carried out.Then,based on the assumption of uniform crack distribution,the law of crack propagation and damage accumulation was described theoretically,and the damage constitutive model suitable for brittle materials was proposed by combining the Zhu-Wang-Tang(ZWT)equation.Finally,the numerical simulation model of the artillery prototype was established and through calculation,the dynamic mechanical characteristics of Nd Fe B in the prototype were analyzed.The calculation results show that the strength of Nd Fe B can meet the requirements of the use in the working process.From the perspective of damage factor,the damage value of the permanent magnet on the far right is larger,and the damage value of the inner ring gradually decreases to the outer ring.展开更多
As the basic protective element, steel plate had attracted world-wide attention because of frequent threats of explosive loads. This paper reports the relationships between microscopic defects of Q345 steel plate unde...As the basic protective element, steel plate had attracted world-wide attention because of frequent threats of explosive loads. This paper reports the relationships between microscopic defects of Q345 steel plate under the explosive load and its macroscopic dynamics simulation. Firstly, the defect characteristics of the steel plate were investigated by stereoscopic microscope(SM) and scanning electron microscope(SEM). At the macroscopic level, the defect was the formation of cave which was concentrated in the range of 0-3.0 cm from the explosion center, while at the microscopic level, the cavity and void formation were the typical damage characteristics. It also explains that the difference in defect morphology at different positions was the combining results of high temperature and high pressure. Secondly, the variation rules of mechanical properties of steel plate under explosive load were studied. The Arbitrary Lagrange-Euler(ALE) algorithm and multi-material fluid-structure coupling method were used to simulate the explosion process of steel plate. The accuracy of the method was verified by comparing the deformation of the simulation results with the experimental results, the pressure and stress at different positions on the surface of the steel plate were obtained. The simulation results indicated that the critical pressure causing the plate defects may be approximately 2.01 GPa. On this basis, it was found that the variation rules of surface pressure and microscopic defect area of the Q345 steel plate were strikingly similar, and the corresponding mathematical relationship between them was established. Compared with Monomolecular growth fitting models(MGFM) and Logistic fitting models(LFM), the relationship can be better expressed by cubic polynomial fitting model(CPFM). This paper illustrated that the explosive defect characteristics of metal plate at the microscopic level can be explored by analyzing its macroscopic dynamic mechanical response.展开更多
The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is f...The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is first carried out in order to determine temperature evolution and to predict the residual temperatures during the burst firing event; 2) The thermo-mecha- nical stresses and deformation caused by both the residual temperature field and the gas pressure are then calculated. The results show that the residual temperature field tends to a steady state with the increasing of rounds. The residual temperature field has much effect on the gun barrel stress and deformation, especially on the assembly area between barrel and water jacket. The gage between the barrel and water jacket is the critical factor to the thermo- mechanical stress and deformation. The results of this analysis will be very useful to develop the new strength design theory of the liquid-cooled gun barrel.展开更多
To explore the wide-frequency damping and vibration-attenuation performances in the application of aerospace components,the cylindrical sandwich shell structure with a gradient core of entangled wire mesh was proposed...To explore the wide-frequency damping and vibration-attenuation performances in the application of aerospace components,the cylindrical sandwich shell structure with a gradient core of entangled wire mesh was proposed in this paper.Firstly,the gradient cores of entangled wire mesh in the axial and radial directions were prepared by using an in-house Numerical Control weaving machine,and the metallurgical connection between skin sheets and the gradient core was performed using vacuum brazing.Secondly,to investigate the mechanical properties of cylindrical sandwich shells with axial or radial gradient cores,quasi-static and dynamic mechanical experiments were carried out.The primary evaluations of mechanical properties include secant stiffness,natural frequency,Specific Energy Absorption(SEA),vibration acceleration level,and so on.The results suggest that the vibration-attenuation performance of the sandwich shell is remarkable when the high-density core layer is at the end of the shell or abuts the inner skin.The axial gradient material has almost no influence on the vibration frequencies of the shell,whereas the vibration frequencies increase dramatically when the high-density core layer approaches the skin.Moreover,compared to the conventional sandwich shells,the proposed functional grading cylindrical sandwich shell exhibits more potential in mass reduction,stiffness designing,and energy dissipation.展开更多
A kind of automatic shift schedule optimization method is provided for a tracked vehicle with hydrodynamic-mechanical transmission in order to improve its dynamic performance. A dynamic model of integrated hydrodynami...A kind of automatic shift schedule optimization method is provided for a tracked vehicle with hydrodynamic-mechanical transmission in order to improve its dynamic performance. A dynamic model of integrated hydrodynamic-mechanical transmission is built in MATLAB/Simdriveline environment, and an optimum shift schedule is derived by using iSight software to call the dynamic model above, then the shift schedule is achieved after optimization. The simulation results show that the method is significant to improve the dynamic performance and gear-shifting smoothness theoretically and practically.展开更多
Block piezoelectric ceramics(PZTs)are often used in impact igniters to provide activation energy for electric initiators.Under the action of strong impact stress,PZTs release electric energy accompanied by crack initi...Block piezoelectric ceramics(PZTs)are often used in impact igniters to provide activation energy for electric initiators.Under the action of strong impact stress,PZTs release electric energy accompanied by crack initiation,propagation and crushing.At present,the electrical output performance of PZTs in projectile is usually calculated by quasi-static piezoelectric equation without considering the dynamic effect caused by strong impact and the influence of crack propagation on material properties.So the ignition parameters are always not accurately predicted.To tackle this,a PZT dynamic damage constitutive model considering crack propagation is established based on the dynamic impact test and the crack propagation theory of brittle materials.The model is then embedded into the ABAQUS subroutine and used to simulate the electromechanical response of the impact igniter during the impact of a small caliber projectile on the target.Meanwhile,the experiments of projectile with impact igniter impact on the target are carried out.The comparison between experimental and numerical simulation results show that the established dynamic damage model can effectively predict the dynamic electromechanical response of PZTs in the missile service environment.展开更多
Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were...Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were investigated. The forced responses of the mechanical system to mechanical excitation under electric disturbance were also presented. It is known that for the system with electric disturbance, as time grows, beat occurs. When electric disturbing frequency is near to the natural frequencies of the mechanical system or their integer multiple, resonance vibrations occur. The forced responses of the mechanical system to mechanical excitation under electric disturbance are compound vibrations decided by mechanical excitation, electric disturbance and parameters of the system. The coupled resonance vibration caused by electric disturbance and mechanical excitation was discussed as well. The conditions under which above coupled resonance occurs were presented. The results show that when the difference of the excitation frequency and the perturbation frequency is equal to some order of natural frequency, coupled resonance vibrations occur.展开更多
文摘Aseries of [(Fe_(0.6)Co_(0.2)Ni_(0.2))_(0.75-0.03x)B_(0.2)Si_(0.05+0.03x)]_(96)Nb_(4) amorphous alloy composite coatings were prepared by adjusting the silicon content(x=0,1,2,3,4,5,and 6)and their microstructures and tribological properties were investigated by laser cladding technique.Additionally,the effect of Si on the glass forming ability(GFA)of the layers was understood.Results show that an appropriate Si content can refine the microstructure of the FeCoNiBSiNb laser cladding layers and improve the mechanical and tribological properties.The hardness of the coating layer increases monotonically with the Si content.At the Si content of 4.8at%(x=0),the coating layer exhibits a relatively low hardness(734.2HV 0.1).Conversely,at the silicon content of 13.44at%(x=3),the coating layer exhibits the highest hardness(1106HV 0.1).The non-crystalline content and tensile strength exhibit an initial increase,followed by a subsequent decrease.At x=2,the coating exhibits its maximum fracture strength(2880 MPa).However,when x>2,the fracture strength of the coating decreases with an increase in x.Conversely,with an increase in Si content,the wear volume loss initially decreases and then increases.At a Si content of 10.56at%(x=2),the coating exhibits the highest non-crystalline content(42%),the highest tensile strength(2880 MPa),and the most favorable dry friction performance.
基金Project(51775480)supported by the National Natural Science Foundation of ChinaProjects(E2018203143,E2022203050)supported by the Natural Science Foundation of Hebei Province,China。
文摘In this work,the effect of ultrasonic vibration modes on the mechanical properties and relaxation of residual stress in 6061-T6 aluminum alloy was studied.A new ultrasonic vibration Johnson-Cook model was proposed,and the relaxation and distribution of residual stress under ultrasonic vibration were predicted and analyzed using the finite element method(FEM).The mechanical properties of 6061-T6 aluminum alloy under different ultrasonic vibration modes were analyzed through experiments involving notched specimen tensile testing and scanning electron microscopy(SEM)analysis.The findings indicate that ultrasonic vibration treatment during deformation,unloading,and load-holding,as well as treatment with its natural ultrasonic frequency,can effectively release residual stress;however,treatment with its natural frequency has the highest rate of release up to 65.4%.Ultrasonic vibration treatment during deformation better inhibits fracture under the same conditions.The FEM results are in good agreement with the experimental results,and it can be used as a valid tool for predicting residual stress release under ultrasonic vibration.
文摘Fault diagnosis occupies a pivotal position within the domain of machine and equipment management.Existing methods,however,often exhibit limitations in their scope of application,typically focusing on specific types of signals or faults in individual mechanical components while being constrained by data types and inherent characteristics.To address the limitations of existing methods,we propose a fault diagnosis method based on graph neural networks(GNNs)embedded with multirelationships of intrinsic mode functions(MIMF).The approach introduces a novel graph topological structure constructed from the features of intrinsic mode functions(IMFs)of monitored signals and their multirelationships.Additionally,a graph-level based fault diagnosis network model is designed to enhance feature learning capabilities for graph samples and enable flexible application across diverse signal sources and devices.Experimental validation with datasets including independent vibration signals for gear fault detection,mixed vibration signals for concurrent gear and bearing faults,and pressure signals for hydraulic cylinder leakage characterization demonstrates the model's adaptability and superior diagnostic accuracy across various types of signals and mechanical systems.
文摘This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.
基金Project(2024YEE0109100) supported by the National Key R&D Program of ChinaProjects(52074131,52104373) supported by the National Natural Science Foundation of ChinaProjects(2022YFJH001,2024YFJH001) supported by the Science and Technology Plan Program of Qingyuan City,China。
文摘Trace amounts of Zr and V can increase the recrystallization temperature of Al-Mg-Si wrought aluminum alloys,which is expected to regulate the recrystallization grain.In this paper,trace amounts of V and Zr were added to recycled Al-Mg-Si alloys,and their e ffects on the microstructure and mechanical properties of the cast alloys were studied by scanning electron microscopy(SEM)and synchrotron radiation X-ray tomography(SRXT).The results show that the addition of Zr significantly increases the grain sizes due to the“Zr poisoning”;V addition has no significant effect on the grain size.The morphology of Fe-rich phase gradually changes from the large Chinese-script shape to the fine short rod and curved long strip shape,and the distribution uniformity is improved with the combined addition of V and Zr.The three-dimensional(3 D)morphology of Fe-rich phase includes granular,short rod-like,simple branch and multi-branch structures.The individual addition of V and Zr has no significant effect on the morphology of Fe-rich phase;but the combined addition of V and Zr significantly increases the number and volume fraction of Fe-rich phase with small size(diameter£15μm),the number of branches in the largest Fe-rich phase is significantly reduced,resulting in the improvement of elongation.This work provides a theoretical basis for the development of new recycled Al-Mg-Si alloys in industrial application.
基金Project (2007CB714006) supported by the National Basic Research Program of China
文摘The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.
基金Projects(51705018,U1564202)supported by the National Natural Science Foundation of China
文摘The influences of hot stamping parameters such as heating temperature,soaking time,deformation temperature and cooling medium on the phase transformation,microstructure and mechanical properties of 30MnB5 and 22MnB5 are investigated and analyzed in this work.The quenching experiment,tensile testing,hardness measurement and microstructure observation were conducted to obtain the mechanical and microstructural data.The results indicate that 30MnB5 possesses a higher tensile strength but a lower elongation than 22MnB5,if hot stamped at the same process parameter.The tensile strength and hardness of the hot stamped specimens decrease under inappropriate heating conditions for two reasons,insufficient austenitization or coarse austenite grains.The austenitic forming rate of 30MnB5 is higher than that of 22MnB5,because more cementite leads to higher nucleation rate and diffusion coefficient of carbon atom.More amount of fine martensite forms under the higher deformation temperature or the quicker cooling rate.
基金Project(2020B090922002)supported by Guangdong Provincial Key Field Research and Development Program,ChinaProjects(51875215,52005189)supported by the National Natural Science Foundation of ChinaProject(2019B1515120094)supported by Guangdong Provincial Basic and Applied Basic Research Fund,China。
文摘Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufacturing highlights the capability in manufacturing FGMs with a high geometrical complexity and manufacture flexibility.In this work,the 316L/CuSn10/18Ni300/CoCr four-type materials FGMs were fabricated using SLM.The microstructure and properties of the FGMs were investigated to reveal the effects of SLM processing parameters on the defects.A large number of microcracks were found at the 316L/CuSn10 interface,which initiated from the fusion boundary of 316L region and extended along the building direction.The elastic modulus and nano-hardness in the 18Ni300/CoCr fusion zone decreased significantly,less than those in the 18Ni300 region or the CoCr region.The iron and copper elements were well diffused in the 316L/CuSn10 fusion zone,while elements in the CuSn10/18Ni300 and the 18Ni300/CoCr fusion zones showed significantly gradient transitions.Compared with other regions,the width of the CuSn10/18Ni300 interface and the CuSn10 region expand significantly.The mechanisms of materials fusion and crack generation at the 316L/CuSn10 interface were discussed.In addition,FGM structures without macro-crack were built by only altering the deposition subsequence of 316L and CuSn10,which provides a guide for the additive manufacturing of FGM structures.
基金Project(SKL2020005)supported by the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment,ChinaProject(206Z1803G)supported by Local Science and Technology Development Fund Guided by the Central Government of China。
文摘In this paper,the indirect thermal tensile experiments of 7075 aluminum alloy including the pre-deformation process at room temperature and the final heat tensile process were carried out,the plastic deformation behavior and forming limit of the material in the compound forming process were investigated considering three pre-deformation amounts 4%,9%,14%,two strain rates 0.001 s^(-1),0.01 s^(-1) and four forming temperatures 300℃,350℃,400℃,450℃.In the indirect hot forming process,the material is sensitive to the pre-deformation,strain rate,and forming temperature,when the strain rate is 0.01 s^(-1),the pre-deformation amount is 4%,and the forming temperature is 400℃,respectively,the maximum tensile deformation is 50 mm.Finally,taking the process in which the forming temperature is 450℃ as an example,according to the observation of the microstructure appearance of fracture,the fracture type in the hot forming process was judged as the ductile fracture.By analyzing the microstructure of the specimen treated with the quenching and artificial aging process,the eutectic T(AlZnMgCu)phase and α(Al)matrix formed a network of non-equilibrium alpha binary eutectic.
基金This work was partially supported by the Provincial Natural Science Foundation of Jiangsu(Project no.BK20180474)the Natural Science Foundation of China(Project no.51805263,no.51705253,no.11572158).
文摘This paper puts forward an unprecedented avoidance-striking-arrival problem aiming to address the need for tank's uncertain mechanical systems on the intelligent battlefield.The associated system uncertainties(possibly rapid)are time-varying but bounded(possibly unknown).The goal is to design a controller that enables the tank to aim at and attack the enemy tank while keeping itself(out of the enemy fire zone).The tank maintains this condition until reaching the predefined region.In this paper,an approximate constraint following control method is adopted to solve this problem,and the original constraints are creatively divided into two categories:the avoidance-tracking constraint and the striking-arrival constraint.An adaptive robust control method is proposed and consequently verified through simulation experiments.It is proved that the system fully obeys the avoidance-tracking-constraint and strictly obeys the striking-arrival constraint under the control input.Besides,the control of the tank vehicle running system and tank gun bidirectional stabilization system are unified to deal with the control signal delay caused by complex uncertainties on the battlefield.Overall,this paper reduced the delay of signal transmission in the system while solved the avoidance-striking-arrival problem.
文摘Focused on the dynamics problems of a lunar lander during landing process, the whole process was analysed in detail, and the linear elastic model of the moon soil was established by means of experiments-analogic method. Combining the way of elastic impact with the way of velocity replacement, the dynamics model of damping free vibration dynamics model with 3-degree of freedom(DOF) for lunar lander is obtained according to the vibration mechanics elementary theory. Based on Lagrange equations and the energy principle, the damping free vibration differential equations for the lunar lander with 3-DOF are derived and the equations are solved in simulation ways by means of ADAMS software. The conclusions obtained can be used for the design and manufacture of lunar lander.
基金Project(2020A1515110869)supported by Guangdong Basic and Applied Basic Research Foundation,ChinaProject(GJHZ20190822095418365)supported by Shenzhen International Cooperation Research,China+3 种基金Project(51775351)supported by the National Natural Science Foundation of ChinaProject(2019011)supported by the NTUT-SZU Joint Research Program,ChinaProject(2019040)supported by the Natural Science Foundation of SZU,ChinaProject(ASTRA6-6)supported by the European Regional Development Fund,European Union。
文摘Ti-6Al-4V specimens were fabricated by selective laser melting(SLM)to study the effect of thermal treatment on the phase transformation,elemental diffusion,microstructure,and mechanical properties.The results show that vanadium enriches around the boundary ofαphases with increasing annealing temperature to 973 K,andα′phases transform intoα+βat 973 K.The typicalα′martensite microstructure transforms to fine-scale equiaxed microstructure at 973 K and the equiaxed microstructure significantly coarsens with increasing annealing temperature to 1273 K.The SLM Ti-6Al-4V alloy annealed at 973 K exhibits a well-balanced combination of strength and ductility((1305±25)MPa and(37±3)%,respectively).
基金Projects(2020JJ4578, 2019JJ50604) supported by the Natural Science Foundation of Hunan Province,ChinaProject(19A499) supported by the Key Program of the Scientific Research Foundation of the Education Department of Hunan Province,China。
文摘For non-quenchable dual-phase(DP)steel sheet,the warm forming process can effectively reduce the amount of springback,and the mechanical parameters that influence its elastic and inelastic recovery to decrease exhibit a strong temperature dependence,especially under cyclic loading conditions.In this paper,the monotonic and cyclic loading tests of DP980 steel sheets are conducted at the temperatures ranging from 25℃ to 500℃.The temperature-dependent flow stress,nonlinear elastic recovery,and Bauschinger effect are investigated.The results demonstrate that both the elastic modulus and Bauschinger effect show an exponential law with pre-strain,and decrease with the increase of forming temperature,while there will be an abnormal phenomenon of rebound due to the influence of dynamic strain aging effect.Meanwhile,a linear relationship between the Bauschinger effect and inelastic strain is observed at various temperatures,and the weight of the Bauschinger effect in the total strain reduces with temperature increasing,which indicates that the springback is dominated by linear elastic recovery.Furthermore,the U-draw bending tests are carried out to clarify the influence of Vickers hardness distribution and martensite size effect on the springback behavior.
基金financially supported by the“National Natural Science Foundation of China”[Grant No.52105106]the“China National Postdoctoral Program for Innovative Talents”[Grant No.BX2021126]+2 种基金the“Jiangsu Province Natural Science Foundation”[Grant No.BK20210342]the“Jiangsu Planned Projects for Postdoctoral Research Funds”[Grant No.2021K008A]the“Nanjing Municipal Human Resources and Social Security Bureau”[Grant No.MCA21121]。
文摘With the continuous development of artillery,the disadvantages of hydraulic recoil brakes gradually appear.At the same time,the appearance of high-performance Nd Fe B permanent magnet makes it possible to apply electromagnetic braking technology to recoil mechanism.In this paper,prototype tests of a certain artillery were carried out to verify the feasibility of the electromagnetic brake(EMB)and obtain the electromagnetic braking force.Due to the brittleness of Nd Fe B,in order to eliminate the worry about the safety of EMB,SHPB experiments of Nd Fe B were carried out.Then,based on the assumption of uniform crack distribution,the law of crack propagation and damage accumulation was described theoretically,and the damage constitutive model suitable for brittle materials was proposed by combining the Zhu-Wang-Tang(ZWT)equation.Finally,the numerical simulation model of the artillery prototype was established and through calculation,the dynamic mechanical characteristics of Nd Fe B in the prototype were analyzed.The calculation results show that the strength of Nd Fe B can meet the requirements of the use in the working process.From the perspective of damage factor,the damage value of the permanent magnet on the far right is larger,and the damage value of the inner ring gradually decreases to the outer ring.
基金Science and Technology Project of Fire Rescue Bureau of Ministry of Emergency Management(Grant No.2022XFZD05)S&T Program of Hebei(Grant No.22375419D)National Natural Science Foundation of China(Grant No.11802160).
文摘As the basic protective element, steel plate had attracted world-wide attention because of frequent threats of explosive loads. This paper reports the relationships between microscopic defects of Q345 steel plate under the explosive load and its macroscopic dynamics simulation. Firstly, the defect characteristics of the steel plate were investigated by stereoscopic microscope(SM) and scanning electron microscope(SEM). At the macroscopic level, the defect was the formation of cave which was concentrated in the range of 0-3.0 cm from the explosion center, while at the microscopic level, the cavity and void formation were the typical damage characteristics. It also explains that the difference in defect morphology at different positions was the combining results of high temperature and high pressure. Secondly, the variation rules of mechanical properties of steel plate under explosive load were studied. The Arbitrary Lagrange-Euler(ALE) algorithm and multi-material fluid-structure coupling method were used to simulate the explosion process of steel plate. The accuracy of the method was verified by comparing the deformation of the simulation results with the experimental results, the pressure and stress at different positions on the surface of the steel plate were obtained. The simulation results indicated that the critical pressure causing the plate defects may be approximately 2.01 GPa. On this basis, it was found that the variation rules of surface pressure and microscopic defect area of the Q345 steel plate were strikingly similar, and the corresponding mathematical relationship between them was established. Compared with Monomolecular growth fitting models(MGFM) and Logistic fitting models(LFM), the relationship can be better expressed by cubic polynomial fitting model(CPFM). This paper illustrated that the explosive defect characteristics of metal plate at the microscopic level can be explored by analyzing its macroscopic dynamic mechanical response.
文摘The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is first carried out in order to determine temperature evolution and to predict the residual temperatures during the burst firing event; 2) The thermo-mecha- nical stresses and deformation caused by both the residual temperature field and the gas pressure are then calculated. The results show that the residual temperature field tends to a steady state with the increasing of rounds. The residual temperature field has much effect on the gun barrel stress and deformation, especially on the assembly area between barrel and water jacket. The gage between the barrel and water jacket is the critical factor to the thermo- mechanical stress and deformation. The results of this analysis will be very useful to develop the new strength design theory of the liquid-cooled gun barrel.
基金Supports from the National Natural Science Foundation of China(Grant No.12272094,No.52205185 and No.51975123)the Natural Science Foundation of Fujian Province of China(Grant No.2022J01541 and No.2020J05102)the Key Project of National Defence Innovation Zone of Science and Technology Commission of CMC(Grant No.XXX-033-01)。
文摘To explore the wide-frequency damping and vibration-attenuation performances in the application of aerospace components,the cylindrical sandwich shell structure with a gradient core of entangled wire mesh was proposed in this paper.Firstly,the gradient cores of entangled wire mesh in the axial and radial directions were prepared by using an in-house Numerical Control weaving machine,and the metallurgical connection between skin sheets and the gradient core was performed using vacuum brazing.Secondly,to investigate the mechanical properties of cylindrical sandwich shells with axial or radial gradient cores,quasi-static and dynamic mechanical experiments were carried out.The primary evaluations of mechanical properties include secant stiffness,natural frequency,Specific Energy Absorption(SEA),vibration acceleration level,and so on.The results suggest that the vibration-attenuation performance of the sandwich shell is remarkable when the high-density core layer is at the end of the shell or abuts the inner skin.The axial gradient material has almost no influence on the vibration frequencies of the shell,whereas the vibration frequencies increase dramatically when the high-density core layer approaches the skin.Moreover,compared to the conventional sandwich shells,the proposed functional grading cylindrical sandwich shell exhibits more potential in mass reduction,stiffness designing,and energy dissipation.
基金Sponsored by the National Natural Science Foudation of China(50905016)
文摘A kind of automatic shift schedule optimization method is provided for a tracked vehicle with hydrodynamic-mechanical transmission in order to improve its dynamic performance. A dynamic model of integrated hydrodynamic-mechanical transmission is built in MATLAB/Simdriveline environment, and an optimum shift schedule is derived by using iSight software to call the dynamic model above, then the shift schedule is achieved after optimization. The simulation results show that the method is significant to improve the dynamic performance and gear-shifting smoothness theoretically and practically.
基金supported by the National Natural Science Foundation of China(Grant No.12172232)the project of Key Laboratory of Impact and Safety Engineering(Ningbo University,China)+1 种基金Ministry of Education(CJ202206)supported by the scientific research support plan of introducing high-level talents from Shenyang Ligong University。
文摘Block piezoelectric ceramics(PZTs)are often used in impact igniters to provide activation energy for electric initiators.Under the action of strong impact stress,PZTs release electric energy accompanied by crack initiation,propagation and crushing.At present,the electrical output performance of PZTs in projectile is usually calculated by quasi-static piezoelectric equation without considering the dynamic effect caused by strong impact and the influence of crack propagation on material properties.So the ignition parameters are always not accurately predicted.To tackle this,a PZT dynamic damage constitutive model considering crack propagation is established based on the dynamic impact test and the crack propagation theory of brittle materials.The model is then embedded into the ABAQUS subroutine and used to simulate the electromechanical response of the impact igniter during the impact of a small caliber projectile on the target.Meanwhile,the experiments of projectile with impact igniter impact on the target are carried out.The comparison between experimental and numerical simulation results show that the established dynamic damage model can effectively predict the dynamic electromechanical response of PZTs in the missile service environment.
基金Project(51075350)supported by the National Natural Science Foundation of China
文摘Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were investigated. The forced responses of the mechanical system to mechanical excitation under electric disturbance were also presented. It is known that for the system with electric disturbance, as time grows, beat occurs. When electric disturbing frequency is near to the natural frequencies of the mechanical system or their integer multiple, resonance vibrations occur. The forced responses of the mechanical system to mechanical excitation under electric disturbance are compound vibrations decided by mechanical excitation, electric disturbance and parameters of the system. The coupled resonance vibration caused by electric disturbance and mechanical excitation was discussed as well. The conditions under which above coupled resonance occurs were presented. The results show that when the difference of the excitation frequency and the perturbation frequency is equal to some order of natural frequency, coupled resonance vibrations occur.
