According to the characteristic that the plastic behavior of sheet metal is history-dependent,sequential learning method in deep learning was adopted to predict the plastic constitutive relation of advanced high-strength steel sheet by constructing a long short term memory network. The deformation data under different loading conditions obtained by finite element simulation based on Abaqus were used to train and test the model. The training methods and training characteristics of the model were studied. The established deep learning model accurately predicts the yield behavior and hardening curve of materials without introducing any elastic-plastic physical quantities or constitutive laws. The proposed method is able to represent the plastic constitutive behavior of sheet metal with large data volume and compared with traditional methods,it has great advantages in terms of computational efficiency,model flexibility and robustness.

Compared with the traditional metal plastic forming methods,ultrasonic vibration assisted technology based on Blaha effect can reduce the forming load effectively and improve the formability and surface quality of materials. After more than half a century of the development,ultrasonic vibration assisted technology has become an advanced metal plastic forming method with broad prospects,especially provides a feasible way for the plastic process of high-performance difficult-to-deform alloys. The research progress of ultrasonic vibration assisted acoustic effect mechanism including acoustic softening effect and acoustic residual hardening effect was introduced,and the constitutive model building and numerical simulation research results based on acoustic effect mechanism were presented,and the application status of ultrasonic vibration assisted drawing,punching,extruding and cutting was reviewed. The main deficiencies in the mechanism analysis and application study of ultrasonic vibration assisted forming at present were expounded,the research emphases and development trends of related problems were discussed and prospected.

The sheet metal is subjected to complex current-carrying high velocity deformation within a wide strain rate range during electromagnetic forming (EMF),the macro-micro behaviors exhibit significant difference from conventional quasi-static forming process. Thus,traditional constitutive theories can not be used in the precise prediction of this process. To this end,the characteristics of macroscale mechanical behaviors and microstructure evolution mechanisms of materials during electromagnetic forming were firstly discussed. Then,the necessity and practicability and key points of constitutive modeling were addressed. Subsequently,the modeling ideas,the application effect,the advances and limitations of high velocity constitutive model and current-carrying deformation constitutive model suitable for electromagnetic forming process were comprehensively reviewed. Finally,the outstanding issues of mechanistic constitutive modeling coupling electroplasticity effect within wide strain rate and temperature ranges were prospected.

With the further miniaturization of feature size and the increasing variety of materials in plastic micro-forming,more and more challenges will be faced to produce micro 3D components that meet the requirements of dimensional accuracy and service performance by simply relying on the mold loading. It is urgent to explore new micro-forming principles,new methods and new processes. Electromagnetic micro-forming technology is a high strain rate forming method that utilizes the Lorentz force which is imposed on a current-carrying conductor in the magnetic field. It can effectively overcome the problems of the decline of forming performance and difficulty to guarantee dimensional accuracy in the micro-forming process,and has great potential to expand the application field of plastic micro-forming. Firstly,based on the principle and characteristics of electromagnetic forming,the special effect of high strain rate effect on the material properties in the electromagnetic forming process was introduced.Then,the influence laws and relevant mechanism of size effect on the mechanical behavior and formability of materials in the micro-forming process were comprehensively analyzed. The advantages and disadvantages of the electromagnetic micro-forming technolgy in the ultra-thin sheet metal stamping and micro-nano structure embossing on metal surface were commented in detail. Finally,the opportunities and challenges in theory and process faced by electromagnetic micro-forming technology were summarized and proposed.

The existence of inclusions in metal materials destroys the continuity and uniformity of the materials and easily leads to local stress concentration and micro-cracks.It is a challenge for the development of high-performance alloy structural materials to reveal the influence of inclusion size,shape,properties,volume fraction and continuity between inclusions and matrix under different deformation conditions on ductile fracture.The effects of inclusions on the properties of metal materials were reviewed,and the methods of equivalent inclusions were analyzed and discussed,including Eshelby method,Mori-Tanaka method,self-consistent method,upper and lower bound methods of Voigt and Reuss.The recent advances in multi-scale numerical simulation of inclusion fracturing were summarized.The development trend of inclusion research was prospected,and the problems existing in multi-scale numerical simulation for inclusion research were discussed.

Electrically assisted forming technology combines electrical energy,thermal energy and deformation energy,couplings multi-physical field effects. Joule thermal effect and non-thermal effect generated by electro-thermal-mechanical coupling have multiple effects on mechanical properties and microstructure of materials. Compared with traditional forming process,it has advantages in improving the forming potential of materials and improving the forming quality of components. The effect laws of current on dislocation evolution in the process of electrically assisted forming were reviewed from the aspects of experimental research,theoretical model analysis and finite element analysis. The research progress of electrically assisted theoretical analytical model based on dislocation density was discussed and analyzed. The research status of dislocation evolution in the process of electrically assisted forming was sorted out,which provides a reference for further research on electrically assisted plastic forming.

For two typical metal materials of α+β titanium alloy and austenitic stainless steel,electropulsing treatment (EPT),traditional heat treatment (THT)and quantitative statistics of phase transformation were conducted. The effect of current on the phase transformation was quantitatively analyzed and the microscopic mechanism of current was discussed. The results show that the electricity is able to reduce the transformation temperature and accelerate the transformation process of α→β transformation in titanium alloy,and suppress the martensitic phase transformation in stainless steel. Moreover,the effects of elctropulsing parameters on the phase transformations were quantitatively studied. In titanium alloy,with the increase of current density,the α→β phase transformation temperature is reduced but almost not be influenced by the pulse duty,and its transformation rate is enhanced. In austenitic stainless steel,the martensitic phase transformation was reduced significantly with the increase of current density. The mechanism of current on the nucleation and growth stages of the diffused α→β phase transition of titanium alloy and the strain-induced martensitic phase transformation of stainless steel were revealed based on the current-induced “electron wind” and Joule thermal effects on vacancy,dislocation and other defects.

The development history, constitutive models, and homogenization schemes of crystal plasticity theory with large deformation were reviewed. Several theoretical achievements and typical applications of crystal plasticity were outlined. The theories basis, advantages and disadvantages of both phenomenological and physically based crystal plasticity models were compared and analyzed in terms of flow models, work hardening models, and the evolution of state variables. The characteristics and applications of both mean-field and full-field crystal plasticity models were illustrated. The typical applications of crystal plasticity simulations were introduced from the aspects of anisotropy, texture evolution, non-uniform plastic deformation, formability, size effect, damage and fracture behavior, hot deformation and microstructure evolution, and virtual testing etc. And future development trends in this field were pointed out.

For modern industrial development,magnetic pulse joining technology has great development potential and application prospect as an environmentally friendly heterogeneous material joining technology at room temperature that meets the demand for lightweight and composite performance. Since the beginning of the development of magnetic pulse joining technology,it has been mainly used for tube-tube and tube-bar connections. The principle of magnetic pulse technology for plates,the scope of application,the formulation of process parameters,the deformation behaviors of plates during joining process,the macroscopic and microscopic morphologies of connected joints,the evaluation of joints performance and the magnetic pulse equipments and working coils for plates were summarized and analyzed. On this basis,the current problems that need to be solved for magnetic pulse joining technology of plates were proposed and the future development of the magnetic pulse technology of plates was foreseen.

Aiming at the problems such as the complex shape,small draft angle,high requirement of dimension accuracy,difficulty of shaping thin skirt forging,low production efficiency and qualified rate of forged steel piston,the key points of forging characteristic and process of forged steel piston and forging die design,installation and processing were emphatically analyzed,including die material selection and heat treatment requirements,adding vent hole and ejector hole in die cavity,ring resistance groove arranged on flying-side bridge of forging die and die processing. Through the repeated production practice verification,six designing and processing points were summarized and extracted. The piston forging die produced on this basis has low cost and long single die life. Besides,the forged steel piston has high dimensional precision and good surface quality,and the qualified rate of forgings reaches 98. 9%,and the single shift output reaches more than 800.

According to the structure characteristics of rear floor crossmember, the mold profile was designed reasonably.The 22MnMoB new boron steel was selected and the thermal-mechanical-metallurgical coupling model of rear floor crossmember was established by using finite element software Dynaform to simulate the hot stamping process. The stress, temperature field, thinning rate, hardness and microstructure evolution rules of sheet metal in hot stamping of rear floor crossmember were studied, and the fracture defect of the lower rounded corner was optimized. The microstructure of the side wall of the rear floor crossmember was analyzed by quantitative metallography, and the hardness and thickness of different characteristic points were measured. The results show that the thickness of hot-stamped rear floor crossmember is evenly distributed and the maximum thinning rate is less than 20%, the microhardness is above 480 HV. The experimental results are in good agreement with the simulation results, which provides a reference for the new boron steel complex structural parts.

Ultrasonic vibration has been widely used in various plastic forming processes as an energy input. At present,it is generally believed that ultrasonic vibration superimposed on metal plastic deformation can significantly reduce the forming load,which is called acoustoplastic. The main action mechanisms include volume effect and surface effect. The research progress of the existing theoretical models considering volume effect and surface effect was reviewed respectively. On this basis,the development status of ultrasonic vibration-assisted plastic forming technology in the fields of friction stir welding,rolling,spinning,and micro-forming was introduced from three aspects:the principle of ultrasonic-assisted technology,the focus of using acoustoplastic mechanism and the improvement of ultrasonic-assisted plastic forming device. The main research ideas in the future were proposed.

To improve the riveting quality of aircraft carbon fiber reinforced resin matrix composites (CFRP)components,aiming at the CFRP components riveting damage problem with poor openness of aircraft,the single-side core pulling riveting process with bushings was studied,and the tensile shear properties of joints were studied. The results show that the bushings can effectively limit the uneven expansion of the rivet shank in the CFRP hole. The hole wall of CFRP and expanded bushing are interference fit due to the expansion of rivet shank. Moreover,the excessive expansion of rivet shank can cause riveting damage even with the limitation of the bushings. During tensile shear process,the load-displacement response of specimens exhibits the obvious characteristics of linear growth stage,yield stage and transient fracture failure stage. All specimens fail with rivet pulling out,however,the shear damage zone is also observed in CFRP laminate and the joining hole is compressed and deformed,and the final failure mode is the combined failure mode. Specimens are actually loaded by tension-shear coupling loading due to the secondary bending moment action during the tension-shear process. The shear damage occurs first,and then the riveted head extrudes the hole circumference of the CFRP laminates along the length direction of rivet shank that causing the final pulling out failure of rivet. The bushing effectively participates in the tensile and shear load transfer,but reduces the actual contact area between the riveted head and CFRP laminates. The pulling out failure can be prevented by the process parameters optimization.

The crashworthiness of a new type thin-walled circular tube with axial variable thickness under the working condition of axial quasi-static crushing was studied by numerical simulation,and its mean crushing force calculation formula under this working condition was established.The established finite element model was verified.Two models of 6061 aluminum alloy under different heat treatment processes were established by changing the yield strength of the materials used for experiment,and the finite element analysis model of dual variable properties circular tube with axial variable thicknesses and variable materials was established.According to the simulation results,it is found that the specific energy absorption of the dual variable properties circular tube is increased by 4% without improving the mass of tube body.The theoretical mean crushing force prediction formula of dual variable properties circular tube was derived based on the proposed theoretical crushing model of simple thin-walled circular tube.The results show that the relative error between the simulation analysis results and the theoretical prediction results is within 5%.

The manufacturing process of hot-stamped AA7075 parts of automotive body was simulated by means of electromagnetic induction-assisted high-temperature tensile tests,infrared camera and digital image correlation technology,and the effects of deformation temperature,sheet deformation,natural aging time and paint baking time on the mechanical property of parts were studied. The results show that the tensile strength and yield strength of hot-stamped AA7075 can be improved by increasing the deformation temperature. When the deformation temperature is higher than 400 ℃,the improvement of strength caused by deformation temperature is small; during the forming process,the larger the deformation is,the lower the tensile strength and yield strength of the hot-formed AA7075 is; within 20 d of natural aging,the tensile strength and yield strength of hot-formed AA7075 are basically unchanged,and after 20 d of natural aging,both the tensile strength and yield strength are decreased; the fluctuation of paint baking time has no significant effect on the tensile strength and yield strength of hot-stamped AA7075.

Based on the bionic skeleton,the hexagon honeycomb structure was changed by changing the angle of hexagonal honeycomb wall. The design model and the finite element model of tandem gradient honeycomb( TGH) structures were established and the linear tandem gradient theory was designed,and the quasi static and dynamic in-plane compression process,as well as the mechanical response of tandem gradient honeycomb and homogeneous honeycomb were analyzed under the conditions of same volume and different compression speeds from three aspects,namely deformation mode,nominal stress and energy absorption. The research results show that the deformation mode of tandem gradient honeycomb can be changed by changing the gradient rate λ. The low-speed dynamic strengthening effect of mominal stress in the early equivalent strain stage when gradient rate λ =-0. 0088,but the specific energy absorption is not improved obviously.

To study the relationship between the magnitude and frequency of pulse current and the strength and ductility of T2 pure copper/304 stainless steel composite thin strips,the composite thin strips in two states of soft and hard were prepared by cold rolling combined with annealing at 450 and 970 ℃,respectively. The pulse current-assisted uniaxial tensile tests were carried out. The deformation mechanism of the composite thin strips and the action mechanism of pulse current were analyzed through the microstructure and fracture morphologies observation. The results show that the pulse current can cause the softening of the composite thin strips,and lead to the decrease of the elongation at the same time. When the frequency is constant,the softening and elongation of copper/stainless steel composite thin strips decrease become more obvious as the current increases;but when the current is constant,changing the frequency has little influence on the softening effect. The effect of pulse current on the properties of composite thin strip stems from its regulation on the deformation coordination mechanism of the steel side,which reduces the overall deformation resistance of the composite thin strips by inhibiting the twinning and phase transformation process of the austenite. The soft-state composite thin strips with austenite recrystallized microstructure shows more significant softening than hard-state composite thin strips with rolling deformation.

For joint of Al-Cu dissimilar metal tube, taking the advantages of combination of magnetic pulse welding and brazing, a kind of composite new welding process for dissimilar metal bube was studied. The force conditions under certain capacitance and voltage of magnetic pulse forming external tube workpiece were analyzed by ANSYS. Based on the theory of magnetic pulse welding, the optimal process parameters of magnetic pulse assisted joint were determined. The test was performed by using Zn-3wt.%Al solder foil as the solder. The research results show that an excellent welded joint organization is found at voltage of 8 kV, solder foil thickness of 300 μm, heating temperature of 410℃ for 8 s. The element of weld joint is homogeneous, intermetallic compounds are formed in the region near the copper and α-Al is formed in the region near the aluminum. Mixture composed with a majority of Zn-Al eutectic structure and a small amount of α-Al is formed in the solder layer. The formation of the whole weld organization conforms to the theoretical expectation mechanism, which proves the feasibility of the composite technology.

A new ultra-high temperature and high strain rate compression experiment method was established based on the split-Hopkinson pressure bar,which can effectively test the dynamic mechanical behaviors of material at 1873 K. The synchronous assembly system of incident rod and transmission rod was driven by the motor,and the start-up time of the launching system of the striker and the synchronous assembly system of incident rod and transmission rod was precisely controlled by the high-precision delay controller. It can realize the precise control of cold contact time (less than 10 ms)and the control of impact force in assembly process on the sample,which can avoid the influence of cold contact time on the test results at ultra-high temperature and the plastic deformation or even destruction of the sample caused by impact force in assembly process. Based on this ultra-high temperature and high strain rate compression experiment method,the mechanical behaviors of eutectic high entropy alloy CoCrFeNiTa_0.2Nb_0.1 fabricated by powder plasma arc additive were tested in a wide range of temperature (293-1473 K)and strain rate (0.001-5000 s^-1). The influence laws of temperature and strain rate on its plastic flow behavior and deformation mechanism were analyzed. The variation laws of the third-type strain aging phenomenon appearing in the curve of flow stress of the material with temperature with strain rate and its physical model were obtained.

The buckling and postbuckling deformation and springback phenomenon of 304 stainless steel sheet metal under in-plane compression load were studied.Based on the general LS-DYNA finite element software,the simulation accuracy of several typical constitutive models for buckling deformation was compared and analyzed.Compared with the uniaxial buckling forming experiment,it is found that the simulation accuracy of postbuckling deformation is more dependent on the hardening models and less sensitive to the yield criterions;while compared with the kinematic hardening model,the isotropic hardening model has comprehensive advantage.The biaxial buckling problem with complex shape was calculated using the optimized Barlat yield criterion and Hollomon isotropic hardening model,and the simulation results are in good agreement with the experimental results.

To obtain better cold extrusion forming quality of internal thread, the cold extrusion technology of internal thread was studied and the optimal combination of process parameters was sought. A three-dimensional model of cold extrusion for internal thread was established, and the relationship between the bottom hole diameter of internal thread, extrusion speed and friction coefficient with forming quality and working torque was studied by finite element simulation and test. The relationship between the bottom hole diameter of internal thread and tooth height rate was obtained by numerical simulation; the comparison curves of the extrusion torque and extrusion temperature at four different extrusion speeds were obtained and the effect law of friction coefficient on extrusion torque and extrusion temperature was obtained. Simulation and test results show that when the internal thread of M8 mm×1.25 mm is squeezed, the diameter of the prefabricated bottom hole is Φ7.37-Φ7.42 mm, the extrusion speed is 15-30 r·min^-1, the internal thread formed by extrusion has full tooth shape and good connection strength. In addition, using mineral oil lubrication in the extrusion process can reduce the extrusion torque, and the surface quality of internal thread formed by extrusion is good.

The macroscopic constitutive models developed for plastic deformation of magnesium alloys or other close packed hexagonal metals were summarized. The applications of these models in magnesium alloys were reviewed. It is pointed out that the yield criteria applicable to magnesium alloys must reflect both the anisotropy and tension-compression asymmetry. Generally, the description of anisotropy is realized by the linear transformation method of stress tensor or the generalization method of stress function. The description of the tension-compression asymmetry is realized by adding a tension-compression asymmetry factor or coupling the third stress invariant in the yield function. Additionally, the yield surface interpolation method and the yield function parameter fitting method, used for description of the distortional hardening phenomenon occurred in plastic deformation of magnesium alloys, were explained in detail. These two methods make full use of the stress and strain information at different degrees of plastic deformation, which can directly and accurately reflect the yield surface evolutions of magnesium alloy in monotonic loading process.

The recent research progress on anisotropic fracture models and fracture tests for sheet metals was analyzed and overviewed. It is indicated that the meso-damage mechanics model incorporates the anisotropic damage evolution by accounting for the effects of plastic anisotropy, void shape, size and spacing. The continuum damage mechanics (CDM) model is extended to anisotropic CDM model by expressing the scalar phenomenological damage as a tensorial damage variable; for uncoupled anisotropic fracture models, anisotropic fracture is described by altering the measurement method of equivalent plastic strain increment or through the linear transformation of the stress tensor. The fracture tests under various stress states can be obtained by designing a series of specimens with different shapes or applying different combinations of loads at the specimen boundary. Besides, to design new out-of-plane specimens and set up relevant out-of-plane test is an important trend for sheet metals in the future.

The progressive damage and fracture mechanical behavior of unidirectional graphite fiber reinforced aluminum alloy composites (CF/Al composites) were investigated by combination method of micromechanical numerical simulation and quasi-static compression test, and the influence of fiber volume fraction on the compression mechanical properties of CF/Al composites was also analyzed. The results show that the axial quasi-static compression deformation mechanical behavior of CF/Al composites calculated by the micromechanical finite element model based on hexagonal fiber array is in good agreement with the experimental results. In axial compression, the damage initiates on the interface first, and then the accumulation of interfacial damage induces the local interface failure and matrix damage. At the later stage of deformation, the fiber failures and results in axial compression failure at 45° of the composites. The microstructure of the compression fracture shows the coexistence of interfacial debonding and local fiber fracture, which indicates that the main mechanism of inducing the axial compression failure of composites is the interfacial debonding and the fiber fracture caused by the interfacial debonding. The failure of the matrix alloy is not easy to occur after plastic deformation and damage under the axial compression load.The fiber properties are the main factors that determine the mechanical properties of composites under axial compression. Increasing the fiber volume fraction is beneficial to increase the axial compression elastic modulus and ultimate the strength of composites.

Aiming at the small-diameter thick-walled tube, the forming zone was divided into curvature transition zone and stability zone along the length direction. The influences of process parameters such as feeding speed, bending speed and torsion speed on the curvature of transition zone were analyzed by using finite element numerical simulation. The relationship between the bending angle and the curvature of stability zone of tube was established.Based on DMC2210 motion control card, MFC module in C++ software was used to write the control program and operation interface for processing test through the self-developed spatial tube numerical control bending equipment. The validity of the processed cylindrical spiral tube and spatial variable curvature tube was verified. The results show that the mismatching tolerance is within a reasonable range, which can basically meet requirements of design and use.

Wire and arc additive manufacturing technology is an advanced and efficient additive technology,the residual stress of wire and arc additive manufacturing components seriously affects the mechanical properties of components. Therefore,a large number of scholars have studied how to eliminate and control the residual stress of arc additive components. The methods to eliminate residual stress of arc additive were summarized and analyzed in four parts,i. e.,preparation stage of fuse additive,fuse additive stage,completion stage of each layer of fuse additive and heat treatment stage after fuse additive. The process methods of eliminating additive residual thermal stress and phase transformation stress in the last two stages were summarized and analyzed emphatically,including hammer strike,various mechanical vibration methods and post-additive heat treatment process,choosing appropriate process in the two stage can effectively eliminate the phase transformation stress and the thermal stress in additive manufacturing,which provide guidance for the improvement of mechanical properties of wire and arc additive components.

Based on DEFORM finite element analysis software, the numerical simulation model of the ultrasonic rolling extrusion process of wind power bearing material 42CrMo workpiece was established to study the influence of workpiece rotation speed, feeding speed, amplitude and static pressure on workpiece surface roughness. The experimental design was carried out by BBD (Box-Benhnken) of response surface method, the regression analysis for the simulation results was carried out, and the process parameters were optimized. The results show that the surface roughness of the ultrasonic roller extrusion workpiece increases with the increase of the workpiece rotation speed and feeding speed and decreases with the increase of amplitude and static pressure. When the amplitude and static pressure exceed about 13 μm and 350 N, respectively, the surface roughness increases with the increase of the amplitude and static pressure. The optimum process parameter combination was obtained as: the workpiece rotation speed is 306 r·min^-1, the feeding speed is 18 mm·min^-1, the amplitude is 13 μm, and the static pressure is 301 N.On the basis of the optimum process prameter combination, it is obtained that the predicted value of surface roughness is 0.451 μm, and the experimental value is 0.419 μm, and the predicted value is in good agreement with the experimental value. The surface roughness after the optimization is reduced by 50.12% compared with that before optimization.

To study the high temperature rheological behavior and hot working process window of GH141 superalloy,the isothermal compression experiments of GH141 superalloy were carried out under the conditions of deformation temperature of 1000-1200 ℃ and strain rate of 0.01-10 s^-1,and 20 sets of high temperature rheological data were obtained. Hansel-Spittel constitutive model and hot working maps of GH141 superalloy were established based on high temperature rheological data. The microstructure of different hot compression samples was analyzed. The results show that the regression coefficient of Hensel-Spittel constitutive model to the rheological data of the material is 0.99,and its approximation accuracy is high. When the strain is 0.1,the unstable region appears in the temperature range of 1000~1100 ℃,with a logarithmic strain rate of approximately 1. When the strain is greater than 0.1,the unstable region located in the high-temperature and high-strain-rate region. When GH141 alloy is subjected to hot working at temperatures of 1000 and 1050 ℃,the original coarse microstructure undergoes deformation and elongation,accompanied by the formation of small recrystallized grains along grain boundaries. As the deformation temperature rises to 1100 ℃,some of the original coarse grains are replaced by smaller recrystallized grains,while some original grains remain within the material. When the temperature reaches 1150 and 1200 ℃,all the original coarse grains in GH141 alloy are completely replaced by new and fine recrystallized grains. Microscopic analysis validates the utility of the hot working map in quantifying the extent of dynamic recrystallization in GH141 alloy. Combining the hot working map,microstructure and dynamic recrystallization distribution,the optimal hot working process window for GH141 alloy is determined to be within strain rate range of 0.01-0.1 s^-1 and temperature range of 1150-1200 ℃.

The self-piercing riveting experiments were carried out on the composite plates with four different fiber layers made of[CC]_2s,[GG]_s,[CCG]_s and[GCC]_s and 5052 aluminum alloy plates. The surface forming quality and profile forming quality of the joints were analyzed. The tensile and bending tests were carried out on universal tensile testing machine, and the failure modes were analyzed. The results show that when the static tensile tests for the composite plates with four different fiber layers are carried out by using the same rivet, the tensile strength of the composite plates is[CC]_2s,[GG]_s,[CCG]_s and[GCC]_s, and the failure displacement is[CC]_2s,[CCG]_s,[GG]_s and[GCC]_s from large to small. The bending strength is[CC]_2s,[CCG]_s,[GG]_s and[GCC]_s from large to small when the same rivet is used for bending test. In static tensile test,[CC]_2s and[GCC]_s fail due to rivet pulling off from composite plate, and[GG]_s and[CCG]_s fail due to rivet head fracture. In bending test,[GG]_s,[CCG]_s and[GCC]_s have different degrees of fiber breakage due to shearing pressure, while[CC]_2s is delamination.

The riveting assembly of the third generation wheel hub bearings involves the inner ring-inner flange interference assembly and the shaft-end riveting assembly of the inner flange, which is very important in the control of axial clamping force and bearing clearance, and directly determines the service performance of the wheel hub bearings.To further explore the formation mechanism and precise control method of the axial clamping force, combining with the existing research, the constitute, process characteristics and main performance parameters of the shaft end riveting apparatus of wheel hub bearings were briefly introduced at time sequence. The numerical simulation processes and key simulation technologies of the shaft-end riveting assembly were combed. The influences of the shaft end riveting process parameters on the key structural and performance indexes, such as the axial clamping force, deformation of the inner ring and fatigue life along with the application of finite element analysis and intelligent algorithm in the design and optimization of wheel hub bearing were summarized. Finally, the research directions of shaf-end riveting assembly were prospected.

To establish the model that can accurately predict the material flow behavior of 25 CrMo4 axel steel,the constitutive equation was established using multiple nonlinear regression model.The hot deformation behavior of 25 CrMo4 high-speed railway axel steel with the maximum deformation amount of 60% at different strain rates and different deformation temperatures was studied by Gleeble-3800 testing machine.The results show that the dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate.The double multiple nonlinear regression (DMNR) model was established at the temperature range of 1000-1150℃,and the prediction accuracy was quantified using standard statistical parameters such as correlation coefficient R,average absolute error AARE and root mean square error RMSE.The results show that the experimental and predicted curves of this model are almost consistent at lower deformation temperature.

The two flexible incremental forming methods namely local bending forming method and incremental rolling forming method were proposed aiming at typical doubly curved plate forming for hull plate. The influence of plate thickness, mold gap, punch distance and punch radius on springback radius of plate forming during the local bending forming process and the influence of forming distance on bending radius of plate forming during incremental rolling forming process were studied by finite element analysis (FEA) and orthogonal test. Taking one of doubly curved plates, the sail plate, as the example, based on the ABAQUS/Explicit & Standard solvers platform and the results of orthogonal test, multi-pass forming of finite element simulation for doubly curved plates were taken by using local bending method and incremental rolling method respectively. Finally, the feasibility of the flexible incremental forming methods for the marine steel plate and the reliability of the finite element analysis results were verified by the multi-pass local bending experiment.

Hydro-bulging is a new technology to realize the integral forming and lightweight of automobile parts. Axle-housing is one of the important parts on vehicles. To promote and study the hydro-bulging technology, combining with the research progress of the hydro-bulging technology of small automobile axle-housing, the research status of hydro-bulging technology on the manufacture of small automobile axle-housing was analyzed and summarized. Firstly, the problem of manufacturing small automobile axle-housing by traditional hydro-bulging method was analysed. Then, the new bulging-pressing forming technology was introduced, and the design methods of the axle housing tube piece and the preformed pipe were given.Finally, by comparing the bulging-pressing formed sample piece with the traditional hydro-bulging formed sample piece, the bulging-pressing forming is the development trend of hydro-bulging technology of small automobile axle-housing was expounded. By analyzing and summarizing the research on the hydro-bulging of small automobile axle-housing, reference for the study on hydro-bulging of axle-housing was provided.

The influence of hot-pressing process parameters of surface temperature,forming pressure and die temperature of glass fiber reinforced polypropylene(GF/PP)composites laminates on the forming quality of U-shaped skeleton was studied. The interlaminar shear strength of the U-shaped skeleton was tested,the surface morphologies and dimensional accuracy of section were observed. The results show that when the surface temperature and forming pressure increase,fluidity of resin matrix becomes better,resin matrix redistributes during hot-pressing process,the interlaminar shear strength of U-shaped skeleton increases and the surface roughness is improved. However,excessive surface temperature and forming pressure can extrude the resin,thus reeduce the forming quality. The geometric dimensional accuracy of U-shaped skeleton section is affected by both surface temperature and die temperature. The higher the temperature,the more obvious the elastic forward bending effect. If the forming temperature continues to increase,the forward bending effect tends to be constant. During the forming process of U-shape skeleton,the forming quality of the bottom is better than that of the side area due to the different effects of forming pressure on the bottom and side and the uneven surface temperature of the laminate. The optimal process parameters obtained under the existing conditions are:heating voltage of 70 V,heating time of 60 s,surface temperature of 246.1 ℃,forming pressure of 1.2 MPa,die temperature of 80 ℃.

The morphology, composition, and stress state of the iron oxide scale were used as starting points. The effects of pickling, stretching, and cold rolling methods on descaling of the steel surface were explored by means of SEM, EDS and XRD. The results show that the scale of the iron oxide consists of the outermost layer of red Fe₂O₃,the middle layer of magnetic Fe₃O₄, and the innermost layer of FeO. After four minutes of hydrochloric acid pickling, the spot of the steel plate appears on the surface, and after six minutes, the surface scale of iron oxide is basically removed. The crack has a great influence on the pickling speed. Compared to hydrochloric acid, the composite acid GF2 & GF1 based on phosphoric acid has the advantages of repeated use, no emission, etc., and does not cause crack. Under the same deformation, the descale effect of compressive stress is significantly better than the tensile stress. In order to achieve the effect of breaking the scale, the steel must be forced to produce large deformation.

To improve the straightening accuracy of titanium alloy thin bar and ensure the quality of titanium alloy fasteners, according to material properties of titanium alloy and elastic-plastic theory, the roller shape design method to improve straightening effect using rolling and reverse bending was proposed. In the roller shape design process, a ε_t-10ε_t straightening hardening coefficient model was developed based on the straightening deformation feature of thin bar to describe the stress-strain relationship of thin bar deformation more accurately. The advantages of the rolling and reverse bending straightening were analyzed combining with the Tresca yield criterion, and the roller gap solution model of two-roll straightening for thin bar was established from the view of contact strength, elastic deformation and rolling stress limit. The roller shape design curve of two-roll straightening for thin bar was given on the basis of considering the influence of stress neutral layer offset, material hardening law and residual stress release on the reverse bending curvature ratio combined with specific examples, and the straightening process was numerical simulated. The parameter states which affect the accuracy of bar after straightening were analyzed, and the results show that the straightening accuracy of the bar with the designed roller shape is 0.41 mm·m^-1, the hidden deflection is 0.1737 mm·m^-1, and the prediction accuracy after straightening is less than 0.584 mm·m^-1. Finally, the correctness and validity of the design method were verified by straightening test.

Based on elastic-plastic finite element theory, a three-dimensional dynamic finite element model of nine-roller straightener was established by ABAQUS. The distribution of longitudinal stress in the straightening process and deformation law of straightened plate were analyzed by simulation. On the basis of traditional large deformation bending and straightening plan, the parameter design of reduction schedule was carried out and the plate straightening test by nine-roll straightener was carried out. The simulation results show that the deformation of the plate is mainly concentrated on the longitudinal fibers, and the longitudinal stress in the middle of the plate is about 35% of the stress in the edge. To eliminate the warpage, the longitudinal residual stress difference between each column in the width direction must be controlled. The optimal reverse bending ratio of Q235 plate with thickness of 15 mm is determined to be 2.27/0.38 by optimization. And the test results show that the plate straightening effect is good. After processing, the flatness of the plate is less than 4 mm·m^-1, which is in line with the national standard and the test verifies the correctness of the simulation results. The parameterization model of the roller's reduction procedure can quickly determine the optimal straightening process parameters.

The convexity of Hill'48 quadratic yield criterion was analyzed,the expression for determining the convexity of Hill'48 yield criterion under plane stress was proposed,based on which the convexity conditions under four parameter solving methods were proposed.The results show that the widely used Hill'48 yield criterion and its mathematical expression cannot ensure the absolutely convex.The two cases of non-convex failure of material were discussed by means of finite element method and convexity conditions.The yield locus and the convexity of AA2090-T3 aluminum alloy and DP600 calculated by four solving methods were analyzed.The results show that the convexity conditions of Hill'48 based on different solving methods are different.The convexity conditions of different materials are also significantly different.The yield locus obtained with four-parameters solving method is very close to the one calculated with stress solving method.The yield locus obtained with five-parameters solving method differ greatly from those obtained with the stress or deformation solving method.

To study the influence law of different process parameters of the hot power spinning on forming accuracy and improve the forming quality of hot spun workpieces, taking the thinning ratio, spinning temperature, feeding rate and mandrel preheating temperature as variable factors, the external roundness error, wall thickness deviation, straightness error and internal roundness error as the evaluation indexes, the orthogonal experiment was designed. The hot spinning numerical simulation on connecting rod bushing was carried out by using the finite element simulation software Simufact. By means of range analysis and grey correlation method, the consistent influence rule and optimization parameters were obtained and the experimental verification was carried out. The results show that when the hot power spinning of connecting rod bushing is carried out, the thinning ratio and feeding rate are the main factors affecting the forming accuracy, the mandrel preheating temperature is the secondary factor, and the spinning temperature has the least influence on the forming accuracy. When the thinning ratio is 25%, spinning temperature is 350 ℃, feeding rate is 0.6 mm·r^-1 and mandrel preheating temperature is 200 ℃, the forming accuracy of hot spun workpieces is the highest and the forming quality is the best.

Aiming at the problem that there is big randomness and no quantitative calculation of the key parameters cycle feed range in the Pilger cold-rolling process at present, on the basis of analyzing the influence of the cycle feed range on the deformation characteristics seamless steel tube in the rolling process,taking 304 stainless steel pipe rolling as an example, the numerical simulation model of cycle feed range was established by theoretical calculation to study the influence law of cycle feed range on the metal deformation and the quality of the finished product in the rolling process, and to provide the basis for selecting process parameters. Using three-dimensional finite element software to establish the numerical simulation model, based on the cycle feed range obtained before, the rolling process simulation was carried out. The key data such as the stress state, finished pipe size and residual stress in the rolling forming process were obtained, and combined with the field rolling test to verify whether the finished product can achieve the expected performance. The method of combining theoretical calculation, numerical simulation and experimental verification can be used to provide support for the selection of periodic feed. The error between the finite element simulation results and the experimental results is less than 8%, which verifies the accuracy of the finite element simulation results. The residual stress under the 10 mm feed range calculated by theoretical calculation is reduced by more than 10% compared with the residual stress of 12 mm feed range according to the production experience, which further verifies that the cycle feed range of 10 mm can improve the finished pipe quality in a certain dagree.