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 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.

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.

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.

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.

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.

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.

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%.

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.

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.

Taking Zr metal as the research object, the electro-plastic rolling experiment was conducted, and the electric pulse waveform and the rolling force change during the passing of electric pulse in each pass were compared and observed. The results show that the pure electric-plastic effect only occurs in the duration of the electric pulse in a period. The influence time of single electic pulse on rolling process is far less than that of the period electric pulse. Only in this influence period of single electric pulse, the pulse current and rolling force fluctuation are strictly corresponding. In the strict influence time of single electric pulse, the main influence characteristics of pulse current on rolling force are the fluctuation amplitude and the fluctuation reaction time. With the increase of deformation degree of rolled piece, the fluctuation amplitude of rolling force caused by electric pulse is gradually reduced, and the effect of eletric pulse decreases; with the increase of deformation degree of rolled piece,the fluctuation reaction time of rolling force caused by pulse current is shortened.

The tensile experiments of QP980 and QP1180 ultra high-strength steels at the strain rates ranging from quasi-static to strain rate of 500 s^-1 were completed.The influence law of strain rate on the mechanical properties and fracture characteristics of QP980 and QP1180 was summarized,and the plastic fracture mechanism of QP steel at high strain rate was analyzed.The results show that the yield strength and tensile strength of QP980 and QP1180 increase slightly when the strain rate increases from quasi-static to 500 s^-1,and the uniform elongation and fracture elongation also increase with the increase of strain rate.However,the longitudinal fracture strain of the two materials fluctuates with the increase of strain rate.In addition,QP1180 has a relatively larger fracture strain and better fracture plasticity than those of QP980.At different strain rates,the fractures of both QP980 and QP1180 show circular dimple morphology.With the increase of strain rate,the diameter of circular dimples gradually increases and the depth of dimples becomes deeper.At the same strain rate,the diameter and depth of QP1180 circular dimples are larger than those of QP980.At low strain rates,the plastic strain rate sensitivity of the two materials is low,and there is no significant difference in the"TRIP effect ";when the strain rate exceeds 5 s^-1,the strain rate sensitivity index of the two materials at initial deformation stage is relatively large,and the" TRIP effect"weakens,but the strength of the material still increases.Both the two materials have multi-stage hardening ability characteristics and are insensitive to strain rate.

To analyze the effect of process parameters on rolling force and dimensional precision of tubes, multigroup univariate experiments were carried out on the TSR test mill for billets with diameters Φ40 and Φ42 mm, and the plug advance from 15 to 28 mm, feed angle from 7° to 9° in the piercing section, rolling gap from 34 to 35 mm in the piercing section, and roll rotation speed from 182 to 190 r·min^-1 in the rolling section were investigated as the process-related variables. The results show that the rolling force in piercing section decreases with the increase of plug advance, while the axial force of the plug decreases firstly and then increases. The rolling force in piercing section decreases with the increase of feed angle, while the axial force of the plug increases slightly. When the diameter of the billet keeps constant, the rolling force in piercing section increases with the decrease of the rolling gap. And when the rolling gap keeps constant, it increases with the increase of the diameter of the billet. Meanwhile, when the process parameters in piercing section keep constant, the rolling forces in both sections vary in two pattern under different roll rotation speed in rolling section. The rolling forces decrease with tension rolling, while increase with thrust rolling. Under the analysis of the rolled tubes, it is shown that the accuracy of the wall thickness, the diameter of the tube rolled by micro tension rolling are approximately±0.2 mm and ±0.35 mm, respectively.

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.

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 forging process and dies of a disc-type aluminum alloy automobile wheel hub were designed and optimized.The law of metal flow in forging process was clarified by numerical simulation. In view of the structural characteristics of this kind of disc-type aluminum alloy automobile wheel hub, an embedded tangency design method between pre-forging-final forging die was proposed.Based on the design method, the reasonable reduction amount of pre-forging upper die of 50-70 mm was obtained by numerical simulation. The problem of difficult positioning between the initial billet of wheel hub and pre-forging with dies was solved by the optimized forging process and dies, and the folding defect of final forging was avoided. The forging production tests were carried out by the optimized forging dies and process, and the microstructure characterization and mechanical properties test at different positions of the wheel hub final forging were carried out. The results show that the wheel hub forgings achieve a good forming ability with uniform flash distribution and no folding defect, and the microstructure and mechanical properties of different parts meet the requirements by the proposed design method of pre-forging dies and the recommended reduction amount of pre-forging upper die.

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.

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.

Mesoscale simulation methods are important means to characterize the microstructural changes of metallic materials or the relationship between microstructure and mechanical properties,which can transfer the resultant experiments to process experiments on the basis of reducing the number of experiments,thus the experiments results can be characterized more intuitively. The common mesoscale simulation methods for metallic materials,including the crystal plasticity model,Monte Carlo method,phase field method and cellular automaton method were summerized,the theoretical basis and development history of different methods were reviewed,and their characteristics and limitations were explained. The typical application situations of different methods were introduced from the aspects texture evolution,dynamic recrystallization,solid-state phase transformation and solidification phase transformation of metallic materials. The future development trend of this field was presented,hoping to provide a more informative method for the mesoscale simulation of the microstructure evolution of metallic materials.

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.

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.

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.

In view of the problems of multiple production processes and difficult lightweigh of Venturi tube flowmeter at the present stage,the hydraulic bulging process was proposed to produce Venturi tube flowmeter. To explore the influence of various process parameters on the hydraulic bulging of Venturi tube flowmeter,based on the theory of material mechanics,the single factor numerical simulation was conducted based on the finite element software to explore the loading path,friction factor of contact surfaces and loading pressure with better forming effect. Based on the numerical simulation results,the experimental verification was carried out,and the experimental results were compared with the numerical simulation results. The results show that the change trend of the experimental wall thickness is consistent with that of the simulation wall thickness. The maximum thinning position of simulated wall thickness is located at the junction of the transition zone and the forming zone,the thinning rate is 28.9%,the maximum strain is 0.3043,and the overall wall thickness changes continuously.

For the reality that carbon fiber composite laminates are prone to different froms of damage under impact loading,the low speed impact model of carbon fiber composite laminate was established based on ABAQUS software.The gradual cumulative damage of the composite laminate in low speed impact working condition was analyzed.The delamination damage was simulated by Cohesive interface element,the impact process was numerical simulated calling.Hashin failure criterion and Vumat subroutine,and the effects of process parameters on impact results were analyzed.The results show that the damage of composite laminate occurs at the center of laminate and extend in radial direction,and finally the failure happens at the center of the laminate.The larger the ply angle between the adjacent plies of the laminate is,the better the energy absorption ability is;the larger the impact energy is,the larger the damage area is.However,when the impact energy is more than 27 J,the increase velocity of damage area slows down.

The reasons for the quality defects of rolled products were analyzed from six dimensions (Man, Machine, Material, Method, Measurement, Environment, 5M1E). The filter element of the hydraulic system of the cold rolling simulator is clogged due to human factors, which causes the hydraulic cylinder to jitter and produces chatter defects. By replacing the filter element, the jitter phenomenon is greatly reduced and the chatter defects are eliminated. By optimizing the roll profile configuration of the temper, and unifying the shape of the incoming material of the temper, the strip shape defects are significantly reduced. Through the ″ small crown+non-rolling through the temper″ process measures, the camber defects of hot rolled high-strength steel are significantly improved. By controlling the strip temperature of the recoiling machine within 45℃, the length of the head print defect is greatly reduced. Through standardizing warp defect measurement methods and tools, measurement system analysis (MSA) was used to evaluate the accuracy and precision of the measurement system. Defects such as chatter, shape, camber, head print and warp are common defects of strip steel. Appling the 5M1E analysis method to the quality defect analysis of rolled products is helpful in developing the analysis logic, eliminating interference factors, and locating key influencing factors, solving product quality defects, improving product quality, enhancing corporate competitiveness, and promoting high-quality corporate development.

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 tensile fracture behavior of Q235 steel (cold-rolled, hot-rolled) at low strain rates (0.0001-0.01 s^-1) was investigated by using INSTRON tester. The tensile fracture process of cold-rolled Q235 steel and hot-rolled Q235 steel was numerically simulated by Abaqus. The results show that under low strain rates, with the strain rate increases, the yield stress and peak stress of the steel increase, but the yield stress is more sensitive to the change of strain rate. For Q235 steel, the tensile mechanical properties of cold-rolled steel and hot-rolled steel are different. The strength of cold-rolled steel is higher than that of hot-rolled steel, but its ductility is lower than that of hot-rolled steel, and the peak stress and reduction of area are more sensitive to the change of strain rate. The Johnson-Cook constitutive model parameters of cold-rolled Q235 steel and hot-rolled Q235 steel were obtained based on test data. The rationality and reliability of the description of the model on tensile mechanical behavior of steel were verified.

As the key process of air valve forming,the forming quality of preforming determines the service performance and life of air valve. By analyzing the advantages and disadvantages of hot extrusion and electric upsetting,it can be seen that electric upsetting is more suitable for large-scale air valve billet forming than other forming processes. With the increase of air valve billet size,the forming quality of electric upsetting parts is more difficult to control. The causes of surface wave defects and coarse grain defects were analyzed. The quality control methods of large-scale air valve billet by electric upsetting were summarized from three aspects:forming shape,grain control and shape-grain cooperative control,and the intelligent optimization method of electric upsetting process was further expounded,which provides reference for the actual production of large-scale air valve billet by electric upsetting.

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.

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.

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.

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.

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.

To design the mandrel roll feeding strategy of large profiled ring rolling quickly,a self-adaptive control algorithm for mandrel roll motion based on the uniform growth principle of outer diameter of ring was developed,and the feedback mechanism of rolling defects was introduced to guarantee the rolling stability.Based on the Abaqus platform,the VUAMP subroutine was used to realize the application of the algorithm in finite element simulation of ring rolling.The forming of profiled ring with three different outer diameter growth rates was calculated using the algorithm,and the mandrel roll speed,roundness error and actual outer diameter growth rate of ring under the three schemes were analyzed.The results show that when using scheme two,namely the design value of growth rate of outer diameter of ring is 3.5 mm·s^-1,the stability of rolling process is the highest.According to scheme two,the actual rolling production experiment of profiled ring was completed.The forming of experiment ring is good,and the outer diameter change is consistent with the calculated value.

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 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 ℃.

Based on the wear simulation model of disc cutter in slitting process, the edge wear of disc cutter with different side clearances, radial clearances and edge sharpness was calculated and analyzed. The effects of various process parameters on the depth and distribution of the edge wear were compared. The analysis of slitting energy consumption shows that the law of slitting energy consumption and edge wear is consistent which means that the level of wear can be characterized by the amount of slitting energy consumption. It is found that increasing the side clearance can significantly reduce wear and energy consumption, while changing the radial clearance has little effect; when edge sharpness decreases, wear and energy consumption increase as a whole, but the wear of disc cutter side is reduced. At last, based on the Archard wear theory, the change history of contact compressive stress and relative sliding velocity of the disc cutter edge under different processing parameters were contrasted and analyzed, and the wear model of the disc cutter was established.

The rotary backward extrusion of rare earth magnesium alloy was carried out on Gleeble-3500 torsion unit,and the microstructure and texture evolution at different positions of the extruded cup-shaped parts were studied.The cup-shaped parts of magnesium alloy with refined grains and higher mechanical properties were obtained.The results show that the grains of alloy are remarkably refined after rotary backward extrusion,the inside LPSO phase is in a streamlined distribution,and a kink band is produced in the center.The proportions of small-angle grain boundaries in orientation maps at different positions are relatively small,and discontinuous dynamic recrystallization occurs.The grains in the deformed area are randomly oriented.Along radial direction,the dynamic recrystallization area produced in alloy from the inside to the outside first decreases and then increases,and the texture strength inside is the weakest.The hardness values at different positions are different,and the maximum hardness is located in the center,which is the result of the combined effect of the dynamic recrystallization texture weakening effect and the strengthening of long-range ordered phase structure.

In view of the problem that glass fiber reinforced nylon 66 composite blades of unmanned aerial vehicle were prone to excessive warpage deformation when manufactured by injection molding,to reduce the amount of warpage deformation, the multi-factors orthogonal test method was carried out, the simulation tests were adopted by injection molding simulation software with twenty five times,and the amount of warpage deformation of composite blades under five levels and six factors of melt temperature, mold temperature, injection time, pressure holding time, packing pressure and period time was obtained. The influence degree of each process parameter on the amount of warpage deformation was ranked by range analysis and variance analysis, and an optimal scheme of forming process parameter was achieved. The research shows that the maximum amount of warpage deformation decreases by nearly 40% with the optimal scheme of forming process parameter and the main reasons for warpage deformation of glass fiber reinforced nylon 66 composite parts are regional shrinkage and orientation. Finally, the rationality of the optimal scheme was verified by the actual manufacture of a composite blade.

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.