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With the aim of analyzing the post-deformation Recrystallization (PDRX) of 22MnB5 steel and the grain size evolution after hot forming of the sheet and using the BAEHR 805 A/D thermo-mechanical simulator, several isothermal stress relaxation tests were performed in a temperature range of 800 to 950 °C, a predeformation range of 0.4 to 0.8 and a strain rate range of 0.01 to 0.8 s−1. As a result of isothermal stress relaxation after deformation, PDRX kinetics can be described based on an Avrami equation as a function of temperature, degree of predeformation and strain rate. As the temperature increases, the recrystallization kinetics accelerates. The strain rate also has a positive influence on the fast PDRX. Predeformation has the opposite effect, as the consumption of stored energy occurred in predeformation process of relaxation tests. Furthermore, the microstructure evolution is described as a function of the predeformation parameters. The investigation of the microstructure after isothermal stress relaxation tests showed that the PDRX kinetics corresponds to the calculations. Furthermore, EBSD analysis helped to analyze the effects of certain stress relaxation conditions on the martensite morphology. The results indicate that a lower temperature and higher strain rate lead to fine martensite packages. In contrast, the martensite block width increases when applying higher strain rates.

To determine the flow behavior of SUS304 stainless steel under different conditions, axisymmetric compression tests were conducted over a wide range of forming temperatures (25 °C to 400 °C) and strain rates (10−3 to 10 s−1). Flow curves were obtained for different forming conditions to study the influence of the forming temperature and strain rate on the flow behavior. Moreover, electron backscatter diffraction analysis, X-ray diffraction analysis, transmission electron microscopy, and Feritscope were used to study the microstructure evolution of SUS304 stainless steel under different conditions for determining the underlying reasons for the variations in flow behavior. The experimental results indicated that the flow stress decreased with increasing the forming temperature. With increasing strain rate at 25 °C to 200 °C, the flow stress first increased and then decreased; however, the strain rate had little effect on the flow stress at 300 °C and 400 °C. By analyzing the variation in the phase transformation inside compressed SUS304 stainless steel samples under different forming conditions, the key factors affecting the flow behavior of stainless steel were identified. Finally, by examining the variation in the martensite content and the dislocation density, the dominant deformation mechanism under different forming conditions was determined.

A micromechanical simulation has been performed to study the effect of particle distribution on the mechanical properties and damage behaviors of particle reinforced metal matrix composites (PRMMCs). Two-dimensional (2D) representative volume elements with variable particle size, volume fraction and particle distribution were generated and subjected to finite element simulation. An enhanced continuum model, which incorporates dislocation punching effect at particle-matrix interfaces and Taylor-based nonlocal theory of plasticity in matrix, was used to simulate the mismatch in coefficients of thermal expansion strengthening and particle size-dependent strengthening. Additionally, constitutive damage behaviors were involved in simulating the crack initiation and evolution, considering the ductile damage in matrix and dislocation punching zone, as well as the particle cracking. Simulation results indicate that refining the particle size is helpful to improve the tensile strength and fracture resistance of PRMMCs, whereas the increase of particle clustering volume fraction or severity facilitates damage evolution and deteriorates the mechanical properties. Statistical analysis indicates a negative linear dependence between particle distribution homogeneity and the ductility, given a constant particle size and volume fraction.

Railway axles, which are an important component of railway vehicles, are generally manufactured using high-speed forging processes. To investigate the microstructure evolution and flow behavior during forging processes, a series of isothermal hot compression and heating tests were conducted in the temperature range of 900–1200 °C and strain rate range of 0.01–20 s−1. A strain-compensated Arrhenius constitutive relationship was identified for 25CrMo4 steel, and microstructure evolution kinetics, comprising dynamic recrystallization, metadynamic recrystallization, static recrystallization, and grain growth, were determined. A coupled thermomechanical–metallurgical numerical model was established for the high-speed forging of 25CrMo4 steel axles by using the TRANSVALOR Forge software package. The grain size evolution during the multipass high-speed forging process was predicted, and a full-scale axle was fabricated through high-speed forging to verify the predicted results. The predicted and experimentally observed grain sizes had good agreement. Finally, a series of geometric constraints are proposed for the design of round anvils. The reliability and applicability of the proposed constraints were validated by considering the surface quality and microstructure requirements as well as the forming force during chamfering. The results indicated that the proposed constraints can suitably guide the design of anvils for high-speed forging processes.

Stamping tools play an important role in the stamping process, which directly influences product quality and production efficiency. To evaluate and manage these tools, tool lifetime expressed in terms of the number of times of tool reciprocating motion is an indispensable parameter. Traditional methods for counting tool movements employ mechanical counting devices with presses. In this paper, a new counting method based on the acceleration signals of tool movement is presented that involves installing an acceleration sensor on the tool itself. In order to reduce the effect of noise signals, a Butterworth low-pass filter was first applied to the collecting signals. Then, based on the analysis of the filtering signals of four typical tool motion modes, DPV and T in the return segment of every cycle, also termed uniqueness, are introduced as the threshold parameters. Finally, a count algorithm based on the dynamic threshold values is studied to count tool movement. To verify the accuracy of the counting method, eight typical motion modes of stamping tools were tested. The results show that the proposed method is effective for counting tool movements in various tool motion modes.

In this study, sheet bulk metal forming (SBMF) processes for manufacturing sidewall-thickened cups were explored, including sheet forming processes for the preparation of cup billets and bulk forming processes for sidewall thickening. To avoid forging laps caused by the clearance between the cup corner and die during sidewall upsetting, a locally thickened tailored blank was designed and produced. To form tailored blanks, coining and orbital forming were compared, and a strategy based on a coining process with different lubrication conditions was analyzed. The tailored blanks were drawn to cups, which had sharp corners and were used as billets for the final upsetting operation to avoid the clearance and thus eliminate forging laps. Adopting upsetting with controllable deformation zone (U-CDZ) method, the cup sidewall was thickened. During forming, the buckling on the sidewall and laps on the corner were prevented. The numerical and experimental results indicate that sheet parts with complex sections can be formed using a tailored blank with the U-CDZ method.

Variable-loading path and large strain are two typical features in multistage plastic forming process. Material’s yield surface expands and translates simultaneously as the loading path changes, leading to certain transient phenomena such as Bauschinger effect. Chaboche combined hardening model is widely used in this kind of simulation due to its capability of characterizing the movement and expansion of yield surface. This study provides a parameter calibration method for Chaboche combined hardening model with 3 back stresses in a large strain range. Uniaxial tension-compression cyclic test with constant strain control was conducted for calibrating the Chaboche model firstly. Meanwhile, the flow curve obtained from uniaxial tension test (UT) associated with Swift extrapolation model were employed to provide the stress-strain relation at large strain level. Then, both theoretical analysis and optimal fitting using NSGA-II were used to determine the parameters in Chaboche model by using the data from the small strain cyclic test and the extrapolated UT curve at large strain simultaneously. The calibration result shows a good match with the experimental and extrapolated data, proving the efficiency of the parameter determination manner put forward in this study.

In cold precision forming the heat caused by deformation has a significant influence on the temperature distribution, which might affect the geometry accuracy of the part and tooling life. Well definition of the thermal contact conductance (TCC) between the contact pairs could be helpful to characterize the heat influences. In the present research, an experimental setup was developed to measure the TCC between the tool and specimen. The influence of contact pressure, temperature and surface roughness have been considered. On this basis, a novel model for the prediction of TCC was proposed, and expanded to the large plastic deformation, by involving the effect of contact stress and contact temperature. Correlated sheet metal extrusion experiments and corresponding simulations are applied to verify the model. It is found that the dynamic update of the TCC parameters can improve the prediction accuracy of temperature distribution.

Upsetting with a controllable deformation zone is a newly developed sheet-bulk forming method to thicken the sidewall of a cup. Compared with conventional upsetting, this new method can eliminate the limitation of the slenderness ratio and improve forming quality. However, the risk of premature folding on the outer surface of the thickened cup cannot be ignored. Thus, this study proposes an enhanced die structure to suppress the risk of premature folding. In order to evaluate premature folding, an estimate index is provided. Design of experiments and analysis of variance are adopted to establish a regression model between process parameters and the estimate index. The response surface and contour plot can then be created on the basis of the regression model. With a carefully determined critical value of the estimate index, an optimized die structure can be obtained, for which the risk of premature folding is experimentally proven to be eliminated.

Edge passivation of the punch is a common phenomenon that is induced by wear and which would affect tool life and part quality. To investigate the edge passivation of fine-blanking punch, a wear tester based on sheet metal extrusion was designed. The relevance of the designed tester in terms of the stress state to the fine-blanking process was analyzed via finite element methods. Meanwhile, material flow at the punch edge was studied with pad printing technology, and the effects of the punch geometry and extrusion stroke on the worn profile have been discussed. The results shows that reducing the length of straight lines and radius of arcs results in a large relative sliding distance of material at the punch edge, and for a punch with circular and linear edges, wear on the circular segment is more severe than that on the linear segment. In addition, from the viewpoint of simulation, adaption of the wear coefficient in different periods could lead to a more precise worn profile of the punch.

In the existing shearing processes for fabricating parts such as duplex gears, die roll is difficult to avoid. Accordingly, a method based on sheet-bulk metal forming for fabricating a duplex gear with extremely small die roll in one stroke is proposed in the current work. The process could be divided into three stages according to the forming features: upsetting and shearing stage, lateral extrusion stage, and local filling stage. The die roll appeared in the shearing stage, which could be reduced in the subsequent extrusion and local filling stages. To reveal the underground mechanism, material flows under two situations, as a key factor to influence the forming quality, were compared and investigated. The results revealed that by controlling material flow, one could avoid the defects and reduce the die roll.

To predict fracture initiation in ductile material under nonproportional loadings, an approach considering combined hardening and a fatigue-rule-based damage accumulation law was investigated. Eleven complex nonproportional experiments, including torsion-tension tests, compression-torsion tests, and uniaxial tension-compression cyclic tests were performed. Finite element analysis was conducted on the experimental data to extract information on essential local fractures, such as stress triaxiality and the Lode parameter. The Chaboche combined hardening model was tuned to capture the material hardening characteristics, ensuring a reliable description of the hardening behavior compared with the isotropic hardening assumption. In addition, the inclusion of fracture locus was proposed to determine the predeformation effect on damage evolution. Combined with the fatigue-rule-based damage accumulation laws, the damage evolution can consider the variable strain history. Thus, fatigue-rule-based damage accumulation, together with the combined hardening law, considerably improved the ability to predict fracture onset in cases of torsion-tension loading with respect to the integral-based damage accumulation law.

Buckling is one of the main challenges in thickening the sidewall of a deep drawn cup. To overcome this problem, a novel sheet-bulk forming method, upsetting with a controllable deformation zone, was developed in this study to prevent the buckling during sidewall thickening. In this method, the material from the protective cavity of the die is pushed into the forming cavity under a counter force to establish a stabilised deformation zone, which can eliminate the limitation of the initial slenderness ratio in conventional upsetting methods. The experimental and simulated results reveal that the occurrence of buckling can be successfully avoided through upsetting with a controllable deformation zone. The forming load tends to remain unchanged because of the existence of a stable deformation zone. Additionally, the forming quality can be improved, and a uniform distribution of hardness in the cross section can be obtained, thereby improving the performance-in-service.

Correct prediction of the fracture time and location and their evolution in metallic materials has always been a research hotspot in the field of metal forming. To this end, and in the context of metal forming process simulation, an advanced mathematical material model is crucial. In this paper, we investigate the accuracy of two fully-coupled damage models, one of which is phenomenologically-based and the other one micromechanically-based, in predicting the failure in DP900 steel plates subject to various loading paths. These are applied throughout tests, including tensile tests on unnotched and notched specimens with different notch radii as well as butterfly wing shear tests. Through the comparisons of the numerical and experimental results, in terms of force-displacement curves and fracture strains (or ductility) under wide range of strain paths, the accuracy of the proposed two coupled damage models are discussed.

International audience; Accurate prediction of the fracture occurrence of high strength materials is always the hot spot in the research field of metal-forming process. Appropriate material model is the key issue which can accurately describe the mechanical forming behavior under different forming conditions. However, advanced fully coupled damage/behavior models are heavy to use by engineers and have a high cost in term of calculation consuming time. In this paper, a simple uncoupled damage approach, designed to be easy to use for engineers and accurate as well, is investigated. Two uncoupled damage models, which consider the effect of the Lode angle and the hydrostatic pressure, combing three typical hardening rules, are selected and applied to the damage prediction of DP900 dual-phase steel. The hardening properties and forming limit strains under different loading paths of DP900 are investigated and studied throughout a variety of mechanical experiments, including the uniaxial tensile test, the pre-notched tensile tests with three notched radii, and the butterfly tests. Finally, the prediction accuracy of the used models for DP900 is compared and discussed.

Residual stress after welding has negative effects on the service life of welded steel components or structures. This work reviews three most commonly used methods for predicting residual stress, namely, empirical, semi-empirical and process simulation methods. Basic principles adopted by these methods are introduced. The features and limitations of each method are discussed as well. The empirical method is the most practical but its accuracy relies heavily on experiments. Mechanical theories are employed in the semi-empirical method, while other aspects, such as temperature variation and phase transformation, are simply ignored. The process simulation method has been widely used due to its capability of handling with large and complex components. To improve its accuracy and efficiency, several improvements need to be done for each simulation aspect of this method.

Low frequency vibration–assisted forming (LFVF) with high excitation force and dynamic response is beneficial because of the low load and high forming quality. To reveal the mechanism of LFVF, low frequency vibration–assisted tension (LFVT) with different amplitudes was performed on W-tempered (WT) and peak-aged (T6) 7075 alloy sheets, and the influences of low frequency vibration on the mechanical behaviors and microstructure evolution were investigated. The application of low frequency vibration created a remarkable vibration-softening effect, and a transition from vibration hardening to vibration softening was observed in the LFVT of 7075-T6. Besides, the stress-overshooting phenomenon occurred after vibration excitation in the LFVT of 7075-T6. The vibration-softening effect and stress-overshooting phenomenon were enhanced when the vibration amplitude was increased from 0.078 to 0.243 mm. The ductility of 7075-WT and 7075-T6 sheets could be improved with a vibration amplitude of 0.165 mm. The fracture elongation of 7075-WT and 7075-T6 increased from 17.93% to 13.62%–20.14% and 14.45%, respectively. An increase in the vibration amplitude resulted in a slight increase in the hardness of the 7075-T6 samples, whereas naturally aged 7075-WT samples exhibited the opposite effect. In addition, the low-angle grain boundaries (LAGBs) and dislocation density generally increased with the superimposition of vibration for 7075-WT and 7075-T6, because the vibration stress provided additional energy for the initiation and migration of dislocations. For the LFVT of 7075-T6, the dislocation tangles enhanced by the interaction between precipitates and dislocations resulted in increased hardness and stress overshooting. The LFVT of 7075-WT with a large vibration amplitude resulted in the peak values for the LAGBs and dislocation density because of dislocation annihilation and absorption to the grain boundaries. These results provide a fundamental understanding of LFVF in high-strength aluminum alloys.

This study proposes an economic and effective approach for predicting the die-roll height of fine-blanking components by fully considering the effect of three types of parameters: geometric features of components, process parameters of fine-blanking, and material parameters of fine-blanked sheets. Two prediction submodels that involved geometric features and process parameters individually were established based on a back-propagation artificial neural network (BP ANN), merged into one model, and finally generalised to different materials by correction according to experimental results. During modelling, simulations rather than experiments were used to obtain data for supporting BP ANN considering the demand for a single controlling variable and for saving economic and time costs. Analyses showed that geometric features had a more distinct influence on die-roll height; furthermore, the effect of process parameters is complicated and can be described more suitably by BP ANN. The prediction results of the combined model were favourable compared with the experimental results. Furthermore, the experimental curve used for correction during generalisation of the model showed that a material with higher yield strength generally had smaller die-roll.

Fine-blanking is an effective and economical precision forming process that plays an important role in the manufacturing industry. Several factors, such as material, shape, and blankholder, can affect the quality of products. This paper reports some state-of-the-art research, which includes some changes in the material and shape of products, the evolution of blankholder, and the development of tools and presses. Meanwhile, some key facts about die roll, which is an important indicator when evaluating the quality of products, as well as digital technology, are introduced. Finally, an outlook of fine-blanking is provided with respect to the present situation, demonstrating its challenges and applications in the development of electric vehicles.

Sheet-bulk metal forming, as a new process applied bulk forming on sheet metal to obtain high-quality parts with low weight, attracts the interest of automobile industry for lightweight beneficiation. In this study, the effects of anisotropy on the bulk forming of sheets under large strain were investigated. A duplex gear part of 1060 and 6061 aluminum with several types of teeth was taken as a target part. The billets were located in three different directions during forming. The forming results obtained under stroke settings of 2.0 mm (Al1060) and 1.9 mm (Al6061) were used to measure anisotropy effects. Hill's 48 model was chosen as the anisotropic model. The Lankford coefficients in the model were obtained from uniaxial tension test and cube compression test. The comparison of the data from experiments and the numerical model demonstrated that Hill's 48 model (with Lankford coefficients obtained from cube compression test) most accurately predicted the anisotropy during the sheet shearing and upsetting process.

In order to evaluate the prediction error resulting from using average state variables in the calibration procedure of the ductile fracture criterion, a series of experiments and corresponding simulations were performed to extract the evolution of fracture-related state variables such as stress triaxiality (η), Lode parameter, and equivalent strain to fracture at the fracture initiation points. The average stress triaxiality, average Lode parameter, and equivalent strain to fracture were used to calibrate the Lou-Huh (L-H) ductile fracture criterion. The average induced prediction error was evaluated by comparing the accumulated damage value, which was computed with the calibrated L-H ductile fracture criterion at the fracture initiation point, with the critical threshold value. Comparisons based on a series of experiments covering a wide range of values for stress triaxiality indicated the existence of an average induced prediction error for the compression tests, and demonstrated that different values of embedded-constants C1 and C2 of L-H ductile fracture criterion resulted in entirely different average induced prediction errors. Thus, a parameter study was performed to investigate the influences of C1, C2, the relationship of η and equivalent plastic strain ([Formula: see text]), and the internal function of the integral formula on the average induced relative error. The influence of the relationship of [Formula: see text] could be represented by the influence of the exponent a, the intercept for the stress triaxiality, and the allocation of equivalent strain for the segmented function. Among these influence factors, the value of C2, the value of the exponent a, and the value of the negative intercept for stress triaxiality contributed significantly to an increase in relative error.

The fine-blanking process of ferrite-cementite steels was simulated with a macro-micro multi-scale approach. In the macroscopic simulation, the effects of material and blanking clearance were investigated by evaluating the damage work density of the material in the center of the fine-blanking shearing zone. A series of microstructure-based models with different particle fraction and distribution were generated as sub-models for the microscopic simulations. Microscopic damage in the sub-models was predicted with the damage work model. The simulation results indicated that an increase in particle fraction and the existence of carbide banding accelerated the microscopic damage of the material in the shearing zone during fine-blanking. Micro cracks appeared and extended along the carbide band. In addition, an increase in blanking clearance speeded up the microscopic damage accumulation at the microscale and caused early fracture of the material in the shearing zone at the macro scale. The SEM observations of various fine-blanking specimens substantiated the predictions of the simulations and suggested that severe carbide banding would change the macro crack path in the sheets, adversely affecting the quality of the blanking surface.

Parameter calibration of a ductile fracture criterion determines the prediction accuracy of fracture initiation and propagation in the metal forming process. Methods with various levels of different efficiency and accuracy can be used for parameter calibration. Therefore, in this study, we discussed and analyzed four parameter calibration methods. Whereas two of these methods are based on inverse analysis, the other two are based on analytical methodology. The computational time of the inverse analysis methods is much higher than that of the analytical methods. In addition, the result of an inverse analysis can easily be a local optimum, resulting in large errors for some specific tests. Regarding the analytical methods, the surface-fitting method has a poorer accuracy compared with the integral of fracture threshold value method, likely because of the introduction of average-fracture-related state variables as the inputs of the calibration process.

Two series of experiments were designed and carried out to evaluate the performance of the selected ductile fracture criterion, of which one is the experiments under monotonic loading conditions and the other is the experiments under non-proportional loading conditions. Combined with parallel numerical simulations, the experiments under monotonic loading conditions were utilized to identify the parameters of the fracture criterion with two calibration methods, a conditional one applying several experiments to calculate material constants and an optimization one of surface fitting. The prediction accuracy of fracture related state variables by using the ductile fracture criterion with different calibration methods in regard of the experimental results were estimated. It could be seen that the calibrated L-H fracture criterion via both calibration methods could be qualified for the evaluation of damage evolution in the experiments under monotonic loading conditions. The addition of pre-torsion on the tension test could shift the fracture initiation point from the center to the outside edge. While for the cases under compression-torsion loading conditions, the situation is not consistent due to the cut-off value of stress traxiality used in L-H fracture criterion. With the increase of the pre-loading amount, the prediction accuracy of the identified fracture criterion deteriorates, which is probably caused by the adoption of invariant model parameters or the error of numerical simulation of strain hardening response based on the assumption of isotropic hardening.

A microstructure-based representative volume element (RVE) method is employed for simulating the mechanical properties of the alloy steel 42CrMo4, a typical ferrite–cementite steel with ferrite (α) and spheroid cementite (θ) phases. A series of 2D RVEs with ferrite matrix and globular cementite particles are generated according to various microstructures, among which the geometrically necessary dislocation (GND) accumulation at the α–θ interphase is introduced as a coating layer around the cementite particles. Satisfactory agreement between the simulation and experimental flow curves can be obtained when the ratio of GND layer thickness to particle diameter is 0.25. On this basis, the influences of some modeling parameters such as element type and boundary conditions, as well as some microstructure features like particle size and carbide band, on the mechanical properties are investigated. The results show that small particle size can increase the strength of the material. Carbide band leads to the microstructure inhomogeneity and early finish of uniform elongation, which is potential to cause the loss of ductility and premature failure. These adverse effects become more severe when more cementite particles remain in band or the cementite particles gather denser in carbide band.

The formation of the gear drum clutch involves bulk and sheet forming, and filling the tooth is a key difficulty during the forming process. In this study, four tooth extrusion processes with various extrusion ratios and preform shape were developed, and they were simulated using AFDEX software for examining how the clutch drum influenced tooth forming. Various tooth-filling results were obtained by controlling the extrusion ratio and die cavity in each process. A comparison of the deformation, material flow, and mean stress state among the processes revealed that the stress state was the main determinant of the local flowing material, and it was used to improve the degree of tooth filling. The optimal tooth-filling result was obtained using a two-step extrusion process with an appropriate extrusion ratio and a preform shape.

To improve failure prediction under variable-path-loading conditions, a model combining the stress-based failure limit (SFL) and strain-based damage accumulation (SDA) law, which is named as combined stress-strain-based failure model (CSSFM), was proposed. The integration of SFL enables the proposed model to determine the analytical failure stress and strain, which will be embedded in SDA law, without the influence of loading-path change. The model predicted the failure according to the accumulated damage rather than the analytical failure stress or strain. To evaluate the applicability of the proposed model, parallel simulation was carefully conducted corresponding to a series of two-stage loading tests, namely torsion-tension and compression-torsion tests, reported in the previous publication (Zhuang et al., 2016). Numerical simulations which involved Chaboche combined hardening model with three back stresses were employed to provide necessary variables related to parameter identification of CSSFM. The simulation result was validated by a good accordance between the numerical and experimental load-stroke curves. It is revealed that with the Chaboche combined hardening model, the integrated CSSFM exhibited reasonable performance in describing failure behavior under the reported two-stage loading conditions.

To widen the application of the fine-blanking process, the heat-assisted fine-blanking process for 304 stainless steel plate has been conducted. The quality of the sheared surface and the hardness distribution of the deformed part were studied to determine the influence of the forming condition on forming results and the performance of the deformed part. Furthermore, electron backscatter diffraction and X-ray diffraction analyses were conducted to study the microstructure evolution and phase transformation of the deformed part for determining their forming mechanism and underlying reasons for their hardness distribution. The quality of the sheared surface improved with an increase in the forming temperature. When the temperature was increased to 250 °C, a sheared surface with a full burnish zone was obtained for a linear segment. Moreover, the forming temperature not only affected the hardness value of the deformed part, which reduced with an increase in the forming temperature, but also affected the hardness distribution. The experimental results indicated that the “hardness-affected zone” decreased in size with an increase in the forming temperature. Through microstructure and dislocation density analysis, changes in the quality of the sheared surface and hardness of the heat-assisted fine-blanked 304 stainless steel part could be attributed to the variation in the martensite content and dislocation density of deformed part, both of which decreased with increasing forming temperature.

Shear-cutting methods are more efficient than machining methods for preparing billets from sheet metal. In this study, several shearing methods were applied to prepare semi-finished billets for sheet-bulk metal forming of duplex gears. The influences of shearing features such as fracture, roll over, and grain flow lines on subsequent forming were analyzed. The results indicated that conventional blanking billets with imperfect shapes in the fracture zone could cause defects in the duplex gear in the sheet-bulk metal forming (SBMF) stage. To avoid imperfect shapes in the fracture zone, five types of clean shear-cut billets were prepared. Different roll over values and grain flow lines were achieved for the five billets. SBMF analysis using the clean shear-cut billets indicated that grain flow lines had a major influence on the material flow in subsequent forming. Among the preformed billets, the semi-finished billets produced through backward closed die shearing provide symmetrical grain flow lines, which results in superior symmetry of the outer tooth filling.

A distorted yield surface with a higher curvature in the preloading direction and a rather flat curve in the reverse direction has been observed in numerous materials that experience a preloading process. To describe such distorted yield surfaces, a novel distortional yield model was proposed. The model involves the distorted stress extended from the original version defined by Francois, and can be theoretically applied to any quadratic or nonquadratic yield functions. The original Hill48 and Barlat91 yield criteria were adopted as representatives in this work, for describing the behavior of different steel and aluminum sheets in a two-stage loading experiment. The experimental outcomes obtained from previous publications were employed for the validation of the model. A case of application in a deliberately designed two-stage loading experiment with annealed 6061 aluminum sheet was presented as well. Distinct yield surface distortion has been observed in the second loading stage at small deformation levels with the prestrained sheet metals, and the surface distortion gradually recovers and stabilizes within a small range of strain thereafter. Additionally, initial distortion is positively correlated with the prestrain level. Associated with a novel evolution rule of back stress, the distorted yield surface, as well as the transient phenomena including the Bauschinger effect, orthogonal softening and permanent softening effects in the second loading stage, was successfully described by the proposed model.

The mechanical behavior of an in-situ Al3Ti/A356 composite was studied by three-dimensional (3D) micromechanical simulation with microstructure-based Representative Volume Element (RVE) models. A series of 3D RVEs were automatically generated with A356 matrix and icosahedron shaped Al3Ti particles as representative of various microstructures. Ductile damage of matrix and brittle damage of Al3Ti particles were considered, while perfect interfacial bonding between Al3Ti and Al matrix was assumed. Simulation results were validated by experimental stress-strain curves. Furthermore, the effects of the particle size, volume fraction and distribution of Al3Ti on mechanical properties were simulated by controlling the corresponding parameters in RVEs. The simulation results show that the refinement of particles improves the yield strength and elongation. However, the increase of volume fraction or clustering of the particles reduces the elongation evidently. Additionally, the Young's modulus, yield strength and elongation of the Al3Ti/A356 composite were predicted from different RVE models. The prediction shows that the Young's modulus follows the calculation of Tsai-Halpin equation. The yield strengths are close to the micromechanical approach considering both load bearing and coefficient of thermal expansion (CTE) mismatch strengthening contribution. The relationship between elongation and the properties of the Al3Ti particles is set up by a polynomial fitting, which is generally in agreement with reported experimental results.

Instability is the most common challenge faced in the production of tubular flanged parts, which is usually limited by dimensional parameters, such as the slenderness ratio of height to thickness and the ratio of initial tube thickness to final flange thickness. To extend the formability limit in a single step, an alternative forming method called upsetting with a controllable deformation zone (U-CDZ) is proposed in this paper. In the proposed method, the workpiece is pushed from the holding cavity of a die into the forming cavity. Under an appropriate counter force, a stabilized deformation zone is established, which eliminates the limitation of the initial slenderness ratio in the conventional upsetting method. Detailed analyses of the forming qualities and forming load were performed. Due to the employment of the location zone, the tube flange could be formed at an arbitrary location (at the end of tube or away from the ends) without defects. The feasibility of the U-CDZ method was validated through finite element modelling and metal experiments on aluminium.

A compound deep drawing and extrusion process was proposed in this study to produce the part like geared drum on a servo-controlled press. To improve the formability of the proposed process, the influences of various slide motions like speed motion, oscillation motion, and step motion, on the material performance were studied based on simple standard tensile test and deep drawing tests. And then, specific designed oscillation motion and step motion were adopted in compound deep drawing and extrusion process to evaluate their feasibility. The results showed that by setting a step motion at an early stage of the process, the part could not only achieve high surface quality but also reduce the extent of thickness reduction of the material.

To study the mechanism of ultrasonic vibration assisted forming, the static and vibration assisted compression tests of aluminum 1050 were carried out via a 25 kHz high-frequency ultrasonic vibration device. It is found that vibration reduces the flow resistance and improves the surface topography. The force reduction level is proportional to the ultrasonic vibration amplitude. By using numerical simulation of static and vibration assisted compression tests, the deformation characteristics of material were investigated. Throughout the vibration, the friction between the materials and tools reduces. The stress superposition and friction effects are found to be two major reasons for reducing the force. However, the force reduction because of stress superposition and friction effects is still less than the actual force reduction from the tests, which suggests that softening effect may be one of the other reasons to reduce the force.