Search

With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets. [ABSTRACT FROM AUTHOR]

In order to predict the formability of lightweight materials, the flow stress and fracture behavior of AA5A06 aluminum alloy which is very sensitive to temperature and strain-rate were investigated in this study. First, a modified Misiolek constitutive equation with a work-soften term is proposed to calculate the flow stress of the sheet metal. To predict ductile fracture in sheet forming operations, Cockcroft-Latham damage criterion is applied here and ductile fracture threshold under each condition is estimated using Response Surface Method. Finally, warm hydroforming deep drawing tests were conducted at various conditions and the experiment results are compared with the numerical simulation result to evaluate the new model's feasibility and accuracy in forecasting the mechanical response of the material in warm forming conditions. Results show that the proposed model has a good accuracy compared with the traditional power law models and the FEM simulation conforms well to the tests. [ABSTRACT FROM AUTHOR]

This work focuses on the limit strains of 5754-O aluminum alloy sheets with consideration of the hardening law effect. Based on uniaxial tension test data, the hardening laws of Swift, Voce, LSV and Hockett–Sherby were applied to determine the mechanical properties. The fitted parameters and the Yld2000-2d yield function were introduced into the Marciniak–Kuczynski (M–K) theory to predict the forming limit curve (FLC). This prediction was not consistent with the Nakajima test results. Assessment of the effect of the hardening law on the predicted FLC indicated that the hardening law affected the yield surface evolution through the hardening rate. Afterward, an improved LSV hardening law was proposed to depict the plastic stress–strain relationship, and both the theoretical prediction and the numerical simulation verified the validity of the improved model. The results were compared with the test data, and good agreement was shown. [ABSTRACT FROM AUTHOR]

With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets.

Self-piercing riveting (SPR) is an efficient joining process for bonding sheets through the interlock of rivet flaring. The strength of SPR joints is commonly measured by destructive test. In this study, the metal deformation behaviors in the SPR of aluminum alloy sheets and the mechanical behaviors of the SPR joints in the destructive tests were investigated in order to develop the general strength models of SPR joints. As the important feature in the SPR process, the rivet flaring was quantified by an empirical estimator and utilized to establish the general strength models considering the geometric dimensions of components and tools, the material properties of rivet and sheets, and the load–displacement curve of punch. The predicted strengths of the SPR specimens were verified by the experimental results. All the calculation errors are lower than 8%. Finally, an industrial internet of things (IIoT) was developed to realize the data processing and the SPR joint strength predication. [ABSTRACT FROM AUTHOR]

Yield surfaces of A5052 aluminum alloy sheets with different tempers are modeled by the simplified identification method using the circumscribing polygon. In this method, a polygon circumscribing the equal plastic work contour is determined by uniaxial tensile, equal biaxial tensile and plane strain tensile tests. Anisotropic yield surfaces of A5052 aluminum alloy sheet are modeled by Yld2000-2d (Barlat et al., 2003) and Yld2004-18p (Barlat et al., 2005) yield functions. Both yield functions can express the inscribed curves of the polygons. The modeled yield surfaces of A5052-O agree with the stress points of the equal plastic work contours measured by the reliable bi-axial tensile tests. The proposed method to identify the yield function is effective for aluminum sheet metal. On the other hand, the two identified yield functions show different in-plane plastic anisotropy in the tension-compression combined stress state. To examine the suitability of identified models, the experiments and numerical analyses of the deep drawing tests are carried out. Comparing the experimental and analyzed results, the predicted ear height of drawn cup using the Yld2004-18p yield function agree with experimental results qualitatively. But the prediction of the ear using the Yld2000-2d cannot express the tendency of the experimental one. [ABSTRACT FROM AUTHOR]

Enhancing the impact resistance performance of carbon fiber-reinforced polymer (CFRP) laminates stands as a prominent research focus among various nations. Existing studies have shown a tendency towards arbitrary selection of the inter-ply helix angle values in CFRP laminates, which is accompanied by a limited number of samples representing the chosen helix angles. However, existing studies have shown a relatively random selection of spiral angle values between CFRP laminates, and the sample size of selected spiral angles is limited, posing certain limitations. In order to tackle this problem, we have employed a systematic arrangement of combinations to select the optimal helix angle for CFRP laminates. Inspired by the biological structures of Bouligand, we have sequentially chosen 19 distinct sets of helix angles, aiming to overcome the inherent limitations and enhance the research outcomes in this field. In this study, we established 19 finite element models to investigate the behavior of Bouligand-inspired CFRP composite panels under high-velocity bullet impact. The models were created by selecting 19 sets of helix angles within the range of 0 to 90° with a 5° interval. The results show that the energy absorption of the Bouligand layer-stacking composite plate is better than that of the conventional plate. The optimal spiral angles of the CFRP laminate are 25° and 30°, and the energy absorption characteristics of the laminate are the best at these angles. The impact resistance is also the best at these angles. The energy absorption of the Bouligand layer-stacking composite plate is 396% higher in absorbed internal energy and 361% higher in absorbed kinetic energy compared to the conventional layer-stacking composite plate, significantly improving the ballistic performance of the CFRP bulletproof material and providing a reference for the design of individual protection equipment. [ABSTRACT FROM AUTHOR]

The strain paths of electromagnetic forming limit curve are usually limited due to the restricted design of coil, die, or workpiece. The electromagnetic-driven stamping was suggested to obtain the high-speed forming limit curve of AA5182-O aluminum alloy sheet. The hemispherical punch was pushed by the drive plate with the Lorentz forces to impact on the workpiece. The cross-sectional method was used to determine the experimental limit strains of workpieces. The electromagnetic and mechanical fields were sequentially coupled for numerical simulation of the electromagnetic-driven stamping experiment, and the equivalent plastic strain increment ratios of the necking and safe zones were calculated to determine the simulated limit strains. A series of linear strain paths were attained to contain the uniaxial tension to biaxial tension states. The experimental and simulated forming limit curves showed good agreement to validate the electromagnetic-driven stamping experiment. The electromagnetic-driven forming limit curve was compared with the quasi-static and electromagnetic forming limit curves. Although the electromagnetic-driven forming limit curve is lower than the electromagnetic one, it is higher than the quasi-static one. [ABSTRACT FROM AUTHOR]

The identification of Johnson-Cook parameters and the effect of different temperature gradients on A1050 sheet metal formability were performed. Tensile tests and modified Erichsen were carried out at different temperatures and also combined with numerical simulation to identify Johnson-Cook model parameters and the failure criterion. The obtained parameters were validated using the steam bulge test. A good correlation between numerical and experimental results was obtained in terms of failure behavior during the hot forming process. It was observed that hot forming improves the Erichsen index, and the thermal gradient strongly affects the failure zone position in the deformed specimens. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ballistics / Dandao Xuebao is the property of Journal of Ballistics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ultrasonic metal welding (UMW) enables joining in the solid state at relative low temperatures with short cycle times. This technique is of particular interest for joining metallic glasses to each other or to other materials, because crystallization of the amorphous structure can be prevented due to the low thermal loading and the rapidity of the process. In this work, UMW is applied to join one 1 mm thick sheet of a commercial wrought aluminum alloy (AA5754) and one 0.4 mm thick strip of a commercial Zr-based bulk metallic glass (AMZ4). The introduced heat of the welding process is detected with thermocouples and thermal imaging. To investigate the strength of the joint and the influence on the microstructure, mechanical tensile tests are carried out in combination with scanning electron microscopy and differential scanning calorimetry. The results show that ultrasonic metal welding is a suitable technique to join amorphous bulk metallic glasses to crystalline aluminum alloys. The metallic glass component retains its amorphous structure in the joint, and the joint strength is higher than the strength of the Al sheet. These findings will help to develop future applications of BMG-based multi-material components, including medical tools. [ABSTRACT FROM AUTHOR]

The experimental acquisition of electromagnetic forming limit is significantly confined due to the non-uniform pulse pressure of electromagnetic actuator and the complex deformation behavior of sheet metal. Hence, it was proposed to determine the electromagnetic forming limit diagram of aluminum alloy sheet by combining theoretical model, numerical simulation and experimental verification. The Marciniak–Kuczynski model embedded with Cowper-Symonds rate-dependent hardening model was derived in order to consider the strain rate effect on the electromagnetic formability of aluminum alloy sheet. The self-loop samples were newly designed with long oval coil for electromagnetic forming experiments to accomplish the typical deformation paths of uniaxial tension and plane strain. The strain rates and strain paths were investigated by numerical simulations. With the electromagnetic forming limits under uniaxial tension and plane strain conditions, the Marciniak–Kuczynski model was calibrated to fully determine the electromagnetic forming limit diagram. The electromagnetic bulging experiment was carried out to validate the electromagnetic forming limit diagram. Compared with the quasi-static forming limit diagram, the electromagnetic forming limit diagram of AA5182-O aluminum alloy is much higher. The electromagnetic forming limits under uniaxial tension, plane strain and equal-biaxial tension conditions are improved by 43%, 53% and 59%, respectively. [ABSTRACT FROM AUTHOR]

In the roll-hemming forming process of door cover, the non-metallic flanging adhesive and the interaction between light metal and flanging adhesive will affect the manufacturing accuracy and performance of the door cover, and increase the difficulty of roll-hemming forming and quality control of automobile body sheet with adhesive. Therefore, a numerical analysis model for roll-hemming forming of aluminum alloy sheet with adhesive was proposed based on the finite element method and the smooth particle hydrodynamic (FEM-SPH) method. First, SPH was used to simulate the extrusion flow process of the flanging adhesive, and a roll-hemming simulation model of sheet metal with adhesive was established in combination with FEM. Then, an experimental platform for two-pass roll-hemming forming of aluminum alloy sheet with adhesive was built, and the roll-hemming loss and surface wave coefficient were taken as the roll-hemming forming quality index to analysis and verify the validity of the numerical model. After that, the quality change between the first pass and the last pass and the key process parameters affecting quality were studied based on the orthogonal test method. Finally, the fitting relationship between roll-hemming forming quality and process parameters was established. The results show that the roll-hemming loss and the surface wave coefficient of the last pass are reduced compared with the first pass. The process parameters that affect the surface wave coefficient in descending order are flanging height, fillet radius, TCP-RTP value, and roller diameter. The process parameters that affect the roll-hemming loss in descending order are TCP-RTP value, fillet radius, flanging height, and roller diameter. The fitting relationship can support the prediction of roll-hemming forming quality of aluminum alloy sheet with adhesive.

Abstract Accurate quantification of external force is the key to improve the high-precision hemming of autobody closure panels. However, the mechanism of external force on forming quality of complex contour sheet metal with adhesive is not clear subjected to geometric curvature and materials. In the present study, taking the curved edge aluminum sheet as the research object, SPH (smooth particle hydrodynamics) is introduced to simulate the viscous adhesive, and the SPH-FEM (Finite element method) coupling model of adhesive and panels considering the viscosity-pressure effect is established. The numerical simulation of the roller hemming process is carried out, then the validity and reliability of the proposed method are verified by measuring the external force in real time using triaxial force sensor. The multi-step forming process and the effect of external force on the roll in/out, surface wave and plastic strain of aluminum alloy sheet under the viscosity-pressure effect are studied, and the relationship between process parameters and external force is discussed. Results show that the coupling SPH-FEM model can well reflect the hemming process of curved edge structure. The normal force is about 2–3 times of the tangential force in the pre and final hemming process. Compared with the case without adhesive, the surface wave of flange part of the hemming with adhesive is slightly larger. The normal force and the tangential force increase about 90 N and 30 N respectively, when the height increases by 1 mm. It provides an important basis for the accurate control of hemming trajectory and the improvement of manufacturing quality of autobody closure panels.

The recession of elastic modulus happening in the plastic deformation of sheet metals had a big influence on the springback prediction in sheet metal forming processes. To study the recession law of elastic modulus for 7075 aluminum alloy sheets, the conventional cyclic loading experiments were used and a new bending-unloading experiment with the assistance of DIC strain measuring system was designed to test the elastic modulus. The testing results show that the elastic modulus has a significant decline with the growth of plastic deformations and the recession law of elastic modulus is influenced by the stress states during deformation. The recession laws obtained by two experiments were applied to the springback simulation of forming processes for a beam with shape C. The comparison between the results of simulations and experiments shows that the analysis results of springback from the recession law of cyclic loading experiments are better than that from the bending-unloading experiments. The prediction accuracy of the four springback angles is increased by 42%, 7%, 40% and 200% separately. [ABSTRACT FROM AUTHOR]

Aiming at the high-speed friction stir welding deformation and thickness reduction of 1 mm 6061-T6 aluminum alloy sheet, the characteristics of the axial pressure of the welding process and its influence on the joint structure and mechanical properties were analyzed in this paper. Experiments were performed to optimize process parameters. A fuzzy controller with axial pressure error and its change rate as input and welding speed as output had been designed to realize axial pressure control during friction stir welding. The welding axial pressure fluctuates slightly around the target value, and the system was stable with the controller. Besides, the microstructure of the corresponding weld nugget area was uniform, dense, and the transition area was uniform without obvious welding defects. The joint hardness distribution was stable with the classic "W" shape distribution. The mechanical properties of the joint were excellent, and the tensile strength reaches 195 MPa, which was about 70% of the base material (290 MPa). [ABSTRACT FROM AUTHOR]

This paper is concerned with accurate prediction on the fracture strain and fracture forming limit curve (FFLC) by calibrating the material constants by the specimens with reasonable shapes and sizes. The Lou–Huh ductile fracture criteria (DFC) in analytic and integral forms were adopted, and the theoretical formulas in various stress states were derived. The process and basis for calibrating the material constants of DFC by hybrid experimental–numerical method were described in detail. Moreover, the material constants calculated by different test groups including the uniaxial tensile, plane strain and shear specimens with different shapes and sizes vary enormously, and the optimal test group was determined to calibrate the material constant of DFC. Meanwhile, it can be found that the different material constants greatly impact on the magnitude and shape of the fracture strain and FFLC, and the effect of each material constant on the fracture strain and FFLC was analyzed and compared in this paper. Finally, the FFLCs theoretically calculated by DFC in analytic and integral forms were verified by the experimental forming limiting data of the bulge test. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The strain rates of sheet metal often reach several 103 s−1 in various high speed forming processes, and how to determine the strain-rate-sensitive hardening behavior of sheet metal at such high strain rate is an essential issue. The dynamic bulge experiment of aluminum alloy sheet was performed by using electromagnetic pulse forces. The strain-rate-sensitive parameters of hardening models were inversely identified by minimizing the discrepancy between the simulated and experimental displacements of specimen after electromagnetic bulge. The strain-rate-sensitive hardening models of Johnson-Cook and Cowper-Symonds were determined for 2024-O aluminum alloy sheet. Both the models showed that 2024-O aluminum alloy sheet exhibits a positive strain rate sensitivity when the strain rate rises higher than 500 s−1. The flow stresses of Johnson-Cook model increase very slightly when the strain rate ranges from 500 s−1 to 3500 s−1, and they increase about 10% when compared with the quasi-static ones. Meanwhile, the flow stresses of Cowper-Symonds model increase progressively and more significantly. They increase from about 5–35% when the strain rate changed from 500 s−1 to 3500 s−1. The electromagnetic hole-flanging experiment was also conducted to verify that Johnson-Cook model is more accurate for strain-rate-sensitive hardening model of 2024-O aluminum alloy sheet at high strain rates of 103 s−1. [ABSTRACT FROM AUTHOR]

Accurate quantification of external force is the key to improve the high-precision hemming of autobody closure panels. However, the mechanism of external force on forming quality of complex contour sheet metal with adhesive is not clear subjected to geometric curvature and materials. In the present study, taking the curved edge aluminum sheet as the research object, SPH (smooth particle hydrodynamics) is introduced to simulate the viscous adhesive, and the SPH-FEM (Finite element method) coupling model of adhesive and panels considering the viscosity-pressure effect is established. The numerical simulation of the roller hemming process is carried out, then the validity and reliability of the proposed method are verified by measuring the external force in real time using triaxial force sensor. The multi-step forming process and the effect of external force on the roll in/out, surface wave and plastic strain of aluminum alloy sheet under the viscosity-pressure effect are studied, and the relationship between process parameters and external force is discussed. Results show that the coupling SPH-FEM model can well reflect the hemming process of curved edge structure. The normal force is about 2–3 times of the tangential force in the pre and final hemming process. Compared with the case without adhesive, the surface wave of flange part of the hemming with adhesive is slightly larger. The normal force and the tangential force increase about 90 N and 30 N respectively, when the height increases by 1 mm. It provides an important basis for the accurate control of hemming trajectory and the improvement of manufacturing quality of autobody closure panels. [ABSTRACT FROM AUTHOR]

Premature fracture of aluminum alloy sheet in blanking process will seriously reduce the forming quality and production efficiency of blanking parts. The purpose of this study is to explore the feasibility of using acoustic emission (AE) technique to detect the crack propagation behavior of metal sheet during blanking. AE analysis results provide effective information about plastic deformation and damage evolution. However, this technique cannot determine the depth of internal damage and the state of crack propagation. The displacement field measured by digital image correlation (DIC) method makes it possible to monitor the evolution of strain field and crack initiation during deformation. Therefore, a coupled real-time tracking method of AE and DIC is proposed to measure the deformation and damage evolution process that occur in blanking sheet. Research findings suggest that this method provides a complete and accurate description for the diverse damage evolution process of blanking aluminum alloy sheet. AE is a promising technique used to characterize and quantify the crack propagation process of metallic sheets in blanking. [ABSTRACT FROM AUTHOR]

Ultrasonic metal welding (UMW) enables joining in the solid state at relative low temperatures with short cycle times. This technique is of particular interest for joining metallic glasses to each other or to other materials, because crystallization of the amorphous structure can be prevented due to the low thermal loading and the rapidity of the process. In this work, UMW is applied to join one 1 mm thick sheet of a commercial wrought aluminum alloy (AA5754) and one 0.4 mm thick strip of a commercial Zr-based bulk metallic glass (AMZ4). The introduced heat of the welding process is detected with thermocouples and thermal imaging. To investigate the strength of the joint and the influence on the microstructure, mechanical tensile tests are carried out in combination with scanning electron microscopy and differential scanning calorimetry. The results show that ultrasonic metal welding is a suitable technique to join amorphous bulk metallic glasses to crystalline aluminum alloys. The metallic glass component retains its amorphous structure in the joint, and the joint strength is higher than the strength of the Al sheet. These findings will help to develop future applications of BMG-based multi-material components, including medical tools.

Electromagnetic forming is a high-speed forming process, and it can generate high contact force between the sheet metal and die. Therefore, the effects of die counter-impact on aluminum alloy sheet during electromagnetic forming were numerically and experimentally investigated. Firstly, the numerical simulations of electromagnetic free forming and electromagnetic die forming were performed with the Gurson-Tvergaard-Needleman damage model. When the aluminum alloy sheet impacted the die, an unignorable normal stress occurred along the thickness direction. The void volume fraction was reduced due to the negative stress triaxiality, and the residual stress became smaller. Secondly, the effect of die counter-impact on the pre-deformed aluminum alloy sheet was numerically inspected for quasi-static and dynamic hybrid electromagnetic forming. Compared with the electromagnetic die forming of aluminum alloy sheet without pre-deformation, the void volume fraction and residual stress reductions were more significant for the pre-deformed aluminum alloy sheet. Finally, the aluminum alloy sheets after different electromagnetic forming experiments were compared by optical microscope and Vickers hardness. The results show that the damage suppression and hardness enhancement are attributed to the effect of die counter-impact, especially for the hybrid quasi-static and dynamic forming processes. [ABSTRACT FROM AUTHOR]

In the present study, crystal plasticity models applicable for reproducing the work-hardening behavior under various loading paths of an A5083-O Al alloy sheet were examined. The loading paths under consideration were tension, reverse loading from compression to tension, simple shear, and biaxial tension. The accumulated-slip-based hardening model with the extended Voce hardening law provided good predictive accuracy for work-hardening behavior under uniaxial loadings. In contrast, it could not reproduce anisotropic hardening under biaxial tension, which was observed in the experimental results. In the case of dislocation-density-based hardening models, the work-hardening behavior under both uniaxial loadings and biaxial tension was reproduced fairly well when an anisotropic property in the interaction matrix was considered. On the basis of these results, a new accumulated-slip-based hardening model was proposed, in which the effects of latent hardening were considered in calculation of accumulated slip. The new model allowed prediction of anisotropic hardening under biaxial tension as in the case of the dislocation-density-based hardening model. This result suggested that the predictive accuracy of anisotropic hardening was more affected by the modelling of the latent hardening and interaction matrix than by the choice of internal variables of hardening, i.e., accumulated slip or dislocation density. [ABSTRACT FROM AUTHOR]

Bending deformation behavior of 6061 aluminum alloy sheets after different aging times was investigated using three-point bending tests. The bending deformation was analyzed experimentally and using finite-element (FE) analysis. The results showed that the strength of the material increased with aging time, resulting in a decrease of bending radius and bending thickness in the fillet region, and an increase of the neutral layer offset and springback angle. A strain-hardening exponent n with a power function model was introduced following correlation analysis of the main factors. Regression models of the bending parameters were established based on evaluation of the t-Student relevant parameters. The accuracies of the regression and FE springback models in predicting the springback angle were compared with experimental results. The regression model showed higher accuracy in predicting the springback angle. This modeling method can be extended to predict deformation behavior of aluminum alloy structures and provide a theoretical basis for the design of lightweight automotive structures. [ABSTRACT FROM AUTHOR]

Al-Mg alloys have the properties of anisotropy, temperature softening and strain rate hardening in warm forming conditions. The former could be modeled by an advanced non-quadratic yield function. The rate-dependent characteristic could be modeled by viscoplastic constitutive models. Up to now, few investigations have combined a viscoplastic model with advanced yield functions for warm forming simulation, especially by an implicit finite element (FE) program. In this investigation, the warm forming simulation of AA5182-O alloy was presented via Abaqus/Standard, considering the viscoplasticity and anisotropy. The established viscoplastic model could well reflect the nearly rate-independent initial yield stress of the selected material, and its parameters could be easily calibrated. The numerical implementation of the viscoplastic model associated with Yld2000 and Yld2004 yield functions was carried out using an implicit integration algorithm, and the algorithmic tangent was deduced. Results accordance between the simulation and experiment, including warm uniaxial tension test and warm deep drawing test of AA5182-O, showed the rationality of the established material model and the corresponding implicit implementation scheme. [ABSTRACT FROM AUTHOR]

• A modified GTN model considering the effects of anisotropy and shearing on micropore evolution is introduced. • The constitutive model is compiled into a VUMAT subroutine for numerical simulation to accurately predict the plastic deformation of aluminum alloy sheet. • The parameters in constitutive model are calibrated by inverse FE method and the validity of the modified GTN model is verified through the uniaxial tensile experiment. • A FE model of the mould-sheet coupling system is further developed to improve the forming performance. Traditional GTN meso-damage model, neglecting the effect of anisotropy or shearing on the evolution of microvoid, leads to the lower predictive capabilities of forming defects for aluminum alloy sheets. In this paper, a modified constitutive model of aluminum alloy sheet considering the effect of both anisotropy and shearing is proposed, and the corresponding model parameters are calibrated by inverse finite element method and uniaxial tensile test of the smooth strip sheet without hole. Then, the constitutive equation of the modified model is compiled into a VUMAT subroutine using backward Euler integration algorithm and FORTRAN language to perform subsequent numerical simulation in ABAQUS/Explicit, the validity of the proposed shear-corrected GTN model is also verified through the uniaxial tensile experiment of the strip sheet with a hole in the middle. Finally, finite element (FE) model of the mould-sheet coupling system is developed based on the modified GTN model, and the influence of punching speed, blank holder force, friction coefficient and dwell time on the forming performance of AA5052 aluminum alloy sheet is investigated. The results show that ductile fracture of aluminum alloy sheet is most prone to exist on the upper fillet of part. [ABSTRACT FROM AUTHOR]

In the paper, the disc sheet of 2024 aluminum alloy was shaped precisely into a flat-bottom cup by two stage laser shocking, and its microstructure evolution was studied by Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) in detail. The investigations show that the grains are elongated and continuously refined by continuous dynamic recrystallization during two stage laser shock sheet forming (TSLSSF). With the increase of strain of metal sheet, the transformation from low-angle grain boundaries and high dislocation densities to high-angle grain boundaries and low dislocation densities occurs, which improves the strength and plasticity of the processed material in comparison with the untreated material. The impact affects significantly the texture evolution process of aluminum alloy sheet under two stage forming. After laser shocking, the textures of the aluminum alloy sheet tend to be stabilized at the β-Fiber and a strong P texture is also formed. Due to the combined effect of grain size and dislocation density, the hardness of the second impact material increases less than that of the first impact. The research provides a reference for the application and development of laser shock forming. • The microstructure evolution of the material after laser shocks was characterized. • The proportion of low-angle grain boundaries first rises and then falls. • The ratio of dislocation density first enhances and then drops after laser shocks. • The textures of the sheet are inclined to be stabilized at β-Fiber and P component. • The hardness increase after the second impact is less than that after the first. [ABSTRACT FROM AUTHOR]

The friction stir joining experiment was performed on a 6061-T6 aluminum alloy sheet 1 mm thick by optimization of different process parameters, and the microstructure and performance analysis of the joint area using a metallographic microscope, friction and wear testing machine, and scanning electron microscope were evaluated. The results show that the crystalline grains in the joint area of the specimen were refined under a given parameter, and the precipitation of the reinforcing phase improved the performance of the joint area. The best parameters for grain refinement were found to be a rotation speed of 8000 rpm and a traverse speed of 300 mm/min. The specimen obtained at 15,000 rpm and 200 mm/min exhibited the smallest milling weight loss. The smallest average friction coefficient of the specimen was observed at 8000 rpm and 300 mm/min. The friction weight loss trend of the specimens obtained under each parameter was basically the same as the friction coefficient. The wear form of each specimen was found to be mainly the adhesive wear, accompanied by the abrasive one. [ABSTRACT FROM AUTHOR]

This paper presents soft computing-based modeling and multi-objective optimization of process parameters in single-point incremental forming (SPIF) of aluminum alloy sheet in order to obtain desired deformed shape with optimal formability satisfying multiple objectives. Response surface methodology and adaptive neuro-fuzzy inference system (ANFIS)-based models were developed to predict the responses based on the experimental data collected according to central composite design of experiments considering tool diameter, feed rate and step height as inputs, and outputs, namely forming wall angle, deformed sheet thickness and surface roughness. Inverse analyses were also performed to determine the set of input parameters to achieve desired outputs. Two different algorithms, namely back-propagation and hybrid, were employed to train the ANFIS in batch mode with the help of experimental data. The performances of the developed models were tested through real experimental data and also cross-validation methods. ANFIS trained by hybrid algorithm was found to be slightly better than that trained by the back-propagation algorithm in terms of prediction accuracy. Desirability function and a non-dominated sorting genetic algorithm were utilized for performing multi-objective optimization in SPIF, and the obtained optimal results were found satisfactory compared to the experimental data. The proposed approach could provide a reliable guidance for selection of suitable parameters in SPIF to achieve desired formed parts. [ABSTRACT FROM AUTHOR]

Ultrasonic metal welding is an energy-efficient, fast and clean joining technology without the need of additional filler materials. Single spot ultrasonic metal welding of aluminum to steel sheets using automotive materials has already been investigated. Up to now, further studies to close the gap to application-relevant multi-metal structures with multiple weld spots generated are still missed. In this work, two different spot arrangements are presented, each consisting of two weld spots, joined 0.9 mm thick sheets of wrought aluminum alloy AA6005A-T4 with 1 mm sheets of galvannealed (galvanized and annealed) dual-phase steel HCT980X. An anvil equipped with variable additional clamping punches was used for the first time. The tensile shear forces reached 4076 ± 277 N for parallel connection and 3888 ± 308 N for series connection. Temperature measurements by thermocouples at the interface and through thermal imaging presented peak temperatures above 400 °C at the multi-metal interface. Microscopic investigations of fractured surfaces identified the Zn layer of the steel sheets as the strength-limiting factor. Energy-dispersive X-ray spectroscopy (EDX) indicated intermetallic phases of Fe and Zn in the border areas of the weld spots as well as the separation of the zinc layer from the steel within these areas.

• Fusion architecture is based on feature layer construction of Thermography and Ultrasound. • The blurring phenomenon of infrared thermal imaging and the blind area of ultrasonic bulk wave can be avoided. • All of the surface, sub-surface and internal defects can be detected without fail inspection in motion scanning. Aluminum alloy is widely used in industry. Generally, the ultrasound testing as one of the non-destructive testing technologies has been applied to the metal sheet inspection for guarantying the quality of the production. However there exist challenges if only single ultrasound testing is applied. The near-field area of ultrasonic method remains limitation for detection. This paper investigates a robust data fusion model for comprehensive defects detection by hybriding inductive thermography and ultrasound testing in dynamic scanning. The proposed data fusion architecture is based on feature layer construction and it is able to cover the entire inspection from the surface, near surface and inside of the specimen. The experiment result demonstrates that the measurement of defects position and contour is accurate and reliable. It is easier to achieve automatic inspection through visualization and feature extraction. This method is effective and reliable for comprehensive detect and measurement metal plate. [ABSTRACT FROM AUTHOR]

Abstract A clear understanding of temperature variation of the sheet metal in immersion quenching process is indispensable for microstructural evolution of the metal material. It means specimen temperature variation in immersion quenching process remains to be further investigated. This work focuses on temperature variation of the 7075 aluminum alloy sheet in the immersion quenching process with the consideration of thermal radiation, boiling process and thermal convection. The proposed mathematical model was validated by the experiment data under different specimen positions and quenchant temperatures. Furthermore, the effects of the instability coefficient α in film boiling stage and the wetting parameter w p in transition boiling stage on temperature variation in boiling process were theoretically investigated. Both the experiment results and the theoretical prediction indicated that the temperature variation curves of different measuring points in boiling process are parallel during the quick immersion quenching process, and the temperature change rate in quenching procedure only depends on the quenchant temperature and the boiling stage. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In the process of laser shock forming, fracture and failure are tend to occur at the center of deformation in metal sheets, which seriously affect the formability of metal sheets under laser shock forming. This paper adopts different process parameters and carries out a series of experiments on the laser shock forming for aluminum alloy 3003H16, investigates failure behaviors in the process of forming, and studies and analyzes the mechanisms of such failures as well as their relationships with limit forming depths. This study reveals three primary failure mechanisms for 3003H16 fracturing under laser shocks, including spallation failure, thinning failure, and mixed failure. The limit forming depths of sheets under different failure mechanisms are different. The spallation failure has the least depth, and the thinning failure has the largest one. It is necessary to select appropriate process parameters for the forming to avoid spallation and improve the formability of sheets under laser shocks. [ABSTRACT FROM AUTHOR]

The aim of this work was to study the formability of 5754-O aluminum alloy sheet through utilizing the finite element M–K approach. The uniaxial tensile test and the Nakajima test were performed respectively for determining the mechanical properties and the forming limit strain pairs. The finite element M–K approach considering the Swift model, the Yld2000-2d yield function and the groove orientation was developed through utilizing software Abaqus. The predicted forming limit curve (FLC) agreed well with the Nakajima test results. Furthermore, the limit strains with the consideration of pre-strain under uniaxial tensile condition were experimentally determined, and numerically predicted by the original M–K approach. The numerical limit strains under different pre-strain paths and pre-major strains showed that the M–K approach could only predict partial FLC when the effective strain caused by the pre-strain was larger than the one at plane strain state. This phenomenon was interpreted by the evolution of the stress state in the groove of the M–K theory, i.e., the change of the strain path in loading process resulted in the stress state rotation, and consequently made the ratio of major strain increment in the groove to that out the groove increase when the stress state in the groove approached the stress state at plane strain state. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies of rubber-pad forming process of AA5182 aluminum alloy sheet. The influences of load velocity and rubber pad height for characteristic of polyurethane rubber are investigated firstly by compression tests. It can be concluded that the load force increases quickly with decreasing of rubber pad height. The expansion diameter of polyurethane rubber is insensitive to load velocity at 40 and 60 mm height. Then the deformation characteristic of rubber-pad forming, states of strain, and stress is analyzed to compare with conventional drawing. Furthermore, AA5182 aluminum alloy sheets with thickness of 0.8 and formed target part with diameter of 80 mm and height of 15 mm are investigated under different load velocity varying from 50 to 500 mm/min. The load velocity, load force, and distribution of thickness are analyzed in detail. Results show that the maximum thickness reduction occurs at the bottom corner of the formed part. And the maximum thinning decreases to 20.0% for v = 50 mm/min, 20.0% for v = 100 mm/min, 17.5% for v = 300 mm/min, and 17.5% for v = 500 mm/min. At last, the forming process for target part with diameter of 80 mm and height of 20 mm is also investigated under different load velocity. The results confirmed that it is difficult to form the desired shape. [ABSTRACT FROM AUTHOR]

Aluminum alloy sheets have drawn more and more attention in recent years in the automobile industry for the purpose of weight loss and energy saving. Hot forming-quenching (HFQ) integrated process (also called hot stamping) has been developed recently for heat-treatable aluminum alloy forming to improve the formability, overcome the springback of the part. In this paper, in order to investigate the formability and lubricationof a B-pillar in hot stamping with 6061 and 7075 aluminum alloy sheets, different solution heat treatment (SHT) temperatures, SHT time and lubricants were used in the stamping experiments.The forming precision detections were also carried out after trimming. The results showed that the B-pillar wrinkled badly and cracked or even broke into pieces in cold stamping with or without lubricants.The B-pillar also cracked in hot stamping without lubricants. With the help of properlubricants, B-pillars with no crackand better surface quality could be obtained. The failure mechanismswere also explained in the present work. Besides,forming precision of most regions ranged from -1mm to 1 mm and there are still large errors in the local regions of the both ends of the B-pillar. [ABSTRACT FROM AUTHOR]

Electromagnetic forming is a high-speed forming technology using pulsed Lorentz force to drive the deformation of metal sheet, it can improve poor formability of metal sheet at room temperature, such as aluminum alloy. But the traditional electromagnetic free bulging technology can only form conical parts, it is difficult to form bottom region flat parts even using flat bottom mold. Electromagnetic incremental forming technology not only can manufacture the large-size sheet part, but also form bottom region flat part. So basing on the concave die electromagnetic incremental forming technology is proposed. The process of forming bottom region flat part by the electromagnetic incremental forming technology is analyzed with experiment and numerical simulation methods. The effects of the discharge voltage, coils moving trajectory and high-speed impaction interaction between concave die and sheet on sheet formability are also discussed. [ABSTRACT FROM AUTHOR]

The deformation behavior was characterized using uniaxial tensile and free bulging testing. Digital Image Correlation (DIC) system was used to probe the full strain fields during the whole bulging process. Thickness distribution of the friction stir welded (FSW) sheet was analyzed and compared with the base metal. The flow stress of FSW joint was lower than that of base metal at the temperature of 400 °C and initial strain rate of 0.001 s −1 . The ultimate tensile strength of FSW joint was about 70% of the base metal. The deformation was concentrated in the nugget zone of the weld during both uniaxial tensile tests and free bulging tests at high temperature, exhibiting significant inhomogeneous deformation characteristic. The bulging height of FSW sheet was only 50% of the base metal. The directions of major strains of weld zone and adjacent base material in the FSW sheet were vertical to each other during bulging tests. Such an incompatible deformation behavior resulted in the poor formability of FSW sheet compared with base metal. [ABSTRACT FROM AUTHOR]

Hot granule medium pressure forming (HGMF) is a technology in which heat-resistant granules are used to replace liquids or gases in existing flexible-die forming technology as pressure-transfer medium. Considering the characteristic of granule medium that seals and loads easily, the technology provides a new method to realize the hot deep-drawing forming on high strength aluminum alloy sheet. Based on the pressure-transfer performance test of granule medium and the material performance test of AA7075-T6 sheet, plastic mechanics analysis is conducted for the areas, such as the flange area, force-transfer area and free deforming area, of cylindrical parts deep-drawn by HGMF technology, and the function relation of forming pressure is obtained under the condition of nonuniform distribution of internal pressure. The comparison between theoretical result and experimental data shows that larger deviation occurs in the middle and later period of forming process, and the maximum theoretical forming force is less than the experimental value by 24.6%. The variation tendency of the theoretical thickness curve is close to the practical situation, and the theoretical value basically agrees well with experimental value in the flange area and the top area of spherical cap which is in the free deforming area. [ABSTRACT FROM AUTHOR]