Search

• 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]

• 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]

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]

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]

Recently automobile components need to have various characteristics that are hard to be fulfilled using a single material for satisfying the several demands like weight saving, cost cutting and crash safety with trade-off relationship. Thus bonding or joining methods of dissimilar materials are necessary. However it is difficult to weld steel and aluminum together. Therefore the authors developed an alternative solid phase bonding method “spot-bonding”. In this method, the plastic deformation by cold forging would enable metallic bonding of two dissimilar metals. In this study, this method was applied to bonding of 590MPa-class high tensile strength steel and A2017P aluminum alloy sheets. The joint strength was measured by cross tension testing. When the amount of punch indentation is increased, the joint strength became higher. With the same depth of punch indentation as the total thickness, the joint was broken in the steel base metal blank but not at the interface. Finite element analysis was performed in order to consider the deformation behavior during the bonding process. The parameters on the bonding interface such as surface expansion ratio, surface pressure and relative slippage of two blanks became larger with increase in amount of punch indentation. Furthermore, the bonded region was predicted by calculating the total friction work and the evaluation factor of real contact area that depended on surface expansion and surface pressure. [ABSTRACT FROM AUTHOR]

This study investigates the stress state dependentfracture of several high strength aluminum sheet alloys, AA6013-T6, AA7075-T6 and a developmental AA7xxx-T76 alloy. These alloys are targeted for use in automotive structural applications for which accurate knowledge of the fracture loci are required to support crash safety simulations. A generalized Drucker–Prager (GDP) model to describe the fracture locus was proposed and calibrated to the measured fracture strains under simple shear, uniaxial, plane strain and biaxial tension. Calibration of the fracture loci was undertaken directly using measured fracture strains and direct integration of stress based on the measured strain histories. The calibrated fracture loci using the GDP function exhibited good agreement with the measured data across the range of the stress state conditions. An advantage of the GDP model is the admission of fracture asymmetry in uniaxial and biaxial tension which is not captured using the Hosford–Coulomb model. The experimental fracture loci were then paired with a damage model for non-linear strain paths and used to simulate three-point bend experiments on structural hat channel sections. For each material, the load response and onset of fracture were well predicted. • Investigated the fracture behavior of 6000- and 7000-series aluminum sheet alloys. • Performed simple shear, uniaxial, plane strain and biaxial tension tests. • Employed the Barlat Yld2000 and Hockett–Sherby functions for plasticity modeling. • Calibrated the Generalized Drucker–Prager fracture model based on the measured data. • Numerically validated the fracture model based on a three-point bend experiment. [ABSTRACT FROM AUTHOR]

Abstract: CO2 Lasers in general, and Nd:YAG lasers in particular, are widely used for cutting of reflective sheetmetals to obtain the exceptional good quality cut. Due to shorter wavelength of Nd:YAG laser, it is reflected by lesser extent from the metallic surfaces. This paper presents the modelling and optimization of cut quality characteristics during Nd:YAG laser cutting of aluminum alloy thin sheet along the curved profile. The cut quality characteristics considered are average kerf deviation (D a ) and average kerf taper (T a ). The essential input process parameters are identified as arc radius of curve profile, oxygen pressure, pulse width, pulse frequency and cutting speed. First, second order response surface model was developed for each D a and T a using hybrid approach of Taguchi methodology (TM) and response surface methodology (RSM). The effect of input process parameters on each cut quality (D a and T a ) was also studied. Second, preferred operating laser cutting parameters were obtained using grey relational analysis (GRA) with entropy measurement (EM) to minimize D a and T a together. In the present study a L27 orthogonal array (OA) is used for experimentation. The entropy measurement (EM) method is employed for the calculation of weights corresponding to each quality characteristic D a and T a . Finally, significant improvement in T a has been observed from the verification results. [Copyright &y& Elsevier]

Abstract: Individual grains in a polycrystal rotate during plastic deformation. This leads to a change in the crystallographic texture, and results in an increase or decrease of the macroscopic flow stress of the material. Such a change of strength as a result of grain rotations is called geometrical or texture hardening/softening. In the present study, for textured aluminum alloy sheets, the geometrical hardening/softening effect in the in-plane plane-strain stretching mode is numerically investigated using a generalized Taylor-type polycrystalline model. It is found that the cube texture () exhibits significant geometrical hardening when the major stretching direction is inclined at 45° relative to the orthotropic axes, and that a cube texture rotated about the normal direction (ND) shows a notable degree of geometrical hardening for any in-plane orientation of the sheet. Using the Marciniak-Kuczyński-type approach, forming limits for these textured sheets are analyzed. It is found that geometrical hardening definitely enhances the formability. It is, therefore, strongly suggested that texture control guided by the present results may be highly effective in producing aluminum alloy sheets with higher formability. [Copyright &y& Elsevier]

Abstract: In order to establish the efficacy of electromagnetically assisted sheet metal stamping (EMAS), the formability of 5052 aluminum alloy sheet in a quasi-static–dynamic tensile process is experimentally investigated using a combined quasi-static tension and the pulsed electromagnetic forming (EMF) method. Data on the formability of aluminum alloy 5052-O employing this combined loading method is compared with data for traditional quasi-static tensile tests. Results show that the formability of aluminum alloy sheet undergoing a quasi-static–dynamic tensile process is dramatically increased beyond that exhibited in quasi-static tensile tests, and a little higher than or at least similar with that obtained in the fully dynamic EMF process. The forming limits of aluminum samples with both low and high pre-strain levels are almost similar in quasi-static–dynamic tensile process, which makes it possible stretching the sheet to a higher quasi-static pre-strain level without weakening its total quasi-static–dynamic formability. This would enable the use of a quasi-static pre-form fairly close to the quasi-static material limits for design of an EMAS process in manufacturing large aluminum alloy shell parts. [Copyright &y& Elsevier]

Abstract: The lower formability of aluminum alloy sheet greatly limits its application in reducing weight of stamping parts. This paper proposes a new strategy to optimize the variable blank holder force (BHF) and determine the drawing limit under the constant and variable BHF. The optimization strategy is based on the analysis of BHF formability window and integrated into FEM code to obtain time and spatial optimal BHF that applies on segmental binders. And then a stepped rectangular box of 60mm drawing height with 10 segmental binders is adopted to validate the optimization strategy. The constant BHF experiment and the derived trajectory of optimal BHF are verified on a multipoint variable BHF hydraulic press and the experiment results correspond well with those of FEM optimization. This new BHF optimization strategy helps to determine time and spatial optimal BHF profiles simultaneity in a single round of FEM simulation, which makes it an effective method. [Copyright &y& Elsevier]

Abstract: A new thermo-mechanical treatment using resistance heating is devised to produce fine grained aluminum alloy sheets. To examine the effectiveness of the treatment, simulating experiments are conducted using a heat-treatable 6061 aluminum alloy, and the grain size, hardness property, and tensile properties are measured and compared with those of the conventionally heat-treated sheets. The results are summarized as follows: (1) resistance heating at a current density of about 100Amm−2 realizes heating the aluminum alloy sheet into the solution temperature range in 2s, (2) complete achievement of rapid solution treatment by the resistance heating requires the condition that the precipitates exist finely in the matrix, (3) the new treatment decreases the grain size by approximately one-half but the mechanical properties are not remarkably improved. [Copyright &y& Elsevier]

A so-called damage percolation model is linked with a finite element model of a sheet forming process to offer a comprehensive study of ductile damage evolution. In the current study, a damage percolation code is linked with LS-DYNA, an explicit dynamic FEM code used to introduce local strain gradients and compliance effects due to damage-induced softening. The linked model utilizes a Gurson-based yield surface to account for the softening effects of void damage, while the local damage development and void linkage events are modeled using the damage percolation code. The percolation code accepts detailed second phase particle fields from image analysis of a 2.0×1.6 mm optical micrograph of AA5182 aluminum alloy sheet. The model is applied to a stretch-flange stamping process which is known to be a damage-sensitive operation. The critical conditions for fracture are predicted for various initial stretch flange hole sizes. [Copyright &y& Elsevier]

• Proposed a new test method for characterizing fracture limits in non-linear strain paths. • Characterized fracture limits in non-linear strain paths with the pre-strain path between simple shear and uniaxial tension. • Proposed a new ductile fracture criterion considering tension and shear fracture mechanisms. • Assessed capability of four models to predict fracture limits in non-linear strain paths. A good knowledge of forming limits at fracture (FLF) for aluminum sheets exhibiting poor formability at room temperature in various non-linear strain paths (N-LSPs) is essential for fully exploiting their forming ability and avoiding their fracture failure. However, the FLF over a wide range of strain states in N-LSPs with pre-strain paths between uniaxial tension and simple shear cannot be determined through the existing two-stage loading test methods. To solve the problem and fill the gap, a new two-stage loading test method employing an optimized butterfly specimen is proposed in this paper, in which strain path changes are controlled by changing biaxial loading conditions acting on the specimen. To validate the capability of the new test method to characterize the FLF in the N-LSPs and investigate the effect of the loading path changes on aluminum 6K21-T4 sheet formability at fracture, different proportional and non-proportional loading experiments using the butterfly specimen obtained from the aluminum sheets are performed. Experimental results indicate that the forming limit strains at fracture over a wide scope of strain states in the N-LSPs can be effectively determined by utilizing the proposed method, thus filling the gap mentioned above. Additionally, four newly developed ductile fracture criteria (a new model proposed in this paper, Hu−Chen 2017, Lou−Huh 2012 and MMC3) together with a non-linear damage accumulation rule (N-LDAR) are employed to forecast the FLF for the 6K21-T4 sheets in the N-LSPs. The results show that both the proposed new model with the N-LDAR and the Hu−Chen model along with the N-LDAR can provide the highest prediction accuracy for the FLF in the N-LSPs. However, the prediction accuracy of the proposed model is much higher that of the Hu−Chen 2017 model for aluminum alloy 5083-O sheets. Image, graphical abstract [ABSTRACT FROM AUTHOR]