•Directional properties of EDD and AA5052 predicted using Hill48 and Yld2000-2d model.•Predicted yield loci were calibrated using tensile and stack compression test data.•Failure limits were ...estimated implementing anisotropy yield theory in MK and BW model.•Use of polar effective plastic strain based limits was demonstrated through case studies.•Predictive accuracy of estimated fracture limit was validated in 3D triaxiality locus.
In the present study, experimental and theoretical analyses were performed to predict the failure strain of EDD and AA5052 sheet metals. In this context, uniaxial tensile tests and stack compression tests were conducted to assess the anisotropic constants of two different yield models viz. Hill48 and Yld2000-2d. Further, the calibrated models were used to estimate the directional properties and yield loci of the investigated sheet metals, and the results were successfully validated with the experimental data. Additionally, the forming limit diagram (FLD) and fracture forming limit diagram (FFLD) were analytically predicted using Marciniak–Kuczyński (MK) model and Bao–Wierzbicki (BW) ductile damage model implementing different yield theories. The estimated failure limits were compared with the experimental necking and fracture strain data obtained from the punch stretching (PS) tests, and found that the theoretical models incorporating Yld2000-2d yield theory best described the experimental limiting strains. Furthermore, the best predicted MK-FLD and BW-FFLD was used for failure strain analyses of three different sheet metal forming experiments such as two-stage forming, single point incremental forming (SPIF) and deep drawing. It was observed that the MK-FLD and BW-FFLD failed to predict the necking and fracture strain of different pre-strained sheets in the principal strain locus. Hence, all the strain data were transposed into polar effective plastic strain (PEPS) locus using Yld2000-2d yield model, and the PEPS based failure limit was developed. It was found that the MK-FLD and BW-FFLD predicted the respective limiting strains in PEPS locus efficiently. Moreover, all the experimental fracture strains were converted into 3D stress triaxiality locus and concluded that the calibrated BW fracture loci had a good predictive efficiency of all the fracture strains obtained from various forming tests.
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In existing electromagnetic sheet metal forming processes, the sheet metal is typically deformed away from the coil under repulsive Lorentz forces. This deformation mode makes it difficult to apply ...the forming technology to dent repair without disassembly of the automobile body and aircraft fuselage. To solve this problem, a new electromagnetic attractive forming process with a low-frequency discharge current was developed in this work. Different from previous attractive forming methods, only a single coil and a single power supply are required that is low cost and easy to implement. Both numerical and experimental studies have demonstrated that an AA1060-H24 aluminum alloy sheet with a thickness of 1 mm can be effectively attracted towards the coil with a maximum deformation of more than 8 mm after a single discharge. More importantly, the mechanism of the attractive forming process has been clarified in detail through the analysis of the Lorentz force characteristics and deformation process of sheet metal. It has been pointed out that the current waveform after the first peak plays a vital role in improving the attractive force and the attractive forming process, which can be optimized by introducing a crowbar circuit. Meanwhile, it is found that the deformed shape of sheet metal caused by a repulsive force helps to facilitate the subsequent reverse deformation under an attractive force. This is also an important reason why an obvious attractive forming can be achieved, although the attractive force is much smaller than the repulsive force during the forming process. The obtained results have the significance for fundamental understanding of electromagnetic forming process, and further applications can be expected using the developed forming method.
While the first generation of floating photovoltaics (FPV) was designed for operation in freshwater reservoirs, the technology is currently expanding to marine territories. In this paper, an FPV ...structure made from formed aluminum alloy sheets in AA5083-H111 is subject to a multi-stage numerical investigation in LS-DYNA. Quasi-static directional tensile experiments and disc-compression tests are conducted to characterize the plastic anisotropy of the rolled aluminum sheets. An anisotropic yield criterion with associated flow rule and combined isotropic-kinematic strain hardening is employed to simulate the drawing and springback of a subsection of the full structure, obtaining predictions of residual stresses, effective plastic strains, thickness change, and the process-induced geometrical imperfections. In order to analyze the performance of the formed structure under operational loads, a novel approach for submodeling that overcomes the usual requirement of precise geometric compliance enables driven variables to be obtained from a global service load model that is based on the idealized computer-aided design. The method is used to analyze geometrical, mechanical, and material-related process effects on operational stresses that are important to consider in fatigue analysis. Residual stresses were confirmed to significantly affect fatigue, while the stress increase often seen as a result of material thinning was essentially eliminated by the redistribution of internal forces. Furthermore, a parametric investigation showed that the magnitudes of the residual stresses largely depend on the alloy’s kinematic hardening properties, emphasizing the importance of proper plasticity models.
•The friction model in the mixed lubrication regime is presented.•Model uses measured workpiece and tools surface topographies.•The lubricant pressure is determined using the average Reynolds ...equation.•Flow factors are determined for measured surface topographies.•The model is implemented in FE code for forming simulations.
In deep drawing processes, mixed lubrication friction regime is common in which the friction condition is governed by solid–solid asperity contacts and lubricant pressure. In this study, a friction model in the mixed lubrication regime is developed that accounts for the effect of the surface topographies of sheet and tool on the lubricant pressure distribution. The overall friction due to solid–solid asperity contacts and lubricant pressure is determined using a coupled hydrodynamic and boundary friction models. The model is utilized in an in-house FE code (DiekA) for deep drawing simulations. In the FE simulations, the lubricant pressure is determined by solving the average Reynolds equation. The flow factors required in the average Reynolds equation are determined separately using measured tool and sheet surface topographies. Cross-die experiments are performed at different lubricant amounts to validate the friction model at a component level. The results show that punch force vs. displacement and strain field from experiments and FE simulations (using the new friction model) correlate very well.
This paper presents a user-friendly function under non-associate flow rule to capture anisotropic hardening (or evolution of yield surface) and the curvature of yield loci for body-centred cubic ...(BCC) and face-centred cubic (FCC) under the proportional loading conditions. The calibrated model for BCC and FCC metals is applied to illustrate the hardening behavior of uniaxial tension along different loading directions and of the equibiaxial tension for several steels and aluminum alloys (718AT, QP980, AA5182-O and AA 6xxx-T81) to evaluate its accuracy. The prediction is compared with the experimental results and modeling results of several popular plasticity models. The comparison demonstrates that the proposed model is pressure-insensitive, relatively simple for numerical implementation, capable of illustrating the different yielding behaviors between BCC and FCC metals and, capable of accurate modeling of flow curves under directional loading directions and equibiaxial tension both under the plane stress and triaxiality loading conditions. The proposed model is also flexible on adjusting the curvature of the yield surface between uniaxial tension and equibiaxial tension. Accordingly, the proposed anisotropic hardening model is useful to illustrate anisotropic hardening behaviors under uniaxial and equibiaxial tension.
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•An anisotropic hardening model is proposed as a function of the second and third stress invariants.•The model is pressure insensitive under non-associate flow rule.•The model can differentiate the yielding behavior between BCC and FCC materials.•The flow curves under uniaxial tension along RD, DD, TD and equibiaxial tension are precisely modelled.•The model can also illustrate the anisotropic hardening behavior under spatial loading.
The hole expansion test is an appropriate evaluation method for assessing the formability of automotive parts, where fracture prediction using simulated localized thickness is crucial. However, the ...accurate thickness prediction in the hole expansion test remains challenging. In this study, the selection of yield functions and calibration strategies were investigated to accurately predict the thickness of advanced high-strength steel subjected to the hole expansion test. An accurate description of the material anisotropy is important for thickness prediction because of the generation of various multiaxial stress states. To describe plastic anisotropy, a series of uniaxial tension, bulge, and in-plane biaxial tension tests were conducted on DP980 steel. Because conventional biaxial tension tests for DP980 steel showed a small strain range owing to its low ductility, a new laser-welding-reinforced biaxial tension test was developed to investigate the anisotropy of the plane strain at large strains. Differences in the ratio of the plastic strain rates were observed between the conventional and new tests. Finally, a hole expansion test and corresponding finite element simulations were conducted with different yield functions and calibrations for the Yld2000–2d yield function. The thickness strain profiles along the hole circumference and 3 mm inward were measured and predicted using simulations. In conclusion, both the yield stress and the ratio of plastic strain rates in the plane strain state were equally important for accurate thickness prediction during the DP980 hole expansion test. Furthermore, the crack location was inconsistent with the thinnest region in the experiment, which might be because of the shear fracture anisotropy encountered in DP980 steel.
•New laser welding assisted biaxial tension test to characterize large plastic strain in plane strain.•Investigated Yld2000-2d calibration strategies to use different inputs.•Simultaneously important strength and plastic strain ratio of plane strain for thickness prediction in hole expansion.•Crack direction not corresponding to thinnest position owing to shear fracture anisotropy in AHSS.
•A constitutive model based on the non-associated flow rule was developed for orthotropic anisotropic materials.•This model was constructed by coupling a non-quadratic function and a quadratic ...function for higher modeling accuracy.•A framework to continuously capture the anisotropic hardening throughout the loading process was proposed and explained.•The model can be applied under a general three-dimensional stress condition.•The model is easy to be implemented and user-friendly for practical use.
An anisotropic constitutive model based on the non-associated flow rule that is combined with non-quadratic and quadratic functions was developed for orthotropic anisotropic sheet metals. The non-quadratic Barlat's YLD91 function was applied for the description of the anisotropy in the yield stresses, and the classical quadratic Hill48 function was adopted to describe the anisotropy in the plastic deformation. A continuous scheme for capturing the anisotropic hardening based on the implicit YLD91 function was proposed for higher modeling accuracy. The anisotropic parameters can be obtained from three directional uniaxial tensile tests and a hydraulic bulge test. The developed model can be applied under a general three-dimensional condition. The developed model was implemented into the finite element code ABAQUS as a user material subroutine (UMAT). To evaluate the capability of the developed model, directional uniaxial tension and prediction of the yield surface were considered, and a circular hole expansion process with the JSH590R sheet were simulated using different material models. A suitable static-implicit analysis and solid elements were applied. The comparison between the experimental and simulation results indicates that the modeling accuracy can be improved by applying the developed model. Furthermore, the simple formulations can also contribute to cost saving in the parameter acquisition process and computation. It is concluded that the developed anisotropic model can be used as an alternative and user-friendly method in solving the common industrial problems with large plastic deformation.
An accurate description of the material yielding behavior is of great importance for a trustworthy prediction of complicated forming processes via numerical analysis. For metal sheets, the work ...hardening rate, in general, varies according to the loading directions and conditions due to the texture developed during cold rolling processes, and accordingly, the yield surface evolves with a variation of its shape and size during plastic deformation. The non-uniform evolution of the yield surface becomes a non-negligible issue especially for the materials showing the severe tension/compression asymmetry on the yielding behavior with respect to the loading direction. A primary concern here is that the advanced yield criteria previously developed normally feature an isotropic expansion of the yield surface which is determined at an initial yielding stage and thereby neglect the evident changes in the shape of the yield surface as implied by experimental tests. In this paper, a solution to the challenge of modeling a general criterion, which accurately describes the evolution of the anisotropy/asymmetry-induced distortional yielding behavior, is proposed using neither any interpolation nor optimization techniques for the calibration of the yield surface. The new criterion is proposed based on the Stoughton and Yoon (2009) criterion, which features non-associated flow rule, with the multiplication of two additional terms referred to as scaling and asymmetry functions. The proposed criterion was successfully applied to various types of metallic materials to validate its noticeable flexibility and general applicability in describing the anisotropic/asymmetric yielding behavior. An extensive comparison of the experimental results with the predictions from the proposed criterion reveals that the proposed criterion provides sufficient predictability on the subsequent evolution of the anisotropy/asymmetry-induced distorted yield surface for various metallic materials over a broad range of plastic strain level, strain rate, and temperature.
•The evolution of the anisotropy/asymmetry-induced distortional yielding behavior is proposed.•The new criterion is proposed based on the Stoughton and Yoon (2009) criterion, which features non-associated flow rule.•The proposed criterion was successfully applied to various types of metallic materials.•The proposed criterion provides sufficient predictability on the subsequent evolution of the distorted yield surface.
As a promising solution to the growing demand for lightweighting, hot stamping has gained considerable applications in the automotive industry. Over the past few decades, the market for hot stamping ...has experienced explosive growth, with ongoing advancements offering potential for further expansion of its applications. This paper provides a historical overview of hot stamping alongside an in-depth analysis of future trends. Scientific publications, patents and industrial applications of hot stamping are systematically reviewed, with major developments in materials, processes, tools, and other relevant aspects being highlighted. Through data analysis, the current state of hot stamping is comprehensively depicted, and the trends in the development of hot stamping are revealed. Additionally, the future of extending hot stamping technologies to a broader range of materials is discussed, with suggestions furnished from both academic and industrial perspectives.
This paper aims to develop a lightweight convolutional neural network,
WearNet
, to realise automatic scratch detection for components in contact sliding such as those in metal forming. To this end, ...a large surface scratch dataset obtained from cylinder-on-flat sliding tests was used to train the
WearNet
with appropriate training parameters such as learning rate, gradient algorithm and mini-batch size. A comprehensive investigation on the network response and decision mechanism was also conducted to show the capability of the developed
WearNet
. It was found that compared with the existing networks,
WearNet
can realise an excellent classification accuracy of 94.16% with a much smaller model size and faster detection speed. Besides,
WearNet
outperformed other state-of-the-art networks when a public image database was used for network evaluation. The application of
WearNet
in an embedded system further demonstrated such advantages in the detection of surface scratches in sheet metal forming processes.
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