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•The original and shear-modified GTN ductile fracture criteria are utilized during the stretch bending process.•The original GTN model can be used only in processes where the stress ...state is the same as the calibration test stress state.•The evolution of damage, principal strains, and displacement of fractures under different forming conditions are investigated.
In this paper, the original and shear-modified GTN ductile fracture criteria are utilized to investigate the fracture behavior of the AA6061-T6 aluminum alloy sheet during the stretch bending process. An appropriate calibration strategy is presented to find the unknown coefficients of the fracture models. In this way, different tension tests such as uniaxial tension, plane strain, notched tension, and shear tension specimens are utilized. Results show that the shear-modified GTN model calibrated by the mentioned tension tests is able to predict the onset of fracture of the stretch bending process with a 5% error, while the original GTN model, calibrated by the uniaxial tension is unable to predict the fracture properly. Since the accuracy of fracture prediction depends on the stress state, the effects of the calibration test on onset of fracture were investigated. It is shown that using the original GTN model with a proper calibration test (plane strain tension) can achieve a good accuracy with 3.5% error in the stretch bending process. In addition, results show that any change in the friction coefficient and bending radius in the stretch bending process can lead to different fracture behavior. Several investigations are carried out to examine the evolution of damage and displacement of fractures in the stretch bending process under different forming conditions.
•Measured monotonic tension, compression, and load reversals data for three steels are used to adjust parameters of the FE-EPSC model.•Geometrical shape changes after U-draw/bending forming are ...predicted using the FE-EPSC multi-level simulation framework.•Accounting for backstress fields is revealed as critical for the accurate predictions of part geometries upon U-draw/bending.•Hardening and carrying over residual stress fields are essential for predicting part shape changes involving pre-strained sheets.•Increase in the amount of springback with sheet strength is determined by simulating U-draw/bending of DP 590 and DP 1180.
This work is concerned with predicting geometrical shape changes in sheet metal forming using a multi-level simulation framework that considers the directionality of deformation mechanisms acting at the single-crystal level and microstructural evolution. The multi-level model is an elasto-plastic self-consistent (EPSC) homogenization of single-crystal behavior giving the constitutive response at each finite element (FE) material point. Numerical solution of a boundary value problem over geometry is then obtained using continuum finite elements at the macro-level. First, a set of model parameters for the evolution of slip resistance of ferrite and martensite and backstress are established by fitting a comprehensive set of mechanical data for dual-phase (DP) steels 590, 780, and 1180 using one-element model. Next, the potential of the FE-EPSC modeling framework is illustrated by carrying out a set of hat-shaped draw-bending simulations of the steel sheets. The evolution of geometry after hat-shaped draw-bending and springback is predicted and verified with experimental measurements for as-received DP 780. In doing so, the role of accounting for backstress is revealed as critical for the accurate prediction of the part geometry. The same process simulation involving a pre-strained sheet of DP 780 is compared with a corresponding experiment to reveal the role of strain hardening and residual stress on the subsequent part shape changes after the hat-shaped draw-bending test and springback. Finally, the same process simulations involving DP 590 and DP 1180 are performed to confirm the effect of strength on the geometrical shape changes of the sheets after springback.
The simulation of manufacturing processes has significant importance. The research and development of metal forming simulation started in the 1960s from the elastoplastic analysis of a simple plastic ...deformation, and it now covers a wide range of forming processes. The accuracy and applicability of metal forming simulation have significantly progressed, driven by the development of plasticity theory and numerical methods such as the remeshing technique and contact analysis algorithm. Now the targets of metal forming simulations are undergoing a transition from the macroscale analysis of deforming bodies to coupled analyses of deformations of deforming bodies and tools, and multiscale analyses of microstructure and texture. Past achievements of metal forming simulation show that it has reached the level of ‘visualizing forming phenomena’, but it will continue to evolve in the digital era, impacting the digital society and factories of the future, where machines work autonomously without human intervention. Emergent technologies require advanced materials, augmented reality, and, of course, metal forming simulation. In this paper, we reinforce the role of simulation as a means of performing computational (virtual) experiments and as a tool for the high-fidelity numerical visualization and quantification of unknown, unmeasurable, and invisible phenomena in formed components and their assembly. We will also discuss simulation–machine interactions, such as online simulation with process operation, to realize the triad of ‘process operation – data – simulation’ in the near future.
A model for the evolution of ductile damage in the sense of void fractions using artificial neural networks (ANN) is proposed. In contrast to constitutive damage models, the damage prediction is ...solely based on experimental data and has no underlying assumptions for the damage evolution law. This guarantees that the experimental observations are captured correctly. High resolution experimental void data obtained by scanning electron microscopy with a minimum single void area of 0.02 μm2 are used as training data. The loading state is obtained from finite element simulations. The equivalent plastic strain is used to describe the load amplitude and the triaxiality as well as the normalised Lode angle are utilised to characterise the loading type. Different strategies for the training of the model as well as the prediction are analysed. The model is used to visualise the loading state-dependent damage evolution. Furthermore, it is applied to two different bending processes. It is shown that the prediction quality highly depends on the experimental and numerical data used for training. If the loading states of the application problem are within the domain of the training data, the prediction quality is good and even better than constitutive models used in literature.
In order to predict defects, improve performance, and streamline operations, machine learning techniques are becoming ever more indispensable in manufacturing processes, mainly in sheet metal ...forming. Incorporating neural networks into the process of sheet metal forming is the subject of this article's exhaustive examination of recent developments and applications. Exploring datasets from a variety of sheet metal forming processes, numerous machine learning models, including ensemble and single learning techniques are investigated. The functionality of this method extends to various tasks, including the prediction of springback in cold-rolled anisotropic steel sheets. The review provides a conclusion section that presents the main implementation methodologies and how they address to some manufacturing issues.
The energy demand and CO2 emissions of the steel processing industry are a global challenge. During conventional steel processing, the treatment of iron ore and steel in a molten state heavily ...contributes to this problem. This paper provides an in-depth investigation of the benefits and technical requirements of an alternative processing pathway with minimal energy and CO2 burdens. Our proposed method, scrap metal consolidation (SMC) by rolling, is adapted from roll bonding, a scalable metal bonding technique, commonly used for niche composite applications to achieve material properties unattainable by monolithic alloy design. SMC transforms steel scrap into hot rolled steel in solid state without melting. Based on pre-published high-fidelity industrial data, we determined that processing hot rolled steel from scrap in the solid state would consume 94% less energy compared to the primary steel processing route with 94% less CO2 burden. Compared to conventional recycling methods, the energy savings of SMC would be 86%, with an 84% decrease in CO2 emissions. The proposed method is described in detail, and the process windows for AISI 1008 mild steel and SS304 stainless steel were determined in terms of rolling temperature and reduction using a lab-scale rolling mill at a temperature range of 700–1100 °C. The formability of the consolidated mild steel is also evaluated via the hemisphere punch test, a standard industrial test for assessing the formability of sheet metals. While the fracture height of consolidated specimens is in the 9.27–10.62 mm range, the monolithic sample has a fracture height of 10.34 mm. The test results show that the consolidated sheets have comparable formability to monolithic specimens. These investigations altogether demonstrate that SMC-by-rolling is a feasible and environmentally sustainable alternative for conventional steelmaking or recycling processes.
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•Solid-state consolidation of steel scrap uses 94% less energy than primary processing.•Compared to recycling, scrap metal consolidation saves 84% of process CO2 emissions.•Process boundaries for mild and stainless steel follow a reverse S-curve trend.•Test results exhibit comparable formability for roll-bonded and monolithic samples.•Most sheet metal forming operations don't cause opening stress, reducing failure risk.
Due to the change from mass production to mass personalized production and the resulting intrinsic product flexibility, the automotive industry, among others, is looking for cost-efficient and ...resource-saving production methods to combining global just-in-time production. In addition to geometric manufacturing flexibility, additive manufacturing offers a resource-saving application for rapid prototyping and small series in predevelopment. In this study, the FDM process is utilized to manufacture the tooling to draw a small series of sheet metal parts in combination with the rubber pad forming process. Therefore, a variety of common AM polymer materials (PETG, PLA, and ABS) is compared in compression tests, from which PLA is selected to be applied as sheet metal forming die. For the rubber pad forming process, relevant processing parameters, i.e., press force and rubber cushion hardness, are studied with respect to forming depth. The product batch is examined by optical evaluation using a metrological system. The scans of the tool and sheet metal parts confirm the mechanical integrity of the additively manufactured die from polymer and thus the suitability of this approach for small series in sheet metal drawing processes, e.g., for automotive applications.
•A stress-based shear ductile fracture criterion is proposed to improve the prediction accuracy of failure for lightweight metals.•The mechanical behavior of AA5182-O sheet is uncovered from tension ...to equibiaxial tension.•The direct and inverse engineering methods are adopted to calibrate the fracture parameters.•The stress state-related fracture behavior of AA5182-O is numerically simulated.•The fracture limits of AA2024-T351 alloy from compression to tension is described by the sDF2016 criterion.
Failure in lightweight metal forming is a big challenge currently and prevents their widely application in weight reduction of automobile and aerospace structures. A stress-based shear ductile fracture criterion is introduced in this study to improve the prediction accuracy of failure for lightweight metals. The criterion (sDF2016) is developed based on the DF2016 criterion thereby endowing the criterion with the precise fracture predictability under wide stress states of shear, uniaxial tension, plane strain tension and equibiaxial tension. Besides, the criterion takes into account the stress state effect on fracture in a form of the stress triaxiality, the maximum shear stress and the Lode parameter. The sDF2016 criterion is also expected to be less sensitive to strain path changing effect because sDF2016 describe the onset of fracture in stress space. For the verification of the proposed sDF2016 criterion, the experiments are carried out for AA5182-O sheet with central hole, notched, in-plane shear and bulging specimens. Plastic deformation is accurately modeled by the Swift-Voce hardening law and the Drucker yield function. The sDF2016 criterion is then calibrated both by the direct and inverse engineering approaches, which is applied to predict fracture initiation under distinct stress states. The modeled result indicates that the calibrated sDF2016 criterion based on the inverse engineering method predicts the fracture stroke with a higher accuracy than the direct approach. The sDF2016 criterion is also used to depict fracture limits of AA2024-T351 alloy from compression to tension. The application shows that the proposed ductile fracture criterion is capable of modeling the fracture limits for sheet metals under various loading conditions from shear to plane strain tension.
The role of friction in the forming of automotive parts composed of ultra-high-strength lightweight metals has become increasingly important as industry attempts to overcome inferior formability and ...springback against enhanced strength. At the tool-design stage, finite-element simulations should use more accurate and efficient friction models that account for complex friction behavior between the metal and tool surfaces. Complex friction behavior is commonly dependent on contact pressure, sliding velocity, microscale surface effects (or roughness), and lubrication, among other factors. This study presents a microscale, asperity-based friction model of mixed-boundary lubrication. The developed hydrodynamic friction model is based on the load-sharing concept, which considers the lubrication area and metal-to-metal contact separately. Lubricant film thickness is calculated to couple the existing boundary lubrication model, and film lubrication behavior is formulated using finite-element programming of the Reynolds equation to obtain the hydrodynamic pressure. The proposed computational framework is validated by simulating an in-line incremental die-forming process. The result shows that the predicted friction law with multi-scale, mixed-boundary lubrication can be efficiently applied to realistic sheet-metal-forming simulations with reasonable accuracy by accounting for complex frictional behavior.
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•The asperity-based friction model of mixed boundary lubrication is presented.•The hydrodynamic pressure and file thickness can be calculated via new friction model.•The new friction model effectively integrates the concept of load-bearing.•Complex frictional behavior is accounted in the real sheet-metal-forming process.
Isogeometric analysis (IGA) has been used with great success when combined with incremental methods to simulate sheet metal forming. In this paper, we present the development of one-step inverse IGA ...based on the total deformation theory of plasticity. For a large number of industrial stamping parts, the membrane effects are dominant. Thus, we adopted an isogeometric membrane element to predict the flattened contour of the initial blank from the energy-based initial solution estimation approach. In addition, we used the Newton–Raphson algorithm for nonlinear plastic iterations to evaluate the thickness and equivalent strain and stress of the final stamping parts. We applied our framework to square box and S-rail surface models for demonstration. The results for these two examples illustrate the performance of one-step inverse IGA and its applicability to the integrated design of sheet metal forming.
•We develop a one-step inverse isogeometric analysis method for simulating sheet metal forming.•The isogeometric membrane element is adopted to predict the flattened contour of initial blank.•We use Newton–Raphson algorithm to evaluate the thickness and equivalent strain/stress of the final stamping parts.•Numerical examples illustrate the performance of one-step inverse IGA and its applicability to the integrated design of sheet metal forming.
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