https://popups.uliege.be/esaform21/index.php?id=88 Coordinator: Dr. Gabriela Vincze Co-organisers: Prof. Frederic Barlat, Prof. Toshihiko Kuwabara, Prof. Dorel Banabic, Dr. Holger Aretz, Dr. Sam Coppieters, Prof. Sandrine Thuillier Description: The aim of this mini-symposium is to discuss the formability of metallic materials. Namely, their ability to undergo plastic deformation and result in products with minimum damage and defects. Limiting mechanisms are not restricted to plastic flow localization, fracture and spring back, which are only a few examples under consideration. Contributions based on experimental, theoretical and numerical approaches and leading to a better understanding of the relationship between material properties, mechanical and thermal loading, and other environmental constraints on the formability of metallic materials are encouraged. Mini Symposia fr Wed, 03 Mar 2021 09:37:33 +0100 Wed, 14 Apr 2021 09:58:13 +0200 https://popups.uliege.be/esaform21/index.php?id=88 0 https://popups.uliege.be/esaform21/index.php?id=1511 Warm forming is widely used as increasing the temperature is a solution to improve the formability of aluminum alloys. The stress (or strain) state is one of the most important factors affecting the formability of metals. In warm forming, the temperature and strain rate also play an important role on the deformation and fracture behavior. Figuring out the relationship between formability, temperature, strain rate and stress state is of great importance for providing more understanding of ductile fracture in warm forming conditions. Therefore, the objective of this work is to investigate the influence of temperature on the ductile fracture of a 6000 series aluminum alloy sheet metal under different stress states. Dogbone specimens, notched tensile specimens with different radius, tensile specimens with a central hole and shear specimens are used to cover a wide range of stress states. The hybrid experimental-numerical approach is used to identify the fracture strain and the corresponding stress state parameters (i.e. stress triaxiality and Lode parameter). To this end, fracture tests are carried out at 200°C using a tensile machine to determine the instant of fracture. Numerical simulations of the tensile tests are performed in 3D with the finite element code Abaqus to predict the strain field and calculate the evolution of the stress state. To accurately model the material behavior the positive strain rate sensitivity in the flow stress response at elevated temperature is considered. The results show a strong dependency of the ductile fracture on the temperature, strain rate and stress state. Mon, 22 Mar 2021 20:05:42 +0100 https://popups.uliege.be/esaform21/index.php?id=1511 https://popups.uliege.be/esaform21/index.php?id=1525 The accurate prediction of forming defects is fundamental for the virtual try-out of metallic sheet components. However, the constitutive model can have a strong impact on the numerical predictions, namely the cup earing, the occurrence of wrinkles and the tearing failure. The process conditions considered in this work are the ones established for the “Benchmark 2 – Cup Drawing of Anisotropic Thick Steel Sheet”, proposed under the Numisheet 2018 international conference. The axisymmetric cups are obtained from a steel sheet with 2.8 mm of thickness, resorting to different process conditions to induce different defects. The advanced yield criterion proposed by Cazacu and Barlat is used to define the anisotropic behavior of the blank. The calibration of the material parameters is carried out by fitting the following experimental data from: (i) uniaxial tensile tests performed in every 15º to the rolling direction; (ii) biaxial tension tests to evaluate the directions of the plastic strain rates in the first quadrant of the yield loci. The numerical predictions are compared with the experimental measurements, allowing to assess the accuracy of the finite element model to predict each type of forming defect. The cup earing and the strain localization are accurately predicted, while the wrinkles amplitude is clearly underestimated. Mon, 22 Mar 2021 20:07:36 +0100 https://popups.uliege.be/esaform21/index.php?id=1525 https://popups.uliege.be/esaform21/index.php?id=1536 The hydraulic bulge test represents an effective experimental method to characterise sheet metals since the equivalent strains before failure are much larger than those measured during tensile testing and there is nearly no frictional effect on the results. Recently this test has been proposed not only for extracting data concerning the equi-biaxial strain condition, but to determine the forming limit diagram (FLD) in the range of positive minor strains. In the proposed methodology, different strain paths can be obtained by merely using a test blank having two holes with a suitable geometry and position to be tested, without the need of dies with elliptical apertures. However, a carrier sheet is necessary, thus implying results may be affected by friction effects. This paper proposes a new methodology for the determination of the right side of the Forming Limit Curve (FLC), based on the adoption of local heat treatments aimed at determining different strain paths on the blank to be tested while using the classical circular die for bulge tests. In particular, the formability of the alloy AA5754-H32 was investigated; 3D Finite Element simulations were conducted setting different laser strategies and monitoring the resulting strain path. Results revealed that the proposed methodology supports obtaining many additional points in the right side of the FLC, thus being effective and friction free. Mon, 22 Mar 2021 20:08:58 +0100 https://popups.uliege.be/esaform21/index.php?id=1536 https://popups.uliege.be/esaform21/index.php?id=1621 Among processes involving plastic deformation, sheet metal forming requires a most accurate description of plastic anisotropy. One of the main sources of mechanical anisotropy is the intrinsic anisotropy of the constituent crystals. In this paper, we present the single-crystal yield criterion recently developed by Cazacu et al. [1] and its application to the prediction of anisotropy in uniaxial tension of strongly textured polycrystalline sheets. Namely, it is shown that using this single crystal yield criterion the Lankford coefficients exist and have finite values for all loading orientations. Moreover, the variation of both the yield stress and Lankford coefficients with the crystallographic direction can be expressed analytically. An application of this criterion to forming a cylindrical cup from a single crystal of (100) orientation is presented. Finally, we show that using this single-crystal model, one can describe well the effect of the spread around an ideal texture component on the anisotropy in uniaxial tensile properties of a polycrystal. Mon, 22 Mar 2021 20:18:49 +0100 https://popups.uliege.be/esaform21/index.php?id=1621 https://popups.uliege.be/esaform21/index.php?id=1640 The manufacturing of oval tubes for automotive components from sheets consists of several steps, from the flat sheet to a tube with expanded ends. It involves roll-bending of tubes, welding and several expansion processes with segmented tools. Forming steps in this process are subject to springback after the release of tools. Finite-element-simulations offer an efficient method to predict the springback behavior. For the industrial application it is important to identify the processes which contribute significantly to springback. At first glance one might expect that the consideration of the whole process chain is required to predict the final shape of such tubes. It turns out, that springback is related to the later stages of the process. The difference in springback behavior of circular and oval tubes is investigated. A simulation model is validated on the basis of experiments for circular tubes and applied to predict the final shape of oval tubes. This offers the perspective to adjust the tooling design at an earlier design stage to respect all the influences in the process on the final geometry and therefore meet tighter tolerances. Mon, 22 Mar 2021 20:21:14 +0100 https://popups.uliege.be/esaform21/index.php?id=1640 https://popups.uliege.be/esaform21/index.php?id=1961 Two categories of experiments have been performed to obtain the experimental forming limits of a ferritic stainless steel from uniaxial to equibiaxial tension, including Nakajima tests and tensile tests of flat specimens with different geometries of the central hole as well as the notched dog bone. The plasticity behavior of the investigated material is described using an evolving non-associated anisotropic plasticity model, which is calibrated based on experimental results of uniaxial tensile tests along different loading directions. A damage mechanics model is calibrated and validated based on the global force and displacement response of tensile tests. Finite element simulations of the Nakajima tests and the tensile tests of various geometries have been performed using the anisotropic material model. A novel spatio-temporal method is developed to evaluate the forming limits under different stress states by quantitatively characterizing the plastic strain distribution on the specimen surface. The forming limits have been independently determined from finite element simulation results of tensile specimens and Nakajima specimens using the spatio-temporal evaluation method. The forming limits obtained from numerical simulations of these two types of experiments are in good agreement with experimental results. Tue, 23 Mar 2021 11:21:39 +0100 https://popups.uliege.be/esaform21/index.php?id=1961 https://popups.uliege.be/esaform21/index.php?id=2168 Automotive stamping is a multi-stage process where a sheet material is drawn in first stage and then redrawn, flanged and pierced in subsequent stages. In the first draw stage, continuous strain path change is induced in the material while a discontinuous strain path change occurs when the material is processed in the subsequent stages of a multi-stage stamping operation. The strain path transition can potentially alter the forming limit of the material. Previous research has investigated the effect of the discontinuous mode of strain path change by loading the sample in one strain path, unloading it, then reloading it in a second path. Thus, discontinuous strain path change was obtained. In this work, the effect of continuous strain path change was investigated with a novel experimental design that allowed cruciform samples to change strain path continuously without unloading. The work was carried out in two stages. In the first stage, the design of the cruciform sample was verified with finite element modelling to ensure the occurrence of continuous strain path change and this was validated experimentally using DX54 material by capturing full-field strain measurements data using digital image correlation technique. The size of the experimental apparatus permitted it to be placed inside a scanning electron microscope chamber. In the second stage, the validated test method was used to evaluate microstructural changes during the deformation including full-field strain and texture evolution. The micro-strain evolution showed rotation of strain bands while the texture evolution conveyed grain rotation during continuous strain path change. Tue, 23 Mar 2021 14:01:05 +0100 https://popups.uliege.be/esaform21/index.php?id=2168 https://popups.uliege.be/esaform21/index.php?id=2509 Air bending is a widely used method for forming ultra-high strength steels (UHSS). However, the limited formability of UHSS poses some challenges for the bending process in the form of strain localisation, surface defects, punch detachment (multi-breakage) and pseudo-polygonal “nut-like” shape of the bend. In this study, the bendability of three UHSS grades (700, 900 and 1100 MPa) is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. The differences in the extent of multi-breakage and the bend shapes are also studied, and these observations are correlated with the findings from the bending force and strain measurements. The differences between the investigated UHSS grades are significant. The 900 MPa grade produces more localised strain distributions and pronounced multi-breakage compared to the other grades, along with a more polygonal “nut-like” geometry. The reasons and effects of the multi-breakage phenomenon, as well as the causes for the observed differences in the behaviour of the materials are discussed in this paper. The presented results and the measurement data provide more information about the behaviour of the investigated materials in bending, and can be used for improving bending simulation, numerical models, and workshop instructions. Tue, 23 Mar 2021 20:56:14 +0100 https://popups.uliege.be/esaform21/index.php?id=2509 https://popups.uliege.be/esaform21/index.php?id=2706 Material characteristics such as yield strength, failure strain, strain hardening and strain rate sensitivity parameter are affected by loading speed. Therefore, the strain rate dependency of materials for plasticity and failure behavior is taken into account in crash simulations. Moreover, a possibility for consideration of instability at multi-axial dynamic loadings in crash simulations is the use of dynamic forming limit curves (FLC). In this study, the dynamic FLC of the press hardened automotive steel Usibor 1500 (AlSi coated 22MnB5) is investigated. The experimental results are obtained from a unique high-speed Nakajima setup. Two models are used for the numerical prediction. One is the numerical algorithm CRACH as part of the modular material and failure model MF GenYld+CrachFEM 4.2. Furthermore, the extended modified maximum force criterion considering the strain rate effect is also used to predict the dynamic FLC. The comparison of the experimental and numerical results are presented and discussed. Wed, 24 Mar 2021 18:46:39 +0100 https://popups.uliege.be/esaform21/index.php?id=2706 https://popups.uliege.be/esaform21/index.php?id=3869 The integration of forming in the fatigue modelling of cold-formed components significantly improves the predictive accuracy of the estimated life. The current study investigated the fatigue behaviour of a bent specimen made from a 5 mm thick, S900MC high strength steel plate. Because of its superior static and dynamic strength, this grade is progressively used for hollow cold-formed sections in mobile applications. However, it exhibits a strong stress saturation as well as limited formability. In this regard, a finite element modelling framework was adopted from previous research and further developed to integrate bending in the fatigue modelling and life estimation procedure. However, this framework currently ignores the possible influence of kinematic hardening and associated Bauschinger effect. For this reason, a numerical study was performed that compares isotropic with kinematic hardening for this specific application. First, the characteristic behaviour of these models was verified in a virtual tension-compression test. Subsequently, they were implemented in forming simulation followed by fatigue loading. Herein, the stress-strain evolution was investigated and a multi-axial fatigue criteria was used to map the sensitivity of the estimated life to the type of hardening. In general, the stress that entered the fatigue calculation was at least 21% lower for the kinematic model. As a result, a significant increase of 65% was observed for the estimated fatigue life, yielding a better comparison with experimental data. Mon, 29 Mar 2021 14:52:43 +0200 https://popups.uliege.be/esaform21/index.php?id=3869 https://popups.uliege.be/esaform21/index.php?id=4162 Q&P steels as a "Third Generation" of (AHSS) exhibit excellent tensile properties, which enable producing lightweight sections for the automotive industry and at the same time keep safety requirements. This research aims to predict the proper processing conditions for developing ultra-high-strength Q&P steel with a novel chemical composition of 0.37 C-3.65 Mn- 0.65Si- 0.87 Al- 1.5 Ni- 0.05P, wt. %. To design and optimize proper heat treatment conditions, the phase diagram, CCT curve, and critical temperatures of these alloys were first implemented using THERMO-CALC and JMATE PRO software and Gleeble 3500 machine. The heat treatment process included full austenitization, then quenching at 120°C followed by partitioning at 450°C for different times. The tensile properties, microstructure, and retained austenite volume fraction of heat-treated steel was studied at room temperature by tensile testing machine, optical microscope, and XRD. The finding summarized that partitioning of this steel for 100 s during processing had developed Q&P steel with ultra-high-strength of 1104 MPa with maximum total elongation and strength elongation balance 8.1 % and 8932 MPa %, respectively. The optical micrograph showed that heat-treated specimens at different partitioning times have had a microstructure of tempered martensite, carbide free bainite, and retained austenite. Besides, the retained austenite volume fraction has decreased with increasing partitioning time, which may be due to carbide precipitation during partitioning. Thu, 01 Apr 2021 01:51:44 +0200 https://popups.uliege.be/esaform21/index.php?id=4162 https://popups.uliege.be/esaform21/index.php?id=4322 In this study, a hybrid experimental and numerical investigation is implemented to characterize the plasticity and ductile fracture behavior of a high-strength dual-phase steel. Uniaxial tensile tests are conducted along the three typical directions of rolled sheet metals for the anisotropic plastic behavior, while the hydraulic bulge test is applied for the flow behavior under equiaxial biaxial tension. Further tensile tests are conducted on various featured dog-bone specimens to study the fracture behavior of the material from the uniaxial to plane-strain tension. On the numerical side, the evolving non-associated Hill48 (enHill48) plasticity model considering anisotropic hardening and plastic strain ratio evolution is employed to describe the anisotropic plastic deformation. The extended enHill48 model with damage and fracture formulation is further calibrated and validated in the study to describe the ductile fracture behavior of the steel under various stress states. Through a comparison of the results based on the evolving anisotropic model with the isotropic Mises model, it is concluded that even for materials that show only minor initial plastic anisotropy, it could develop a non-negligible influence on the large plastic deformation and the prediction of both deformation and fracture shows profound improvement with the evolving anisotropic plasticity model. Thu, 01 Apr 2021 18:06:21 +0200 https://popups.uliege.be/esaform21/index.php?id=4322