https://popups.uliege.be/esaform21/index.php?id=90 Coordinator: Prof. Semih Perdahcioglu Co-organisers: Prof. Anne Habraken, Dr. Lionel Leotoing Description: Description: Issued from an academic, a research institution or an industry, any contribution focused on material behaviour modelling from phenomenological macroscopic laws to plasticity, DDD, MD approaches is welcome. CONSTITUTIVE MODELLING FOR ANY MATERIAL: metals like Al, steel, Ti, Mg… but also glass, wood, food, textile, composite… generic or dedicated models covering complex loading paths, high strain rates, high temperatures, cyclic loading… APPROACHES BRIDGING THE SCALES: from atomistic to macroscopic scale, mechanism explanations of formability, hardening, rate sensitivity, anisotropy, toughness, phase transformation… FRACTURE PREDICTION: by continuum damage mechanics, fracture criteria… EXPERIMENTS AND MODELS: experimental procedure of identification of model parameters, or physical mechanisms experimental method applied for model validation (both model and experiments should be described). Mini Symposia fr Wed, 03 Mar 2021 09:38:17 +0100 Sun, 30 May 2021 09:27:48 +0200 https://popups.uliege.be/esaform21/index.php?id=90 0 https://popups.uliege.be/esaform21/index.php?id=524 In the field of impact response of thermoplastic reinforced composites, several investigations about material behaviour in terms of delamination, indentation and fracture mechanism were conducted. Although a significant influence of the polymer temperature on the overall material impact response is expected, a limited number of studies are available in this regard. Most of the available scientific evidence concerns thermosetting composites and thermoplastic composites response only at room temperature. In particular, the purpose of this contribution is to better understand the dissipation mechanisms involved in thermoplastic reinforced composite under impact conditions for different temperatures. Starting from the few available literature data about the modelling of the problem, the aim of the present work is the development of a numerical approach able to reproduce the experimentally tested conditions. An experimental campaign on hot pressed polyamide 6 /basalt plain fabric laminates impact was selected as the benchmark for the numerical approach. The laminates impact response at increasing values of impact energy between 5J and 30J were simulated under three temperature conditions set around the polymer transition temperature (40°C, 80°C and 100°C). By validating the overall numerical model response on the room temperature experiment, considerations about the magnitude of viscous dissipation and its influence, for the different tested temperatures and in function of the adopted lamination technology, were made. Sat, 20 Mar 2021 00:41:36 +0100 https://popups.uliege.be/esaform21/index.php?id=524 https://popups.uliege.be/esaform21/index.php?id=850 Electromagnetic forming is a contactless high-speed forming technique. In this process force transmission is initiated by an electromagnetic field provided by a tool coil. While forming thin sheet metal, the magnetic field is present in the whole depth of the sheet metal by definition. Thus, the magnetic field generates eddy currents in the complete sheet volume. The resulting Lorenz` forces act as body forces and are used for forming. Thereby high strain rates, high temperatures and multiaxial stress fields influence the plastic material properties of the workpiece. In this study, the plastic properties were investigated under real electromagnetic forming conditions. By varying process conditions like charge energy, sheet thickness and die material, the magnetic field and thus the plastic material properties were changed. To visualize the influence of the electromagnetic field, forming experiments were carried out. The strain of the formed sheets was measured. Furthermore, the forming forces were determined by measurements during the electromagnetic forming as well as by finite element simulations. With the measured strain and the determined forming force, a model for the plastic material behavior during electromagnetic forming was evolved. Sun, 21 Mar 2021 22:12:14 +0100 https://popups.uliege.be/esaform21/index.php?id=850 https://popups.uliege.be/esaform21/index.php?id=1496 In modern manufacturing processes such as hot forming or additive manufacturing, the workpiece material undergoes very complex thermomechanical load cycles. The local mechanical properties in the component are process-dependent and the result of the different micro-structure evolution mechanisms in the material. Numerical process simulation tools aim to include more and more of these mechanisms in order to improve the accuracy of the simulations. The mechanical strength of high-performance materials such as Ti-6Al-4V depends on microstructural parameters, which are influenced by the temperature and strain histories. This contribution puts forward an implementation of a new generalized internal variables material model *MAT_GENERALIZED_PHASECHANGE in LS-DYNA. The evolution of internal variables such as phase fractions, grain size and dislocation densities can be predicted by evolution equations, and combined with yield stress models taking the contribution of the phases, grain sizes (Hall-Petch effect), and the dislocation density into account to predict the resulting mechanical properties of the processed material. The benefits of the implementation in the commercial software LS-DYNA is the possibility to solve complex coupled problems. For example, the new material law can be used to simulate hybrid manufacturing processes like forging and an additional additive manufacturing process, where changes in microstructure are highly coupled and important for the part properties. Mon, 22 Mar 2021 20:03:29 +0100 https://popups.uliege.be/esaform21/index.php?id=1496 https://popups.uliege.be/esaform21/index.php?id=1630 Titanium alloys find a wide range of uses, especially in the aeronautic industry because of a combination of favorable specifications in terms of strength-to-weight ratio, corrosion resistance and performance at high temperature. If many works are interested in mechanical properties, as well as microstructure, few of them studied the effect of microstructure on formability. The aim of this work is to study the influence of the microstructure on the formability of β metastable titanium alloys (Ti21S) which are increasingly used in aeronautical applications. For this purpose, two different heat treatments are performed on Ti21S alloy in order to propose different microstructures. Based on uniaxial tensile tests, the elastoplastic hardening behavior and the limit strain in the uniaxial tension state are obtained and allow to determine one point of the forming limit curve (FLC). From these experimental observations, it is shown that the microstructure has an important effect on the formability: precipitation of α phase reduces the formability in comparison with full β phase microstructure. Finally, a finite element M-K model is used and calibrated to predict the whole FLC for the different investigated microstructures. Mon, 22 Mar 2021 20:20:07 +0100 https://popups.uliege.be/esaform21/index.php?id=1630 https://popups.uliege.be/esaform21/index.php?id=1856 In this study, the failure behavior at the interface of ductile materials is investigated. In order to capture the degradation of the tractions at the interface, a cohesive zone (CZ) model is applied. The choice of the type of the CZ approach, i.e. either intrinsic or extrinsic, brings about different drawbacks. The former includes an elastic regime at the interface prior to the failure, which can result in numerical difficulties whereas the latter necessitates the re-meshing of the structure during crack propagation. In order to overcome these problems, the incomplete interior penalty Galerkin variant of the discontinuous Galerkin (DG) method is applied both at the interface and in the bulk instead of the standard conforming finite element method. In addition, the application of the DG method enables to use nonmatching meshes in the discretized model. To treat the bulk, an elastoplastic material model with isotropic hardening as well as different hardening rules for small strains is incorporated into the DG framework. Two numerical examples are computed to study the convergence behavior of the new cohesive discontinuous Galerkin (CDG) method in comparison to that of the conventional models. The new CDG method outperforms the conventional CZ continuous Galerkin elements in the presence of locking effects as well as hanging nodes. Tue, 23 Mar 2021 09:46:45 +0100 https://popups.uliege.be/esaform21/index.php?id=1856 https://popups.uliege.be/esaform21/index.php?id=2403 Modern pipeline steels exhibit complex microstructures that cause mechanical anisotropy in various respects. For instance, strain path effects under non-monotonic loadings are exceptionally pronounced in these steels. Crystallographic texture and morphological anisotropy are the main contributors to strength and hardening directionality in pipeline steels under monotonic loading. In contrast, the dislocation substructure is seen as the primary source for Bauschinger and cross effects during complex non-monotonic loading, e.g. during pipe forming. The Bauschinger effect for example may arise from pile-ups formed at obstacles such as intragranular shear bands, and homo- or heterophase boundaries. The dislocation-based model by Peeters et al. [Acta Mater., 49 (2001), pp. 1607-1619] developed for coarse-grained ferritic steel allows for complex strain path effects through the accumulation of dislocations at micro-shear bands. However, it struggles to reproduce the large Bauschinger effect of ~250MPa in fine-grained bainitic pipeline steel [Bönisch et al., Procedia Manuf., 47 (2020), pp. 1434-1441]. Considering the microstructural differences between the two steel varieties, a promising way to improve the model predictions - especially for the Bauschinger effect - is to incorporate dislocation interactions with phase and/or grain boundaries. In the present work, we introduce this approach and demonstrate the basic capabilities of such a grain boundary-extended Peeters model. By accounting for the formation of pile-ups at grain boundaries the Bauschinger effect is enlarged. Furthermore, by explicitly considering the grain boundary spacing, the model can deliver grain size (Hall-Petch) strengthening. Tue, 23 Mar 2021 18:22:40 +0100 https://popups.uliege.be/esaform21/index.php?id=2403 https://popups.uliege.be/esaform21/index.php?id=2738 The evolution of the macroscopically observed yield surface has been the subject of many studies due to its significant effect on the numerical simulation of metal forming processes. Although macroscopic models exist that aim to define this evolution accurate data for calibration as well as validation of these models are difficult to obtain. One common approach is to use crystal plasticity simulations for analyzing the mesoscopic behavior followed by a homogenization scheme for gathering the aggregate behavior. In this study a similar approach is followed the difference being the choice of the crystal plasticity and homogenization methods. A rate-independent crystal plasticity framework where all slip system activities are solved implicitly using a backward Euler approach in combination with an interior point method for constrained optimization is used for single crystal behavior. The aggregate behavior is obtained using a self-consistent analytical homogenization scheme. The results of the homogenization scheme are compared against full-field crystal plasticity finite element simulations. The determination of the yield surface is done by considering the macroscopic behavior where the strain rate direction and magnitude changes over a threshold during stress-based loading. Wed, 24 Mar 2021 18:52:51 +0100 https://popups.uliege.be/esaform21/index.php?id=2738 https://popups.uliege.be/esaform21/index.php?id=3644 In this paper, a comparison is made between two multiscale methods, namely crystal plasticity finite element and mean field on a material composed of two phases. Both methods are used to homogenize a given microstructure. In order to obtain macroscopic behavior, in the mean field approach, a Self-Consistent scheme is used to evaluate stress and strain partitioning among the phases. In this method, an average of the fields is estimated and local distributions cannot be captured. In parallel, crystal plasticity simulations on Representative Volume Elements (RVEs) composed of hexagonal grains are performed. In these simulations, grain orientations are attributed randomly respecting Mackenzie's distribution function in order to achieve isotropic behavior and macroscopic hardening is extracted from the simulations. The results on macroscopic hardening of both methods are compared to distinguish the extents of validity of mean field homogenization. In addition to Self- Consistent, other mean field schemes such as Voigt, Reuss and Bound-Interpolation are compared in terms of efficiency and accuracy. The comparison manifests that Self-Consistent scheme is capable of predicting material behavior well. Mon, 29 Mar 2021 13:48:00 +0200 https://popups.uliege.be/esaform21/index.php?id=3644 https://popups.uliege.be/esaform21/index.php?id=3876 Packaging steel is characterized by low thickness (0.1 mm – 0.5 mm) and ferritic microstructure resulting from low carbon contents. In combination with continuous annealing processes and temper rolling, this results in only little elongation observed in tensile tests. However, as in real forming processes much higher deformation occurs, it is important to receive true stress-true strain data up to a highest possible level e.g. to characterize material for finite element analysis. Therefore, tensile tests with three different measuring lengths (80 mm, 50 mm, 20 mm) were conducted for the packaging steel TH415. Likewise, the testing speed was reduced to investigate the possibility to receive more elongation under the condition of a constant stress level. The results revealed a significant increase in elongation when using smaller tensile test geometries. As well, the reduction in testing speed leads to much higher elongation while showing only little strain rate influence. While for the 80 mm geometry and standard speed no homogenous forming condition could be reached due to early failure before Lüders strain, this could be improved by using smaller testing specimens and a lower strain rate. Combining the influence of strain rate and geometry a significant increase of more than ten percentage points in elongation was reached. Mon, 29 Mar 2021 14:53:46 +0200 https://popups.uliege.be/esaform21/index.php?id=3876 https://popups.uliege.be/esaform21/index.php?id=4049 The main difficulty presented by the simulation of a global process that includes different forming stages is the correct characterization of the material state at the end of each of these stages, which in turn, are the initial point of the following process. Hardening variables are capable of characterizing the state of the material, which, after a plastic transformation, varies according to the direction of the solicitation and its intensity. The present work carries out an analysis of the influence in the election of the hardening rule used in the behavior law, comparing the most used approach. For a work piece solicited by combined efforts in multiple stages, results are obtained by numerical simulation. A correct choice will allow obtaining reliable predictions, not the solicitations but also to the final geometry and the dissipated energy in the global process, allowing an eventual optimization of such process. Tue, 30 Mar 2021 11:17:20 +0200 https://popups.uliege.be/esaform21/index.php?id=4049 https://popups.uliege.be/esaform21/index.php?id=4067 Tube hydraulic bulging tests with fixed-end conditions are carried out to explore tubular material characteristics for 5049 aluminium. Tube diameter at the center of specimen and pole thickness under different internal pressures are recorded during forming process. Based on experimental data, two types of theoretical models using membrane mechanics and total strain theory are applied to determine the flow stress curve of tubular specimens. A tension specimen is cut from the same tube along longitudinal direction and strain-stress curve is fitted by a universal tensile test. In order to test their accuracy, obtained material parameters from three methods are imported into a finite element model (FEM) and its predicted results are compared with bugle height measured from experiments. The comparison shows that the flow stress curve of 5049 aluminium tube can be identified by these three methods and simulated results from total strain model has a better agreement with experimental measures compared with the other two methods. Tue, 30 Mar 2021 11:36:59 +0200 https://popups.uliege.be/esaform21/index.php?id=4067 https://popups.uliege.be/esaform21/index.php?id=4140 A limited number of material models or flow curves are available in commercial finite element softwares at varying temperature and strain rate ranges for plasticity analysis. To obtain more realistic finite element results, flow curves at wide temperature and strain rate ranges are required. For this purpose, a material model for a medium carbon alloy steel material which is used for fastener production was prepared. Firstly, flow curves of the material were obtained at 4 temperatures (20, 100, 200, 400 °C) and 3 strain rates (1, 10, 50 s-1). Then, experimental data was used to construct an artificial neural networks model (ANN) for the material. 75% of the experimental data was used to train the model and the rest was employed for validation and verification. ANN model used in flow curve prediction was developed using the scikit-learn library on Python. Temperature, strain rate and strain were employed as input parameters and flow stress as output parameter in ANN model. In order to increase the accuracy of the ANN model, the number of hidden layers and the number of neurons were also optimized by mean squared error approach. As a result of studies, an ANN-based material model that can be used for wide range of temperature and strain rate values were developed based on the experimental data. Wed, 31 Mar 2021 14:41:13 +0200 https://popups.uliege.be/esaform21/index.php?id=4140 https://popups.uliege.be/esaform21/index.php?id=4154 Nowadays cellular materials are receiving great attention for their excellent mechanical properties, being applied in energy absorbers or in structural components having optimized mass distribution. In this paper stretch-dominated lattice structures have been considered. A 3D periodic lattice structure of different cell size, TPMS (triply periodic minimal surface), made of epoxy resin by DLP technology was studied. Compression tests at different strain rate (10-3 to 103 1/s) have been performed and a constitutive model to assess the experimental findings has been calibrated. Thu, 01 Apr 2021 00:42:36 +0200 https://popups.uliege.be/esaform21/index.php?id=4154 https://popups.uliege.be/esaform21/index.php?id=4308 For additive manufacturing materials, different process parameters might cause non-negligible microstructural defects. Due to the deficient or surplus energy input during the process, porosity would result in significantly different mechanical responses. In addition, the heterogeneity of the microstructure of additive manufactured material could increase the anisotropic behavior in both deformation and failure stages. The aim of this study is to perform a numerical investigation of the anisotropic plasticity affected by the microstructural features, in particular, texture and porosity. The coupling of the synthetic microstructure model and the crystal plasticity method is employed to consider the microstructural features and to predict the mechanical response at the macroscopic level, including both flow curve and r-value evolution. The additive manufactured 316L stainless steel is chosen as the reference steel in this study. Porosity decreases the stress of material, however, it reduces the anisotropy of material with both two types of textures. Regardless of porosity, grains with <111>//BD fiber of reference material is preferable for high strength requirement while the random orientations are favorable for homogeneous deformation in applications. Thu, 01 Apr 2021 18:02:16 +0200 https://popups.uliege.be/esaform21/index.php?id=4308