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The Benefit of True Fracture Strain on Material Model Parametrization

By means of numerical simulation, cars have become much saver and lighter at the same time (when focusing on chassis and body in white). The ongoing improvement of steel grades for the automotive sector has additionally supported this development. Nowadays, the last percentages of improvements can only be obtained by using the latest steel grades and a very realistic modeling of their strain hardening and failure behavior. In case of hot rolled steels with a thickness of 4.0 mm, this leads more and more often to a modeling based on solid finite elements. Focusing hot rolled steels with high yield strength and high formability, there is in addition the need for a modeling of anisotropic hardening.

Development New MAT Applied Yoshida 6th Order Yield Function and its Verification

Sheet metal forming simulation has become an indispensable tool for design of automobile parts and process design of its die. As for automobile parts, high strength steel and aluminum alloy are applied for them in progress. On the other hand, these lightweight materials are well known as difficult formability, and many problems have occurred in stamping process. In elasto-plastic FEA, there are many factors that determine the analysis accuracy, the material model is especially important. In case of applying associated flow rule, the yield function is key, and the reproductive capability of the material properties are very significant and influential. In LS-DYNA, there are many material models, and various yield function can be applied. MAT36(Barlet’89), MAT37(Hill’48), MAT242(Ylld2000-2D) [1] are commonly used in sheet metal forming. And this time, the MAT model that uses Yoshida 6th order yield function [2] are developed by using USER MATERIAL function in order to improve the accuracy. This MAT model take Yoshida-Uemori kinematic hardening model which is well known to be able to properly reproduce Bauschinger effect into account. And it can also strain dependency of Young’s modulus into account. This yield function is applicable with 16 parameters both to shell elements as well as solid elements, therefore this model is user-friendly for users from this point of view. In addition, it is easy to consider anisotropic hardening which is important factor for accuracy. This model was implemented as MAT_289. In order to verify the analysis accuracy of this material model, the benchmarks of NUMISHEET 2018 [3] are calculated and the calculation results are compared with experimental data. Good results are also obtaine when shell elements are used and another case where application of solid elements are necessary. In this paper, the analysis results of MAT289 or the other MAT models are compared with experimental results.

Evaluation of Simulation Results using Augmented Reality

Simulation has become an important tool in order to design forming processes in a time and cost efficient way. However, simulation results are almost exclusively visualized using conventional laptops or personal computers. Especially, in the press shop an analysis directly at real parts is not possible at the moment. At the same time, there has been a very convincing development in the field of Augmented Reality hardware in recent years. In particular, the iPhone and the iPad of the company Apple as well as the HoloLens of the company Microsoft offer interesting solutions for the industry. Thereby, the Augmented Reality applications are until now limited to CAD-data or assembly problems. Therefore, within scientific contribution a method to visualize simulation results from LsDyna in a simple way is presented. It will be explained, how new simulation results can be loaded on runtime and which use cases can be derived with the technology. In the end, Augmented Reality solutions with HoloLens as well as iPhone/iPad will be compared and evaluated.

Simulation of Sheet Metal Forming using Elastic Dies

Simulation of sheet metal forming is one of the major applications of LS-DYNA. Today, a majority of the forming industry is using Finite Element models to design the stamping dies in order to prevent excessive thinning, wrinkling and producing parts within tolerance by compensating for springback deformation. All these simulations are made using the assumption of rigid forming surfaces. Depending on the type of press, tool design and sheet metal part, this assumption could prove to be incorrect which yields a forming result that depends on the elastic deformation of the stamping die and in some cases the entire stamping press. Such deformations are usually compensated during die try-out by manual rework which is costly and time consuming.

Shell Models with Enhanced Kinematics for Finite Elements in Sheet Metal Forming Simulations

Beyond the shell model of Reissner and Mindlin, which is available in LS-DYNA® for example in shell ELFORM=2/16, there have been many developments in the field of 3d-shell models in recent years [1]. 3d-shell models can be beneficial in sheet metal forming simulations because they allow for three-dimensional stress states. 3d-shell elements are available in LS-DYNA®, e.g. ELFORM=25. In the doctoral dissertation of Fleischer[2] it has been found that under certain conditions this element formulation suffers from an artificial stiffening effect. Although this finding dates back to 2009, this phenomenon has remained unexplained so far. In this contribution, the authors explain the reason for this stiffening effect and show a possibility to remove it. Moreover, an outlook on the development of higher order shell models for sheet metal forming simulation is given.

Numerical Simulation of Electrohydraulic Forming using Coupling of ALE and Lagrangian Elements

Electrohydraulic forming is a high-speed forming process that employs high-pressure shock wave in fluid. When the electric energy is discharged from a capacitor bank, it is transferred to the water through the electrode bar and it makes the fluid into a high-pressure plasma state. Due to the high-pressure water, the sheet can be deformed into the die shape. Because the numerical model of electrohydraulic forming deals with fluid and structural models at the same time, it needs coupling mechanism for parts. Therefore, in this study, numerical model for electrohydraulic forming was developed using the coupling of ALE (Arbitrary Lagrange-Eulerian) and lagrangian mesh. The fluid parts, plasma, vacuum and water, were modelled with ALE elements and structural parts, die, chamber and sheet metal were modelled with general lagrangian mesh. The results of the numerical simulation showed that the plasma and water parts expanded due to the input energy, and the sheet metal was deformed with a speed above 100 m/s due to the pressure wave of the fluid parts.

The Use of LS-DYNA for the Development of a Topology-Optimized Thin-Walled Shell Structure Manufactured by Die-Less-Hydroforming

Within the framework of sovereign research at the KIT Steel & Lightweight Structure and an accompanying research project [1], the aim was, following an idea by Ummenhofer and Metzger, to develop a hinged column with a cross-section tapering from the centre to the two ends. The result is an elegant minimalistic pillar called “Hybridstütze PERFECTO” (in English: Hybridcolumn PERFECTO) that is made of an outer thin stainless steel shell, a core of ultra high-strength steel located in the cross section center and a filling of the space in-between by self-compacting concrete.

Virtual Modeling of Forming Processes in Metal Packaging Industry

Nowadays the finite element method is technical standard in many industry sectors such as automotive manufacturing. Thus the material behaviour for steel applications in this field is extensively developed. In packaging industry, virtual approaches in process- and product development are more the exception. Instead, the cost-intensive and time-consuming trial-and-error method is commonly used to approach the limits of the material specific formability. Packaging steel is characterised by thicknesses between 0.1 to 0.49 mm and thyssenkrupp Packaging Steel offers strengths between 180 to 750 MPa. However, with tougher process limits, especially due to continuous thickness reduction, this method has its limitations. Speaking of material saving and optimisation simulation tools are gaining increasingly importance. In contrast to the automotive industry, established approaches for material characterisation do not exist and not all norms cover that low thickness range for sheet materials. The following work gives an indication of current possibilities for material characterisation of thin steel sheet. A completed validation ensures process and product designing with available material models.

Setting up a Hot Stamping Simulation considering Tool Heating with OpenForm

The steadily growing requirements regarding the carbon footprint of vehicles has motivated the deployment of quenching (hot stamping) as a promisingly manufacturing process for lightweight car bodies in the series production of structural components. Very high part stiffnesses as well as formabilities can be achieved by means of this quenching process with significantly less forming energy and material consumption. This sets new standards both in vehicle safety and vehicle crash performance as well in sustainable and resource-saving mass production of car body components.

Springback in Assembly of Mirror Panels with Stamped Supports for Concentrating Solar Power Applications

Solar collector fields consisting of a large number of heliostats are used to reflect and concentrate sunlight onto a tower receiver (Figure 1a) in concentrating solar power (CSP) plants. In the most common tower CSP configuration, shown in Figure 1b, the concentrated light is used to heat a recirculating molten salt heat transfer fluid. A portion of this flow is used to generate steam immediately to drive a Rankine power cycle, while the remainder is stored in insulated tanks to enable 24 hour dispatchable power generation.