Investigation of surface topography evolution of sheet aluminum under pressure and tension

Besides tool parameters and work piece properties, the accuracy of the finite element analysis depends much on contact conditions between the sheet and the tool. To a large extent, the contact conditions are determined by the material properties of the parts in contact as well as the relative motion and the contact pressure between them. A further factor influencing friction is the sheet surface topography which is changing due to tension, contact and sheet deformation. In this paper, the surface topography evolution under pressure and under tension is presented and discussed. Therefore, basic experiments were done. In the experiments, the influence of different parameters like tension and contact pressure is determined. To analyze the surface topography evolution, pre-defined spots on the samples were traced during the experiments. The changes in the surface topography before and after forming were analyzed by means of roughness measurement. The intention is to get a correlation between flattening or roughness evolution and the parameters of the deformation. This correlation can be used to improve existing friction models used in the FE analysi

Experimental Characterization and Material Modelling of an AZ31 Magnesium Sheet Alloy at Elevated Temperatures under Consideration of the Tension-Compression Asymmetry

Magnesium sheet alloys have a great potential as a construction material in the aerospace and automotive industry. However, the current state of research regarding temperature dependent material parameters for the description of the plastic behaviour of magnesium sheet alloys is scarce in literature and accurate statements concerning yield criteria and appropriate characterization tests to describe the plastic behaviour of a magnesium sheet alloy at elevated temperatures in deep drawing processes are to define. Hence, in this paper the plastic behaviour of the well-established magnesium sheet alloy AZ31 has been characterized by means of convenient mechanical tests (e. g. tension, compression and biaxial tests) at temperatures between 180 and 230 °C. In this manner, anisotropic and hardening behaviour as well as differences between the tension-compression asymmetry of the yield locus have been estimated. Furthermore, using the evaluated data from the above mentioned tests, two different yield criteria have been parametrized; the commonly used Hill'48 and an orthotropic yield criterion, CPB2006, which was developed especially for materials with hexagonal close packed lattice structure and is able to describe an asymmetrical yielding behaviour regarding tensile and compressive stress states. Numerical simulations have been finally carried out with both yield functions in order to assess the accuracy of the material models

Finite element analysis regarding the forming behaviour of symmetric hybrid structures consisting of two sheet metal outer layers and a thermoplastic core

To face challenges like damping effects or weight reduction in the automotive sector, new hybrid material combinations are developed. One possibility is the combination of several symmetric material layers with varying material characteristics to achieve in the component production less weight and appropriate stiffness in comparison to components produced with sheet metal. This article deals with the characterization of deep drawing behaviour of layered sandwich structures. The behaviour of the several layers and the layer interaction have been taken into account for the technical design of a deep drawing process. A material layer characterization is performed. Instabilities as interlaminar failures, ruptures or wrinkling of the structure have been investigated as part of additional experimental characterization tests on the basis of various deep drawing process parameters. Finally, the experimental data is used as input for the numerical modelling and simulation of layered structures. The FE simulation includes the material behaviour of the layers and layer interactions with cohesive zone modelling. Based on the results an important contribution for prediction accuracy in the numerical simulation has been provided

Advanced Wear Simulation for Bulk Metal Forming Processes

In the recent decades the finite element method has become an essential tool for the cost-efficient virtual process design in the metal forming sector in order to counter the constantly increasing quality standards, particularly from the automotive industry as well as intensified international competition in the forging industry. An optimized process design taking precise tool wear prediction into account is a way to increase the cost-efficiency of the bulk metal forming processes. The main objective of the work presented in this paper is a modelling algorithm, which allows predicting die wear with respect to a geometry update during the forming simulation. Changes in the contact area caused by geometry update lead to the different die wear distribution. It primarily concerns the die areas, which undergo high thermal and mechanical loads

Experimental-numerical evaluation of a new butterfly specimen for fracture characterisation of AHSS in a wide range of stress states

Results of an experimental-numerical evaluation of a new butterfly specimen for fracture characterisation of AHHS sheets in a wide range of stress states are presented. The test on the new butterfly specimen is performed in a uniaxial tensile machine and provides sufficient data for calibration of common fracture models. In the first part, results of a numerical specimen evaluation are presented, which was performed with a material model of a dual-phase steel DP600 taken from literature with plastic flow and fracture descriptions. In the second part, results of an experimental-numerical specimen evaluation are shown, which was conducted on another dual-phase steel DP600, which was available with a description of plastic flow only and whose fracture behaviour was characterised in the frame of this work. The overall performance of the new butterfly specimen at different load cases with regard to characterisation of the fracture behaviour of AHSS was investigated. The dependency of the fracture strain on the stress triaxiality and Lode angle as well as space resolution is quantified. A parametrised CrachFEM ductile shear fracture model and modified Mohr-Coloumb ductile shear fracture model are presented as a result of this quantification. The test procedure and results analysis are believed to contribute to current discussions on requirements to AHSS fracture characterisation

Implementation of the Bai and Wierzbicki fracture criterion in QForm and its application for cold metal forming and deep drawing technology

The paper presents implementation of fracture prediction algorithm for a cold metal forming process simulation in the software QForm. Authors programmed the function for calculation of the criterion proposed by Bai and Wierzbicki. Obtained results of the simulation in QForm for a deep drawing process are compared with results of experiments. A good agreement between the simulation and experiment was achieved.Ministry of Education and Science of the Russian FederationDAA

Numerical and experimental investigations on an extrusion process for a newly developed ultra-high-carbon lightweight steel for the automotive industry

In this study the material flow of a newly developed ultra-high-carbon lightweight steel (uhc-steel) with a high amount of aluminum was investigated in an extrusion process. Cylinder compression tests were performed for material characterization and frictional behaviour was determined by using ring compression tests. Numerical simulations were carried to determine the optimal die geometry as well as to calculate the process loads and dominated stresses in the die occurring during the process. Based on the numerical results, an extrusion process was designed and implemented. Experiments showed that the uhc-steel can be formed by extrusion however it is associated with a high wear rate.BMB

Energy-efficient Drive Concepts in Metal-forming Production

Nowadays, efficient drive solutions for the production industry are more important than ever. In view of this, new energy-efficient drive concepts for forming presses and sheet metal feeding systems are developed at the IFUM. The novel press drive is based on a power-split design, which allows a variable ram-kinematics with reduced total costs of ownership in comparison to conventional servo presses. The new feeding concept will be able to realize the contactless feed of electrically conductive sheet metals by means of electromagnetic forces. Since only the sheet metal has to be accelerated, the energy efficiency and feeding rate can be increased significantly.DFG/BE1691/119-1Federal Ministry of Economics and Technolog

Numerical simulation of strain-adaptive bone remodelling in the ankle joint

Background: The use of artificial endoprostheses has become a routine procedure for knee and hip joints while ankle arthritis has traditionally been treated by means of arthrodesis. Due to its advantages, the implantation of endoprostheses is constantly increasing. While finite element analyses (FEA) of strain-adaptive bone remodelling have been carried out for the hip joint in previous studies, to our knowledge there are no investigations that have considered remodelling processes of the ankle joint. In order to evaluate and optimise new generation implants of the ankle joint, as well as to gain additional knowledge regarding the biomechanics, strain-adaptive bone remodelling has been calculated separately for the tibia and the talus after providing them with an implant. Methods: FE models of the bone-implant assembly for both the tibia and the talus have been developed. Bone characteristics such as the density distribution have been applied corresponding to CT scans. A force of 5,200 N, which corresponds to the compression force during normal walking of a person with a weight of 100 kg according to Stauffer et al., has been used in the simulation. The bone adaptation law, previously developed by our research team, has been used for the calculation of the remodelling processes. Results: A total bone mass loss of 2% in the tibia and 13% in the talus was calculated. The greater decline of density in the talus is due to its smaller size compared to the relatively large implant dimensions causing remodelling processes in the whole bone tissue. In the tibia, bone remodelling processes are only calculated in areas adjacent to the implant. Thus, a smaller bone mass loss than in the talus can be expected. There is a high agreement between the simulation results in the distal tibia and the literature regarding. Conclusions: In this study, strain-adaptive bone remodelling processes are simulated using the FE method. The results contribute to a better understanding of the biomechanical behaviour of the ankle joint and hence are useful for the optimisation of the implant geometry in the future

Numerical investigations on the strain-adaptive bone remodelling in the periprosthetic femur: Influence of the boundary conditions

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