Papers by Keyword: Forming Simulation

Abstract: Aligned discontinuous fibre reinforced composites (ADFRC) have demonstrated an improved formability for small to medium sized parts with complex geometries compared to the continuous fibre based prepreg due to their stretchability along the fibre direction. The process simulation tool developed for this class of materials so far mostly concerns their tensile behaviour along the fibre direction. However, neglecting other deformation modes like the in-plane shear in a forming simulation may pose risks for the correct prediction of formed shape. This study verified a strategy which adopts previously developed analytical micromechanical models for tensile and in-plane shear deformation of ADFRCs, in a finite element framework. The implementation is validated by comparing results from virtual shear tests against experiments at different temperatures. This was then followed by virtual forming experiments on a doubly curved geometry, in which the tensile and shear properties of the material were varied separately to study the effects of each deformation mechanism on the simulated forming behaviour of the material.

Abstract: Accurate prediction of forming behavior in dry textile reinforcements requires constitutive models that capture both in-plane and out-of-plane deformation mechanisms. This work presents the development and validation of advanced bending models for unidirectional non-crimp fabrics (UD-NCFs) that exhibit two distinct characteristics: side-dependent behavior arising from asymmetric stitching and glass fiber backing, and nonlinear behavior characterized by decreasing bending stiffness with increasing curvature. Based on cantilever bending tests with optical moment–curvature measurement, five mathematical formulations (piecewise linear, polynomial, power law, logarithmic, and exponential) used to describe the moment-curvature relation were systematically evaluated using the coefficient of determination R². The piecewise linear and logarithmic models achieved the highest accuracy, with R² values approaching unity across all fiber orientations and bending directions. These models were implemented in ABAQUS/Explicit via the VUGENS user subroutine and validated through virtual cantilever tests, demonstrating good agreement with experimental deflection curves within the standard deviation bands. Application to hemispherical forming simulations revealed significant differences in wrinkle prediction between linear and nonlinear models. While the classical linear model based on Peirce predicted a single pronounced wrinkle in fiber direction, the nonlinear models captured additional wrinkles in the transverse direction and wider wrinkle patterns in fiber direction. Side-dependent models exhibited slightly increased wrinkle amplitudes compared to non-side-dependent models, particularly in fiber direction. The developed framework allows for a more accurate virtual process design than the current state of the art for composite forming operations by accounting for the side-dependent and nonlinear bending characteristics of UD-NCF materials.

Abstract: Binder stabilized preforms are getting increased attention in the wind turbine industry with the aim to increase automation in the production of large blades. In this context a preform is a stack of dry unidirectional glass fiber non-crimp fabrics (UD-NCF), which is consolidated using a polymeric binder. The preform is manufactured in a separate mold, and subsequently placed in the main blade mold. During placement of preforms, fiber wrinkling may occur due to the deformation of the preform. To accommodate this problem, we propose a predictive simulation model that can be used to investigate how different process parameters influence the wrinkle creation. Most forming simulation models in the literature consider frictional laws in the inter-ply interface for multi-layered fabrics. In this work the binder interfaces between the layers are modelled using a cohesive traction-separation law to accurately model binder degradation and wrinkle creation during preform deformation. The model predictions are compared with full thickness preform coupon specimens.

Abstract: This work presents sensitivity analyzes of the influence of deviations in the shear stress vs. shear angle curves of bias extension tests of fiber-reinforced thermoplastics on the results of forming simulations. The investigations are carried out on the basis of a double dome benchmark geometry from the Ford Motor Company. Its experimental results of shear angle values and wrinkling are compared to the simulation results. The initial values for sensitivity analyzes are the shear stress-shear angle curves determined within further preliminary investigations on the basis of different sample sizes and cutting directions. Then these are gradually scaled. Finally, it will be discussed which deviations in the shear stress-shear angle curve are permissible in order to achieve a maximum deviation of 20% between simulation results and the real part. This is assumed to be the target value for this study.

Abstract: Finite element method is used in this study for analyzing the process of chrome molybdenum tapping screws and discussing the effect of different process parameters on the formability of tapping screws. In the research process, SolidWorks matched with 3D scanning is first used for drawing the physical mold, which is then imported to DEFORM, a finite element forming software, for the tapping screws forming simulation and analysis. Through the spring constant adjustment of three different sliding upper dies, the simulation results and the physical measurement size are compared the difference in diameter or length before and after the formation, which does not exceed 2.38% at most. The research result could assist manufacturers in establishing the forming analysis process of tapping screws to find out the optimal mold and process parameters. In addition to prevent tail screws from defects in the production process, it could be used for the development and process evaluation of new-style screws.

Abstract: In this work, the influences of deviations of material properties (used material is aluminium for both metal sheets), hole geometry (diameter, chamfer at the bottom and rounding at the top) and offset between punch and hole on the quality of a clinched connection are analysed. The analyses were done with numerical forming simulations, which were validated by experimental tests. For each process parameter, models were built up to simulate the forming process. After simulation of the forming process, it was possible to measure the resulting undercut and to identify the dependency between process parameters and width of undercut. This shows the influence of each investigated parameter on clinch quality and enables to set tolerances as high as possible but small enough to get the required undercut in the clinched connection.

Abstract: The paper describes a comprehensive management system concept and implementation of the development of the production strain crystallization vessel of molybdenum sheet for the production of single crystal sapphire.

Abstract: Forming, press hardening and welding are a well-established production processes in manufacturing industry, but predicting the finished geometry and the final material properties of the processed parts is still a major issue. In particular, deformations caused by welding are often neglected in the virtual process chain, although they have to be compensated for in order to fulfill the requirements on shape tolerance. This presentation will give an overview on novel features of LS-DYNA implemented particularly for welding simulations.To begin with, new keywords will be presented that allow applying the heat generated by the weld torch. LS-DYNA offers a very convenient way to define the well-known Goldak heat source, but it is also possible to define arbitrarily shaped torch geometries.In order to obtain a predictive model for welding simulations, specific material models have been devised in LS-DYNA. The properties of filler material in weld seams are accounted for by a ghost material approach. Material is initialized as ghost material and is activated, i.e. it is given base material properties, when the temperature reaches the melting point. This approach has been implemented for a relatively simple thermo-elasto-plastic material formulation *MAT_CWM as well as for the more complex material law *MAT_UHS_STEEL. The latter has initially been implemented for press hardening simulations and is able to predict the microstructure of steel alloys including phase transformations and the resulting mechanical properties.In this contribution, details of the material formulations and novel features are presented. Examples will demonstrate how these features can be applied to multistage processes including several forming and welding stages.

Abstract: There have been many efforts to investigate and develop a numerical damage and failure models during metal forming process of lightweight alloys. Due to the difficulties experienced during experimental determination of the incurred damage during forming of lightweight alloys, many researchers have sought to predict the damage, failure and forming limit curves using numerical simulations. Conventional finite element analysis of metal forming processes for lightweight parts which have been subjected to a nonlinear strain history often breaks down due to numerical difficulties. Many scientific research works have attempted to use different mathematical methods to model the damage progression and failure of alloying material under large deformation. The damage initiation, progression and also failure of alloys are a result of accumulated damage under plastic deformation [1-3]. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. However, these methods have serious short comes in predicting the damage and failure in metal forming process with strain rate effects. In the present study, following the in-depth study of damage initiation and progression in lightweight alloys, a frame work has been setup to develop a numerical model for damage accumulation during forming process. Based on the existing damage theory, a mathematical extension for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. An experimental program has also been carried out using samples made from lightweight alloys. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.

Abstract: Redistribution of residual stresses in a stamped sheet metal leads to the springback phenomenon. Springback phenomenon is well predicted for some mild steel materials, but not for steels with higher strengths. Nowadays, one of the most used tools to stamping optimization is usage of numerical simulations. In this paper was investigated sheet metal behavior under cyclic tension-compression test. Special fixture which serves as a buckling prevention of sheet metal in the compression phase of measuring stress-strain curve was designed. Obtained stress-strain curve was used to the definition of kinematic hardening model in numerical simulation. This model was verified with the real experiment in deep drawing process.