E17
Materials 3

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13:05
conference time (CEST, Berlin)
Integration of Materials Modelling into Processing Simulation – The Current Status
28/10/2021 13:05 conference time (CEST, Berlin)
Room: E
Z. Guo, N. Saunders, J-P. Schillé (Sente Software, GBR)
Z. Guo, N. Saunders, J-P. Schillé (Sente Software, GBR)
Computer-aided engineering (CAE) simulation is increasingly used in metals industry to speed up manufacturing and production, and material data have been an integral part ever since such simulations were made possible. Recent advancement in computing power has been driving the simulation capabilities forward, from only being able to deal with simple heat transfer in the early days to the current coupled analysis of a multitude of physical phenomena. Such phenomena include heat transfer (thermal field), deformation mechanics (stress/strain field) and phase transformations (microstructural field). An accurate coupling of these phenomena is essential to achieve reliable simulation, which demands the availability of a wide range of material data, from physical and thermophysical properties to rheological properties as well as phase transformation kinetics. The traditional way of obtaining such data is through experimentation, which is not only expensive and time-consuming, but even impossible in cases where accurate simulation requires the property of each phase involved rather than that of the alloy. To provide reliable and cost-effective material data for process simulation, computer-based models must be developed so that such properties can be readily calculated, which is the so-called materials modelling. Processing simulation essentially consists of two types of modelling. One is the materials modelling – the modelling of composition-processing-microstructure-property relationships; the other is the CAE simulation typically based on finite-element or finite-difference analysis and alike. For historical reasons, the development of these two types of modelling techniques falls into two separate research areas, resulting in two types of computer software, each performing fairly well in its own field but no links exist between them. While the advanced computing power has made the integration of materials modelling into processing simulation possible, the demand for higher accuracy in simulation results has made it necessary. Modelling materials properties and behaviour has been the focus of our research in the past two decades. It incorporates a spectrum of material models covering thermodynamics (the CALculation of PHAse Diagrams, or CALPHAD approach), phase transformation kinetics, and microstructure-property relationships. Most of the material data required for processing simulation can now be readily calculated and then easily transferred to many commercial CAE tools for the simulation of casting, welding, forming, heat treatment and additive manufacturing of various industrial alloys such as Fe-, Ni-, Ti-, Al- and Mg-based alloys. This paper first reviews the development of material models over recent years, followed by recent case studies on processing simulation of some industrial alloys. The simulation practice at present leaves materials design outside the optimisation loop of product design and manufacturing, which reduces the potential design space and may result in suboptimal end products. The necessity of material data in simulation means an alloy has to be physically prepared and have its properties measured before any simulation of its processing becomes possible. The case studies presented here therefore have demonstrated great potential, as most of the material data essential for processing simulation can now be reliably calculated for the first time. It has become a real possibility to merge materials design and processing optimisation into one complete design space, and we are moving one-step closer towards true virtual design.
Materials modelling; Processing simulation; Virtual design; CALPHAD
13:25
conference time (CEST, Berlin)
Further Development of a Simulation Model for the Description of the Crystallization Kinetics of Semi-crystalline Thermoplastics
28/10/2021 13:25 conference time (CEST, Berlin)
Room: E
F. Winkelmann (DLR - Deutsches Zentrum für Luft- und Raumfahrt, DEU)
F. Winkelmann (DLR - Deutsches Zentrum für Luft- und Raumfahrt, DEU)
During the transition from the melt into the solid phase semi-crystalline thermoplastics form crystalline regions. The amount of the crystals and their grow rate depend on the material properties and the cooling conditions. These regions significantly change the mechanical and technical properties, such as stiffness, elongation or chemical resistance, of a component. Knowledge about the degree of crystallization (fraction of crystalline regions) resulting from a manufacturing process can therefore help to better predict and evaluate the component properties obtained. Furthermore, the influence of process parameters on the degree of crystallization can be investigated and experimental effort can be reduced. The calculation of the degree of crystallization is shown here on the example of the additive manufacturing process Filament Fuse Fabrication (FFF). In this process, a polymer melt is deposited through a nozzle and the component is created layer by layer. In additive manufacturing with its complex cooling conditions, the degree of crystallization influences not only the material properties but also the component properties, such as the bonding (inter layer strength). The aim is to apply a known crystallization model to the example of AM optimized PEEK. The model is implemented in Abaqus, in order to be able to predict the degree of crystallization of semi-crystalline thermoplastics, based on the existing temperature conditions in the FFF process. Since crystallization depends on many process and material parameters, the prediction of crystallization kinetics is quite complex. The approach chosen is based on a formula that is a further development of the Avrami approach. In addition to temperature-time data, this also includes parameters determined by fitting differential scanning calorimetry (DSC) curves. DSC measurements with different cooling rates are considered. By using the different DSC data, the cooling rate dependent degrees of crystallization can be calculated. A Python script for fitting the parameters of semi-crystalline thermoplastics is developed, various fitting strategies are tested and rising problems are discussed. The resulting crystallization model is applied to a simplified 2D model of an FFF process. Individual beads are considered, which are activated sequentially to model the deposition process. Individual thermal boundary conditions are set for each activation step to model the cooling as accurately as possible. The effects are discussed and modelling recommendations derived.
crystallization, additive manufacturing, fitting, differential scanning calorimetry, semi-crystalline thermoplastics
13:45
conference time (CEST, Berlin)
Viscoelastic Simulation of Fast Assembly Processes to Improve Handling of Elastomer Seals
28/10/2021 13:45 conference time (CEST, Berlin)
Room: E
C. Wehmann, C. Schüle (Trelleborg Sealing Solutions GmbH, DEU); A. Astbury (Trelleborg Sealing Solutions Inc., USA)
C. Wehmann, C. Schüle (Trelleborg Sealing Solutions GmbH, DEU); A. Astbury (Trelleborg Sealing Solutions Inc., USA)
In today’s serial production processes, automation and cycle time reduction is critical. Many industries require short cycle times and a high degree of automation driven by high volumes and extreme cost pressure. Therefore, assembly of sealing systems is often done automatically with short cycle times. The speed of the automatic assembly process is limited by the strength of the seal material. In general, forces and stresses acting on the seal during assembly increase with speed due to inertia. In case of elastomer seals, stresses also increase due to the viscoelasticity of the material. The higher the rate of deformation, the higher the stresses inside the material. Considering typical cycle times and material properties, the effect of viscoelasticity is more significant compared to the effect of inertia when considering elastomer seals. Furthermore, the maximum occurring stresses depend on the type of assembly machine and the design of the handling grippers. If the assembly speed is too high or the design of the grippers is not appropriate, the seals can often break or show other permanent damage. Furthermore, it can lead to poor performance of the sealing system after installation. The present contribution considers the effect of viscoelasticity on the speed limit during assembly and the effect of the design of the grippers on the maximum occurring stress. On the one hand an O-ring is analyzed and on the other hand a seal with a more complex cross section is simulated. In addition, two different types of elastomers are modeled: an HTV silicone elastomers and an HNBR elastomer. The investigations are be carried out by finite element analyses which are capturing the viscoelastic material properties. The viscoelastic material properties are derived from different material tests, which will be described in the contribution. Furthermore, the corresponding viscoelastic material model will be described in detail. The contribution will also include an overview about the state of the art of assembly simulations of seals and about the state of the art of viscoelastic material models. There are no numerical investigations documented in literature, where fast assembly processes of seals were simulated and the rate-dependent material behavior was taken into account. Finally, the simulation results will be compared to fast assembly tests of sealing systems in order to verify the simulation procedure. It will be demonstrated how simulation allows an improvement of the handling process during assembly and how it can insure successful operation of both the assembly process and the resulting seal performance after assembly.
viscoelasticity, finite element analysis, seal assembly, rate-dependency, damage, rubber
14:05
conference time (CEST, Berlin)
Material Data Fusion of CAE and Experimental Data in a Case Study for a Car Seat Back Shell
28/10/2021 14:05 conference time (CEST, Berlin)
Room: E
J. Lienhard, T. Herrmann, T. Schweiger, F. Huberth (Fraunhofer IWM, DEU)
J. Lienhard, T. Herrmann, T. Schweiger, F. Huberth (Fraunhofer IWM, DEU)
The benefit of fused data from different virtual and experimental resources like CAD, FEM, DIC IR and laser scanners is demonstrated on a recyclable car seat back shell and its mechanical impact testing. Component properties depend on its shape, its material condition and its manufacturing process. Along the whole product lifecycle nowadays a huge amount of data accrues. The aim is the use of this information to improve products and save resources. To understand the mechanics of materials in use and forecast component behavior in simulations, the MaterialDataFusion (MDF) tool was created. MDF correlates information geometrically and in time to one set of fused data. Within the virtual geometry of a component, all available data are registered in a common coordinate system with local accuracy. MDF is able to correlate all data on a common grid. The grid can be created within the tool by using standard shells or solids Finite Element (FE) meshes. The local FE-size can be adjusted dependent on the spatial resolution of the data. Across all scales, data on different levels brought together. To use the accumulated information for the parametrization or validation of material models, the correlation process also can be performed using predefined meshes from usual FE-Preprocessors imported in MDF. That meshes are used within the correlation as an information carrier. The correlated information grid is than exported as a data frame, which contains the local available static or time dependent information on each node. One can include porosity, fiber orientation, heat treatment history, microstructure information, deformation and heat development in mechanical tests and all data measured or simulated on components. As an example, along the product chain of a recyclable car seat shell, consisting of fiber placed and molded basalt fiber laminates and polylactic acid (PLA), different data from multiple institutions where fused in MDF and used to validate a complex hybrid material model. An automatic registration in MDF and the interfaced to process ontologies are part of ongoing works.
Data-Fusion, Impact, hybrid-material-model
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