Christian Poppe - Academia.edu (original) (raw)

Papers by Christian Poppe

Research paper thumbnail of Comparative experimental and numerical analysis of bending behaviour of dry and low viscous infiltrated woven fabrics

Composites Part A-applied Science and Manufacturing, Sep 1, 2019

Wet compression moulding (WCM) provides high-volume production potential for continuous fibre-rei... more Wet compression moulding (WCM) provides high-volume production potential for continuous fibre-reinforced composite components via simultaneous draping and infiltration. Experimental and theoretical investigations proved strong mutual dependencies between resin flow and fabric deformation, which are not fully understood yet. This limits development of suitable process simulation methods and applies in particular for the characterisation of infiltrated bending behaviour-essential for an accurate prediction of draping effects. Therefore, a comparative characterisation of the bending behaviour of dry and infiltrated woven fabrics is presented using a modified cantilever and a rheometer bending test. Experimental results reveal both, rate-and viscosity-dependencies. A comparison of the quantitative results exposed an explicable systematic deviation between the two tests, whereas qualitative results are comparable. Finally, Finite Element forming simulations, comprising two bending models corresponding to cantilever and rheometer test are performed to evaluate the experimental findings on component level.

Research paper thumbnail of Experimental and numerical investigation of the shear behaviour of infiltrated woven fabrics

Composites Part A-applied Science and Manufacturing, Nov 1, 2018

Wet compression moulding (WCM) as a promising alternative to resin transfer moulding (RTM) provid... more Wet compression moulding (WCM) as a promising alternative to resin transfer moulding (RTM) provides highvolume production potential for continuously fibre reinforced composite components. Lower cycle times are possible due to the parallelisation of the process steps draping, infiltration and curing during moulding. Although experimental and theoretical investigations indicate a strong mutual dependency arising from this parallelisation, no material characterisation setups for textiles infiltrated with low viscous fluids are yet available, which limits a physical-based process understanding and prevents the development of proper simulation tools. Therefore, a modified bias-extension test setup is presented, which enables infiltrated shear characterisation of engineering textiles. Experimental studies on an infiltrated woven fabric reveal both, rateand viscosity-dependent shear behaviour. The process relevance is evaluated on part level within a numerical study by means of FE-forming simulation. Results reveal a significant impact on the global and local shear angle distribution, especially during forming.

Research paper thumbnail of Systematic approach for the development of an FE-based process simulation framework for wet compression moulding of continuously reinforced composites

Wet compression moulding (WCM) provides large-scale production potential for continuously fibre r... more Wet compression moulding (WCM) provides large-scale production potential for continuously fibre reinforced structural components as a promising alternative to resin transfer moulding (RTM). Lower cycle times are enabled by parallelisation of the key process steps draping, infiltration and curing during moulding, which is called viscous draping. Experimental and theoretical investigations prove strong mutual dependencies between the physical mechanisms, especially between the resin (fluid) and the stacked laminate [1-4]. To enable a time and cost efficient product and process development throughout all design stages, accurate process simulation tools are desirable. Hitherto, a lack of systematic investigation and understanding of these mutual dependencies prevent further development of suitable numerical methods. Existing sequential draping and mould filling simulations models that are suitable for the RTM process cannot be directly applied to the WCM process, due to the above outlin...

Research paper thumbnail of Optimisation of manufacturing process parameters using deep neural networks as surrogate models

Procedia CIRP, 2018

Optimisation of manufacturing process parameters requires resource-intensive search in a high-dim... more Optimisation of manufacturing process parameters requires resource-intensive search in a high-dimensional parameter space. In some cases, physics-based simulations can replace actual experiments. But they are computationally expensive to evaluate. Surrogate-based optimisation uses a simplified model to guide the search for optimised parameter combinations, where the surrogate model is iteratively improved with new observations. This work applies surrogate-based optimisation to a composite textile draping process. Numerical experiments are conducted with a Finite Element (FE) simulation model. The surrogate model, a deep artificial neural network, is trained to predict the shear angle of more than 24,000 textile elements. Predicting detailed process results instead of a single performance scalar improves the model quality, as more relevant data from every experiment can be used for training. For the textile draping case, the approach is shown to reduce the number of resource-intensive FE simulations required to find optimised parameter configurations. It also improves on the best-known overall solution.

Research paper thumbnail of Modeling and validation of gripper induced membrane forces in finite element forming simulation of continuously reinforced composites

Nucleation and Atmospheric Aerosols, 2017

Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle c... more Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle components has become a considerably important process during the past years due to its large-scale production potential. However, depending on process conditions and material behavior, macroscopic defects such as fiber fracture, gapping or wrinkling are feasible. To counteract such defects, blank holders or grippers, which introduce membrane forces in the laminate, can be employed in the forming process. Usually, the number and location of grippers, as well as direction and magnitude of gripping forces are determined by a cost and time consuming "trial and error" process design. Therefore, an advanced gripper system for online monitoring of gripper forces, elongations and rotations during thermoforming is presented in this work. Along with the kinematics of the grippers, the measured forces supply the beforehand mostly unknown boundary conditions for FE forming simulation. Based on a modeling approach for FE forming simulation of CFRPs implemented in the commercially available FE solver Abaqus, appropriate modeling techniques for gripper-assisted forming are outlined. These modeling techniques are applied to two different generic geometries and the simulation results are compared with a good agreement to experimental tests.

Research paper thumbnail of Virtuelle Produktentwicklung mittels Simulationsmethoden und KI

Lightweight design, Dec 1, 2019

und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Kom... more und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Komplexität und Entwicklungsaufwand aktueller Leichtbaulösungen. Wissenschaftler am KIT untersuchen, wie zukünftig Simulationen und maschinelles Lernen kombiniert werden können, um Entwicklungsprozesse zu beschleunigen. Die durchgängig virtuelle Prozesskette Eine virtuelle Prozesskette ermöglicht die direkte Verknüpfung von Design und finalem FKV-Bauteil unter Berücksichtigung der Wechselwirkungen zwischen Material und

Research paper thumbnail of Experimental and numerical investigation of the contact behavior during FE forming simulation of continuously reinforced composites in wet compression molding

Nucleation and Atmospheric Aerosols, 2019

An approach for rapid prediction of textile draping results for variable composite component geom... more An approach for rapid prediction of textile draping results for variable composite component geometries using deep neural networks

Research paper thumbnail of Towards 3D Process Simulation for In Situ Hybridization of Fiber-Metal-Laminates (FML)

Key Engineering Materials

Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and i... more Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and inherent corrosion resistance.To speed up manufacturing and simultaneously increase the geometrical complexity of the produced FML parts, Mennecart et al. proposed a new single-step process combining deep-drawing with infiltration (HY-LCM). Although the first experimental results are promising, the process involves several challenges, mainly originating from the Fluid-Structure-Interaction (FSI) between deep-drawing and infiltration. This work aims to investigate those challenges to comprehend the underlying mechanisms. A new close-to-process test setup is proposed on the experimental side, combining deep-drawing of a hybrid stack with a linear infiltration. A process simulation model for FMLs is presented on the numerical side, enabling a prediction of the dry molding forces, local Fiber Volume Content (FVC) within the three glass fiber (GF) interlayers, and simultaneous fluid progressio...

Research paper thumbnail of Zeit- und kosteneffiziente Prozess- und Produktentwicklung für den Hochleistungs-Faserverbundleichtbau mittels Nasspresstechnologie

Großserientaugliche Produktionsprozesse von Hochleistungs-Faserverbundkunststoffen stellen aufgru... more Großserientaugliche Produktionsprozesse von Hochleistungs-Faserverbundkunststoffen stellen aufgrund der gewünschten Prozesseffizienz bei gleichzeitiger Realisierung herausragender gewichtsspezifischer Materialeigenschaften ein wichtiges, zukunftsträchtiges Themenfeld dar. Im Automotive-Bereich kommen diese Prozesse verstärkt zur Anwendung, insbesondere bei Premiumfahrzeugen und im Rahmen der E Mobilität. Der erheblichen Gewichtseinsparung und hohen Energieeffizienz von Leichtbaustrukturen stehen bisher jedoch noch hohe Entwicklungs- und Stückkosten (Material, Prozessaufwand) gegenüber. Neben den verschiedenen Varianten der Resin Transfer Moulding (RTM) Technologie bietet sich zur Herstellung leichter, komplex geformter Strukturbauteile das Nasspressverfahren als Großserienanwendung an. Durch Parallelisierung von Prozessschritten in Verbindung mit hochreaktiven Harzsystemen können niedrigere Zykluszeiten erreicht werden als beim RTM-Verfahren. Da für den Nasspressprozess bisher weder...

Research paper thumbnail of Towards numerical prediction of flow-induced fiber displacements during wet compression molding (WCM)

ESAFORM 2021, 2021

Wet compression molding (WCM) provides large-scale production potential for continuous fiber-rein... more Wet compression molding (WCM) provides large-scale production potential for continuous fiber-reinforced structural components due to simultaneous infiltration and draping during molding. Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficient – a considerable economic advantage. Experimental and numerical investigations prove strong mutual dependencies between the physical mechanisms, especially between resin flow (mold filling) and textile forming (draping), similar to other liquid molding techniques (LCM). Although these dependencies provide significant benefits such as improved contact, draping and infiltration capabilities, they may also lead to adverse effects such as flow-induced fiber displacement. To support WCM process and part development, process simulation requires a fully coupled approach including the capability to predict critical process effects. This work aims to demonstrate the suitability of a macroscopic, fully c...

Research paper thumbnail of A 3D process simulation model for wet compression moulding

Composites Part A: Applied Science and Manufacturing, 2021

Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-r... more Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-reinforced structural components due to simultaneous infiltration and draping during moulding. Due to thicknessdominated infiltration of the laminate, comparatively low cavity pressures are sufficient-a considerable economical advantage. Similar to other Liquid Compression Moulding (LCM) processes, forming and infiltration strongly interact during process. However, the degree of forming is much higher in WCM, which disqualifies a sequential modelling approach. This is demonstrated in this work via experimental characterisation of the interaction between compaction and permeability of a woven fabric and by trials with a transparent double dome geometry, which facilitates an in situ visualization of fluid progression during moulding. In this light, and in contrast to existing form filling approaches, a forming-inspired, three-dimensional process simulation approach is presented containing two fully-coupled macroscopic forming and fluid-submodels. The combined model is successfully benchmarked using experimental double dome trials with transparent tooling.

Research paper thumbnail of Continuous Process Simulation for Continuous Fiber Reinforced Composites

Research paper thumbnail of Modeling and validation of gripper induced membrane forces in finite element forming simulation of continuously reinforced composites

AIP Conference Proceedings, 2017

Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle c... more Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle components has become a considerably important process during the past years due to its large-scale production potential. However, depending on process conditions and material behavior, macroscopic defects such as fiber fracture, gapping or wrinkling are feasible. To counteract such defects, blank holders or grippers, which introduce membrane forces in the laminate, can be employed in the forming process. Usually, the number and location of grippers, as well as direction and magnitude of gripping forces are determined by a cost and time consuming "trial and error" process design. Therefore, an advanced gripper system for online monitoring of gripper forces, elongations and rotations during thermoforming is presented in this work. Along with the kinematics of the grippers, the measured forces supply the beforehand mostly unknown boundary conditions for FE forming simulation. Based on a modeling approach for FE forming simulation of CFRPs implemented in the commercially available FE solver Abaqus, appropriate modeling techniques for gripper-assisted forming are outlined. These modeling techniques are applied to two different generic geometries and the simulation results are compared with a good agreement to experimental tests.

Research paper thumbnail of Estimating Optimum Process Parameters in Textile Draping of Variable Part Geometries - A Reinforcement Learning Approach

Procedia Manufacturing, 2020

Fine-tuning of manufacturing processes for optimum part quality requires many resource-intensive ... more Fine-tuning of manufacturing processes for optimum part quality requires many resource-intensive trial experiments in practice. To reduce the experimental effort, physics-based process simulations in conjunction with optimisation algorithms can be applied, e.g. finite-element-models and evolutionary algorithms. However, they generally require considerable numerical expertise and long computation times. Efficient optimisation of such expensive-to-evaluate models often employs surrogate-based optimisation (SBO). SBO constructs numerically inexpensive approximations of the original model, which guide the optimiser in the parameter space. This allows concentrating costly simulations on the most promising regions. While SBO significantly reduces the computational load in many cases, current SBO-strategies are inevitably problem-specific and cannot be reused in other, even similar situations. Consequently, subtle problem variations, e.g. minor geometry changes in material forming, require an entirely new optimisation and all previous numerical effort is in vain. Thus, surrogate techniques with generalised applicability are an open field of research. Machine Learning techniques using convolutional neural networks (CNNs) are capable of 'learning' complex system dynamics from data. In this work, CNNs are used to extend the predictive capabilities of SBO towards variable instead of fixed manufacturing settings. Specifically, material draw-in optimisation in textile forming ('draping') for variable geometries is studied. Using reinforcement learning, a CNN is trained to estimate optimum positions of pressure pads during draping of a pre-specified class of box-shaped geometries. Once trained, the CNN interprets a forming result and infers beneficial pad positions. Unlike conventional SBO strategies, it can also give recommendations for variable geometries from the selected geometry class. The paper shows that, in principle, CNNs are able to extract information from a range of different forming tasks and apply it to a new, unknown situation. Since they reuse information gained from previous simulations, they are considered a viable option for future, generalised SBO-strategies.

Research paper thumbnail of Material Modeling in Forming Simulation of Three-Dimensional Fiber-Metal-Laminates – A Parametric Study

Procedia Manufacturing, 2020

Forming of fiber-metal-laminates (FML) into complex geometries is challenging, due to the low fra... more Forming of fiber-metal-laminates (FML) into complex geometries is challenging, due to the low fracture toughness of the fibers. Several researchers have addressed this topic in recent years. A new manufacturing process has been introduced in our previous work that successfully combines deep drawing with thermoplastic resin transfer molding (T-RTM) in a single process step. During molding, the fabric is infiltrated with a reactive monomeric matrix, which polymerizes to a thermoplastic after the forming process is completed. In our previous work, a numerical modeling approach was presented for this fully integrated process, investigating a hybrid laminate with 1 mm thick metal sheets of DC04 as top layers and three inner glass fiber layers. Although initial results were promising, there were still some pending issues regarding the modeling of material behavior. The current study aims to address several of these open issues and to provide a general modelling framework for future enhancements. For this purpose, the existing modelling approach is extended and used for parameter analysis. Regarding the influence of different material characteristics on the forming result, shear, bending and compression properties of the fabric are modified systematically. It is shown, that the compression behavior and particularly the tension-compression anisotropy of the fabric is of high importance for modelling the combined forming of fabric and metal. The bending and shear properties of the fabric are negligible small compared to the metal stiffness which dominates the draping process. Finally, it is demonstrated that modelling the fabric layers using continuum shells provides a promising approach for future research, as it enables a suitable way to account for transversal compaction during molding.

Research paper thumbnail of A 3D Modelling Approach for Fluid Progression during Process Simulation of Wet Compression Moulding – Motivation & Approach

Procedia Manufacturing, 2020

Wet compression moulding (WCM) provides large-scale production potential for continuous fibre-rei... more Wet compression moulding (WCM) provides large-scale production potential for continuous fibre-reinforced structural components due to simultaneous infiltration and draping during moulding (viscous draping). Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficienta considerable economic advantage. Experimental and numerical investigations prove strong mutual dependencies between the physical mechanisms, especially between resin flow and textile forming. Understanding and suitable modelling of these occurring physical mechanisms is crucial for process development and final part design. While existing modelling approaches are suitable for infiltration of preformed fabrics within various liquid moulding technologies, such as CRTM/RTM or VARI, WCM requires a fully coupled simulation approach for resin progression and concurrent stack deformation. Thus, the key challenge is to efficiently link these two aspects in a suitable framework. First, this work demonstrates that a three-dimensional approach for fluid progression during moulding is needed to capture WCM-process boundary conditions. In this regard, a novel test bench is used to investigate the impact of infiltration on the transversal compaction behaviour of a woven fabric. Moreover, the test setup is applied to determine the in-plane permeability values of the same material corresponding to the beforehand applied compaction states. Results are verified by comparison with an existing linear test setup. In the second part, initial steps towards a three dimensional extension of an existing 2D modelling approach are outlined. For this purpose, a macroscopic FE-based three-dimensional formulation of Darcy's law is utilized within a User-Element in ABAQUS/EXPLICIT. Essential mechanisms within the element are presented. Additional control volumes (FE/CV) are applied to ensure mass conservation. Eventually, it is demonstrated, that the simulation model can predict the average fluid pressure beneath a punch during pre-infiltrated compaction experiments. Finally, major benefits and forthcoming steps for a fully-coupled 3D modelling approach for WCM are outlined.

Research paper thumbnail of Capabilities of Macroscopic Forming Simulation for Large-Scale Forming Processes of Dry and Impregnated Textiles

Procedia Manufacturing, 2020

Forming of continuously fibre-reinforced polymers (CoFRP) has a significant impact on the structu... more Forming of continuously fibre-reinforced polymers (CoFRP) has a significant impact on the structural performance of composite components, underlining the importance of forming simulation for CoFRP product development processes. For an integrated development of industrial composite components, efficient forming simulation methods are in high demand. Application-oriented method development is particularly crucial for industrial needs, where large and complex multi-layer components are manufactured, commercial FE software is used, and yet high prediction accuracy is required. To meet industrial demands, this contribution gives an insight in macroscopic forming simulation approaches that utilize the FE software ABAQUS in combination with user-defined material models and finite elements. Three CoFRP forming technologies are considered, which are in industrial focus due to their suitability for mass production: textile forming of dry unidirectional non-crimp fabrics (UD-NCF), thermoforming of pre-impregnated UD tapes and wet compression moulding (WCM). In addition to the highly anisotropic, largestrain material behaviour that composite forming processes have in common, the three process technologies face various process-specific modelling challenges. UD-NCFs require material models that capture the deformation behaviour and the slippage of the stitching. Thermoforming of UD tapes is highly rate-and temperature-dependent, calling for rheological membrane and bending modelling. Moreover, a thermomechanical approach including crystallisation kinetics enables the prediction of potential phase-transition during forming and resulting defects in the semicrystalline thermoplastic matrix. For simultaneous forming and infiltration in wet compression moulding, a finite Darcy-Progression-Element is superimposed with the membrane and shell elements for forming simulation, capturing infiltration-dependent material properties. The three outlined technologies illustrate the complexity and importance of further simulation method development to support future process development.

Research paper thumbnail of Virtuelle Produktentwicklung mittels Simulationsmethoden und KI

Lightweight Design, 2019

und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Kom... more und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Komplexität und Entwicklungsaufwand aktueller Leichtbaulösungen. Wissenschaftler am KIT untersuchen, wie zukünftig Simulationen und maschinelles Lernen kombiniert werden können, um Entwicklungsprozesse zu beschleunigen. Die durchgängig virtuelle Prozesskette Eine virtuelle Prozesskette ermöglicht die direkte Verknüpfung von Design und finalem FKV-Bauteil unter Berücksichtigung der Wechselwirkungen zwischen Material und

Research paper thumbnail of Virtual Product Development Using Simulation Methods and AI

Lightweight Design worldwide, 2019

Increased material diversity and higher component requirements along with shorter development cyc... more Increased material diversity and higher component requirements along with shorter development cycles increase the complexity and development effort of today's lightweight solutions. Scientists at KIT are investigating new opportunities to combine simulations and machine learning to accelerate development processes. Research and development have been paving the way for increasingly capable material and design solutions using fiber-reinforced polymers (FRPs) for many decades. However, the enormous effort required for a manufacturable component design and process setup hinders the potential to achieve lightweight design. Using efficient design methods is the only way to realize the significant potential of FRPs in the final product in an economically viable manner, thereby justifying higher material costs. This holds in particular for medium-and large-scale production processes where the interaction between component performance and commercial requirements is particularly strong, Figure 1 © KIT | FAST Holistic approach Requirements for economic lightweight solutions Exemplary implementation within a virtual process chain Virtual prediction of material-and process-specific interactions for a reliable and efficient design.

Research paper thumbnail of Development of a Modular Draping Test Bench for Analysis of Infiltrated Woven Fabrics in Wet Compression Molding

Key Engineering Materials, 2019

The wet compression molding (WCM) process enables short cycle times for production of fiber-reinf... more The wet compression molding (WCM) process enables short cycle times for production of fiber-reinforced plastics due to simultaneous infiltration, viscous draping and consolidation in one process step. This requires a comprehensive knowledge of occurring mutual dependencies in particular for the development of process simulation methods and for process optimization. In this context, it is necessary to develop suitable test benches to enable an evaluation of the outlined viscous draping behavior. In order to evaluate and suitably design the draping process, grippers are mounted on a surrounding frame, which enables targeted restraining of the local material draw-in during forming. In supporting the development of the new test bench, first experimental and simulation results are compared, which thereby enables a first validation of the simulation approaches. Results show a good agreement between experimental and numerical results in terms of shear deformation and final gripper displace...

Research paper thumbnail of Comparative experimental and numerical analysis of bending behaviour of dry and low viscous infiltrated woven fabrics

Composites Part A-applied Science and Manufacturing, Sep 1, 2019

Wet compression moulding (WCM) provides high-volume production potential for continuous fibre-rei... more Wet compression moulding (WCM) provides high-volume production potential for continuous fibre-reinforced composite components via simultaneous draping and infiltration. Experimental and theoretical investigations proved strong mutual dependencies between resin flow and fabric deformation, which are not fully understood yet. This limits development of suitable process simulation methods and applies in particular for the characterisation of infiltrated bending behaviour-essential for an accurate prediction of draping effects. Therefore, a comparative characterisation of the bending behaviour of dry and infiltrated woven fabrics is presented using a modified cantilever and a rheometer bending test. Experimental results reveal both, rate-and viscosity-dependencies. A comparison of the quantitative results exposed an explicable systematic deviation between the two tests, whereas qualitative results are comparable. Finally, Finite Element forming simulations, comprising two bending models corresponding to cantilever and rheometer test are performed to evaluate the experimental findings on component level.

Research paper thumbnail of Experimental and numerical investigation of the shear behaviour of infiltrated woven fabrics

Composites Part A-applied Science and Manufacturing, Nov 1, 2018

Wet compression moulding (WCM) as a promising alternative to resin transfer moulding (RTM) provid... more Wet compression moulding (WCM) as a promising alternative to resin transfer moulding (RTM) provides highvolume production potential for continuously fibre reinforced composite components. Lower cycle times are possible due to the parallelisation of the process steps draping, infiltration and curing during moulding. Although experimental and theoretical investigations indicate a strong mutual dependency arising from this parallelisation, no material characterisation setups for textiles infiltrated with low viscous fluids are yet available, which limits a physical-based process understanding and prevents the development of proper simulation tools. Therefore, a modified bias-extension test setup is presented, which enables infiltrated shear characterisation of engineering textiles. Experimental studies on an infiltrated woven fabric reveal both, rateand viscosity-dependent shear behaviour. The process relevance is evaluated on part level within a numerical study by means of FE-forming simulation. Results reveal a significant impact on the global and local shear angle distribution, especially during forming.

Research paper thumbnail of Systematic approach for the development of an FE-based process simulation framework for wet compression moulding of continuously reinforced composites

Wet compression moulding (WCM) provides large-scale production potential for continuously fibre r... more Wet compression moulding (WCM) provides large-scale production potential for continuously fibre reinforced structural components as a promising alternative to resin transfer moulding (RTM). Lower cycle times are enabled by parallelisation of the key process steps draping, infiltration and curing during moulding, which is called viscous draping. Experimental and theoretical investigations prove strong mutual dependencies between the physical mechanisms, especially between the resin (fluid) and the stacked laminate [1-4]. To enable a time and cost efficient product and process development throughout all design stages, accurate process simulation tools are desirable. Hitherto, a lack of systematic investigation and understanding of these mutual dependencies prevent further development of suitable numerical methods. Existing sequential draping and mould filling simulations models that are suitable for the RTM process cannot be directly applied to the WCM process, due to the above outlin...

Research paper thumbnail of Optimisation of manufacturing process parameters using deep neural networks as surrogate models

Procedia CIRP, 2018

Optimisation of manufacturing process parameters requires resource-intensive search in a high-dim... more Optimisation of manufacturing process parameters requires resource-intensive search in a high-dimensional parameter space. In some cases, physics-based simulations can replace actual experiments. But they are computationally expensive to evaluate. Surrogate-based optimisation uses a simplified model to guide the search for optimised parameter combinations, where the surrogate model is iteratively improved with new observations. This work applies surrogate-based optimisation to a composite textile draping process. Numerical experiments are conducted with a Finite Element (FE) simulation model. The surrogate model, a deep artificial neural network, is trained to predict the shear angle of more than 24,000 textile elements. Predicting detailed process results instead of a single performance scalar improves the model quality, as more relevant data from every experiment can be used for training. For the textile draping case, the approach is shown to reduce the number of resource-intensive FE simulations required to find optimised parameter configurations. It also improves on the best-known overall solution.

Research paper thumbnail of Modeling and validation of gripper induced membrane forces in finite element forming simulation of continuously reinforced composites

Nucleation and Atmospheric Aerosols, 2017

Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle c... more Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle components has become a considerably important process during the past years due to its large-scale production potential. However, depending on process conditions and material behavior, macroscopic defects such as fiber fracture, gapping or wrinkling are feasible. To counteract such defects, blank holders or grippers, which introduce membrane forces in the laminate, can be employed in the forming process. Usually, the number and location of grippers, as well as direction and magnitude of gripping forces are determined by a cost and time consuming "trial and error" process design. Therefore, an advanced gripper system for online monitoring of gripper forces, elongations and rotations during thermoforming is presented in this work. Along with the kinematics of the grippers, the measured forces supply the beforehand mostly unknown boundary conditions for FE forming simulation. Based on a modeling approach for FE forming simulation of CFRPs implemented in the commercially available FE solver Abaqus, appropriate modeling techniques for gripper-assisted forming are outlined. These modeling techniques are applied to two different generic geometries and the simulation results are compared with a good agreement to experimental tests.

Research paper thumbnail of Virtuelle Produktentwicklung mittels Simulationsmethoden und KI

Lightweight design, Dec 1, 2019

und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Kom... more und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Komplexität und Entwicklungsaufwand aktueller Leichtbaulösungen. Wissenschaftler am KIT untersuchen, wie zukünftig Simulationen und maschinelles Lernen kombiniert werden können, um Entwicklungsprozesse zu beschleunigen. Die durchgängig virtuelle Prozesskette Eine virtuelle Prozesskette ermöglicht die direkte Verknüpfung von Design und finalem FKV-Bauteil unter Berücksichtigung der Wechselwirkungen zwischen Material und

Research paper thumbnail of Experimental and numerical investigation of the contact behavior during FE forming simulation of continuously reinforced composites in wet compression molding

Nucleation and Atmospheric Aerosols, 2019

An approach for rapid prediction of textile draping results for variable composite component geom... more An approach for rapid prediction of textile draping results for variable composite component geometries using deep neural networks

Research paper thumbnail of Towards 3D Process Simulation for In Situ Hybridization of Fiber-Metal-Laminates (FML)

Key Engineering Materials

Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and i... more Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and inherent corrosion resistance.To speed up manufacturing and simultaneously increase the geometrical complexity of the produced FML parts, Mennecart et al. proposed a new single-step process combining deep-drawing with infiltration (HY-LCM). Although the first experimental results are promising, the process involves several challenges, mainly originating from the Fluid-Structure-Interaction (FSI) between deep-drawing and infiltration. This work aims to investigate those challenges to comprehend the underlying mechanisms. A new close-to-process test setup is proposed on the experimental side, combining deep-drawing of a hybrid stack with a linear infiltration. A process simulation model for FMLs is presented on the numerical side, enabling a prediction of the dry molding forces, local Fiber Volume Content (FVC) within the three glass fiber (GF) interlayers, and simultaneous fluid progressio...

Research paper thumbnail of Zeit- und kosteneffiziente Prozess- und Produktentwicklung für den Hochleistungs-Faserverbundleichtbau mittels Nasspresstechnologie

Großserientaugliche Produktionsprozesse von Hochleistungs-Faserverbundkunststoffen stellen aufgru... more Großserientaugliche Produktionsprozesse von Hochleistungs-Faserverbundkunststoffen stellen aufgrund der gewünschten Prozesseffizienz bei gleichzeitiger Realisierung herausragender gewichtsspezifischer Materialeigenschaften ein wichtiges, zukunftsträchtiges Themenfeld dar. Im Automotive-Bereich kommen diese Prozesse verstärkt zur Anwendung, insbesondere bei Premiumfahrzeugen und im Rahmen der E Mobilität. Der erheblichen Gewichtseinsparung und hohen Energieeffizienz von Leichtbaustrukturen stehen bisher jedoch noch hohe Entwicklungs- und Stückkosten (Material, Prozessaufwand) gegenüber. Neben den verschiedenen Varianten der Resin Transfer Moulding (RTM) Technologie bietet sich zur Herstellung leichter, komplex geformter Strukturbauteile das Nasspressverfahren als Großserienanwendung an. Durch Parallelisierung von Prozessschritten in Verbindung mit hochreaktiven Harzsystemen können niedrigere Zykluszeiten erreicht werden als beim RTM-Verfahren. Da für den Nasspressprozess bisher weder...

Research paper thumbnail of Towards numerical prediction of flow-induced fiber displacements during wet compression molding (WCM)

ESAFORM 2021, 2021

Wet compression molding (WCM) provides large-scale production potential for continuous fiber-rein... more Wet compression molding (WCM) provides large-scale production potential for continuous fiber-reinforced structural components due to simultaneous infiltration and draping during molding. Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficient – a considerable economic advantage. Experimental and numerical investigations prove strong mutual dependencies between the physical mechanisms, especially between resin flow (mold filling) and textile forming (draping), similar to other liquid molding techniques (LCM). Although these dependencies provide significant benefits such as improved contact, draping and infiltration capabilities, they may also lead to adverse effects such as flow-induced fiber displacement. To support WCM process and part development, process simulation requires a fully coupled approach including the capability to predict critical process effects. This work aims to demonstrate the suitability of a macroscopic, fully c...

Research paper thumbnail of A 3D process simulation model for wet compression moulding

Composites Part A: Applied Science and Manufacturing, 2021

Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-r... more Wet Compression Moulding (WCM) provides large-scale production potential for continuously fibre-reinforced structural components due to simultaneous infiltration and draping during moulding. Due to thicknessdominated infiltration of the laminate, comparatively low cavity pressures are sufficient-a considerable economical advantage. Similar to other Liquid Compression Moulding (LCM) processes, forming and infiltration strongly interact during process. However, the degree of forming is much higher in WCM, which disqualifies a sequential modelling approach. This is demonstrated in this work via experimental characterisation of the interaction between compaction and permeability of a woven fabric and by trials with a transparent double dome geometry, which facilitates an in situ visualization of fluid progression during moulding. In this light, and in contrast to existing form filling approaches, a forming-inspired, three-dimensional process simulation approach is presented containing two fully-coupled macroscopic forming and fluid-submodels. The combined model is successfully benchmarked using experimental double dome trials with transparent tooling.

Research paper thumbnail of Continuous Process Simulation for Continuous Fiber Reinforced Composites

Research paper thumbnail of Modeling and validation of gripper induced membrane forces in finite element forming simulation of continuously reinforced composites

AIP Conference Proceedings, 2017

Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle c... more Thermoforming of multilayered, thermoplastic tape-laminates into lightweight structural vehicle components has become a considerably important process during the past years due to its large-scale production potential. However, depending on process conditions and material behavior, macroscopic defects such as fiber fracture, gapping or wrinkling are feasible. To counteract such defects, blank holders or grippers, which introduce membrane forces in the laminate, can be employed in the forming process. Usually, the number and location of grippers, as well as direction and magnitude of gripping forces are determined by a cost and time consuming "trial and error" process design. Therefore, an advanced gripper system for online monitoring of gripper forces, elongations and rotations during thermoforming is presented in this work. Along with the kinematics of the grippers, the measured forces supply the beforehand mostly unknown boundary conditions for FE forming simulation. Based on a modeling approach for FE forming simulation of CFRPs implemented in the commercially available FE solver Abaqus, appropriate modeling techniques for gripper-assisted forming are outlined. These modeling techniques are applied to two different generic geometries and the simulation results are compared with a good agreement to experimental tests.

Research paper thumbnail of Estimating Optimum Process Parameters in Textile Draping of Variable Part Geometries - A Reinforcement Learning Approach

Procedia Manufacturing, 2020

Fine-tuning of manufacturing processes for optimum part quality requires many resource-intensive ... more Fine-tuning of manufacturing processes for optimum part quality requires many resource-intensive trial experiments in practice. To reduce the experimental effort, physics-based process simulations in conjunction with optimisation algorithms can be applied, e.g. finite-element-models and evolutionary algorithms. However, they generally require considerable numerical expertise and long computation times. Efficient optimisation of such expensive-to-evaluate models often employs surrogate-based optimisation (SBO). SBO constructs numerically inexpensive approximations of the original model, which guide the optimiser in the parameter space. This allows concentrating costly simulations on the most promising regions. While SBO significantly reduces the computational load in many cases, current SBO-strategies are inevitably problem-specific and cannot be reused in other, even similar situations. Consequently, subtle problem variations, e.g. minor geometry changes in material forming, require an entirely new optimisation and all previous numerical effort is in vain. Thus, surrogate techniques with generalised applicability are an open field of research. Machine Learning techniques using convolutional neural networks (CNNs) are capable of 'learning' complex system dynamics from data. In this work, CNNs are used to extend the predictive capabilities of SBO towards variable instead of fixed manufacturing settings. Specifically, material draw-in optimisation in textile forming ('draping') for variable geometries is studied. Using reinforcement learning, a CNN is trained to estimate optimum positions of pressure pads during draping of a pre-specified class of box-shaped geometries. Once trained, the CNN interprets a forming result and infers beneficial pad positions. Unlike conventional SBO strategies, it can also give recommendations for variable geometries from the selected geometry class. The paper shows that, in principle, CNNs are able to extract information from a range of different forming tasks and apply it to a new, unknown situation. Since they reuse information gained from previous simulations, they are considered a viable option for future, generalised SBO-strategies.

Research paper thumbnail of Material Modeling in Forming Simulation of Three-Dimensional Fiber-Metal-Laminates – A Parametric Study

Procedia Manufacturing, 2020

Forming of fiber-metal-laminates (FML) into complex geometries is challenging, due to the low fra... more Forming of fiber-metal-laminates (FML) into complex geometries is challenging, due to the low fracture toughness of the fibers. Several researchers have addressed this topic in recent years. A new manufacturing process has been introduced in our previous work that successfully combines deep drawing with thermoplastic resin transfer molding (T-RTM) in a single process step. During molding, the fabric is infiltrated with a reactive monomeric matrix, which polymerizes to a thermoplastic after the forming process is completed. In our previous work, a numerical modeling approach was presented for this fully integrated process, investigating a hybrid laminate with 1 mm thick metal sheets of DC04 as top layers and three inner glass fiber layers. Although initial results were promising, there were still some pending issues regarding the modeling of material behavior. The current study aims to address several of these open issues and to provide a general modelling framework for future enhancements. For this purpose, the existing modelling approach is extended and used for parameter analysis. Regarding the influence of different material characteristics on the forming result, shear, bending and compression properties of the fabric are modified systematically. It is shown, that the compression behavior and particularly the tension-compression anisotropy of the fabric is of high importance for modelling the combined forming of fabric and metal. The bending and shear properties of the fabric are negligible small compared to the metal stiffness which dominates the draping process. Finally, it is demonstrated that modelling the fabric layers using continuum shells provides a promising approach for future research, as it enables a suitable way to account for transversal compaction during molding.

Research paper thumbnail of A 3D Modelling Approach for Fluid Progression during Process Simulation of Wet Compression Moulding – Motivation & Approach

Procedia Manufacturing, 2020

Wet compression moulding (WCM) provides large-scale production potential for continuous fibre-rei... more Wet compression moulding (WCM) provides large-scale production potential for continuous fibre-reinforced structural components due to simultaneous infiltration and draping during moulding (viscous draping). Due to thickness-dominated infiltration of the laminate, comparatively low cavity pressures are sufficienta considerable economic advantage. Experimental and numerical investigations prove strong mutual dependencies between the physical mechanisms, especially between resin flow and textile forming. Understanding and suitable modelling of these occurring physical mechanisms is crucial for process development and final part design. While existing modelling approaches are suitable for infiltration of preformed fabrics within various liquid moulding technologies, such as CRTM/RTM or VARI, WCM requires a fully coupled simulation approach for resin progression and concurrent stack deformation. Thus, the key challenge is to efficiently link these two aspects in a suitable framework. First, this work demonstrates that a three-dimensional approach for fluid progression during moulding is needed to capture WCM-process boundary conditions. In this regard, a novel test bench is used to investigate the impact of infiltration on the transversal compaction behaviour of a woven fabric. Moreover, the test setup is applied to determine the in-plane permeability values of the same material corresponding to the beforehand applied compaction states. Results are verified by comparison with an existing linear test setup. In the second part, initial steps towards a three dimensional extension of an existing 2D modelling approach are outlined. For this purpose, a macroscopic FE-based three-dimensional formulation of Darcy's law is utilized within a User-Element in ABAQUS/EXPLICIT. Essential mechanisms within the element are presented. Additional control volumes (FE/CV) are applied to ensure mass conservation. Eventually, it is demonstrated, that the simulation model can predict the average fluid pressure beneath a punch during pre-infiltrated compaction experiments. Finally, major benefits and forthcoming steps for a fully-coupled 3D modelling approach for WCM are outlined.

Research paper thumbnail of Capabilities of Macroscopic Forming Simulation for Large-Scale Forming Processes of Dry and Impregnated Textiles

Procedia Manufacturing, 2020

Forming of continuously fibre-reinforced polymers (CoFRP) has a significant impact on the structu... more Forming of continuously fibre-reinforced polymers (CoFRP) has a significant impact on the structural performance of composite components, underlining the importance of forming simulation for CoFRP product development processes. For an integrated development of industrial composite components, efficient forming simulation methods are in high demand. Application-oriented method development is particularly crucial for industrial needs, where large and complex multi-layer components are manufactured, commercial FE software is used, and yet high prediction accuracy is required. To meet industrial demands, this contribution gives an insight in macroscopic forming simulation approaches that utilize the FE software ABAQUS in combination with user-defined material models and finite elements. Three CoFRP forming technologies are considered, which are in industrial focus due to their suitability for mass production: textile forming of dry unidirectional non-crimp fabrics (UD-NCF), thermoforming of pre-impregnated UD tapes and wet compression moulding (WCM). In addition to the highly anisotropic, largestrain material behaviour that composite forming processes have in common, the three process technologies face various process-specific modelling challenges. UD-NCFs require material models that capture the deformation behaviour and the slippage of the stitching. Thermoforming of UD tapes is highly rate-and temperature-dependent, calling for rheological membrane and bending modelling. Moreover, a thermomechanical approach including crystallisation kinetics enables the prediction of potential phase-transition during forming and resulting defects in the semicrystalline thermoplastic matrix. For simultaneous forming and infiltration in wet compression moulding, a finite Darcy-Progression-Element is superimposed with the membrane and shell elements for forming simulation, capturing infiltration-dependent material properties. The three outlined technologies illustrate the complexity and importance of further simulation method development to support future process development.

Research paper thumbnail of Virtuelle Produktentwicklung mittels Simulationsmethoden und KI

Lightweight Design, 2019

und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Kom... more und höhere Bauteilanforderungen bei gleich zeitig kürzer werdenden Entwicklungszyklen erhöhen Komplexität und Entwicklungsaufwand aktueller Leichtbaulösungen. Wissenschaftler am KIT untersuchen, wie zukünftig Simulationen und maschinelles Lernen kombiniert werden können, um Entwicklungsprozesse zu beschleunigen. Die durchgängig virtuelle Prozesskette Eine virtuelle Prozesskette ermöglicht die direkte Verknüpfung von Design und finalem FKV-Bauteil unter Berücksichtigung der Wechselwirkungen zwischen Material und

Research paper thumbnail of Virtual Product Development Using Simulation Methods and AI

Lightweight Design worldwide, 2019

Increased material diversity and higher component requirements along with shorter development cyc... more Increased material diversity and higher component requirements along with shorter development cycles increase the complexity and development effort of today's lightweight solutions. Scientists at KIT are investigating new opportunities to combine simulations and machine learning to accelerate development processes. Research and development have been paving the way for increasingly capable material and design solutions using fiber-reinforced polymers (FRPs) for many decades. However, the enormous effort required for a manufacturable component design and process setup hinders the potential to achieve lightweight design. Using efficient design methods is the only way to realize the significant potential of FRPs in the final product in an economically viable manner, thereby justifying higher material costs. This holds in particular for medium-and large-scale production processes where the interaction between component performance and commercial requirements is particularly strong, Figure 1 © KIT | FAST Holistic approach Requirements for economic lightweight solutions Exemplary implementation within a virtual process chain Virtual prediction of material-and process-specific interactions for a reliable and efficient design.

Research paper thumbnail of Development of a Modular Draping Test Bench for Analysis of Infiltrated Woven Fabrics in Wet Compression Molding

Key Engineering Materials, 2019

The wet compression molding (WCM) process enables short cycle times for production of fiber-reinf... more The wet compression molding (WCM) process enables short cycle times for production of fiber-reinforced plastics due to simultaneous infiltration, viscous draping and consolidation in one process step. This requires a comprehensive knowledge of occurring mutual dependencies in particular for the development of process simulation methods and for process optimization. In this context, it is necessary to develop suitable test benches to enable an evaluation of the outlined viscous draping behavior. In order to evaluate and suitably design the draping process, grippers are mounted on a surrounding frame, which enables targeted restraining of the local material draw-in during forming. In supporting the development of the new test bench, first experimental and simulation results are compared, which thereby enables a first validation of the simulation approaches. Results show a good agreement between experimental and numerical results in terms of shear deformation and final gripper displace...