https://popups.uliege.be/esaform21/index.php?id=364 Publications of Auteurs Maik Gude fr 0 https://popups.uliege.be/esaform21/index.php?id=4293 Thermally supported clinching (Hotclinch) is a novel promising process to join dissimilar materials. Here, metal and fibre-reinforced thermoplastics (FRTP) are used within this single step joining process and without the usage of auxiliary parts like screws or rivets. For this purpose, heat is applied to improve the formability of the reinforced thermoplastic. This enables joining of the materials using conventional clinching-tools. Focus of this work is the modelling on mesoscopic scale for the numerical simulation of this process. The FTRP-model takes the material behaviour both of matrix and the fabric reinforced organo-sheet under process temperatures into account. For describing the experimentally observed phenomena such as large deformations, fibre failure and the interactions between matrix and fibres as well as between fibres themselves, the usage of conventional, purely Lagrangian based FEM methods is limited. Therefore, the combination of contact-models with advanced modelling approaches like Arbitrary-Lagrangian-Eulerian (ALE), Coupled-Eulerian-Lagrangian (CEL) and Smooth-ParticleHydrodynamics (SPH) for the numerical simulation of the clinching process are employed. The different approaches are compared with regard to simulation feasibility, robustness and results accuracy. It is shown, that the CEL approach represents the most promising approach to describe the clinching process. Thu, 01 Apr 2021 17:51:44 +0200 Thu, 01 Apr 2021 17:51:44 +0200 https://popups.uliege.be/esaform21/index.php?id=4293 https://popups.uliege.be/esaform21/index.php?id=4266 Liquid composite molding (LCM) has established as a high quality manufacturing process for fiber reinforced composite structures. In order to reduce cycle times significantly, novel fast curing matrix resins are being introduced into series production. These put high requirements on process control and part reproducibility. Problems that may be encountered in this context involve process-induced distortion and surface waviness resulting from anisotropic and cure-dependent material properties. Numerical simulations represent a powerful approach to avoid the use of costly trial-and-error methods. For this reason, a simulation approach is being developed which aims at the prediction of residual stresses and accompanying effects on different length scales. Based on a resin characterization comprising reaction kinetics, cure-dependent relaxation modulus as well as thermal expansion and pressure-dependent chemical shrinkage, a generalized MAXWELL model is selected to describe the process-related mechanical behavior of the thermoset. Taking into account the influence of the process parameters on the resin properties enables a detailed analysis of process-property-relationships. By this, the developed simulation approach offers the possibility of a comprehensive analysis of both local and global process-induced phenomena and hence prevention of flaws. Thu, 01 Apr 2021 17:37:36 +0200 Thu, 01 Apr 2021 17:37:36 +0200 https://popups.uliege.be/esaform21/index.php?id=4266 https://popups.uliege.be/esaform21/index.php?id=4252 The use of reinforcing bars has been known for more than 150 years in construction sector, in order to compensate the limited tensile strength of concrete. Steel is the most widespread and standardized rebar material. As industry targets a reduction of resource consumption and increased freedom of design, novel materials come into the scope of current research efforts. In this context, carbon fiber reinforced polymers (CFRP) have become a promising candidate for rebar materials as they offer excellent corrosion resistance and mechanical properties. Their use enables significant reduction of concrete cover in future buildings and cost-efficient maintenance of bridges. The resin system used for manufacturing of CFRP rebars dictates possible applications. Thermoplastic polymers offer the advantage of formability in a molten state. On the other hand, they provide limited heat and fire resistance, what hinders further industrialization. In contrast, thermosets deliver high mechanical and thermal properties due to their polymeric network structure. This is also the reason for their restricted formability after gelation has occurred. However, it is known that epoxy resins may sustain substantial plastic deformation when being deformed at elevated temperatures and in a partial cure state. In this work, a commercially available resin system is selected and qualified for potential use in thermoset-based CFRP rebars. Based on the resin characterization comprising reaction kinetics as well as tensile and compressive tests at partial cure, general guidelines and limits for secondary forming are derived. The feasibility is demonstrated by bending tests on CFRP stripes with varied fiber orientation. Thu, 01 Apr 2021 17:32:01 +0200 Thu, 01 Apr 2021 17:32:01 +0200 https://popups.uliege.be/esaform21/index.php?id=4252 https://popups.uliege.be/esaform21/index.php?id=3807 The economical production of lightweight structures with tailor-made properties and load-adapted geometry is limited using conventional technologies. Additive manufacturing processes offer a high potential to meet these requirements, where the established solutions are based primarily on thermoplastics matrix systems. From a process-technological point of view, thermoplastics enable simplified processing, but only a limited range of applications for high-performance components. These limitations are due to their comparatively low heat resistance, low melting temperatures and limited adhesion to embedded reinforcing fibers. In contrast, thermosets show high potential for realization of high- performance lightweight structures with adaptable properties. The present work employs a UV-curing thermoset resin for the impregnation of a continuous filament strand for 3D printing. The main challenge is to reconcile the crosslinking reaction of the thermoset and the process velocity during impregnation and cure. The liquid polymer must provide low initial viscosity to impregnate the filaments and a sufficiently high cure rate and dimensional stability after discharge from the print head to ensure sufficient bonding strength to the substrate. To demonstrate feasibility, a prototypic print head with UV-LED activation was designed and implemented. With a robot-guided printing platform, the 3D-deposition of continuous fiber-reinforcements without additional supporting structures can be realized. To derive initial process parameters, reaction and thermos-mechanical properties are determined by rheometer measurements. Impregnation and cure behavior of the glass fiber reinforced resin is investigated. The presented results provide a reliable process window and a straightforward process monitoring method for further enhancement of the conceived 3D printing process. Mon, 29 Mar 2021 14:43:22 +0200 Thu, 08 Apr 2021 20:40:09 +0200 https://popups.uliege.be/esaform21/index.php?id=3807 https://popups.uliege.be/esaform21/index.php?id=2781 In lightweight design, clinching is a cost-efficient solution as the joint is created through localized cold-forming of the joining parts. A clinch point’s quality is usually assessed using ex-situ destructive testing methods. These, however, are unable to detect phenomena immediately during the joining process. For instance, elastic deformations reverse and cracks close after unloading. In-situ methods such as the force-displacement evaluation are used to control a clinching process, though deviations in the clinch point geometry cannot be derived with this method. To overcome these limitations, the clinching process can be investigated using in-situ computed tomography (in-situ CT). However, a clinching tool made of steel would cause strong artefacts and a high attenuation in the CT measurement, reducing the significance of this method. Additionally, when joining parts of the same material, the sheet-sheet interface is hardly detectable. This work aims at identifying, firstly, tool materials that allow artefact-reduced CT measurements during clinching, and, secondly, radiopaque materials that can be applied between the joining parts to enhance the detectability of the sheet-sheet interface. Therefore, both CT-suitable tool materials and radiopaque materials are selected and experimentally investigated. In the clinching process, two aluminium sheets with radiopaque material in between are clinched in a single-step (rotationally symmetric joint without cut section). It is shown that e.g. silicon nitride is suited as tool material and a tin layer is suitable to enhance the detectability of the sheet-sheet interface. Wed, 24 Mar 2021 18:59:21 +0100 Sat, 10 Apr 2021 13:51:32 +0200 https://popups.uliege.be/esaform21/index.php?id=2781 https://popups.uliege.be/esaform21/index.php?id=355 Unidirectional non-crimp fabrics (UD-NCF) provide the highest lightweight potential among dry textile materials. Compared to multiaxial NCF, the fabric layers in UD-NCF enable a more targeted tailoring. Compared to woven fabrics, the fibres of UD-NCF are straight without weakening undulations. However, the formability of UD-NCF is more challenging compared to woven fabrics. The yarns are bonded by a stitching and the deformation behaviour highly depends on this stitching and on the slippage between the stitching and the fibre yarns. Moreover, distinct local draping effects occur, like gapping and fibre waviness, which can have a considerable impact on the mechanical performance. Such local effects are particularly challenging or even impossible to be predicted by macroscopic forming simulation. The present work applies a previously published macroscopic UD-NCF modelling approach to perform numerical forming analyses and evaluate the prediction accuracy of forming effects. In addition to fibre orientations and shear angles, as investigated in previous work, the present work also provides indication for fibre area ratios, gapping, transverse compaction and fibre waviness. Moreover, the prediction accuracy is validated by comparison with experimental tests, where full-field strains of inner plies are captured by prior application of dots onto the fibre yarns, by measuring them via radiography and applying a photogrammetry software. The modelling approach provides good prediction accuracy for fibre orientations, shear strains and fibre area ratio. Conversely, normal fibre strains, indicating fibre waviness, and transverse strains, indicating gapping, show some deviations due to the multiscale nature of UD-NCF that cannot be captured entirely on macroscopic scale. Fri, 19 Mar 2021 17:12:09 +0100 Mon, 29 Mar 2021 17:40:40 +0200 https://popups.uliege.be/esaform21/index.php?id=355