https://popups.uliege.be/esaform21/index.php?id=77 Coordinator: Dr. Pierpaolo Carlone Co-organisers: Prof. Remko Akkerman, Prof. Emmanuelle Abisset-Chavanne, Prof. Philippe Boisse, Prof. Stepan Lomov, Prof. James A. Sherwood Description: The use of composite materials is expanding rapidly in various fields, in particular in civil aeronautics. These high level applications of composite materials created a significant demand for scientific knowledge and computational tools for composite material manufacturing. The mechanical behavior of the composite materials in service is dominated by the fiber orientation and density. The forming process, in turn, determines the fiber distribution. Hence, not only the in-service performance (stiffness, damage, fatigue…) has to be predicted, but certainly also the complex manufacturing processes, of which there are many. Their knowledge and their modelling are essential for the analysis of the composite structures in service. Since2001 and the Liege ESAFORM conference, an annual “Composite forming processes” mini symposium gathers researchers from Europe, and also from USA, Asia and Australia, who can present their works and exchange their points of view concerning research in the field of composite forming. The ESAFORM conference thus became a privileged and single place for this subject. Experimental and numerical “benchmarks” were set up on in-plane shear properties, double dome forming and friction. They are discussed within the composites forming mini-symposia. The topics of the developed sessions concern in particular: Material characterization; Constitutive laws during forming; Forming simulations; Mesoscopic analyses; Resin injection; Permeability, Fiber suspensions, Thermoforming; Contact and friction; Benchmark efforts, Natural fibres as reinforcement, Additive manufacturing of composites. Mini Symposia fr Wed, 03 Mar 2021 09:27:47 +0100 Thu, 22 Apr 2021 16:58:59 +0200 https://popups.uliege.be/esaform21/index.php?id=77 0 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 https://popups.uliege.be/esaform21/index.php?id=355 https://popups.uliege.be/esaform21/index.php?id=366 In recent years, advanced manufacturing processes have been developed to increase the speed of production in order to reduce production costs. At the scale of thermoplastic composites, the translation is the combination of advanced manufacturing processes. The focus in this study is more specifically on the coupling of automated lay-up (AFP) and stamp forming processes. To date, a consolidation process, such as press-consolidation of thermoplastic composites, obtained blanks. Several trials have begun using an automated fiber placement consolidation to reduce manufacturing time and use unidirectional material. However, the combination of AFP and stamp forming is useful if it optimizes this process without the blank’s full consolidation, which by resulting reduces the manufacturing time. This study estimates blank characteristics through thermal history imposed by a more rapid manufacturing process. A set of blanks with varying process parameters is produced to investigate the influence at the microscopic scale. The interface behaviour is observed with optical microscope and image processing. A statistical study applied to the process is carried out in order to relate the material observations to the input parameters. The results of this study are used for the study of the next process of the combination: the stamp forming. Fri, 19 Mar 2021 17:29:04 +0100 https://popups.uliege.be/esaform21/index.php?id=366 https://popups.uliege.be/esaform21/index.php?id=376 In this study, a sequential thermoforming and squeeze flow simulation approach for Glass Mat Thermoplastic (GMT) material is proposed and applied to a hat section geometry using input properties based upon Tepex flowcore, a long glass fiber reinforced polyamide (PA/GF) mat manufactured by Lanxess. First, a fully-coupled thermomechanical simulation is conducted based on a purely Lagrangian description, to efficiently capture thermoforming. Subsequently, relevant state variables are mapped and initialized for a Coupled-Eulerian-Lagrangian (CEL) approach. The CEL approach is adopted to accurately capture squeeze flow, which is not possible by a purely Lagrangian description. While numerical techniques differ, both approaches use the same three-dimensional and thermomechanical constitutive equations including an equation of state, a nonlinear viscosity model, and crystallization kinetics, implemented through a material user-subroutine (VUMAT) for the commercially available simulation software package ABAQUS/Explicit. Fri, 19 Mar 2021 17:35:11 +0100 https://popups.uliege.be/esaform21/index.php?id=376 https://popups.uliege.be/esaform21/index.php?id=475 In recent years, the concepts of industry 4.0 are widely spreading in many different sectors, from agriculture to home automation, from transportation systems to manufacturing processes. One of the pillars of this concept is related to the use of robotic cells. The focus of the present work is the robotic automated layup of dry fibrous preforms to be employed in liquid composite molding (LCM) processes. In particular, the article describes a software tool developed to simulate the automated placement and layup of fiber fabrics and tissues on complex shape molds by means of a robotic system. The tool has been coded in Matlab language. An end-effector has been appositely designed for the fiber layup and it has been included in the model. The simulation provides as output the path generation and the configuration of the robotic arm and of end effector along the entire layup process. The implemented code has been compared with the commercial software RoboDK. Fri, 19 Mar 2021 22:51:39 +0100 https://popups.uliege.be/esaform21/index.php?id=475 https://popups.uliege.be/esaform21/index.php?id=496 During the forming stage in the RTM process, deformations and orientations of yarns at the mesoscopic scale are essential to evaluate mechanical behaviors of final composite products and calculate the permeability of the reinforcement. However, due to the high computational cost, it is very difficult to carry out a mesoscopic draping simulation for the entire reinforcement. In this paper, a macro-meso scale simulation of composite reinforcements is presented in order to predict mesoscopic deformations of the fabric in a reasonable calculation time. The proposed multi-scale method allows linking the macroscopic simulation of the reinforcement with the mesoscopic modelling of the RVE through a macromeso embedded analysis. On the base of macroscopic simulations using a hyperelastic constitutive law of the reinforcement, an embedded mesoscopic geometry is first deduced from the macroscopic simulation of the draping. To overcome the inconvenience of the macro-meso embedded solution which leads to unreal excessive yarn extensions, local mesoscopic simulations based on the embedded analysis are carried out on a single RVE by defining specific boundary conditions. Finally, the multi-scale forming simulations are investigated in comparison with the experimental results, illustrating the efficiency of the proposed approach, in terms of accuracy and CPU time. Sat, 20 Mar 2021 00:05:47 +0100 https://popups.uliege.be/esaform21/index.php?id=496 https://popups.uliege.be/esaform21/index.php?id=506 In composite sheet preforming, the combination of binder-ring force and friction induce in-plane tension that mitigates the onset of wrinkling, but too much force can induce tearing. Thus, the processing conditions must be designed to strike a balance between these competing manufacturing-induced defects. Compounding the challenge to prescribe the appropriate processing conditions is the potential change in thickness of the sheets as a function of in-plane shear. The variation in the thickness from point to point in the ply stack will result in a nonuniform pressure under the binder ring. In the current research, the preforming step is simulated using a discrete mesoscopic modeling approach in LS-DYNA. Thickness-stretch shell elements are used to capture the evolution in the sheet thickness and the in-plane shear stiffness of the deformed sheet. Finite element simulations and preforming experiments are completed for the same processing conditions. The preliminary results for the punch force as a function of displacement, the state of shear over the part surface, and the distribution and magnitude of the wrinkles showed excellent correlation between the model and the experiment. The simulation results show that the shape of the punch force vs. tool depth curve gives insight into the onset of wrinkles. The simulation is then used to predict a binder-ring force that would mitigate wrinkle formation in a four-layer preform. Sat, 20 Mar 2021 00:19:42 +0100 https://popups.uliege.be/esaform21/index.php?id=506 https://popups.uliege.be/esaform21/index.php?id=759 Thermoforming is an attractive process for the low-cost high-volume manufacture of textile-reinforced composite structures with complicated geometries. Tool/ply and ply/ply frictions play critical roles during forming. The friction between the binder ring and the blank induce an in-plane tensile stress that mitigates wrinkling. Unwanted wrinkling can develop across the part if the in-plane stresses are too low but tearing of the material can occur if the applied stresses are too high. Understanding the role that friction plays during thermoforming can give insight on how to mitigate these manufacturing-induced defects in the part. In the current work, the coefficients of friction for two unidirectional cross-ply ultra-high molecular weight polyethylene (UHMWPE) materials are characterized as a function of pressure, fiber orientation, side of material, and pulling rate for [0/90/0/90] cross-ply sheets. The materials are tested at multiple fiber orientations to understand the influence that fiber direction has with respect to the coefficients of friction and on each respective side of the material to understand how surface topology influences the coefficients of friction. The results of the testing are found to correlate with modified Hersey numbers. Sun, 21 Mar 2021 13:07:11 +0100 https://popups.uliege.be/esaform21/index.php?id=759 https://popups.uliege.be/esaform21/index.php?id=883 Finite element (FE) forming simulation offers the possibility of a detailed analysis of the deformation behaviour of engineering textiles during forming processes, to predict possible manufacturing effects such as wrinkling or local changes in fibre volume content. The majority of macroscopic simulations are based on conventional two-dimensional shell elements with large aspect ratios to model the membrane and bending behaviour of thin fabrics efficiently. However, a three-dimensional element approach is necessary to account for stresses and strains in thickness direction accurately, which is required for processes with a significant influence of the fabric’s compaction behaviour, e.g. wet compression moulding. Conventional linear 3D-solid elements that would be commercially available for this purpose are rarely suitable for high aspect ratio forming simulations. They are often subjected to several locking phenomena under bending deformation, which leads to a strong dependence of the element formulation on the forming behaviour [1]. Therefore, in the present work a 3D hexahedral solid-shell element, based on the initial work of Schwarze and Reese [2,3], which has shown promising results for the forming of thin isotropic materials [1], is extended for highly anisotropic materials. The advantages of a locking-free element formulation are shown through a comparison to commercially available solid and shell elements in forming simulations of a generic geometry. Additionally, first ideas for an approach of a membrane-bending-decoupling based on a Taylor approximation of the strain are discussed, which is necessary for an accurate description of the deformation behaviour of thin fabrics. Mon, 22 Mar 2021 09:49:49 +0100 https://popups.uliege.be/esaform21/index.php?id=883 https://popups.uliege.be/esaform21/index.php?id=970 Pultrusion is an established and efficient process for producing continuous fiber-reinforced composites. The resin systems that are currently most frequently used are unsaturated polyesters and vinylesters. These have a long pot life, are well known, and have good processing properties. Highly reactive resins such as polyurethane (PU) and amine hardening epoxy have been in use for a few years. These resin classes are remarkable for their extended range of properties. This opens up new application fields for pultrusion technology but poses challenges for the processing technology. Short pot lives of just a few minutes require a modified process: closed injection pultrusion (CIP). Various approaches about the design and layout of the internal geometry of the injection and impregnation chambers (ii-chamber) are the subject of ongoing research. Numerous parameters influence the impregnation process in the ii-chamber and the quality of the resulting composite. In this study, two innovative, highly reactive resins for use in the pultrusion process were analyzed, both resins based on aliphatic polyurethanes. In phase 1 of the experiments, a commercial aliphatic polyurethane-system for pultrusion applications was used. In Phase 2, the recently developed bio-based aliphatic polyurethane-system for pultrusion applications was used for the study's main experiments. The aim of the study was to analyze the material and processing properties with various modifications of the impregnation setup. Therefore, a newly developed ii-chamber and die were tested. The ii-chamber was designed to enable easy adjustment of some of the main influencing parameters during the pultrusion process. A test strategy was developed to evaluate the properties of the composites. An assessment of the influence of the process- and die-based parameters should enable an evaluation of the optimal processing settings by analysis of the material characteristics. The most significant effect of variations in the pultrusion process was found in the interlaminar shear strength (ILSS). ILSS was analyzed for all process variations for both resin systems. Mon, 22 Mar 2021 10:44:54 +0100 https://popups.uliege.be/esaform21/index.php?id=970 https://popups.uliege.be/esaform21/index.php?id=1580 Composite materials can be produced by several technologies, such as Liquid Composite Manufacturing (LCM). In this technology, a fabric can be formed by highly double curved punch geometries. During its forming, the fabric is submitted to several deformations and mechanical stresses, like biaxial tensile stress, shear, bending, compaction and friction. The cumulative effect of these stresses leads to the appearance of different types of defects such as wrinkles, buckles, sliding, etc. These defects may have a significant influence on the mechanical properties of the final composite materials. In order to understand the forming mechanisms of these defects, as well as their effect on the behavior of composite materials, an experimental machine was designed and built. The aim of this machine is to generate different types of defects with controlled and adjusted amplitudes (calibrated defects), in samples of a fabric. These samples are then used to manufacture composite samples with calibrated defects, by an LCM process. The defected composite samples are then tested and compared with composite samples without defects. The obtained results have identified the experimental parameters corresponding to the appearance of different types of defects. Mon, 22 Mar 2021 20:14:18 +0100 https://popups.uliege.be/esaform21/index.php?id=1580 https://popups.uliege.be/esaform21/index.php?id=1607 Simulations at microscopic scale are subject of research in many fields of continuous fiber reinforced materials. They allow the virtual characterization with clearly defined boundary conditions and the investigation of effects that cannot easily be observed in experimental tests, such as crack initiation. While the influence of differently detailed modeling, such as variable fiber radii, is well investigated for consolidated composite materials, that influence is not well investigated for dry yarns. The effect of different modeling aspects on the shearing of statistical volume elements (SVE) is object of this study. Those aspects are in particular the SVE’s size and side ratio, the deformation velocity, the friction coefficient and the initial stress of the elements. The investigations have shown that the deformation of the SVEs is very sensitive to changes of the named parameters. Especially parameters that influence the number of fiber contacts or the friction forces have a noticeable effect on the shear stress. In addition, changes in the velocity have a significant impact on the deformation. Therefore, it is necessary to characterize the fiber and yarn parameters precisely and transfer them into the simulation model to obtain a realistic deformation behavior. Mon, 22 Mar 2021 20:16:39 +0100 https://popups.uliege.be/esaform21/index.php?id=1607 https://popups.uliege.be/esaform21/index.php?id=1938 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 coupled, three-dimensional process simulation approach, to predict the process behavior during WCM, including flow-induced fiber displacements. The developed fluid model is superimposed to a suitable 3D forming model, which accounts for the deformation mechanisms including non-linear transverse compaction behavior. A strong Fluid-Structure-Interaction (FSI) enforced by Terzaghi’s law is applied to assess flow-induced fiber displacements during WCM within a porous UD-NCF stack in a homogenized manner. Accordingly, resulting local deformations are considered within the pressure field. All constitutive equations are formulated with respect to fiber deformation under finite strains. Results of a parametric study underline the relevance of contact conditions within the dry and infiltrated stack. The numerically predicted results are benchmarked and verified using both own and available experimental results from literature. Tue, 23 Mar 2021 10:43:52 +0100 https://popups.uliege.be/esaform21/index.php?id=1938 https://popups.uliege.be/esaform21/index.php?id=2056 During forming of complex fiber-metal laminates (FML), compressive stress zones occur. In pure textile forming, these compressive stresses typically lead to extensive wrinkling. In FML forming, however, wrinkling is partly hindered by the metal layers. Thus, combined stress states occur, where compression influences the deformation. In forming simulation, these compressive stresses can lead to erroneous formation of shear bands within the fabric layer, if the deformation behavior is not modelled correctly. Simple fabric models neither consider interactions between roving directions nor model interactions between membrane strains and shear strains. More advanced invariant-based hyperelastic material models are able to capture these interactions, but only consider tension and shear, while disregarding compression. A common assumption is to set the fabric compression stiffness close to zero. Experimentally, the in-plane fabric compression stiffness has not been determined so far. However, in FML forming, the compression stiffness and the combined compression-tension-shear behavior becomes relevant. In this article, the authors summarize and analyze the capacity of state-of-the-art fabric material models to predict the deformation behavior of fabrics under combined loading. Based on these findings, conclusions are drawn for a new macroscopic modeling approach for woven fabrics, including coupling of tension, compression and shear. Tue, 23 Mar 2021 12:37:11 +0100 https://popups.uliege.be/esaform21/index.php?id=2056 https://popups.uliege.be/esaform21/index.php?id=2299 Recent years have seen the development and democratization of continuous fibre composite materials for the manufacture of primary aeronautical structures. Composite materials exhibit excellent specific properties compared to aluminium alloys historically used for these applications. The need in cadence improvement leads the aeronautic industry to consider new processes for primary aeronautical structures manufacturing. Therefore, new dry reinforcements are developed, such as the HiTape® reinforcement designed by Hexcel Reinforcements. HiTape® plies are designed for automated laying in order to build dry stacks that can be formed and infused/injected by a liquid resin afterwards to greatly increase the production rates. To understand and predict results from the forming stage, numerical models are considered as a useful tool. In this work, we propose a new computational approach to model the forming stage of dry HiTape® stacks. The HiTape® ply is a slender structure, exhibiting a transversely isotropic behaviour in large deformations as well as a non-linear bending behaviour. Another particularity is that the bending stiffness of the ply is not directly related its membrane stiffness. When stacks are considered, inter-ply phenomena (opening and sliding) appear and greatly influence the bending stiffness of the structure. To model every of these specificities, diverse techniques are used: solid-shell elements are considered to answer the ply slenderness, embedded elements approach helps to model the membrane/bending behaviours decoupling, frictional cohesive zone model stands for inter-ply phenomena and the particular behaviour of the ply is described using a non-linear physical-invariant based hyperelastic constitutive. The finite element (FE) software Abaqus will be used in this work. Tue, 23 Mar 2021 15:59:16 +0100 https://popups.uliege.be/esaform21/index.php?id=2299 https://popups.uliege.be/esaform21/index.php?id=2520 The originality of this work consists of studying the stamping behaviour of tufted and un-tufted multi-layer carbon preforms. Several tufted preforms with different stratifications have been manufactured. The stamping test was carried out using a hemispherical punch and conducted at two blank-holder pressures (0.05 and 0.2 MPa). The experimental data show that the addition of tufting yarn, the number of layers and the blank-holder pressure significantly affected the forming behaviour: the tufted preform presents a higher punch force, lower material drawin and shear angles with significant structural defects than the un-tufted preform. The increase of the blank-holder pressure increases all these characteristics and emphasizes the structural defects on the fibrous reinforcements. Similarly, the transition from two layers to four layers lamination at the same blank-holder pressure is followed by an increase of the punch force, reducing the material draw-in and the shear angles especially those measured at the transient zone, and causes more structural defects on all stamped preforms. Therefore, two localized tufting configurations, Right Localized Tufted and Inclined Localized Tufted, at the stamping transition area have been proposed. The results show that these two configurations present a minimum punch force and a maximum material draw-in similar to those measured on the un-tufted structure. The shear angles are much greater than those recorded on the conventionally (fully) tufted preform. Thus, the localized tufting in the most stressed areas proves to be the most suitable solution for the stamped preforms. Wed, 24 Mar 2021 13:08:08 +0100 https://popups.uliege.be/esaform21/index.php?id=2520 https://popups.uliege.be/esaform21/index.php?id=2632 Lightweighting in automotive has already been a key research area for decades, and more recently this research driver has been augmented with electrification and sustainability of new mobility solutions. This contribution focuses on the redesign of a passenger vehicle anti-roll bar from the traditional steel design into a braided glass fiber reinforced composite solution. This work focuses on the functional, central part of the anti-roll bar, targeting a significant weight reduction and sustainability improvement. In terms of design and engineering using finite element methods, a multiscale approach of the composite design has been considered. At microscale the braid unit cell and at macro scale a component were modelled. For the microscale of the braided structure, a selection of design variables has been scrutinized, notably the effect of the braiding angle on the shear stiffness. On the macro scale, finite element modelling is adopted to relate the overall performance to the composite structure and part dimensioning. Additionally, high-potential designs have been prototyped by overbraiding and Vacuum-Assisted Resin Infusion processes. Functional performance testing on the prototypes evaluates the adopted simulation strategies and validates the design. Wed, 24 Mar 2021 18:34:36 +0100 https://popups.uliege.be/esaform21/index.php?id=2632 https://popups.uliege.be/esaform21/index.php?id=2659 Forming simulations are a cost-effective solution to mitigate process-induced defects. The models developed to simulate the forming process require material property data for the dominant deformation mechanisms: intra-ply shear, bending, and inter-ply friction. These mechanisms are considered independent, and material property data has to be derived from experimental data for each mechanism separately. However, it is known that the material response to the deformation mechanisms is correlated, as the choice of matrix, fibre, and reinforcement influences the response to all mechanisms. Over the past years a large variety of thermoplastic composites have been characterised, covering a broad field of applications in automotive and aerospace industry. This makes it possible to start correlating the forming behaviour of thermoplastic composites. In this study, the effect of the constituents of a composite on the forming behaviour is analysed. To this end, a Bayesian cross-classified multilevel model with varying intercepts was applied, and the effects found by the model were analysed. Correlations were found between the effect of the constituents and their properties. The study confirms that the matrix material is an important indicator for the forming behaviour. Wed, 24 Mar 2021 18:38:43 +0100 https://popups.uliege.be/esaform21/index.php?id=2659 https://popups.uliege.be/esaform21/index.php?id=2667 The main focus of the study is the determination of residual stresses developed in thermoplastic composites during tape placement. An experimental characterization of the residual stresses is carried out and based on the measurement of the curvature variation with temperature for unsymmetrical laminates. The tested plates are made of APC-2 and processed on the SPIDE-TP, a filament winding machine based in Cetim, France. A thermo-mechanical model based on the modified laminate theory is used in this work. Heat transfer and crystallization are taken into account in the model, allowing the description of the evolution of the mechanical properties of the composite during the whole process. The model is able to predict the residual stresses present at the end of the process. The results showed stress gradients through the thickness of the laminates where the transverse residual stresses can reach up to 20 MPa. In addition, the results showed that increasing the mandrel temperature reduces the crystallization and thermal gradients in the laminate thickness. Wed, 24 Mar 2021 18:40:03 +0100 https://popups.uliege.be/esaform21/index.php?id=2667 https://popups.uliege.be/esaform21/index.php?id=2693 The originality of this study lies in the real-time monitoring of the crosslinking steps of the polyester resin during the Liquid Resin Infusion (LRI) process of polymer-matrix composites (PMC) by a simple measurement of the electrical capacitance variation of a PZT (Lead Zirconate Titanate) transducer embedded into the heart of the fibrous stack. Three mass rates of a Methyl Ethyl Ketone Peroxide (MEKP) hardener were tested (1wt%, 1.5wt% and 2.5wt%). The electrical capacitance showed a very sensitivity to the crosslinking kinetics while identifying the key steps of the physicochemical transitions of the thermosetting matrix. To identify the promising potential of the PZT transducer as a real-time curing assessment tool of the thermosetting resins, and understand its capacitance signature, the LRI device was multi-instrumented by various non-destructive testing (NDT) techniques such as acoustic emission (AE) and infrared thermography (IRT). The obtained NDT results are confronted with the ones conducted using the oscillatory rheology tests. The agreement between the two types of results (NDT and rheological) allows determining the gelation and vitrification phases of the polyester resin impregnating six plies of 2/2 twill glass fabrics. Wed, 24 Mar 2021 18:44:01 +0100 https://popups.uliege.be/esaform21/index.php?id=2693 https://popups.uliege.be/esaform21/index.php?id=2727 Metallization is a common strategy employed to enhance the electrical and thermal conductivity of polymer matrix composite materials. Nevertheless, metallic deposition on polymer-based materials is challenging due to the inherent limitations related to high temperature exposure of the substrate. In this article, a new technique for the manufacturing of composite laminates and the subsequent metallization by cold spraying of metallic powder is presented. The composite manufacturing route is based on the production of thermoplastic-thermoset hybrid substrates and consisted of two main stages: in the first stage the partial impregnation of a reinforcement textile by a thermoplastic film was promoted by hot pressing compaction. Afterwards, the prepared lamina was vacuum bagged with other reinforcing layers and impregnated by the thermoset catalyzed resin by a vacuum infusion process. Finally, the thermoset and thermoplastic layers were co-cured to increase the adhesion of the substrate with the thermoplastic film. The metallization of composite laminate was obtained through the cold spraying technique, depositing powders on the thermoplastic surface layer. The effect of processing parameters on the coating deposition, quality and microstructure was reported and discussed. Wed, 24 Mar 2021 18:51:23 +0100 https://popups.uliege.be/esaform21/index.php?id=2727 https://popups.uliege.be/esaform21/index.php?id=2771 With a growing interest in the application of carbon fibre Sheet Moulding Compound (SMC), a number of commercial software packages have been developed for the simulation of compression moulding of SMC. While these packages adopt different algorithms and meshing strategies, the constitutive material model and processing control are usually adapted from injection moulding process simulation. Little has been done in the literature for assessing the capabilities of these software as design tools, and more importantly, validating the process simulation results using experimental data. This paper aims to provide an independent and comprehensive assessment of existing well-known process simulation software for SMC compression moulding. The selected software will be compared in terms of material models, and available processing settings in order to determine their robustness as a compression moulding design tool. The predictive accuracy of the software will also be assessed by comparing the compression force and filling patterns against the experimental data. Wed, 24 Mar 2021 18:58:02 +0100 https://popups.uliege.be/esaform21/index.php?id=2771 https://popups.uliege.be/esaform21/index.php?id=2973 Press forming of thermoplastic unidirectional (UD) carbon fiber reinforced laminates is an attractive production method in the aerospace industry for cost-effective manufacturing of high-performance parts. The possible formation of wrinkling defects in the formed parts has led to the development of predictive, finite element based, process simulation tools. The material behavior during the forming process is described based on the governing deformation mechanisms, being intra-ply shear, inter-ply and tool-ply slippage and bending. Intra-ply shear is especially important when forming parts having double curvature. The intra-ply shear behavior of fabric-based composite materials is often characterized using the bias extension method but has not successfully been applied to thermoplastic UD tapes yet. This work describes the application of bias extension experiments on cross-ply UD laminates at forming conditions to characterize the intra-ply shear material behavior. The test procedure was designed to prevent deconsolidation and improve load introduction, promoting specimen integrity and reduce shear buckling during testing. Preliminary results show that the material exhibits rate-dependent behavior. A video extensometer was used to measure the shear deformation in the center of the specimen. Additionally, a deformation analysis was performed using a grid of lines on the specimen, where the theoretical areas of constant shear according to a pin-jointed net can be recognized but are not fully uniform. In particular, shear banding parallel to the fiber direction is observed on the outer ply at a length scale below the grid size used for the deformation analysis suggesting a yield point and softening behavior on the meso scale which is not directly evident from the macroscopic response. Thu, 25 Mar 2021 18:17:14 +0100 https://popups.uliege.be/esaform21/index.php?id=2973 https://popups.uliege.be/esaform21/index.php?id=3015 In the aeronautic industry, thicker and more complex composite parts are required. Multi-layered reinforcements are widely used to achieve a certain thickness for the composite part. The tufting technology has become one of the most effective three-dimensional (3D) reinforcement technologies to improve the through-the-thickness mechanical properties of multi-layered reinforcements. A finite element model is proposed for the simulation of tufted reinforcements preforming. The textile reinforcement is modelled by shell elements, and the tufting thread is modelled by bar elements. A specific contact algorithm is developed to manage the interaction between reinforcements and tufting threads. This meso-macroscopic approach reduces the number of finite elements and saves calculation time compared to a mesoscopic model. The model shows a good prediction of deformations during the forming on a hemispherical shape. Fri, 26 Mar 2021 16:50:42 +0100 https://popups.uliege.be/esaform21/index.php?id=3015 https://popups.uliege.be/esaform21/index.php?id=3695 Hot press forming is an attractive production technology to fulfil the increasing demand for complex fiber-reinforced thermoplastic parts. Over the years, process simulation tools on press forming have shown to be very helpful in facilitating the design stage for defect free parts production. One of the important deformation mechanisms considered in process simulations is the relative slip of successive plies or ply-ply friction, of which the underlying principles need to be better understood in order to improve the overall predictive simulation quality. In particular the use of steady-state friction values, neglecting the transient response, is questionable as experiments showed that shear stress overshoots can be as high as three times the long-time value. The phenomenon of the overshoot at start-up shear is analyzed. Possible explanations include nonlinear viscoelasticity and a slip relaxation effect giving rise to wall slip, which are discussed using relevant ply-ply friction measurements carried out on a dedicated friction test set-up. Experimental results on UD C/PEEK show that the shear stress build up and subsequent relaxation comply with nonlinear viscoelasticity. However, the long-time shear stress fails to match the matrix material’s viscosity, possibly due to a yield stress. The flow curve corrected for a yield stress resembles the effects of wall slip. A transient model according to these findings will enhance the accuracy of press forming simulation software. Mon, 29 Mar 2021 14:13:44 +0200 https://popups.uliege.be/esaform21/index.php?id=3695 https://popups.uliege.be/esaform21/index.php?id=3706 A model, based on the Van Wyk model, is developed to predict the compaction behaviour of stack sequence of dry fabric plies, and is used a set of 3 parameters (stiffness k, pressure sensitivity n and initial fibre ratio Vf0) with P = (k(Vf- Vf))n. The method originality is to construct the behaviour law of a complex stack sequence by the assembly of elementary behaviours. Elementary behaviours are identified using initial experimental compaction tests and are linked to the interaction of a fabric ply with its surrounding environment (another fabric ply or the surface of the compressive mould). This proposed modelling approach have been tested on various carbon, flax and carbon/flax hybrid stack sequence, and seems efficient to predict their compaction behaviour. Its validity is limited to the range of stack sequence of a reduced number of plies. With stack sequence made of numerous fabric plies, some new phenomena must be taken into account. In complement we proposed a method to decompose the compaction behavior curve into three stages (rigid body movement of the fabric plies, nesting of the plies, densification). This method is relevant to compare easily some compaction curves and to evaluate the internal strain state of a stack sequence. Mon, 29 Mar 2021 14:17:05 +0200 https://popups.uliege.be/esaform21/index.php?id=3706 https://popups.uliege.be/esaform21/index.php?id=3740 Fibre-reinforced thermoplastics (FRTP), such as organo sheets or laminates, are increasingly being used in large-scale automotive production. The high weight-saving potential, high specific strengths and stiffnesses as well as processing times suitable for large-scale production are some of the reasons for using these materials. However, the formability of such semi-finished products is severely limited by the fibre reinforcement, which can lead to fibre breakage, fibre displacement or wrinkling in complex-shaped components. In order to increase the formability, an FRTP semi-finished product is developed, which consists of discontinuous tapes. Due to the local sliding of the tape sections, a pseudo-plastic material behaviour is achieved. Experimental uniaxial tensile tests at elevated temperatures are used to investigate the forming behaviour of the material for different tape lengths and overlap lengths. Subsequently, this tensile test is numerically modelled in order to fit the pseudo-plasticity to the experimental data by a virtual parameter identification. With the help of the parameters determined from the numerical tensile test, the sliding behaviour of the tape sections can be used for forming simulations in order to achieve a higher prediction quality. Mon, 29 Mar 2021 14:23:33 +0200 https://popups.uliege.be/esaform21/index.php?id=3740 https://popups.uliege.be/esaform21/index.php?id=3756 This study presents the results of a double dome forming study for fiber reinforced thermoplastics to give an estimation about wrinkles size and fiber angle values. The parts were formed with an industry-oriented process at different forming temperatures and fiber directions (0 °/ 90 ° and ±45 °). They were formed without blank holder to allow wrinkling. The investigated material is a glass fiber –reinforced polyamide 6 with three layers of twill fabric (TEPEX® Dynalite 102-RG600(3)/47 %). The wrinkles are measured with a laser scanner. The shear angles were calculated using image analysis in MATLAB. It determines the fiber directions and calculates the fiber angles at their crossing points. Afterwards, areas with positive and negative shear angle values will be identified and discussed: These areas are in an axially symmetrical formation. At one side there are positive shear angles and on the other side there are negative shear angles. But results show, that absolute values differ. Furthermore, the results show, that shear angles increase with increasing forming temperatures and wrinkles size decrease. The results of this work will be used for the validation of FE forming models of double dome part in further studies. Mon, 29 Mar 2021 14:26:34 +0200 https://popups.uliege.be/esaform21/index.php?id=3756 https://popups.uliege.be/esaform21/index.php?id=4017 Polymer-based AM methods are the most mature additive technologies for their versatility and variety of products obtainable. The addition of fibre reinforcement can also confer to the manufactures produced good mechanical properties. Unfortunately, several applications are still precluded because polymers cannot guarantee appropriate electrical conductivity, erosion resistance and operating temperature. Aiming to overcome these issues, the metallization of the surfaces emerges as a possible solution. Unfortunately, thermoplastic polymers exhibit thermosensitive behaviour and run the risk of being damaged when traditional metallization techniques, which require the melting of metal powders which will act as a protective coating. For this reason, studies have focused on Cold Gas Dynamic Spray, an additive manufacturing technology, which exploits kinetic energy to favour the adhesion of metal particles rather than the increase in temperature. In this work, a first attempt is made to verify the feasibility of cold spray coatings on 3D printed composite substrates, produced by means of Fused Filament Fabrication (FFF) technique. FFF technology allows the deposition of two different types of filaments by using a double extruder. These composite fibres within 3D printed parts manage to give the object a resistance comparable to that of a metal part with lower production cost and a high degree of automation. These structures, made of ONYX, a Nylon matrix in which short carbon fibres are dispersed, and reinforced with long carbon fibres, are designed to better fit the CS deposition. Aluminium coatings have been produced and a characterization campaign has been carried on. Tue, 30 Mar 2021 10:01:16 +0200 https://popups.uliege.be/esaform21/index.php?id=4017 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 https://popups.uliege.be/esaform21/index.php?id=4252 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 https://popups.uliege.be/esaform21/index.php?id=4266 https://popups.uliege.be/esaform21/index.php?id=4743 Peculiarities of the pultrusion manufacturing process lead to the occurrence of spring-in deformations, whereas their value depends on the pulling speed. In this article experimental and numerical analysis was carried out for glass fiber/vinyl ester resin 75 × 75 × 6 mm L-shaped profiles pultruded at pulling speeds of 200 and 600 mm/min. Spring-in angles of produced profiles were determined on the same day of manufacturing when profiles cooled down to room temperature. Higher pulling speeds provoked increased values of spring-in. 2D numerical model accounting for thermo-chemical and mechanical composite’s behavior during pultrusion was implemented in ABAQUS software. Cure Hardening Instantaneous Linear Elastic (CHILE) constitutive law was used to describe matrix resin Young’s modulus evolution. Since both unidirectional (UD) rovings and fabric material were utilized, effective mechanical properties of UD and fabric layers were calculated in accordance with Self-Consistent Field Micromechanics (SCFM) approach. Spring-in angles determined within experimental and numerical studies were compared and a good correlation was found: the errors were 12.6% and 6% for the pulling speed of 200 and 600 mm/min, respectively. Thu, 08 Apr 2021 20:31:13 +0200 https://popups.uliege.be/esaform21/index.php?id=4743