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This article proposes two approaches for a tailored geometrical deviation compensation for Laser-Powder-Bed-Fusion production. The deviation compensation is performed by a non-rigid deformation of the manufacturing geometry in each iteration to reduce the geometrical deviations from the target geometry. It is important for geometric compensation approaches to separate deterministic deviations from random scatter, since compensating scatter can result in unstable behaviour. In order to compensate only deterministic deviations two novel approaches for a local estimation of the scatter are successfully introduced and tested using a hybrid model of a series production cycle. [ABSTRACT FROM AUTHOR]

With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets. [ABSTRACT FROM AUTHOR]

With the rapid development of lightweight automobiles, the clinching joint technology of ultra-high-strength steel with aluminum alloy sheets have been paid more and more attention. However, due to significant differences in plastic deformation capabilities between the two metals, particularly the difficulty of steel sheet deformation, conventional clinching processes often result in insufficient joint interlocking or fracture issues. Although the preliminary use of clinching processes with preforming methods has shown some effectiveness in connecting two types of sheets, the bond strength is not high. This study employs finite element simulation and orthogonal optimization methods to investigate the impact of relevant process parameters on joint morphology in clinching processes with preforming. Under the condition of optimizing process parameters, a clinching punch with an added pressure-step structure was proposed to compact the joint and further enhance joint quality. Experimental verification demonstrates the feasibility of the improved clinching processes with preforming for bonding ultra-high-strength steel and aluminum alloy sheets.

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Fibre-reinforced composites (FRCs) are already well established in several industrial sectors such as aerospace, automotive, plant engineering, shipbuilding and construction. The technical advantages of FRCs over metallic materials are well researched and proven. The key factors for an even wider industrial application of FRCs are the maximisation of resource and cost efficiency in the production and processing of the textile reinforcement materials. Due to its technology, warp knitting is the most productive and therefore cost-effective textile manufacturing process. In order to produce resource-efficient textile structures with these technologies, a high degree of prefabrication is required. This reduces costs by reducing the number of ply stacks, and by reducing the number of extra operations through final path and geometric yarn orientation of the preforms. It also reduces waste in post-processing. Furthermore, a high degree of prefabrication through functionalisation offers the potential to extend the application range of textile structures as purely mechanical reinforcements by integrating additional functions. So far, there is a gap in terms of an overview of the current state-of-the-art of relevant textile processes and products, which this work aims to fill. The focus of this work is therefore to provide an overview of warp knitted 3D structures. [ABSTRACT FROM AUTHOR]

Vacuum infusion (VI) is a liquid moulding process used to manufacture fibre-reinforced polymer composite parts. The VI process for non-crimp fabric (NCF) preforms is one of the most promising processes for improving the quality and cost efficiency of traditional processes using prepregs and autoclave curing. An understanding of the preform thickness behaviour in the compaction, wetting, and curing stages is necessary to optimise the overall process and obtain high-performance composite parts. In this study, the influence of the material, preforming, and infusion parameters on the thickness of four different carbon NCF laminates were investigated. The preforming behaviour includes the influence of the NCF composition, such as the presence of an organic binder or the number of compaction steps. Infusion was characterised using dielectric analysis (DEA). The properties of the resulting composites were analysed in terms of the fibre volume fraction (FVF) and porosity, as measured using X-ray computed tomography (CT). The main consequence of the outcome of the present study is that, from a manufacturing point of view, downward through-thickness resin infusion offers benefits in terms of thickness, FVF, and porosity tolerance. In addition, the acquired results allow for the identification of the main settings for an optimised consolidation strategy, which could be used for manufacturing NCF composite parts.

In various industries, hydrogen is used as the main raw material, as an auxiliary material, and/or as a fuel. Oil refining and petrochemical enterprises consume up to 50 % of the hydrogen produced. A promising method is proposed for hydrogen production, which consists in preliminary thermolysis of heavy oil stock, followed by catalytic conversion of steam-gas products, which makes it possible to reduce hydrogen production cost. The method will allow greater degree of feedstock processing and expansion of refinery feedstock base. [ABSTRACT FROM AUTHOR]

The use of hemp fibers for the manufacturing of reinforcements for composite materials is not well common, despite a growing interest of natural fibers in this field of application. In addition to the choice of the type of fiber used, the choice of the type of reinforcement plays an important role in the final properties of the composite material. Unidirectional or woven fabrics are widely used as reinforcement to achieve advanced properties at the scale of composite, depending on the specifications of the final material. In this study, a quasi-unidirectional fabric and two woven fabrics (one balanced and one unbalanced in terms of fiber content) are studied to compare their properties at different levels: mechanical and preforming properties of the reinforcements in dry state and mechanical properties of composite materials reinforced by these fabrics. The objective is to highlight the advantages and drawbacks of both types of reinforcements (woven fabrics and quasi-unidirectional fabrics) in order to be able to select the most suitable reinforcement according to the specifications of the final composite part. As a result, the quasi-unidirectional reinforcement showed enhanced properties both at fabric and composite scale. These structures based on hemp fibers present promising properties that concur structures made of flax and already available on the market. [ABSTRACT FROM AUTHOR]

Abstract A successive tooth forming process for producing large modulus spur gears (m>2.5 mm) is firstly proposed in this paper to break the restrictions of large forming load and large equipment structure of traditional plastic forming. It contains the preforming stage and the finishing stage. In the first stage, the die with a single-tooth preforms gear teeth one by one through several passes. In the second stage, the other die with multi-teeth refines the preformed teeth into required shape. The influence of total pressing depth and feed distribution in preforming stage on final forming quality is analyzed by numerical simulation, and the reasonable process parameters are presented. Successive tooth forming experiments are carried out on the self-designed gear forming device to verify the optimal simulation results. Gears without fold defects are well formed both in simulations and experiments, proving the feasibility of this method. Compared with the whole die forging process, the new technology has advantages of smaller load and simpler tooling, which shows a good potential for manufacturing large modulus and large size spur gears.

AbstractPreforming processes can be used for automated manufacturing of fiber reinforced polymers. Different technologies are used for processing of dry textile fabrics into 2D or 3D preforms. Due to missing tack of dry fabrics, auxiliary binder systems are used for fixation of the fabrics onto a substrate material and in order to achieve sufficient adhesion between layers. In this study, seven reactive and non-reactive tackifying agents have been dissolved in neat resin samples of three epoxy resin systems, showing different degrees of solubility and a variation on neat resin tensile properties (ΔσAVG = 20%) as well as a reduction on thermal properties (up to ΔTg = −18 °C). Subsequently, fiber reinforced polymers were manufactured using Liquid Resin Infusion techniques in order to characterize the influence of binder systems on water absorption (cs,max = 1.38 wt%) and Interlaminar Shear Strength (ILSS). It was shown that ILSS properties are negatively affected by non-reactive tackifying agents (up to −27%).

The preforming design during closed-die forging is a necessary step to achieve complete die-filling to accomplish a defect-free product. It involves steps for the optimal design of the preform shape and helps in reducing the forging load and die wear due to uniform deformation. The present paper investigates a case of a closed-die forging process using a modified preforming criterion for an optimal design of the preform. The process involved the deformation of a cylindrical shaped preform into an axi-symmetric double-hub flange component within a closed-die set. The criteria of preforming stages were validated by computing and comparing the total energy dissipated during the forging of actual preforms and the corresponding enveloping imaginary pancake preforms theoretically. Three different intermediate closed-die forging stages were considered to validate the preforming criteria using the concept of shape complexity factor. Further, these factors were critically examined for the proper die cavity fills. [ABSTRACT FROM AUTHOR]

A novel preforming process was developed for non-crimp fabric (NCF) materials that generated in-plane tension through discontinuous blank boundary conditions. The method employed magnetic clamps and was designed to be both flexible and scalable, with clear routes to industrialisation. The capability of the process was explored in physical trials for a hemispherical and a cubic geometry. Characterisation of a biaxial veiled NCF showed the veil had a dominant effect on the bending mechanics. Subsequently a macroscale finite element model was developed to include an efficient bending idealisation and non-orthogonal in-plane material behaviour. Finally, global process optimisation of the preforming process was demonstrated. The optimisation approach used Gaussian process modelling with a periodic kernel to estimate the wrinkle size for untested clamping arrangements and then deployed Bayesian optimisation to find the optimal configuration. Results indicated that distributed magnetic clamping was effective and amenable to surrogate modelling. [ABSTRACT FROM AUTHOR]

Fiber injection molding is an innovative process for the resource-efficient production of near net-shape long fiber preforms. The filling of the mold is crucial for the repeatability and uniformity of the produced preforms. For improving the fiber injection process a control system based on image processing has been developed. With a camera the current mold filling is recorded and processed by artificial neural networks. This information on the filling state is used for an adaptive control of the injection nozzle. The control system is validated experimentally with results showing improved reproducibility of the fiber injection molding process. [ABSTRACT FROM AUTHOR]

When thermoplastic resin-toughened carbon fiber (CF) composites are formed by liquid resin transfer molding (RTM), the conventional methods cannot be used to set the fabric preform, which affects the overall mechanical properties of the composites. To address this challenge, the benzoxazine-based tackifier BT5501A was designed, a preforming–toughening bifunctional CF fabric was fabricated by employing thermoplastic polyaryletherketone (PEK-C), and an aviation RTM-grade bismaleimide (BMI) resin was used as the matrix to study the effect of the benzoxazine-based tackifier on the thermal curing property and heat resistance of the resin matrix. Furthermore, the preforming and toughening effects on the bifunctional CF fabric reinforced the BMI resin composites. The tackifier BT5501A has good process operability. The application of this tackifier can advance the thermal curing temperature of the BMI resin matrix and decrease the glass transition temperature of the resin, compared to that of the pure BMI resin. Furthermore, when the tackifier was added into the CF/PEK-C/BMI composites, the obtained CF/BT5501A/PEK-C/BMI composites had comparable compression strength after impact, pit depth, and damage area, compared to the CF/PEK-C/BMI composites, while the tackifier endowed the fabric preform with an excellent preforming effect. [ABSTRACT FROM AUTHOR]

This work investigates the effects of out‐of‐autoclave processing parameters on glass/epoxy composite void content. Void quality measurement was done via ultrasonic C‐scan combined with image processing algorithm and burn off testing. Results showed that type of mould release, edge breather, debulking and intensifier as the variable processing parameters influenced the glass/epoxy composite void content. [ABSTRACT FROM AUTHOR]

A successive tooth forming process for producing large modulus spur gears (m>2.5 mm) is firstly proposed in this paper to break the restrictions of large forming load and large equipment structure of traditional plastic forming. It contains the preforming stage and the finishing stage. In the first stage, the die with a single-tooth preforms gear teeth one by one through several passes. In the second stage, the other die with multi-teeth refines the preformed teeth into required shape. The influence of total pressing depth and feed distribution in preforming stage on final forming quality is analyzed by numerical simulation, and the reasonable process parameters are presented. Successive tooth forming experiments are carried out on the self-designed gear forming device to verify the optimal simulation results. Gears without fold defects are well formed both in simulations and experiments, proving the feasibility of this method. Compared with the whole die forging process, the new technology has advantages of smaller load and simpler tooling, which shows a good potential for manufacturing large modulus and large size spur gears. [ABSTRACT FROM AUTHOR]

In the present experimental study, influence of process parameters in hybrid incremental sheet forming (HISF) is studied. Stretch forming combined with ISF is used for forming of conical parts. Stretch forming or preforming is done in order to get the intermediate shape and thickness distribution. On the same setup final part shape is obtained using the conventional ISF process. A low cost hemispherical-ended wooden preforming tool is used for the preforming purpose. Tools used for ISF process are also hemispherical-ended in shape but having smaller diameters and are made up of stainless steel SS-305. Experiments are designed according to design of experiment (DOE) Taguchi method. Analysis of variance (ANOVA) is used to analyse the effect of process parameters namely preforming depth, tool diameter and pitch on response geometric accuracy. It is found that there is considerable effect of tool diameter on geometric accuracy of the formed part. Also, forming time is reduced considerably due to the preforming operation. [ABSTRACT FROM AUTHOR]

Single-diaphragm forming is a cost saving alternative to labor-intensive ply-by-ply layup. This paper reports on forming of flat uncured multi-angle prepreg stacks into C shape. The main focus is on the forming-process profile , which has attracted little attention in previous studies on the topic. Hexcel’s M21E/IMA prepreg is examined within the study to analyze the particular effect of the prepreg’s interleaf layers on the forming process and vice versa. Specimens with different multi-angle stackings were formed at 40, 60 and 80 °C, on male tools with 4, 6 and 8 mm radii. It is shown that the composed infrastructure setup allows for a precise control of the recipient pressure profile. The forming status is monitored based on a resistance-measurement-based approach, whose application suggests a two-phase forming process characteristic. Recipient pressure levels of 60 and 510 mbar below ambient pressure were identified as practical for gentle forming. It could be shown that interleaf layers of M21E/IMA specimens are not harmed considerably by the forming procedure. Overall, the proposed forming process led to prepreg preforms of adequate quality, suitable for series production.

Electro-Hydraulic Forming (EHF) is a high rate sheet metal forming process based on the electrical discharge of high voltage capacitors in a water-filled chamber. During the discharge, the pulsed pressure wave propagates from the electrodes and forms a sheet metal blank into a die. The performed literature review shows that this technology is suitable for forming parts of a broad range of dimensions and complex shapes. One of the barriers for broader implementation of this technology is the complexity of a full-scale simulation of EHF which includes the simulation of an expanding plasma channel, the propagation of waves in a fluid filled chamber, and the high-rate forming of a blank in contact with a rigid die. The objective of the presented paper is to establish methods of designing the EHF processes using simplified methods. The paper describes a numerical approach on how to define the shape of preforming pockets. The concept includes imposing principal strains from the formed blank into the initial mesh of the flat blank. The principal strains are applied with the opposite sign creating compression in the flat blank. The corresponding principal stresses in the blank are calculated based upon Hooke’s law. The blank is then virtually placed between two rigid plates. One of the plates has windows into which the material is getting bulged driven by the in-plane compressive stresses. The prediction of the shape of the bulged sheet provides the information on the shape of the preforming pockets. It is experimentally demonstrated that using these approaches, EHF forming is feasible for forming of a fragment of a decklid panel and a deep panel with complex curvature. [ABSTRACT FROM AUTHOR]

To solve the difficulties associated with integral precise extrusion forming for complex components of magnesium alloy, Deform-3D finite element simulation software was used to conduct numerical analyses for the forming process. Different extrusion schemes were used for determining the overall extrusion difficulties associated with special-shaped thin-walled complex components of magnesium alloy. The effects of a preformed blank on the filling and formation of folding defects in the forming process were studied. Based on the principle of minimum energy in the process of plastic deformation and the law of least resistance, volume predistribution and equal distance flow quantitative compensation methods were put forward. These methods were used to optimize the size and structure of the preform, forming a uniform material flow distribution. They also enabled one to manifest a uniform material flow velocity distribution, reduce the forming load, and avoid the creation of folding and filling defects during the final forming, for the realization of an efficient and reliable preform optimization design for magnesium alloy profiled complex components. The results obtained from a forming test, microstructure and mechanical properties test showed that the mechanical properties of the extruded component all met the service indexes. This design method can provide a theoretical reference for preforming design of profiled complex components. [ABSTRACT FROM AUTHOR]

Recycling carbon-fibre-reinforced plastic (CFRP) and recovering high-cost carbon fibre (CF) is a preoccupation of scientific and industrial committees due to the environmental and economic concerns. A commercialised nonwoven mat, made of recycled carbon fibre and manufactured using carding and needle-punching technology, can promote second-life opportunities for carbon fibre. This paper aims to evaluate the mechanical and preforming behaviour of this nonwoven material. We focus on the influence that the fibre orientation distribution in the nonwoven material has on its mechanical and preforming behaviour at the preform scale, as well as the tensile properties at composite scale. The anisotropy index induced by fibre orientation is evaluated by analysing SEM micrographs using the fast Fourier transform (FFT) method. Then, the anisotropy in the tensile, bending, and preforming behaviour of the preform is inspected, as well as in the tensile behaviour of the composite. Additionally, we evaluate the impact of the stacking order of multi-layers of the nonwoven material, associated with its preferred fibre orientation (nonwoven anisotropy), on its compaction behaviour. The nonwoven anisotropy, in terms of fibre orientation, induces a strong effect on the preform mechanical and preforming behaviour, as well as the tensile behaviour of the composite. The tensile behaviour of the nonwoven material is governed by the inter-fibre cohesion, which depends on the fibre orientation. The low inter-fibre cohesion, which characterises this nonwoven material, leads to poor resistance to tearing. This type of defect rapidly occurs during preforming, even at too-low membrane tension. Otherwise, the increase in nonwoven layer numbers leads to a decrease in the impact of the nonwoven anisotropy behaviour under compaction load.

Electro-Hydraulic Forming (EHF) is a high rate sheet metal forming process based on the electrical discharge of high voltage capacitors in a water-filled chamber. During the discharge, the pulsed pressure wave propagates from the electrodes and forms a sheet metal blank into a die. The performed literature review shows that this technology is suitable for forming parts of a broad range of dimensions and complex shapes. One of the barriers for broader implementation of this technology is the complexity of a full-scale simulation of EHF which includes the simulation of an expanding plasma channel, the propagation of waves in a fluid filled chamber, and the high-rate forming of a blank in contact with a rigid die. The objective of the presented paper is to establish methods of designing the EHF processes using simplified methods. The paper describes a numerical approach on how to define the shape of preforming pockets. The concept includes imposing principal strains from the formed blank into the initial mesh of the flat blank. The principal strains are applied with the opposite sign creating compression in the flat blank. The corresponding principal stresses in the blank are calculated based upon Hooke’s law. The blank is then virtually placed between two rigid plates. One of the plates has windows into which the material is getting bulged driven by the in-plane compressive stresses. The prediction of the shape of the bulged sheet provides the information on the shape of the preforming pockets. It is experimentally demonstrated that using these approaches, EHF forming is feasible for forming of a fragment of a decklid panel and a deep panel with complex curvature.

A critical process step within the liquid composite moulding constitutes in the preforming of two‐dimensional textile material into a near‐net‐shape and load‐capable fibre structure by stamp forming. This paper presents fundamental material experiments on the shearing behaviour, bending properties and friction behaviour considering the binder quantity and forming temperature. In addition, the influence of the process time on the resulting stability of the preform is examined. The findings indicate that the quantity of the binder as well as the forming temperature and the process time have a great influence on the preform quality. [ABSTRACT FROM AUTHOR]

Single-diaphragm forming is a cost saving alternative to labor-intensive ply-by-ply layup. This paper reports on forming of flat uncured multi-angle prepreg stacks into C shape. The main focus is on the forming-process profile , which has attracted little attention in previous studies on the topic. Hexcel's M21E/IMA prepreg is examined within the study to analyze the particular effect of the prepreg's interleaf layers on the forming process and vice versa. Specimens with different multi-angle stackings were formed at 40, 60 and 80 °C, on male tools with 4, 6 and 8 mm radii. It is shown that the composed infrastructure setup allows for a precise control of the recipient pressure profile. The forming status is monitored based on a resistance-measurement-based approach, whose application suggests a two-phase forming process characteristic. Recipient pressure levels of 60 and 510 mbar below ambient pressure were identified as practical for gentle forming. It could be shown that interleaf layers of M21E/IMA specimens are not harmed considerably by the forming procedure. Overall, the proposed forming process led to prepreg preforms of adequate quality, suitable for series production. [ABSTRACT FROM AUTHOR]

This paper presents a novel method combining the preforming and multi-tooth plowing processes to fabricate aluminum-based ultrathin flat heat pipes (UTFHPs). The use of a preforming process makes it more effective to machine arrayed microgrooves on the inner wall of UTFHPs. The multi-tooth plowing process helps greatly increase the capillary pressure and hydrophilicity of the heat pipe wick. The morphologies of the wick structures are characterized and a self-designed experimental platform is constructed to investigate the thermal performances of UTFHP samples under incremental heat loads. The results indicate that the multi-tooth plowing process is able to significantly reduce the minimum thermal resistance of the heat pipe by 83%. The thermal resistance of the UTFHP with a unilateral porous wick is smaller than that based on a central porous wick at the same liquid filling rate. The UTFHP has excellent radial temperature uniformity with the minimum radial temperature difference of 1.2 °C, because the structures made by multi-tooth plowing can effectively reduce the temperature difference. [ABSTRACT FROM AUTHOR]

The automated manufacturing of wind turbine rotor blades needs binder systems which meet the requirements for online processing, show good preforming properties and do not affect the mechanical performance of the glass fiber reinforced polymer (GFRP) composites. In this study, especially the binder effect on the mechanical performance of corresponding glass fiber reinforced polymer is focused on. Three commercially available thermoplastic binders of different chemical composition and solubility in a rotor blade proven epoxy resin are used: Grilon MS (strongly soluble), D 2433E (partially soluble) and K140 (non-soluble). After manufacturing the binder-modified glass fiber reinforced polymer plates by the vacuum-assisted resin infusion technique, their mechanical performance is investigated with respect to binder solubility and concentration (1–3 wt.%). The mechanical characterization is based on tensile and compression tests – both longitudinal (0°) and transversal (90°) – as well as shearing tests (±45°). It is found that the glass fiber reinforced polymer strength and stiffness is strongly controlled by binder solubility and content. In the case of limited binder solubility and insolubility (D 2433E and K140), the performance of the composites reduces significantly as binder content increases. In contrast, stiffness and strength are not affected by the soluble binder Grilon MS, regardless of its content. These glass fiber reinforced polymer results strongly correspond with the results obtained for binder modified resin plates in a previous study. This correlation highlights the fact that binder ability for the preforming process might be classified by a simple pre-test for solubility and mechanical properties using the modified resin instead of applying the costly and time-intensive manufacturing steps of glass fiber reinforced polymer plates. [ABSTRACT FROM AUTHOR]

Manual preforming of dry CF-layers is still one of the biggest cost factors for infusion process. Compare to the manual preform process, the difficulty for the automated process lies in pick-and-place system, in gripper deformation depending on components curvature and in fixation of all the individual CF-layers. DLR has developed gripper for fully automated pick-and-place system, which can manage challenges caused by material properties such as low material rigidity and draping for complex geometry. Until now, thermoplastic binding material or double- sided adhesive tape was used for fixing the CF-layers. The main focus of this work is the combination of the newly developed fixation method with RTM6 resin and gripper system. Due to subsequent infiltration with the same resin additional binding material can be avoided. For new automated preform process fixing end-effector sprays automatically a thin layer of RTM6 (0,094 g/m) on the surface before placing the fabric. The resin quantity and spray position depends on CF-layer size and deformation of gripper. The resin can also be applied during the lay-up process. Thereafter adhesive bonding between two CF-layers or between CF-layer and mold is generated by applying a minimum pressure with the gripper. As the gripper is developed for best draping process the fixation area, where pressure must be applied, has been simulated. Only on these simulated position RTM6 has been sprayed automatically with robot. Afterwards the additional press-on movement for robot was realized with automatic pick-and-place system. This complete automated preform process has been validated on 4 m diameter Pressure-Bulkhead. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the local fiber orientation and the local fiber volume content within composite parts provides an opportunity to predict the structural behavior more reliably. Utilizing forming simulation methods of dry or pre-impregnated fabrics allows for predicting the local fiber orientation. Additionally, during the forming process, so-called draping effects like waviness, gapping or shear-induced transverse compression change the local fiber volume content. To reproduce and investigate such draping effects, different manufacturing tools have been developed in this work. The tools are used to create fabric samples with pre-defined deformation states, representing the different draping effects. The samples are evaluated regarding the resulting fiber volume content. The experimental results are compared with the predictions of an analytical solution and of a numerical solution based on draping simulation results. Furthermore, the interaction of the draping effects at arbitrary strain states is discussed regarding the resulting fiber volume content. [ABSTRACT FROM AUTHOR]

Abstract Carbon fiber reinforced plastics (CFRPs) are attracting growing attention in industry because of their enhanced properties. Preforming of thermoset carbon fiber prepregs is one of the most common production techniques of CFRPs. To simulate preforming, several computational methods have been developed. Most of these methods, however, obtain the material properties directly from experiments such as uniaxial tension and bias-extension where the coupling effect between tension and shear is not considered. Neglecting this coupling effect deteriorates the prediction accuracy of simulations. To address this issue, we develop a Bayesian model calibration and material characterization approach in a multiscale finite element preforming simulation framework that utilizes mesoscopic representative volume element (RVE) to account for the tension-shear coupling. A new geometric modeling technique is first proposed to generate the RVE corresponding to the close-packed uncured prepreg. This RVE model is then calibrated with a modular Bayesian approach to estimate the yarn properties, test its potential biases against the experiments, and fit a stress emulator. The predictive capability of this multiscale approach is further demonstrated by employing the stress emulator in the macroscale preforming simulation which shows that this approach can provide accurate predictions. [ABSTRACT FROM AUTHOR]

A comprehensive novel investigation into the characterisation of interply friction behaviour of thermoset prepregs for high-volume manufacturing was conducted. High interply slipping rate and normal pressure typically used for high-volume manufacturing present challenges when preforming carbon fibre reinforced plastics. The study involved multiple reinforcement architectures (woven and unidirectional with the same rapid-cure resin system) which were characterised using a bespoke interply friction test rig used to simulate processing conditions representative to press forming and double diaphragm forming. Under prescribed conditions, woven and unidirectional prepregs exhibit significantly different frictional behaviour. Results demonstrated the unidirectional material obeys a hydrodynamic lubrication mode. For the woven material, a rate-dependent friction behaviour was found at low normal pressure. At higher normal pressure however, the woven material exhibited a friction behaviour similar to that of a dry reinforcement and significant tow displacement was observed. Post-characterisation analysis of test-specimens showed significant resin migration towards the outer edges of the plies, leaving a relatively resin-starved contact interface. The findings generate new knowledge on interply friction properties of thermoset prepreg for high-volume manufacturing applications, yet reveal a lack of understanding of the influence of tow tensions as well as the pre-impregnation level for a range of processing conditions. [ABSTRACT FROM AUTHOR]

Automation of the preforming process brings up two opposing requirements for the used engineering fabric. On the one hand, the fabric requires a sufficient drapeability, or low shear stiffness, for forming into double-curved geometries; but on the other hand, the fabric requires a high form stability, or high shear stiffness, for automated handling. To meet both requirements tailored non-crimp fabrics (TNCFs) are proposed. While the stitching has little structural influence on the final part, it virtually dictates the TNCFs local capability to shear and drape over a mold during preforming. The shear stiffness of TNCFs is designed by defining the local stitching geometry. NCFs with chain stitch have a comparatively high shear stiffness and NCFs with a stitch angle close to the symmetry stitch angle have a very low shear stiffness. A method to design the component specific local stitching parameters of TNCFs is discussed. For validation of the method, NCFs with designed tailored stitching parameters were manufactured and compared to benchmark NCFs with uniform stitching parameters. The designed TNCFs showed both, generally a high form stability and in locally required zones a good drapeability, in drape experiments over an elongated hemisphere. [ABSTRACT FROM AUTHOR]

Scope of the presented work is a detailed comparison of a macroscopic draping model with real fibre architecture on a complex non-crimp-fabric preform using a new robot-based optical measurement system. By means of a preliminary analytical process design approach, a preforming test centre is set up to manufacture dry non-crimp-fabric preforms. A variable blank holder setup is used to investigate the effect of different process parameters on the fibre architecture. The real fibre architecture of those preforms is captured by the optical measurement system, which generates a threedimensional model containing information about the fibre orientation along the entire surface of the preform. The measured and calculated fiber orientations are then compared with the simulation results in a three-dimensional overlay file. The results show that the analytical approach is able to predict local hot spots with high shear angles on the preform. Macroscopic simulations show a higher sensitivity towards changes in blank holder pressure than reality and limit the approach to precisely predict fibre architecture parameters on complex geometries. [ABSTRACT FROM AUTHOR]

Endless fiber reinforced plastics based on thermoplastic matrices permit shorter cycle times compared to thermoset resin based composites as no curing step is needed and ancillary times can be reduced. In this work an approach towards thermoplastic composites based on unidirectional endless fiber reinforced tapes (UD tapes) will be discussed and technical solutions along the processing chain from UD tape to final part will be introduced. The processing approach developed by Neue Materialien Bayreuth GmbH aims in manufacturing structural light weight parts based on thermoplastic matrices including integrated injection molded edges and ribs at cycle times between 60 and 90 seconds. At present, the costliest step within the processing chain for endless fiber reinforced thermoplastic composites is represented by the preform production. State of the art preforming concepts result in high material scrap (often above 25%), which consequently leads to elevated material costs. Furthermore, current machine technologies are too slow to serve in line with the cycle time of an injection molding press. In this paper a novel concept for a high-speed tape laying machine will be presented. The new equipment uses combinations of UD-tapes with different width in order to compromise between minimum laying time and reduced scrap. Current cost estimations show the potential to reduce the costs for production of 2D preforms up to 30% compared to cutting blanks from woven fabric-based organosheets. [ABSTRACT FROM AUTHOR]

Due to their outstanding mechanical properties, fiber reinforced composites are particularly suitable for lightweight applications. Especially hollow structures made of braided hybrid yarn hoses offer a high application potential as the unconsolidated hoses provide a good drapability and thus allow the fabrication of complex shaped torsion- and bend-resistant structures. At present, the shaping and preforming of braided hoses is usually performed manually. To enable a high volume production of lightweight hollow structures, automated preforming technologies are required. This article discusses a new technical approach which allows a fully automated preforming of braided hybrid yarn hoses. Starting with pre-fabricated and rolled up quasi-endless braided hoses, the conceived automation system has to cut several segments from the hose and subsequently pull them above each other to produce a multi-ply preform. For an automated process, a reproducible and damage-free manipulation of the hoses has to be ensured during preforming. Therefore, the process is analyzed and concepts for unrolling and cutting of the endless hoses as well as stacking and fixation of the obtained segments are developed and evaluated experimentally. As a result of the investigation, a fully automated preforming station is built up. [ABSTRACT FROM AUTHOR]