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An efficient way to reduce direct operating costs in aerospace applications is to lower the overall weight. In this context, thermoplastic composites offer a high potential for weight reduction. However, their application requires time and cost-optimized process technologies. Thermoplastic tape laying with subsequent out-of-autoclave consolidation represents such a process technology. Typical process chains consist of several automated steps that can influence the component's quality. Hence, a cross-process approach is applied to identify relevant process parameters. This paper focuses on minimizing the gaps between parallel-placed tapes and thereby reducing their influence on the laminate's porosity. A geometrical model is developed and validated to predict the maximum gap sizes for a tape-laying process as a function of process accuracy, material accuracy, and process parameters. Based on this, a methodological approach is presented to minimize the influence of gaps on porosity. It is validated using automated tape laying and a novel low-pressure consolidation process. The findings make an important contribution to understanding the development of porosity along the process chain for the manufacture of thermoplastic composites for aerospace applications. It can be shown that the approach enables the prediction of gap sizes and allows to minimize their influence on porosity. [ABSTRACT FROM AUTHOR]

Sandwich structures benefit from the geometrical stiffening effect due to their high cross-sectional area moment of inertia. Transferred to carbon fiber-reinforced plastic (CFRP) components, the needed amount of carbon fiber (CF) material can be reduced and with it the CO2 footprint. The combination of a light foam core with continuous fiber-reinforced face sheets is a suitable material combination for lightweight design. Traditionally, CFRP sandwich structures with a foam core are manufactured in a two-step process by combining a prefabricated foam core with fiber-reinforced face sheets. However, in addition to the reduction in the used CFRP material, manufacturing processes with a high efficiency are needed. The objective of this paper is the sandwich manufacturing and characterization by using the Direct Sandwich Composite Molding (D-SCM) process for the one-step production of CFRP sandwich structures. The D-SCM process utilizes the resulting foaming pressure during the reactive polyurethane (PUR) foam system expansion for the impregnation of the CF-reinforced face sheets. The results of this work show that the production of sandwich structures with the novel D-SCM process strategy is feasible in one single manufacturing step and achieves good impregnation qualities. The foam density and morphology significantly influence the core shear properties and thus the component behavior under a bending load. [ABSTRACT FROM AUTHOR]

To increase the use of fiber reinforced lightweight structural components in the automotive industry, their manufacturing processes have to obtain demanding economic requirements. One possibility is to use Compression Resin Transfer Molding (CRTM), which is fast and can be highly automated. One disadvantage can be the very high cavity pressure during injection. To avoid this disadvantage, a pressure-controlled RTM (PC-RTM) process was developed. PC-RTM uses a variable mold gap height and an embedded pressure sensor to control the cavity pressure actively during mold filling. In this work, we investigate this process by experiments and simulations with varying initial mold gap and controlled cavity pressure. We show that PC-RTM is a viable manufacturing process with short cycle times and high robustness. Furthermore, the simulations are validated by comparison to the experiments and show the same process characteristics. [ABSTRACT FROM AUTHOR]

Abstract Due to application-specific tailoring, continuous fiber reinforced plastics (CoFRP) provide an exceptional lightweight potential and are particularly suited for structural components. The use of CoFRP specifically for weight reduction of the automotive car body is the major focus of this feature article. Automotive mass production requires fast and qualified, thus highly automated and material efficient manufacturing technologies. Consequently, CoFRP manufacturing for automotive differs considerably from conventional CoFRP manufacturing for aerospace, particularly in terms of higher throughput with higher investment, but lower operating effort. Furthermore, automotive structures have smaller dimensions with more complex shapes, which makes it more challenging to avoid forming defects and to ensure complete injection. Since manufacturing makes the main difference between automotive and aerospace composite components, this feature article puts emphasis on the process technologies and on the corresponding material behavior and process simulation methods. For a holistic product design of automotive CoFRP components, a simultaneous virtual description and virtual optimization of both manufacturing process and structural capacity is necessary. Production effects must be considered in the part design and, thus, must be reliably predicted by process simulation as well as taken into account in subsequent simulation steps. This feature article therefore evaluates the current state of the art in the continuous virtual representation of CoFRP process chains, including the process steps forming, injection and curing. Furthermore, the integrated optimization along this CAE chain is a key factor for an economic part design and therefore another major subject of this article. [ABSTRACT FROM AUTHOR]

• Orientation dependent fiber breakage modeling approach. • Fiber length and orientation dependent flow modeling. • Coupling of transient fiber breakage modeling and fiber dependent viscosity and flow modeling. Injection molding is one of the most important processes for manufacturing discontinuous fiber reinforced polymers (FRPs). The matrix of FRPs shows a transient chemo-thermomechanical behavior and the fibers create anisotropy influencing physical properties. Hence, FRPs are complex materials, but also likely used in volume production. In this work, the fiber-induced anisotropic behavior during mold filling is modelled with an anisotropic fourth order viscosity tensor. The viscosity tensor takes second and fourth order fiber orientation tensor, fiber length and non-Newtonian matrix viscosity into account. In this way, the macroscopic simulation captures the influence of the flow field on the fiber re-orientation and vice versa. The fiber orientation tensor is used to determine reference fibers in every element for calculation of hydrodynamic forces. This information is used in a novel fiber breakage model, based on buckling of fibers in Jeffery's orbit. The result is a macroscopic molding simulation with not only transient fiber orientation distribution, but also fiber length distribution. Due to the anisotropic viscosity tensor, the predicted fiber breakage influences the material's viscosity and flow behavior, which is also visible in the simulated cavity pressure. The results are validated with injection molding experiments, performed with a glass fiber reinforced phenolic compound, showing good agreement. [ABSTRACT FROM AUTHOR]

Manufacturing parts with the resin transfer molding (RTM) process enables the inline integration of load transmission elements (e.g. inserts). During the preforming process, the inserts are installed in the dry fabric and, consequently, influence the following mold filling stage of the RTM process because fiber structure in the vicinity of the insert may considerably vary. Particularly, a high fiber volume fraction next to the insert raises the risk of a formation of dry spots close to the embedded insert. In this study, the influence of an insert on the RTM mold filling is analyzed experimentally and numerically. Two different insert geometries are analyzed: a standard insert and an optimized insert. For a detailed analysis, the influence of the local fiber structure around the insert is included in the simulation. This is realized by analyzing CT images of manufactured parts and transferring the fiber structure information to the simulation model. [ABSTRACT FROM AUTHOR]

The manufacturing process of Sheet Molding Compound (SMC) influences the properties of a component in a non-deterministic fashion. To predict this influence on the mechanical performance, we develop a virtual process chain acting as a digital twin for SMC specimens from compounding to failure. More specifically, we inform a structural simulation with individual fields for orientation and volume fraction computed from a direct bundle simulation of the manufacturing process. The structural simulation employs an interpolated direct deep material network to upscale a tailored SMC damage model. We evaluate hundreds of virtual specimens and conduct a probabilistic analysis of the mechanical performance. We estimate the contribution to uncertainty originating from the process-induced inherent random microstructure and from varying initial SMC stack configurations. Our predicted results are in good agreement with experimental tensile tests and thermogravimetric analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

Compression molding of Sheet Molding Compounds (SMC) is a manufacturing process in which a stack of discontinuous fiber-reinforced thermoset sheets is formed in a hot mold. The reorientation of fibers during this molding process can be either described by macroscale models based on Jeffery's equation or by direct mesoscale simulations of individual fiber bundles. In complex geometries and for long fibers, direct bundle simulations outperform the accuracy of state-of-the-art macroscale approaches in terms of fiber orientation and fiber volume fraction. However, it remains to be shown that they are able to predict the necessary compression forces considering non-isothermal, non-Newtonian and compaction behavior. In this contribution, both approaches are applied to the elongational flow in a press rheometer and compared to experiments with 23% glass fiber volume fraction. The results show that both models predict contributions to the total compression force and orientation reasonably well for short flow paths. For long flow paths and thick stacks, complex deformation mechanisms arise and potential origins for deviation between simulations models and experimental observations are discussed. Furthermore, Jeffery's basic model is able to predict orientations similar to the high-fidelity mesoscale model. For planar SMC flow, this basic model appears to be even better suited than the more advanced orientation models with diffusion terms developed for injection molding. • Characterization of matrix viscosity, transverse thermal properties, compaction behavior, and mold friction for UPPH glass fiber SMC. • Comparison of pressures in a press rheometer between macroscale model, mesoscale model (Direct Bundle Simulation) and experiments. • Jeffery's equation predicts orientation similar to a high fidelity direct simulation method for long SMC fibers in planar elongational flow. [ABSTRACT FROM AUTHOR]