In Selective Laser Sintering, fibres are strongly orientated during the powder recoating process. This effect leads to an additional increase of anisotropy in the final printed parts. This study investigates the influence of process parameter variation on the mechanical properties and the fibre orientation. A full factorial design of experiment was created to evaluate the processing parameters of recoating speed, layer thickness and laser power on the part’s modulus of elasticity. Based on the mechanical testing, computed tomography was applied to selected samples to investigate the process-induced fibre microstructure, and calculate the fibre orientation tensors. The results show increasing part stiffness in the deposition direction, with decreasing layer thickness and increasing laser power, while the recoating speed only shows little effect on the mechanical performance. This complies with computed tomography imaging results, which show an increase in fibre orientation with smaller layer thickness. With thinner layers, and hence smaller shear gaps, shear stresses induced by the roller during recoating increase significantly, leading to excessive fibre reorientation and alignment. The high level of fibre alignment implies an increase of strength and stiffness in the recoating direction. In addition, thinner layer thickness under constant laser energy density results in improved melting behaviour, and thus improved fibre consolidation, consequently further increasing the mechanical properties. Meanwhile, the parameters of recoating speed and laser power do not have a significant impact on fibre orientation within their applicable process windows.

Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.

Rigidly foldable origami tessellations exhibit interesting kinematic properties. Several tessellation types (most prominently Miura-ori) have shown potential for technical usage in aerospace and general lightweight construction. In addition to static (e.g., as core structures for sandwich components) and single-layer kinematic (e.g., deployable) applications, new possibilities arise from the combination of several layers of tessellations with congruent kinematics. This paper presents an analytical description of the kinematics of multilayered, or stacked, globally plane tessellations which retain rigid/isometric foldability by congruent, compatible movement.

Commercial aircrafts require insulation to protect passengers in the cabin from thermal and acoustic loads. The conventional insulation in aircrafts consists of blankets made from layers of glass wool wrapped in foil that keeps the glass wool from being adversely affected by the environment. There is a potential to improve the thermal and acoustic properties of the cabin by replacing the interior panels with conventional secondary insulation by new panels combined with vacuum insulation panels (VIP). This article is focusing on the study of the VIP integration into the interior panels. First, the new structure solutions are defined on the basis of a requirement analysis for interior panels and VIP and theoretical analysis. Second, the manufacturing feasibility study for the new solutions is performed. The results show that the new structures can be manufactured. Third, the thermal properties of the new structure solutions are measured. The test results show a decrease of thermal conductivity of the new panels by a factor of 3–6 compared to the conventional solutions. Finally, the impact of the hot molding press on the vacuum maintaining inside the VIP is investigated. The trials demonstrate that the high barrier films can withstand high-temperature and pressure conditions and that the thermal conductivity of the test specimens didn’t worsen after 1 year.

The application of fiber-reinforced thermoplastic mono-material sandwich panels has many advantages, such as recyclability, reduction in processing cycle times, integration of additional elements by means of welding, and a great potential for in-line production. The most efficient way to produce a curved thermoplastic sandwich panel is thermoforming, which has several challenges. One of them is to achieve a higher thermal gradient in the panel. On the one hand, the temperature at the skin–core interface must exceed the softening point of the polymer to reach a sufficient bonding degree. On the other hand, the core should not be overheated and overloaded to avoid its collapse. Furthermore, several fiber distortions, such as wrinkles or buckles, can be developed during thermoforming. All these flaws have a negative impact on the mechanical performance of the sandwich structure. The objective of this study is the development of a simulation tool for the thermoforming process, which can replace the time-consuming trial-and-error-based method. Therefore, a coupled thermomechanical model was developed for a novel thermoplastic sandwich structure, which is able to predict the temperature distribution and its influence on the mechanical properties of the panel. Experimental trials were conducted to validate the thermomechanical forming model, which demonstrated a good agreement with numerical results.

The Fused Filament Fabrication process (FFF) is an additive manufacturing process for thermoplastic polymers based on material extrusion. It offers a large range of material options and high potential for manufacturing parts with complex geometry. Mechanical properties of parts produced with this method are, however, highly anisotropic and depend on process parameters and resulting inner mesostructures. The relationships between process parameters, mesostructures and mechanical properties are complex. Characteristics of the FFF mesostructures, such as voids and the interfaces between filaments, cannot yet be sufficiently taken into account in macroscopic design methods. In this work, a method for homogenising mechanical properties is developed. This is based on the inner FFF mesostructure: shape and size of the voids are determined using micrographs and the size of the coalescence areas between the filaments is also estimated. Representative volume elements with periodic boundary conditions are then created in a finite element environment and homogenised mechanical properties are derived. These are compared with analytical and experimental values, and the results are discussed. The method presented here provides an approach on how different characteristics of FFF mesostructures can be transferred to macroscopic simulations. Results of the numerical approach are in good agreement with the experimental data.