Key Engineering Materials Vol. 742

Abstract: Hybrid textile-based composites possess an enormous potential for energy and resource efficient large-scale production, with freedom in and high specific mechanical properties. This paper covers the connection of available and established production processes for textiles in a differential process chain for the manufacturing of complex shaped and elastic sandwich components. The technology enables both stiffness and comfort through elasticity.OLU-Preg^®-organic sheets, polyurethane foam cores and 3D-spacer fabrics form the targeted properties of demonstrator models. This article refers to the demonstrator part “bucket seat”. To show the benefit of complex composite material, the lightweight and mechanical properties of the sandwich structures are tested in several variations of core and comfort shapes. Absolute and specific improvements of performance are shown in static and dynamic examinations. An Analysis of coupling effects, deformation and failure behavior of the multi-material design (MMD) complete the scientific approach of the structure-property relationships of hybrid composites.

Abstract: Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO₂/TiO₂ supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

Abstract: Sandwich structures are ideal for planar parts which require a high bending stiffness ata low weight. Usually, sandwich structures are manufactured using a joining step, connecting theface sheets with the core. The PUR spraying process allows to include the infiltration of the facesheet fibres, the curing of the matrix and the joining of the face sheets to the core within one processstep. Furthermore, this manufacturing process allows for the use of open cell core structures withoutinfiltrating the core, which enables a comparison of different material configurations, assembled bythe same manufacturing process. The selection of these materials, with the aim of the lowest possiblemass of the sandwich composite at a constant bending stiffness, is displayed systematically within thiswork.It could be shown that the bending modulus calculated from the component properties matched theexperimentally achieved values well, with only few exceptions. The optimum of the bending modulus,the face sheet thickness and the resulting effective density could be calculated and also matched theexperimental values well. The mass-specific bending stiffness of the sandwich composites with corestructures of open cell aluminium foams was higher than with closed cell aluminium foams, but wasexceeded by sandwich composites with Nomex honeycomb cores.

Abstract: . In technical applications components are often exposed to vibrations with a broad range of frequencies. To ensure structural integrity and a convenient usage for the customer, materials with good damping characteristics are desirable. Especially stiff and lightweight structures tend to be prone to vibrations. Fibre metal laminates (FML) offer great potential for lightweight design applications due to their good fatigue behavior. By using carbon fiber reinforced plastics (CFRP) as part of the laminates very good strength and stiffness to weight ratios can be obtained. To improve the damping characteristics of this hybrid material an additional layer of elastomer can be added between the CFRP and the metal, generating a fiber-metal-elastomer laminate (FMEL). In this present study the damping behavior of different layups of FMEL was examined. Two different metal sheets and two types of elastomer were used, also the layup of the constituents was variated. Vibrations were induced with a frequency range from 100 Hz to 20 kHz by mounting the laminates onto a speaker. The vibration response was measured with a piezoelectric accelerometer. Eventually the different laminate layups were compared with each other to determine the influence of the individual constituents regarding the damping characteristics. The different elastomer types and prepreg layups affected the damping of vibrations, whereas the use of different metal sheet materials showed only little influence.

Abstract: Using the Damascus technique and forging steel plates with different carbon concentrations results in a composite material with a layered structure and combines the properties of the individual materials. Detailed investigations on old Sax swords from the 8^th century indicate that Damascus steels were also used for decoration by applying the inlay technique. For the replication of a Sax sword a steel blade was manufactured and the Damascus steel inlay was upset by forging. From a test sample a cross section was investigated by means of metallographic methods. Of high interest are the intersections between the Damascus steel inlay and the core of the blade. After metallographic preparation the various microstructures were characterized by light optical microscopy and Vicker ́s microhardness measurements were performed.

Abstract: Within the framework of the bilateral CORNET projects MeTexCom and MeTexCom2, new approaches were developed and tested to improve the adhesion strength of metal textile composites, with a focus on the targeted roughening of aluminum surfaces and the development of new acoustically insulating nonwovens. The metal textile composites were produced by melting thermoplastic components of the textile composites without a separately applied adhesive.For improved adhesion strength between metal and textile, roughness was generated on the metal surface by means of a novel arc treatment by an anodic polarized TIG process or a cw (continuous wave) fiber laser process. On the one hand, the goal was to produce uniformly rough, untercut surface structures in micro-and nanodimension by means of a highly dynamic arcing process. On the other hand, a similar approach was pursued with the cw laser method by using a single-mode as well as a multi-mode laser.

Abstract: The integration of fibers, especially tailor fiber placement (TFP), in metal matrices offers one way to generate composite materials with increased specific strength compared to the unreinforced metal matrix. The TFP can be adapted according to the final load paths through the component and can be covered partially or fully with the metal. Following this approach load transfer elements can be built, transferring much load and having low mass. First fields of application are identified in building and automotive industry. This work includes the powder metallurgical manufacturing process using Spark Plasma Sintering (SPS) technique, the characterization of the microstructure and the tensile test of different specimens (sintered copper, TFP (as received) and TFP (Cu covered) reinforced copper). Experimental result on 19.5 vol.% TFP (Cu covered) reinforced copper shows an increase of specific strength around a factor of 2.2 compared to pure copper.

Abstract: In order to optimize the design of vibrating screening machines and realize significant weight reductions, the use of hybrid structures is gaining importance. In this context, the joining of FRP and steel and their interactions due to different material properties were investigated. Therefore, quasi-static tests with combined mechanical and thermal loads were carried out. To realize the simultaneous application of physical measurement techniques, e.g. optical and acoustic measurements, and thermal loads, short-wave infrared emitter technique was used instead of thermal chambers. Thus, the mechanical characteristics and acoustic emissions could be determined and assessed. The results show different structural mechanisms of hybrid joining at room and elevated temperatures. The characteristics of failure modes, shear stresses, strains and acoustic emissions could be correlated to determine the damage developments and mechanisms.

Abstract: Laser-structured metal surfaces in combination with thermoplastic compression mould processes allow intrinsic hybrid structures with high-strength connections. Suitable process parameters are still to be identified to provide optimised assembly parameters. Therefore, laser structures with different configurations are applied to steel sheets and compressed with textile reinforced thermoplastic composites to manufacture hybrid structures. Laser processing parameters, such as pulse duration or energy as well as laser scanning strategies and therefore structure dimensions are analysed.After manufacturing, specimens are extracted and characterized in single-lap shear tests comparing different configurations to identify boundary conditions for the laser structuring with optimal bonding characteristics.

Abstract: To meet the comprehensive requirements of lightweight design, a material minded design method will be aimed. A fiber minded solution for load application in fiber reinforced plastics are loop joints, which are mainly applied for introducing high concentrated tensile loads, e.g. in mountings for rotor blades, or in pre-tensioned supporting structures. Usually, these loop joints consist of, diameters in centimeter scale. Miniaturized loop joints with diameters in millimeter scale are applied in transition structures for carbon reinforced plastic-aluminum multi material designs. Factors of miniaturization influencing the mechanical behavior are decoupled for tensile testing. Data from computer tomography provides information on the failure behavior of loop joints. To validate the non-destructive test method microsections will be used.