Technologies for Lightweight Structures (TLS) 2019-01-09T13:43:14+01:00 Prof. Dr. Lothar Kroll Open Journal Systems <p><em>Technologies for Lightweight Structures (TLS)</em> is a peer-reviewed, open access journal that publishes original research articles as well as review articles in the field of multifunctional lightweight structures.</p><p><em>Technologies for Lightweight Structures</em> is aimed at experts from academia and industry who contribute their knowledge to the research and development of lightweight structures and of the corresponding manufacturing technologies. Thus, it serves to increase the unrestricted, interdisciplinary flow of knowledge between users, manufacturers, designers and researchers involved in the promotion of these innovative key-technologies.</p><p>The journal's main language is English, but submissions in German are also welcome.<br /> In order to address a national and international readership alike, submissions in German are professionally translated into English as a journal service after acceptance.<br />Please see our <a href="/about/submissions">Author Guidelines</a> for information on article submission.</p><p><a href="/about/">More about the journal</a></p> Methodological approach to investigate the behavior of the structure under dynamic loading using multiple criteria decision-making method 2018-05-15T08:56:48+02:00 Josef Oleksik Thomas Vietor Srivatsaa Natarajan <p>The main objective of this article is to develop a support approach for designers in the concept phase of the design process. In this paper, two different structures are investigated with metal, composite and hybrid material under dynamic loading with multiple strain rates. The optimum choice of material and structural combination is found by a methodological approach using a Multi Criteria Decision Making Method (MCDM). It uses a stepwise procedure in evaluating the significance of each criterion and ranks the different alternatives. This method is applied to solve various problems in the field of economics, engineering, management. In this article, COPRAS is used to rank different material and structural combination.</p>Cylindrical and rectangular structures are investigated under axial and 3-point bending load. Moreover, three different constellations of material widen the comparison; they are steel and aluminum, composite material with carbon fiber and thermoplastic matrix and hybrid material, with a combination of composite and metal. The output parameters from the simulation such as energy absorption and force, are further mathematically converted to specific energy absorption (SEA), crash-force-efficiency (CFE) and load non-uniformity (LU). PAM-Crash is used as a solver for simulation. 2018-01-16T15:08:22+01:00 ##submission.copyrightStatement## Investigation on inkjet printing for electromagnetic compatibility application 2018-02-15T11:19:22+01:00 Melinda Hartwig Maxim Polomoshnov Ralf Zichner Reinhard R. Baumann The research is focused on the development of inkjet-printed silver grids on flexible films to (I) attenuate electromagnetic waves at 2.45 GHz locally by applying them directly on Wi-Fi or Bluetooth transmitter or to (II) protect electromagnetic compatibility (EMC) sensitive devices close to electromagnetic transmitters. The inkjet printing technology leads to resource, time as well as cost efficient manufacturing and simplifies the adjustment of the pattern design regarding different applications. The research contains a fundamental analysis of the behavior of printed silver patterns on flexible polymer substrates regarding line widths, layer morphology and electrical performance. On that basis the grid pattern for a certain frequency range is simulated. The report shows first simulation results on basis of the given material parameters. The results are the fundamentals for further research on realization of the simulated grid patterns by inkjet printing technology. 2018-01-26T00:00:00+01:00 ##submission.copyrightStatement## Microstructuring of joining areas in aluminum alloy sheets by Jet Electrochemical Machining 2018-02-15T11:19:22+01:00 Rene Schimmelpfennig Matthias Hackert-Oschätzchen André Martin Andreas Schubert In this work the increase of the tensile shear strength by means of microstructuring of the metallic part for ultrasonic vibration assisted joining of hybrid compounds is presented. The aluminum alloy EN AW-5083 and a carbon fibre-reinforced plastic (CFRP) from Bond Laminates are used as a material combination. A suitable method is electrochemical processing (ECM). The microstructuring is carried out with continuous electrolyte free jet machining (Jet-ECM): Characteristic of this technology is the restriction of the electric current to a limited area of the electrolyte jet. After describing the materials and sample geometry used, the Jet-ECM technology and the ultrasonic vibration assisted joining process are explained. The strength of the joint is assessed by means of a tensile shear test. The determined results of the tensile shear strength for hybrid connections between microstructured aluminum sheets and CFRP are compared with those of unstructured aluminum sheets. Furthermore, the influence of the microstructure on the tensile shear strength achieved is discussed using metallographic cross-sections of the joining area. 2018-01-26T00:00:00+01:00 ##submission.copyrightStatement## FAUSST: bridging the gap between steel and fibre reinforced materials 2018-05-07T13:57:23+02:00 Rafael Luterbacher Lars Molter André Sumpf Rigo Peters <p class="AuthorData">Multi-material design is commonly used within lightweight applications to meet certain design constraints. One common challenge across the different industry fields is the joining of materials of different material classes. Bonding and mechanical joining are generally used to overcome this issue. However, in some application fields, such as in the shipbuilding industry, where the interest of applying fibre-reinforced materials is increasing, these processes are not currently feasible due to regulatory and current technical constraints. One potential solution is FAUSST, a textile based transition joint. FAUSST is a hybrid knitted fabric, which is composed of 100% steel on one side and on the other of 100% glass fibres. The steel side is welded to a flat steel and the transition element is subsequently integrated via lamination processes within a fibre-reinforced component. Afterwards, this component is e.g. joined to a steel structure by welding. Depending on the design of the transition element, loads of up to 120 kN per meter joint can be transferred in the presented design with an overlap length of only 10 mm. This transition element, therefore, may lead to more lightweight designs with smoother surfaces for aesthetical, aerodynamic or hydrodynamic surfaces.</p> 2018-01-26T00:00:00+01:00 ##submission.copyrightStatement## Influence of the cooling behaviour on mechanical properties of carbon fibre-reinforced thermoplastic/metal laminates 2018-05-15T08:55:54+02:00 Camilo Zopp Daisy Nestler Nadine Buschner Carola Mende Sven Mauersberger Jürgen Tröltzsch Sebastian Nendel Wolfgang Nendel Lothar Kroll Michael Gehde <p>For several years, thermoplastic hybrid laminates form a new class in the field of material compounds. These laminates consist of fibre-reinforced plastic prepregs and metal layers in alternating order. Compared to conventional thermosetting multilayer composites, these laminates are suitable for large-scale production and can be manufactured with significantly reduced cycle times in the thermoforming process.  </p><p>In the framework of this contribution, the influence of the cooling rate of carbon fibre-reinforced thermoplastic composites and hybrid laminates was investigated with regard to crystallinity and the resulting mechanical properties. Polyamide 6 and thermoplastic polyurethane as matrix systems were examined, in particular.</p>Additionally, the differential scanning calorimetry was used in order to investigate the influence of the cooling rate on the crystallisation behaviour. It could be determined that the cooling rate has a limited influence on the crystallisation of polyamide 6 and this influences the mechanical properties. Furthermore, a reliance of process parameters on the characteristics profile of composite materials and material compounds with thermoplastic polyurethane could be identified. Depending on process conditions, tensile, bending, and interlaminar shear properties fluctuate up to 20 % in fibre-reinforced laminates and up to 32 % in hybrid laminates. Moderate to fast cooling rates result in optimum mechanical characteristics of tensile properties in fibre-plastic-compounds. Fast to very fast cooling rates are advisable for bending and interlaminar shear properties. Highest tensile and bending characteristics are achieved in hybrid laminates by using fast to very fast cooling rates, while interlaminar shear properties tend to be highest in slow to moderate cooling rates. 2018-02-15T00:00:00+01:00 ##submission.copyrightStatement## Smart Process Combination for Aluminum/Plastic Hybrid Components 2018-05-07T13:58:17+02:00 André Albert Wolfgang Zorn Markus Layer Welf-Guntram Drossel Dirk Landgrebe Lothar Kroll Wolfgang Nendel <p class="06-text-body-western"><span lang="en-US">The research on lightweight construction increasingly gains in importance, especially for the automotive industry. New lightweight components ensure the necessary stability of car body parts on the one hand. On the other hand they are supposed to allow a low priced production. Hence, aluminum or magnesium alloys have quite a large share in production engineering. During the last years, research mainly addressed metal/plastic compounds. Weight reduction as well as the capability of producing complex structures are only some of the benefits of this technology. Furthermore, additional functionality can be integrated or functional tasks can be distributed: The metal ensures stiffness and realizes the technical connection to the car body by means of welding, while the plastic enables the insertion of special elements for the joining or assembly process. This paper presents two approaches of realizing a combined process to produce aluminum/plastic-hybrid structures. In a first approach, an active tool is presented to realize the sheet based process. The second approach focusses on the tube-based process and presents the topical state of research within the Federal Cluster of Excellence EXC 1075 “Merge Technologies for Multifunctional Lightweight Structures”.</span></p> 2018-02-16T09:54:31+01:00 ##submission.copyrightStatement## Advanced joining technology for the production of highly stressable lightweight structures, with fiber-reinforced plastics and metal 2018-05-07T11:35:11+02:00 Holger Seidlitz Nikolas Tsombanis Felix Kuke <p>Organic sheets made of fiber-reinforced thermoplastics can make a crucial contribution to increase the lightweight potential of a technical design. They show high specific strength- and stiffness properties as well as good damping characteristics, while being able to show a higher energy absorption capacity than comparable metal constructions. In addition, organic sheets provide good recycling capabilities. Nowadays, multi-material designs are an established way in the automotive industry to combine the benefits of metal and fiber-reinforced plastics (FRP). Currently used technologies for the joining of organic sheets and metals in large-scale production are mechanical joining and adhesive technologies. Both require large overlapping areas to achieve the desired joint strength and stiffness of the technical design. Additionally, mechanical joining is usually combined with “fiber-destroying” pre-drilling and punching processes. This will disturb the force flux at the joint zone by causing unwanted fiber- and inter-fiber failure and inducing critical notch stresses. Therefore, the multi-material design with fiber-reinforced thermoplastics and metals needs optimized joining techniques that don’t interrupt the force flux, so that higher loads can be induced and the full benefit of the FRP material can be used. This article focuses on the characterization of a new joining technology, based on the Cold Metal Transfer (CMT) welding process, that allows to join organic sheets and metals in a load path optimized design. This is achieved by realigning the fibers around the joint zone by the integration of a thin metal pin. The alignment of the fibers will be similar to load paths of fibers inside structures found in nature. A tree with a knothole is always going to align its fibers in principle stress direction. As a result of the bionic fiber design, high joining strengths can be achieved. The increase of the joint strength compared to blind riveting was performed and proven with stainless steel and orthotropic reinforced composites in tensile shear-tests, based on the DIN EN ISO 14273.</p> 2018-02-26T11:57:52+01:00 ##submission.copyrightStatement## The most filigree structure made by remote laser cutting 2018-05-07T13:57:41+02:00 Robert Baumann Patrick Herwig Eckhard Beyer <p><span style="font-family: Arial; font-size: small;">It is well known that the global climate change is the largest challenge for the society of the 21th century. In order for us to manage the resulting consequences, innovative materials for energy efficient applications become more and more important. Open cell metal foam contributes promising solutions to the light weight design, battery applications and renewable energy harvesting. Still, challenges are present concerning the cutting into a defined shape. The remote laser cutting offers a solution for decreasing the production costs as well as the needed component accuracy. Our investigations consider that this technique has a high potential concerning cutting speed which was increased by more than 500 %, compared to state of the art laser separation. Next to that, the contour accuracy was improved as well, resulting in tolerances with less than 30 μm. Together with the forceless process of remote laser cutting, the possibility is given to generate filigree components with a wall thickness less than 0.75 pore sizes. This paper offers insight into the viability of remote laser cutting in overcoming the challenges dealing with mechanical milling or grinding. Investigating the process concerning thermal stress input as well as particle attachments will be the next steps in the future.</span></p> 2018-03-01T00:00:00+01:00 ##submission.copyrightStatement## High-performance machining of fiber-reinforced materials with hybrid ultrasonic-assisted cutting 2018-05-07T13:58:07+02:00 Andrea Stoll Carlo Rüger Katja Busch Thomas Mäder Burkhard Kranz <p><span style="font-family: Arial; font-size: small;">A main approach for sustainable and efficient products is the application of innovative materials like fiber-reinforced plastics. Despite the excellent properties, the machining requirements, especially the hard cutting conditions, restrain the wide application of these materials. Thus a major task is the realization of the required part qualities combined with efficient machining strategies. The project ULTRASPAN, a joint venture of partners from industry and research institutes funded by the BMBF, attends to this challenge. The goal is the development of new hybrid machining concepts and process technologies for enhanced cutting of composite materials with ultrasonic-assistance. Prior condition is the development of novel robust actuators. Therefore, prototypic actuators for longitudinal and torsional vibration systems are developed in the project. Besides the novel actuator concepts, the results of ultrasonic-assisted drilling (UAD) on composite parts are presented in this paper. Machining tests in drilling of fiber-reinforced plastics with the novel prototype actuator systems were performed. Focus of the investigation was the influence of the ultrasonic vibration support on the bore quality. The superimposition of drilling with ultrasonic vibrations influences the process characteristics and engagement of the cutting edge. Machining tests showed the potential to enhance the bore quality with UAD in a certain parameter field.</span></p> 2018-03-06T00:00:00+01:00 ##submission.copyrightStatement## Prefinished Metal Polymer Hybrid Parts 2018-03-29T14:21:56+02:00 Ines Kuehnert Michaela Gedan-Smolka Matthieu Fischer Peter Scholz Dirk Landgrebe Didier Garray In this study, the shaping and assembly behavior of adhesive polymer-metal-composites was investigated in an international cooperation using two step curable uretdione-polyester-based powder coatings (IPF development) which acts simultaneously as a reactive adhesive agent and as a high quality surface finish. To create the composite, a thermoplastic polyurethane (TPU) layer with good compatibility to the powder coating was over-molded onto a powder coated aluminum substrate. A polyamide (PA6) layer was over-molded on to the TPU layer to create a stiff composite structure with possibilities for further functionalization. The TPU-layer in between the metal substrate and the polymer top layer acts as a stress and strain compensation layer. These loads are caused by thermal expansion (under fluctuating temperatures) and external forces/deformation. Another key feature of the composite is the innovative process chain. The powder coating can resist high deformation and therefore the coating is suitable for a future application on to a metal substrate using a coil coating procedure. In addition, the coil could be easily implemented into a production line as a semi-finished product. The prefinished coated metal substrate could be formed (e.g. incremental forming, deep drawing) and inserted in the over-molding procedure. This overall shortened process chain allows not only an effective fabrication of pre-coated semi-finished materials and polymer-metal-joints in high quantities by saving process steps (e.g. cleaning steps, glue application) but also a higher versatility in the following composite production. 2018-03-02T00:00:00+01:00 ##submission.copyrightStatement## Strategy and numerical modelling of a vehicle seat with a lightweight sandwich design for large-scale production 2018-05-07T13:58:29+02:00 Song Ren Kay Schäfer Daisy Nestler Dominik Krumm Stephan Odenwald Lothar Kroll Marc Fleischmann <p>A lightweight vehicle front seat with a sandwich structure, which consists of skin layers made of glass fibre-reinforced thermoplastic prepregs and a core consisting of a warp knitted spacer fabric filled with polyurethane foam, was developed. The strength test simulations of the seat structure were performed using a Finite Element Analysis approach. The results validate the new sandwich design of the vehicle seat with its adequate strength under a static load. With the innovative lightweight design, the mass of the seat was reduced up to 57 % in comparison to the reference seat from conventional mass production. In addition, a manufacturing process was advised for a large-scale production of the lightweight design within one workstation.</p> 2018-03-22T00:00:00+01:00 ##submission.copyrightStatement## Impregnability and Performance of rCF-nonwovens with epoxy resin 2018-05-07T12:38:25+02:00 Jasmin Mankiewicz Ernst Cleve Michael Heber Jochen Stefan Gutmann <p>Currently, the carbon fiber key market increases intensely. In consequence of production, 10–30 % of cost-intensive carbon fiber waste is accumulated by blending fabrics, prepregs which are out of specification and end-of-life products. Because of a landfill ban for carbon fibers, environmental aspects and a cost reduction potential, there is a stronger focus on carbon fiber recycling. Through new recycling methods, the carbon fiber is regained from polymer matrix, but looses its woven structure.</p>One possibility to re-use chopped recycled fibers is through a fiber mat. Carbon fiber nonwovens can be fabricated by a wet-laid process, for example. For recycled fibers without a specific fiber length and sizing, a challenge lies in separating them in dispersion to get homogenous nonwovens and interlink the fibers in the nonwoven. For the first step, stirring and surfactants improve the separation, hydroxyethylcellulose ensures the bonding. Then the nonwoven can be impregnated with thermosets by resin transfer molding (RTM). The University of Applied Science Niederrhein is the first to investigate the whole process chain from handling recycled carbon fibers in order to attain the finished composite. Optical impregnability is inspected and material properties (tensile strength and Young’s modulus) are analyzed and compared to virgin fibers to get information on performance. A density range from 1.18 (5% CF) to 1.4 g/cm³ (40% CF) is very attractive for lightweight constructions as well. 2018-04-13T14:45:35+02:00 ##submission.copyrightStatement## Tailored Fiber Placement in Thermoplastic Composites 2018-04-25T15:33:46+02:00 Axel Spickenheuer Christina Scheffler Lars Bittrich Rico Haase Dieter Weise Didier Garray Gert Heinrich <p>Fiber path optimization methods combined with the Tailor Fiber Placement (TFP) technology provide the optimum correlation between load case and fiber orientation and therefore lead to unmatched component performance with endless fiber composite materials. The aim of this work is the development of an innovative manufacturing technology for thermoplastic composites (TPC) including sizing-adapted commingled glass fiber (GF) / thermoplastic yarns (<em>SpinCom</em> yarns) to be processed by TFP to textile preforms with a variable-axial, load adapted fiber design. Furthermore, these preforms will be consolidated in a low energy and resource consuming process using novel light and low cost forming tools produced by incremental sheet metal forming technology. Finally, a low cost solution for thermal processing even for complex shaped TPC parts will be presented. Heading towards optimized resource and cost efficiency of the whole process chain, first results of <em>SpinCom</em> yarns, fiber path optimization, tool manufacturing and forming procedure are presented and demonstrated using GF/PBT (polybutylene therephthalate) <em>SpinCom</em> yarns and the geometry of a bicycle saddle.</p> 2018-04-25T00:00:00+02:00 ##submission.copyrightStatement## Material-integrated composite humidity sensors for condition monitoring of fiber-reinforced plastics 2018-05-08T16:53:31+02:00 Jörg Martin Kuldeep Shetty Nadine Reimann Stephan Neukirchner Uta Fügmann Heike Illing-Günther Daisy Nestler Arved C. Hübler Klaus Nendel Lothar Kroll Thomas Otto <p>Penetrating water in fiber-reinforced plastics can alter the mechanical properties considerably. To avoid potential resulting failure of the component, we propose continuous monitoring of the humidity inside the material by highly-sensitive humidity sensors based on nano- or microcomposites. Here we report on the inline-capable fabrication and integration of humidity sensors in glass fiber-reinforced polyamide (GF-PA6). Mean water concentrations of less than 0.5 wt. % have been clearly determined inside the laminate.   </p> 2018-05-08T00:00:00+02:00 ##submission.copyrightStatement## Realisation of Sensitive Functionality by the Integration of Electromagnetic Resonators in Composite Materials 2018-05-31T20:00:53+02:00 Toni Dirk Großmann Melinda Hartwig Michael Heinrich Ricardo Decker Christina Symmank Anja Schmidt Steffen Kurth Uwe Götze Reinhard R. Baumann Lothar Kroll Thomas Otto Lightweight structures are gaining importance due to the relevance of saving energy in mobile applications. External stress caused by impacts, deformations or compression injures the composite materials mostly by invisible internal distortions and leads to the degradation of their properties. Thus, an early detection of material damage is significant in applications with a very high level of required reliability. Structural health monitoring (SHM) on demand using functionalised materials can be a solution [1, 2]. The integration of electromagnetic resonators in glass-fibre-reinforced plastics (GFRP) allows the fabrication of materials with passive sensor function used for SHM of composite materials. Conductive patterns with a specific geometry, dimension and alignment show an electromagnetic resonance that can be changed by the arrangement of the resonators or by the surrounded material. Printing technology is an efficient fabrication method regarding resources, time consumption and costs. The additive and selective deposition of conductive ink on flexible substrates shows a great potential to be processed roll-to-roll and subsequently integrated into lightweight structures [3]. The read-out takes place wirelessly by analysing the reflection response of the functionalised structure. The paper considers the modelling, numerical analysis, fabrication and evaluation of a smart structure and its sensor function. Furthermore, in order to create a basis for a successful market introduction and penetration of such innovative smart structures, a concept for an integrated life cycle-related engineering and business modelling [4] is outlined in this paper. 2018-05-31T00:00:00+02:00 ##submission.copyrightStatement## Investigation of bio-based polyamide with short fibers for lightweight structures 2018-12-18T13:33:05+01:00 Roman Rinberg Tobias Hartmann Anton Nikiforov Anton Doynikov Svetoslav Volfson Lothar Kroll <p>In the automotive industry, petrochemical plastics are widespread because glass and carbon fiber-reinforced composites consist exclusively of petroleum-based matrix materials. So far, bio-based plastics couldn’t meet the requirement profile due to their high prices, their inappropriate features and the ineligible quality assurance of their synthesis. But the development of new bio-based polyamides opens the opportunity to replace petroleum-based plastics and may initiate the use of bio-based plastic matrices for fiber-reinforced composites for automotive applications.</p><p>In this study, short fiber-reinforced polyamide 10.10 composites were investigated. Short carbon and glass fibers were used in varying compositions along with different modifiers to optimize the resulting characteristics. Fiber breakage during twin screw extrusion processing was researched and affected by the use of lubricants. The effect of using lubricants was noticed after extrusion. The addition of lubricants caused negative effects on mechanical properties at concentrations higher than 0.5 % wt. Further influences on fiber matrix interactions were investigated by varying the parameters of injection molding and positive effects on tensile properties were recognized. Strengthening effects on resulting composites are discussed in terms of lightweight structure and cost-efficiency.</p> 2018-12-18T00:00:00+01:00 ##submission.copyrightStatement## Cold surface treatments on fiber-reinforced plastics by pulsed laser 2018-12-18T13:33:06+01:00 Jana Gebauer Gerd Paczkowski Jodok Weixler Udo Klotzbach <p>When producing fiber-reinforced plastic (FRP) suitable for mass production, new technologies have to be developed to overcome existing challenges such as increased efficiency in resource consumption or higher process flexibility. In the past, laser processing has been shown to yield important advantages such as non-contact processing, no tool wear and high design flexibility.</p><p>Pulsed laser ablation of FRP offers a promising alternative to state of the art mechanical blasting. The selective matrix removal enables a high potential to improve adhesive bonding, molding processes and coating deposition of lightweight materials, especially FRP-metal or FRP-ceramic hybrids. The resulting increase in surface area exhibits forms lock characteristics and simultaneously provides an expanded interface area. As a result, 40 % higher tensile strength can be reached in pull-off tests compared to a mechanically blasted organic sheet surface, joined by thermal spraying of aluminum on carbon fiber-reinforced epoxy (CFRP).</p> 2018-12-18T00:00:00+01:00 ##submission.copyrightStatement## Technologies for the integration of miniaturised silicon sensor systems in fibre-reinforced composites 2019-01-09T13:43:14+01:00 Benjamin Arnold Ricardo Decker Florian Rost Angelika Bauer Jan Mehner Lothar Kroll Sven Rzepka Thomas Otto Functional integration processes gain more and more importance in lightweight engineering. In this paper we discuss how to improve fibre-reinforced composites with structurally integrated condition monitoring systems, suitable for predicting failure behaviour. Especially commercially available and tested silicon sensors, but also new developments are well-suited for this intention. We present a smart semi-finished textile with integrated silicon sensors for in-situ conditions and process monitoring in fibre-reinforced composites. It consists of a textile substrate tape with integrated electrically conductive fibres and various silicon sensors, applied by micro-injection moulding. A so-called “interposer” is used as an electrical adapter between the microstructures of the sensor system and the mesostructures of the textile. The key technology used for the encapsulation and electrical contacting of the sensor nodes is a two-stage two-component micro injection moulding process, allowing for a cost efficient and application specific mass production. As proof of concept we chose the injection moulding process to investigate the influence of the fabrication process on all electronic components with a silicon stress measurement chip. We performed in-situ measurements of temperature and in-plane mechanical stress for different glass fibre contents of the PA6 melt and tool temperatures and compared the results with a finite element simulation. 2019-01-09T12:04:04+01:00 ##submission.copyrightStatement##