Materials Science Forum Vols. 825-826

Abstract: Portable fire extinguishers need to be reliable and fully functional at all given environmental conditions. Especially in off-shore and power plant applications a specific range of properties is necessary, e.g. corrosive resistance and electromagnetic compatibility. Hence, the application of fiber reinforced composites and fiber composite design offers an alternative to the traditional application of metallic materials.Within the scope of the development of an innovative fire extinguisher, a process-chain for manufacturing of composite fire extinguishers suitable for aggressively corrosive environmental conditions was developed. The aim of the project has been the development of a fire extinguisher with the technology of thermoplastic composite materials. Besides the intended weight reduction, a concept for the realization of a high-volume production suitable process-chain had to be developed. Using a thermoplastic matrix material allows a corrosive-free, non-magnetic and functional integrated design. Within the scope of the research project, the extinguisher container with integrated base and connection for the valve has been dimensioned and designed. The containers geometry with optimized ratio of filling volume, overall part size and material utilization was derived by applying FE analysis. Furthermore, a process-chain for high-volume production was conceived and had been verified by producing functional demonstrators for further testing.The container is made of two glass-fiber reinforced injection molding parts being thermally joined. The leakproofness and sufficient material strength after the joining process were identified as key challenges of the joining process and were overcome with an adapted design of the molded parts. Within the process development, reproducible and high quality weld joints were achieved based on a robust and cost-efficient joining technology. For reliable processing, the specific processing parameters were analyzed and regulations for each processing step deduced.

Abstract: Within this study, the lightweight potential of thin-walled closed hat members, partially supported by hollow cores, consisting of glass foam granulate and a two component epoxy resin, is investigated. Nonlinear finite element analyses are applied to simulate the behavior under quasi-static three-point bending and to find out the lightweight potential. The simulations are validated by experiments on thin-walled side members of the chassis of a recreational vehicle with and without supporting cores. The results show a significant potential for weight reduction by using supporting cores. Related to the weight (F_max/F_g), experiments have shown that the collapse load is 38 % larger in comparison to thin-walled members without supporting cores.

Abstract: Process time reduction and energy/cost savings are usually in the focus of production process improvements. New technologies provide possibilities to achieve significant enhancements for relevant operation figures.Curing cycle times for CFRP manufacturing depend on several requirements: Type of resin, requested glass transition temperature, used equipment and energy source as well as sample size, weight, fibre volume ratio, fibre orientation etc. Conventional methods are mostly based on heat conduction while microwaves offer a selective and volumetric heating of the samples. Process time reduction and energy saving are the positive effects of the microwave curing technology.This paper will give an overview of the current status of this process technology not only focussing on technical aspects but also covering the process and economic effects.This work has been performed under the German BMBF project 02PJ2131, FLAME under the program Energy Efficient Light Weight Construction.

Abstract: In many areas of fiber composite technology there is a great need for a solution of how to manufacture nodal elements and/or ramifications with an optimized force flow process and by machine, i.e. economically. Examples are hubs of wind power plants, branch points in framework constructions in the building industry and air and space travel, the automotive industry, ramified vein prostheses in medical technology, or the connecting nodes of bicycle frames. Motivated by this, the potential of plant ramifications as a model for new compound fiber constructions was investigated. Ramified species with pronounced fiber matrix structure served, inter alia, as biological models. The PBG Freiburg examined tree-formed monocotyledons of the genera Dracaena and Freycinetia [1], the BTU Dresden column cacti of the genera Pilsocereus and Myrtillocactus [2]. The plants exhibit Y-shaped and T-shaped ramifications, whose angles resemble those of the ramified technical construction units that are to be optimised bionically. As the investigations confirm, the ramifications, which are nearly completely unexplored, are characterised by very interesting mechanical characteristics, like e.g. good-natured breaking behavior and good oscillation damping caused by high energy absorption, as well as a high lightweight construction potential. The results demonstrate the high potential for a successful technical transfer of the results of the proposed project.In this paper, three different types of braided branches are represented. Firstly, the aforementioned nature-inspired Y-junctions are shown. Secondly, a type of branch with a special braiding technique that allows branches with asymmetric design of the arms and a braiding technique for the automated production of loop connections is presented.

Abstract: A load dependent and curvilinear respectively variable-axial fibre design can notably enhance the strength and stiffness of lightweight components compared to fibre reinforced structures made of common multiaxial fibre textiles. At the Leibniz-Institut für Polymerforschung Dresden e. V. (IPF) special design strategies are in the focus of current studies. Two currently developed components made of carbon fibre reinforced plastics, a lightweight three-legged stool and a lightweight recurve bow riser, are described within this paper.

Abstract: Today, 3D-printing with polymer plaster composites is a common method in Additive Manufacturing. This technique has proven to be especially suitable for the production of presentation models, due to the low cost of materials and the possibility to produce color-models. But nowadays it requires refinishing through the manual application of a layer of resin. However, the strength of these printed components is very limited, as the applied resin only penetrates a thin edge layer on the surface. This paper develops a new infiltration technique that allows for a significant increase in the strength of the 3D-printed component. For this process, the components are first dehydrated in a controlled two-tier procedure, before they are then penetrated with high-strength resin. The infiltrate used in this process differs significantly from materials traditionally used for infiltration. The result is an almost complete penetration of the components with high-strength infiltrate. As the whole process is computer-integrated, the results are also easier to reproduce, compared to manual infiltration. On the basis of extensive material testing with different testing specimen and testing methods, it can be demonstrated that a significant increase in strength and hardness can be achieved. Finally, this paper also considers the cost and energy consumption of this new infiltration method. As a result of this new technology, the scope of applicability of 3D-printing can be extended to cases that require significantly more strength, like the production of tools for the shaping of metals or used for the molding of plastics. Furthermore, both the process itself and the parameters used are monitored and can be optimized to individual requirements and different fields of application.

Abstract: In modern manufacture, like in automotive industry, high quality products and high output rates as well as low costs are achieved by highly efficient processes. Optimized tool design represents a key factor for such processes, leading to long tool life and hence to low tooling costs. Early in the industrial manufacturing chain of roller bearings for example, hot bars are sheared into billets, which are subsequently transported automatically to the first forming stage of a press. The shear blades should have a high wear resistance at high temperatures. In this study the first bi-metal composite shear blade made by spray-forming has been developed and tested in industrial environment. The composite tool has been deposited in a co-spray forming process to directly combine a hard-facing alloy layer with a hot working steel body in order to take advantage of the high microstructural homogeneity and the low segregation generated in spray forming. After machining, heat treating and quality inspection of the new material composite, the hot working tool was used in manufacture to prove its wear resistance and durability. The results show that the interface properties of the composite are of high quality and the material has a lower vulnerability to cracks after use in production than the conventional tool, respectively material. Only the porous zone near the interface leads to fissures which are partially going deep into the tool. Hence the parameters of the co-spray forming process need to be improved.

Abstract: Large-scale production of carbon fiber reinforced plastics often fails due to the increased material and manufacturing costs. Using the lightweight potential for competitive costs of materials, new construction methods are necessary, which enables an intelligent use of continuous fiber reinforcement, a largely automated production process as well as short cycle times. [1] The combination of continuous fiber reinforcement in the areas of maximum loads and cheaper materials such as long-fiber reinforced thermoplastic offers an efficient material application. Thereby, a required ratio of mechanical properties and attractive cost profile can be achieved.

Abstract: Due to high specific properties and the ability for the realisation of short cycle times within the production process, the use of fiber-reinforced thermoplastic composites offers a high potential for high volume applications. Furthermore, the layered built-up and the according manufacturing processes of these materials give the possibility to integrate functional elements, like electronic components or piezoelectric sensor/actuator modules. Within the collaborative research center CRC/TRR 39 “Production Technologies for light metal and fiber-reinforced composite-based components with integrated piezoceramic Sensors and Actuators”, the integration of piezoceramic modules into lightweight structures ready for series production is investigated. This paper presents the manufacturing process of active fiber-reinforced thermoplastic composites. Here, the focus is on experimental investigations covering the process-integrated poling of novel piezoceramic modules during the manufacturing of active fiber-reinforced thermoplastic components. Therefore, laboratory and process-oriented tests are performed for the determination of appropriate parameters for the pressing and poling process. The functionality of the embedded and poled TPM is validated by the excitation of an active component structure and the optical measurement of the vibration behaviour using a laser scanning vibrometer.

Abstract: Sandwich structures consist of one light core layer and two top layers, which form the load-bearing structure. These layers have to be stiff and strong and have to protect the structure against indentations. The main task of the core layer is to keep the top layers in place and to generate a high shear stiffness. In order to obtain the required space between the top layers, the core layer has to have a high specific volume. Different sandwich materials with aluminium or steel top layers and cores of aluminium combs, corrugated aluminium sheets or aluminium foams are already known. In order to obtain better properties in terms of strength fibre-reinforced plastics (FRP) are utilised as top layers; this is the focus of numerous of the current research studies. The sole use of these materials leads to negative effects regarding the damage and impact behaviour. New top layers with high strength and high stiffness characteristics as well as good damage tolerances are to be expected by utilising metal layers in combination with endless fibre-reinforced plastics, so called hybrid laminates. These hybrid laminates combine the positive properties of metals (e.g. ductility) and fibre-reinforced plastics (e.g. tensile strength). The focus of this investigation lies on the production and characterisation of sandwich structures with aluminium foam core layers and hybrid laminate top layers. The foam cores consist of closed pore aluminium foams produced by utilising ingot and powder metallurgical techniques. The top layers consist of glass fibre-reinforced thermoplastics and aluminium layers. The production of the sandwich materials is realised by means of thermal pressing.