Materials Science Forum Vols. 825-826

Abstract: Polysilazane-based coatings were prepared on dense and porous substrates by dip-coating. Both the pure, liquid polymer and polymer solutions in cyclohexane were investigated. Relevant properties of the coating solutions, including rheological properties and surface tension, were determined and used to predict the resulting layer thickness as a function of dip-coating parameters on dense borosilicate glass substrates. A good correlation between existing model (Landau and Levich) and experiment was found for the pure polymer. In the presence of a solvent, evaporation phenomena led to a predicted coating thickness that is much less than the experimental value for all dip coating withdrawal spends. The introduction of a correction factor was found to adequately describe the deviation. In case of porous substrates, the coating thickness could not be predicted using the model due to infiltration of the base structure, resulting in an interpenetrating ceramic composite layer after pyrolytic conversion of the preceramic polymer compound. When preparing polymer-derived ceramic films on porous base materials, e.g. for membrane applications, this phenomenon has to be taken into account.

Abstract: The entire simulation process for long fiber reinforced thermoplastics is examined to determine the effective mechanical properties which are influenced by the microstructural fiber orientation state. Therefore, flow and fiber orientation simulations are conducted and the obtained fiber orientation tensors are used in two-scale structural simulations. The fiber orientation distributions as well as the mechanical properties are compared with micro-computed tomography data and results from threepoint bending tests performed by dynamical mechanical analysis (DMA), respectively. The validated results show that prediction of the essential mechanical properties is possible with the applied combinated methods and that the knowledge of the fiber orientation and its gradients is of crucial importance for the entire simulation process.

Abstract: This study investigates how roughness and coatability of sheet moulding compound (SMC) components can be improved by modifying the surface morphology of the compression tool. A modular tool was developed that allowed to mould SMC work pieces simultaneously with different tool surfaces. In this study, mainly the tool roughness was modified using various surface treatments. Three different SMC formulations were applied to mould 2D components using the modular system. It was found that the demoulding was affected by both the tool morphology and the SMC formulations. Contamination of the tool by SMC material could be reduced by chrome-plating. The morphology of the tool was transferred to the SMC work piece if the structures were larger than 5 µm. The adhesion strength of a coating system differed for the three SMC formulations. While two of them showed generally good coatability, the coating adhesion on the third formulation decreased with increasing roughness of the tool used for moulding.

Abstract: Composite materials have been introduced in the 90’s in the car racing, naval and aeronautic sectors for weight reduction purposes. In the automotive industry, the introduction of composite materials to reduce also the weight of the vehicles leads to additional challenges for Virtual Prototyping on top of difficulties already encountered with metallic structures modeling. The impact of manufacturing on product performance is critical for composites, as the imperfections from the process may greatly affect the statics and crash performance of the final composite component. The paper will describe the state of the art of ESI Composite Solution on global composite manufacturing simulation chain (Forming, Injection, Curing, and Distortion) and how it couples to Structure/Crash through selected industrial examples.

Abstract: The development of high performance products at lowest possible product development-time and costs is the demand of the plastics industry today. A successful use of process simulation to describe the behavior of complex structures and to minimize the technical and economic risks for companies requires application and process-relevant material data.The pvT-behavior of polymers is an essential parameter for process simulations. Especially the dependence of the specific volume of pressure and temperature [1, 2] under process conditions is not mapped to the existing measurement methods.In this study pvT measurements were performed on selected amorphous and semi-crystalline polymers (PP, HDPE, POM, PBT, and ABS) with a Pirouette pvT device, a combination of a dilatometer and Couette rheometer. The specific volume was determined as a function of temperature (25-300°C) and at pressures ranging between 200-1000 bar. On top of that, the influence of the cooling rate was also investigated by pvT measurements performed at cooling rates of 0.1°C/s, 1°C/s and 100°C/s.The coefficients for the 2nd domain Tait pvT-model, which is implemented in the software Autodesk Moldflow, were determined by fitting the experimental pvT data and comparing them with the measured curves. As a result, the semi-crystalline polymers show a shift of the transition temperature to lower temperatures and a reduction in the specific volume in the melt is observed. For validation, in a case study shrinkage results in real were compared with the simulation.

Abstract: Since energy resources are limited, there is a strong need for efficient technologies, which are suitable for large scale production. Therefore, an innovative Continuous Orbital Winding Technology was developed within the Federal Cluster of Excellence EXC 1075 “MERGE Technologies for Multifunctional Lightweight Structures” at TU Chemnitz. This continuous orbital winding (COW) technology is aiming for mass-production-suited processing of special semi-finished fiber reinforced thermoplastic materials. The new process chain and modular concept allows the implementation of other technologies and special applications, e.g. sensor integration. The COW process is a combination of thermoplastic tape winding and automated thermoplastic tape laying technology.The technological aim is to produce structural components with variable closed cross sections having rotationally symmetric and asymmetric sections. In addition, the machine concept is specifically designed to realize flexible layer constructions. The experimental part geometry was determined and it is intended to carry out pilot studies in order to validate the functionality.The key challenge is the desired processing speed for mass production. Therefore, an exemplary cross-section contour has been derived and used for the realization of the demonstrative concept. In this special concept the number of discontinuous moved assembly units was reduced. Furthermore, the appropriate and effective drive system was dimensioned by using inverse kinematics.For the fundamental experiments unidirectional fiber reinforced thermoplastic tapes are used. These investigations imply the level of consolidation in critical areas. The achievable maximum processing speed is of prime importance. These results will be used for further optimizations and specifications.

Abstract: The reuse of CF-wastes (rCF) is desirable due to the energy-intensive manufacturing, high price and the disposal problem of carbon fibers. It is a challenging process to spin yarn from rCFs in a short staple spinning production line which ensures a much higher strength later in the manufacturing of CFRP (carbon fiber reinforced plastics) parts than that of the parts from rCF-nonwovens or, from short-fiber reinforced injection molded parts. This spinning technology consists of several subsequent processes such as carding, drafting and spinning on a flyer frame. It is possible to produce hybrid yarn up to 2000 tex, which fineness is similar like a roving. The machines used to produce yarn for this purpose were specially modified and adapted, so that the brittle CF can be processed smoothly. Carded and draw frame slivers with different fiber lengths and mixing ratios were produced and later the high-quality hybrid yarn has been spun with different yarn twists.

Abstract: Modern civil engineering is characterized by resource and energy efficiency, and functional integration. The focus of modern architecture is therefore increasingly on free-formed buildings with organic shapes and biomorphic structures. The basis of new buildings still consists of conventional materials like steel, glass and reinforced concrete. However, the applicability of these materials is limited, regarding lightweight design, freedom of design, efficiency and functional integration. Innovative projects either cannot be implemented, or would be put to enormous costs and expenditure of resources.The theoretical and experimental basis for this functionally integrated support structure was established within the scope of the research project “New lightweight structural components and processing technologies for the application in support structures”, supported by the Sächsische Aufbaubank SAB.The main objective was to develop material and design for a lightweight modular support structure and to implement it by means of innovative production methods. New approaches included the application of glass-fiber-reinforced plastic (GFRP) due to its favorable mechanical properties, low susceptibility to corrosion and load-adjusted dimensioning.In connection with the realization of the production, different technological concepts were analyzed with reference to their suitability, integration of required force transmission and further functions during and after production. The lightweight elements were analyzed on a laboratory scale with regard to their production and their mechanical properties. A holistic production and tool concept resulted from these tests, that pictures the complete process chain from textile to component. The results were implemented in practice in form of an interactive honeycomb-bridge which was built in Chemnitz.

Abstract: Molding techniques and manufacturing of components consisting of fibre reinforced polymers are mostly controlled processes. However, finishing of such materials can even today still be seen as a very challenging and not completely controlled process, which often has a non-satisfying machining quality as result. This paper deals with different topics in the field of machining FRP. On the one hand, it deals with ideas for possible evaluation mechanisms in order to classify the resulting machining quality of FRP when machining with a cutting edge. Referring to this, a framework for the definition of an international standard in measuring machining quality on FRP parts is presented. On the other hand, a possible assistance system with the aim to improve the demanding cutting process as well as a tool life experiment, are investigated. The results of these practical experiments are presented and evaluated.

Abstract: This paper documents the initially made and generally applicable systematisation and classification for optimised design of automotive cylinder heads by using hybrid compound material solutions. Proceeding from this background, different technical variants for design and manufacture of cylinder heads are presented. The intention is to combine different materials, so that locally different stresses in modern cylinder heads may be taken up through the specific use of appropriate materials. On the basis of fundamental investigations into the bonding behaviour of different materials, appropriate opportunities for an effective reduction resp. overcoming of the interfering oxide layer are derived. With this in view new design approaches are presented. As the basis for assessment and evaluation of their performance potential different FEM and CFD calculations for temperature field analysis, strength prognosis and fatigue strength are shown. Finally special casting tests regarding the practical feasibility of the appropriate conceptions in production are presented.