Abstract: Fast curing of carbon fiber reinforced plastics (CFRPs) is limited by the degradation of the resin under high temperatures and by the development of internal strains. The authors counter these problems by adding nanoparticles to the matrix of CFRPs. In the presented work various volume fractions of nanosized aluminum oxide particles are integrated into the epoxy resin RTM6. To demonstrate the increased heat flow within the CFRP component, thermal conductivity tests are presented. Results show increasing values as the filler content is raised.With increasing filler content the reaction speed is also accelerated. This effect is analyzed by differential scanning calorimetry. It is shown that the particle surface has a catalytic effect on the curing of the epoxy resin. The results of the author also show that the added nanoparticles not only change the material composition, but also modify the network of the epoxy resin. In a series of experiments it is demonstrated how nanoparticles decrease the chemical shrinkage. The results show a reduction of the shrinkage higher than the volume fraction of the nanoparticles, which can be explained by the formation of interphases. Thermal mechanical analysis also confirms a decreased thermal shrinkage due to the integration of nanoparticles. Finally, the inspection of L-shaped CFRPs samples with different filler contents show the ability of nanofillers to decrease the spring-in.In summary, the integration of aluminum oxide decreases the thermal as well as the chemical shrinkage, increases the thermal conductivity and accelerates the chemical reaction.Overall, these changes in curing behavior lead to an increased dimensional stability of the CFRPs. Thus, nanoparticles may be one way of overcoming the disadvantages of fast curing cycles.
Abstract: Natural fiber reinforced polymers have gained increasing interest in research with the aim of replacing conventional reinforcements, such synthetic or glass fibers. In this work, whole paper sheets of copy, filter and newspaper were used for fabricating cellulose fiber reinforced polypropylene composites with MAPP as a coupling agent. By varying the amount and type of paper, the influence of these parameters on the mechanical properties was observed. The laminates were produced by a film hand stacking method and hot pressing. The characterization was carried out by tensile and flexural testing. Remarkable results were obtained for copy and newspaper composites at a fiber content of 30 and 40 vol.-%. In summary, structural paper reinforced composites with attractive mechanical properties were obtained, indicating the high potential of whole paper sheets as polymer reinforcement.
Abstract: The qualitative and quantitative assessment of the aging behavior of polymers and polymeric products depends on a substantial characterization of the materials properties and is linked to a multi-parametric approach. However, the choice of suitable polymer diagnostics test methods as well as parameters for the characterization of the material behavior are important. The aging of products can be attributed to complex factors and due to the superposition of different factors, the generation of simple relationships is impossible. Important materials for the automotive industry are fiber-reinforced PA6 materials, which can fulfill the requirements related to the mechanical properties like stiffness, strength, toughness as well as other properties. However, the knowledge for the assessment of different climate conditions as well as media on the aging behavior of such materials is not complete. For this reason, it is essential to describe the behavior with a material-physical approach.
Abstract: Rising weight and cost requirements in the automotive industry have led to an increasing substitution of metals by short-or endless-fiber reinforced thermoplastics. The use of thermoplastic matrices is necessary to meet the cycle time challenges which arise from large production quantities. The substituted components are often applied in the chassis or motor compartment, which means an exposition to environmental influences, e.g. moisture or thawing salts, during the entire operating lifetime. The degradation of the material properties of PA6GF30 due to a longtime exposition in DI (deionized) water, sodium-and calcium-chloride solutions is investigated and the fracture behavior examined by scanning electron microscopy analysis. Also, the fatigue properties were determined on a special test rig, which allows the spraying of the specimen with the different fluids during the mechanical cyclic testing.
Abstract: Vacuum Assisted Resin Transfer Molding (VARTM) fabricated FRP laminates generally show significantly small void contents. The apparent difference in void content is generally attributed to the difference in the resin infusion driving force, i.e., vacuum versus injection pressure. In the present study, we contrast the influence of processing parameters on the impregnation quality of FRP laminates. Application of different vacuum pressures (500, 800 and ~103 mbar) during VARTM results in different impregnation velocity due to different compaction levels produced. Composite laminates were realized using epoxy resin reinforced with carbon (CF) or glass continuous (GF) fibers. Two different textile architectures, namely unidirectional non-crimp fabrics (UD) and woven-mat (0/90), were used and various processing conditions were employed. Optical microscope observations revealed an unexpected trend relatively to the intra and inter bundle voids concentration with respect to the impregnation velocity, especially using UD-CF and UD-GF reinforcements and low impregnation rate. Tensile and three point bending tests highlighted the strong impact of fiber material and architecture on mechanical properties, whereas the presence of voids played a slight influence on the fiber dominated characteristics analyzed.
Abstract: Microfibrillar reinforced composites (MFC) are self-reinforced polymer-polymer composites, consisting of a cold drawn (fibrillized) phase in an isotropic matrix. They are manufactured via melt blending of two immiscible polymers with different melting temperatures, followed by a subsequent cold drawing and thermal annealing step. The present study examines the manufacturing of composite material out of melt-spun microfibrillar reinforced filaments. Polypropylene (PP) and Polyethylene terephthalate (PET) were chosen as the low-melting matrix and the high-melting reinforcement phase, respectively.The filaments were woven to flat textile structures and processed to composites via hot pressing. They represent a bidirectional reinforced composite, comparable to other fiber reinforced polymers. To ensure optimized processing the influence of relevant parameters has been investigated with respect to mechanical properties of the MFC‑filaments and the derived composites. In addition, the morphology was visualized by SEM imaging after all manufacturing steps. An important observation was that the reinforcing fibrils are still intact after thermal processing, leading to a significant increase in mechanical properties of the resulting composites. Quasistatic tensile tests show more than 100 % higher modulus and more than 50 % higher strength of the only 20 wt-% reinforced PET‑PP composites compared to neat PP. The influence of the amount of PET reinforcement, the variation in processing conditions and composite layup were investigated. Additionally, an outlook on the melt-spinning of blends with Polyamide (PA) is given. In future work it is meant to show that a broad spectrum of tailored properties can easily be achieved by such polymer blends and composites outperforming existing homopolymers as well as thermoplastic composites like short glass‑fiber‑reinforced Polypropylene.The material cost reduction thanks to adding cheaper mass‑production polymers and the transfer onto conventional manufacturing lines is meant to ensure the feasibility of industrial production. The low density and excellent recycling options of these composites underline their potential for automotive and aircraft applications.
Abstract: Additive Manufacturing (AM) received a lot of attention in the last years. Organizations are using AM systems for a range of applications such as prototypes for fitting an assembly, tooling components, patterns for prototype tooling, functional parts and many more. Nearly a third is applied for functional parts . Hence, the SL method provides a smoother surface finish than other AMT. Not only is the smoother surface a benefit but the good precision is also a positive feature. The ongoing development of new material systems and applications make them suitable alternatives for conventional series production like injection molding or machined-core fabrication for foundry use. Small to middle series cores for faucets with quantities from around 50,000 pieces produced using AM methods are already a reality . From the economical point of view, the SL is a cheap and fast process in comparison to AM systems. The SL technology used in this work is based on an active mask exposure, the digital light processing (DLP). The term DLP refers to the digital mirror devices which are used for selectively tuning individual mirrors on and off in order to selectively expose a photosensitive resin with visible or ultraviolet light. The resin contains a photoinitiator which triggers radical polymerization when irradiated with light. The polymerization process leads to a solidification of the resin, leading finally to a solid polymer part . A digital Mirror Device (DMD) chip acts as a dynamic mask to expose a defined area on the bottom of a transparent material vat above the optical system. The generated picture enables layer-wise polymerization of the photosensitive resin resulting in a 3-dimensional object. The light source radiates light with a wavelength of 460 nm which means blue visible light. At this wavelength the curing takes place. At the Institute of Materials Science and Technology at the Vienna University of Technology six generations of these Blueprinter machines have been developed and built to date. The largest parts that a Blueprinter can currently generate are 110 x 110 x 80 mm3 with a resolution of 25 x 25 x 25 μm3. The wall thickness can go down to four pixels which means one tenth of a millimetre.
Abstract: Based on their properties, PPS fibers are a promising material for reinforcing elastomeric components that are subjected to high mechanical and thermal loads. The use of this material is at present hindered because of the low adhesion between the fiber and matrix. Atmospheric pressure plasma treatments based on the dielectric barrier discharge were performed on PPS fibers using air as reactive gas for different treatment durations in order to improve the adhesion. The effects of these treatments have been characterized by determining the surface energy, and the residual tensile strength as well as by analyzing the surface chemistry. Required conditions for an improved wetting behavior and a significant increase in the polar component of the surface energy could then be identified.
Abstract: The electrically induced heating of textile composite materials is already applied in the clothing and outdoor use. However, making thin, flexible and washable heating layers remains a challenge. Based on various polymers thin electrically heatable polymer sheets were developed using multi-walled carbon nanotubes as electrically conductive fillers in silicone, polyurethane as well as polyvinylchloride. To prepare the membranes a knife coating process was applied. The viscosity of the polymer masses, the particle alignment, the percolation as well as the electrically and heating properties of the membranes were investigated.