Papers by Keyword: Hybrids

Abstract: Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and inherent corrosion resistance.To speed up manufacturing and simultaneously increase the geometrical complexity of the produced FML parts, Mennecart et al. proposed a new single-step process combining deep-drawing with infiltration (HY-LCM). Although the first experimental results are promising, the process involves several challenges, mainly originating from the Fluid-Structure-Interaction (FSI) between deep-drawing and infiltration. This work aims to investigate those challenges to comprehend the underlying mechanisms. A new close-to-process test setup is proposed on the experimental side, combining deep-drawing of a hybrid stack with a linear infiltration. A process simulation model for FMLs is presented on the numerical side, enabling a prediction of the dry molding forces, local Fiber Volume Content (FVC) within the three glass fiber (GF) interlayers, and simultaneous fluid progression. The numerical results show that the local deformation of the hybrid stack and required forces are predictable. Furthermore, lateral sealing of the hybrid stacks leads to deviations from the intended initially one-dimensional fluid progression. Eventually, the numerical results demonstrate that most flow resistance originates from geometrically critical locations. Future experimental and numerical work will combine these insights to focus on the flow evaluation during deformation and a successful part-level application.

Abstract: Martensitic Ni-Mn-Ga based alloys are known for the Magnetic Shape Memory (MSM) effect, which upon application of an external magnetic field can generate a strain up to 12 % depending on the microstructure of the martensite. The MSM effect occurs by rearrangement of the martensite variants, which is most advantageous in single crystals. Single crystals are, however, rather tedious to produce and there has been attempts to achieve MSM effect in polycrystals. However, in polycrystals the magnetic field induced shape change remains low as compared to single crystals. As an alternative to the former, hybrid MSM materials offer several advantages. When compared to single crystals, hybrids have extended freedom of shaping, lower raw material price, relatively large MSM strain and easier manufacturability. Embedding MSM particles into a suitable polymer matrix results in actuation function or good vibration damping performance. In the present study we report on the mechanical, structural and magnetic properties of MSM polymer hybrids, which are prepared by mixing gas-atomized Ni-Mn-Ga MSM powder into epoxy matrix and aligning the magnetic particles in a magnetic field.

Abstract: In order to exploit full potential of hybrid materials, it is necessary to develop optimized load-dependent component designs, new manufacturing processes and joining technologies. Structural integrity concerning the interfaces between the single materials of the hybrid component poses a key factor to success. In this case, adhesion often constitutes the limiting factor for the maximum transferable load. In this investigation, a load-oriented innovative concept to increase the structural integrity of hybrid plastic-metal parts was developed. Local mechanical undercuts on the metal surface were created to generate an additional mechanical interlocking effect between the join partners. The aim is to find the best surface structure geometry to enhance mechanical bonding. Therefore, metal samples were structured by a new process and transferred to hybrid specimens by injection molding. For comparison, specimens with adhesive bonding (epoxy resin) of metal and plastic were prepared. The join partners aluminum AlCuMg1-2017 and PA6 as well as PA6GF30 were investigated. The evaluation of an increase in the structural integrity was determined using tensile tests. A significant improvement in joint strength compared with direct joining using adhesive bonding was achieved.

Abstract: This work aims to evaluate the immobilization of glucose oxidase (GOx) with CoFe₂O₄ nanoparticles and hybrids CoFe₂O₄/APTS. The nanoparticles were synthesized by combustion reaction and silanized using 3-aminopropyltrimethoxysilane (APTS). The samples were characterized by XRD, FTIR, magnetic measurements and immobilization of GOx. The results indicated single phase of spinel CoFe₂O₄ and the addition of APTS did not alter the structure of the ferrite. The characteristic bands of spinel and characteristic bands were observed in the silane silanized sample proving the silanization of nanoparticles of CoFe₂O₄. The CoFe₂O₄ nanoparticles and the hybrid had saturation magnetization of 58.0 and 53.0 emu/g and coercivity of 1.14 kOe and 1.15, indicating that the silanization does not interfere with the magnetism of the particles. The immobilized GOx was obtained with values of 0.047 and 0.050 mg/g efficiency of 84.86 and 80.30% for CoFe₂O₄/APTS and CoFe₂O₄.

Abstract: The possibility to carry out sports activities is one of the factors which increase the quality of life for the citizens of a city. The city of Bratislava ranks among the biggest places of sport activities in Slovakia. Most of the sport facilities were, however, built in the past century; therefore they do not fulfill the demands of technical condition, economic efficiency, do not meet the international criteria of professional sport and do not meet the broad spectrum of the modern sport activities, especially for the younger age group users. It is needed to modernize and build the new sport buildings in all areas of sport, at school sports, sport for all and also in professional and performance sport activities. In accordance with the new trends in design of sports facilities, there is a need to reduce servicing costs, to improve implementation of technologies that increase the quality, safety and economy efficiency. The priority is the creation of multifunctional or hybrid facilities, which can offer the widest range of activities to users. In this report, the survey of the condition of existing sports facilities in Bratislava and proposal for possible solutions to the revitalization or the design of new facilities with sport function is published. The combinations of different activities which are compatible and suitable for multifunctional facilities are also published here.

Abstract: The possibility of enhancing mechanical properties by incorporation of polymeric components to sol-gel derived materials is extremely attractive to prepare macroporous scaffolds, leading to materials with potential applications in both hard and soft tissue regeneration. In this work bioactive glass-polyvinyl alcohol hybrids were developed and their mechanical behavior was evaluated. Hybrids were synthesized by adding polyvinyl alcohol to a sol-gel precursor solution, which was then foamed with the addition of a surfactant and vigorous agitation. The foams were cast, aged and dried at 40°C. A cleaning step to decrease the acidic character of the obtained hybrids was undertaken by immersion in a NH4OH solution. The mechanical behavior of the hybrids was evaluated in compression using both stress and strain control tests. Hybrid foams had a high porosity varying from 60-90% and the macropore diameter ranged from 10 to 600 µm. The modal macropore diameter varied with the inorganic phase composition and with the polymer content in the hybrid. The strain at fracture of the as prepared hybrid foams was substantially greater than pure gel-glass foams. The cleaned hybrids presented a slightly higher strength and lower deformation than the as prepared foams.

Abstract: In this study, it is shown that it is possible to prepare carboxymethyl-chitosan/Ca-P hybrids using an innovative “auto-catalytic” co-precipitation method, namely by using an acid and an oxidant bath. The X-ray diffraction (XRD) patterns evidenced the formation of crystalline calcium-phosphate precipitates when using an acid bath, while amorphous ones were obtained for those produced in the oxidant bath. The Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM/EDS) studies revealed that the extent of the polymer precipitation and formation of calcium-phosphates is directly dependent on the pH and composition of the baths. Furthermore, by conducting bioactivity tests in a simulated body fluid (SBF) followed by the SEM/EDS analysis it was possible to detect the formation of an apatite layer with a cauliflower-like morphology on the surface of hybrids prepared by the acid bath, after 7 days of immersion. These results are quite promising because they can allow for the production of bioactive and biodegradable 3D porous scaffolds to be used in bone tissue engineering applications.

Abstract: Hybrid bioactive glass-polyvinyl alcohol foams for use as scaffolds in tissue engineering were developed through the sol-gel route. Hybrids produced by this route present a high acidic character due to the catalysts added during processing and may also contain residual organics after the drying step. Therefore, an additional cleaning step is necessary to produce biocompatible materials. In this study hybrid PVA/bioactive glass foams were cleaned using various procedures and cytotoxicity evaluation was conducted. All the cleaning methods used increased the cell viability levels compared to samples not subjected to a cleaning procedure. The most effective cleaning procedure used was the immersion in NH4OH solution. The cleaning procedure changed the composition and pore structure of the final material.