Research on Engineering Structures and Materials

23-34

Authors: Mutlu Karasoglu, Serdar Karaoglu, Taylan Sinan, Tugce Tekin

The aim of this study is to investigate the effect of mechanical milling and hot pressing process parameters on the density and strength of Al-10%B4Cp composites. For this research, powder mixtures consisting of Al matrix and B4C reinforcement particles were prepared by mechanical milling. Powder mixtures were milled for different times (5, 10, 15 and 20 hours) in a high energy planetary ball mill. In the milling vials, 10wt% B4C particle reinforcements were added to aluminum matrix powders. Average particle size of B4C and Al powders were 77μm and 63μm respectively. Powder mixtures were compacted as cylindrical samples by uniaxial hot pressing at 30 MPa. Specimens were hot pressed in nitrogen atmosphere at temperatures of 500-550-600 °C for 15-30- 45 minutes. Effects of milling and hot pressing variables on microstructure and mechanical properties were investigated by means of density and hardness measurements and compression tests. Microstructures of powders and compacts were investigated by microscopy techniques. Density measurements showed that compressibility of powders decreased with increasing milling times. Density, hardness and compressive yield strength values were increased with increasing hot pressing temperature and durations.

45-52

Authors: Canan Uraz

Electroless metal plating is a coating technique which relies on reduction of metal ions with an autocatalytic chemical reduction process. Ionic liquids are defined as compounds that are sensitive to the environment due to their low pressure that can be negligible, their high heat resistance, and a higher ionic conductivity, to be electrochemically rich, to have wide open liquid range, to have a range of high polar solubility. In this study, the effects of ionic liquids were investigated in the electroless metal plating process over ABS plastic. For this purpose electroless baths were prepared by using two different types of ionic liquids (EMIC & DCA) for copper and nickel plating. Experiments were carried out with 120-500 grit sandpaper and at 80°C plating bath temperature for 30-120 minutes of deposition time and at different pH values as 8-9. X-Ray XDL-B System, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used for the characterization and the amount of deposits. According to the experimental and analytical results, the metal plating on ABS plastic was succeeded with two different ionic liquid additions. On the contrary of the traditional processes with chromic and sulphuric acids, the etching and the plating processes were performed with environmentally friendly chemicals. In this way, both it will be provided a significant benefit to public health, and it will be brought innovation to the metal plating industry with the environmentally friendly ionic liquid catalyst.

63-73

Authors: Veikko Sajaniemi, Alp Karakoç, Jouni Paltakari

The present study aims at understanding the mechanical and thermal properties of natural fibers in a polymer matrix without strong adhesion between the two constitutes. For this purpose, four types of pulps, which are refined and unrefined pine and birch kraft pulps, were used together with polypropylene without any compatibilizer. One constituent pulp based and composite pulp fiber-polypropylene handsheets were prepared by standard laboratory sheet preparation method followed by hot pressing process. In addition to these handsheets, pure polypropylene sheets were also formed as the reference. The produced handsheets were tested to determine their tensile properties following the ISO 1924-2 standard for paper and board. During these tests, infrared thermal imaging was also carried out with FLIR A655SC thermal camera with frame rate of 200 Hz and thermal resolution of 50 mK so as to investigate the thermal behavior. As a result of the experiments, it was deduced that the chosen methods produced composites with unsatisfactory properties. In addition, microstructures of the investigated handsheets were analyzed with scanning electron microscopy (SEM) indicating the heterogeneous mixing of constituents and existence of material defects, which was mainly due to the inherent incompatibility of hydrophilic natural fibers and hydrophobic thermoplastics. The study aims at paving a way for improved natural fiber-polymer composite manufacturing methods, a requirement for better understanding the natural fiber and polymer matrix bonding practices.

85-95

Authors: Hasan Yavuz Ünal, Selay Sert Çok, Fatoş Koç, Nilay Gizli, Yeliz Pekbey

Nowadays, silica aerogels have been widely used in many applications due to their extremely low density, low thermal conductivity and high specific surface area. Many researchers have proved that the addition of the nanoparticles into thermoset polymers resin has influenced the mechanical properties of the composites. Epoxy resins are one of the mostly used thermoset polymers. Although they have superior mechanical strength, they are usually suffered from their fragile structure. There are several additives such as carbon nanotubes, nanoclay, calcite etc. that can be added to epoxy resins to enhance their mechanical properties such as tensile strength, modulus of elasticity, break strain. In this study, the silica aerogels were added as nano-fillers into epoxy to investigate the effect of the silica aerogel content on the mechanical performance of silica aerogel–epoxy composites. Two different silica aerogel–epoxy composites were produced with various silica aerogel content (0.5 and 1 wt. %) and effect of aerogel amount on the mechanical and structural properties of final nanocomposites was investigated. Silica aerogels used in the study were synthesized by traditional sol gel method to obtain versatile silica aerogel–epoxy composites. Apart from the classically synthesized silica aerogels, aerogels in the present study contain short chained ionic liquid (IL) as porogenic agents. The effect of the addition of the silica aerogel on the tensile and flexural properties of final composites were observed by the measurement of the tension and three-point bending tests, respectively according to ASTM standard. The results have shown that the mechanical behavior of the epoxy resin was significantly influenced by the silica aerogel addition. The mechanical strength of epoxy composite with silica aerogel addition was improved compared to that of the neat epoxy.