Materials Science Forum Vol. 812

Abstract: The renewable resource based polymers and composites, especially the Poly (Lactic Acid) (PLA) and natural, plant fiber reinforced composites are one of the most important research fields of biocomposites. Due to the mechanical properties of PLA, it stands out of the other biodegradable polymers, but in order to be able to use PLA in engineering application, reinforcing of PLA is needed. PLA can be reinforced with natural plant fibers, however their high moisture content can degrade PLA through hydrolysis during processing of PLA and the fibers into biocomposites. In this paper the effect of pre-process drying was analyzed on the mechanical properties of 30 weight% flax, cotton, and jute fabric reinforced PLA biocomposites. The results of pre-process drying tests showed that the optimum drying temperature was 100°C for the PLA and 120°C for the plant fabrics. It was demonstrated that the drying temperature of PLA and the fabrics has significant effect on the mechanical properties of the biocomposites.

Abstract: Graphene nanoplatelets (GnP) reinforced styrene-butadiene rubber (SBR) nanocomposites were produced by two different methods. For reference purpose carbon black (CB) reinforced formulations served. In the first method the components were mixed on a two roll open mill directly. In the second method, GnP was subjected to milling in an attritor mill together with cyclic butylene-terephthalate oligomer (CBT) powder prior to the mixing on two roll mill. Samples were cured in a hot press. The rubber sheets were characterized by tensile and tear tests, and their fracture surfaces inspected in scanning electron microscopy (SEM). Results showed that GnP outperformed CB with respect to reinforcing effect. Previous co-milling of GnP with CBT caused a slight decrease in mechanical properties. SEM images proved, that the co-milling process did not affect significantly the dispersion of GnP, its particles were shredded into smaller pieces, which caused the slight decrease in the mechanical properties.

Abstract: The aluminium alloys are used by the automotive, aerospace industries increasingly because of their numerous advantageous mechanical and chemical properties. Surface roughness measurements are essential in characterization of the features of a machined surface. The most widespread aluminium alloy used in cutting is the die-cast type, alloyed with silicon. Industries prefer using two types of such alloys, the so-called eutectic and hypereutectic alloys reinforced with silicon. In this article the cutting capacities of two die-cast aluminium alloys are examined. The cutting experiments were carried out with design of experiment – DOE (the so-called central composite design – CCD). In the course of the examination three factors were altered (cutting speed – v_c, m/min; feed – f, mm; depth of cut – a, mm), and the main surface roughness parameters used in the industries were taken as output parameters. The parameters of the manufactured surface roughness and their deviation in case of different workpiece-materials, tool-materials and edge-materials were analysed with statistical methods. Besides minimizing surface roughness, another important criterion of the manufacturing system (machine – tools – chuck – workpiece) is its surface roughness maintaining capacity, which was analyzed with coefficient of variation (CV).

Abstract: In-situ synthesized Nb (C,N) reinforced metal-ceramic composite layers were fabricated on nitridable (16MnCr5) and non-nitridable (S235J) steel surface by combined laser melt injection technology and ferritic nitrocarburizing treatment. The feasibility of processing composites layer by an in situ reaction using laser beam were carried out. Beside that the hardness of the treated layers increases up to 1000-1170 HV0.5 in the diffusion zone and after it the hardness of the samples reach 300-450 HV0.5, which is related the Nb alloying depth (1200-1400 μm). The results of the composite layer are presented in this paper.

Abstract: In this study the degradation and ion/zeolite release processes of in vitro aged zeolite loaded polyurethane composites were evaluated. Two in vitro artificial aging solutions were used; artificial lysosomal fluid (ALF) and Gamble ́s solution and the total exposure time was 12 weeks. Periodically, SEM micrographs were taken of the surface of polyester type polyurethane-zeolite composites. After exposure to ALF solution the samples showed round holes and a rougher surface in general over time. Micrographs of the samples immersed in Gamble’s solution exhibited different signs of degradation with damage features on the surfaces, understood as black holes and a rougher surface pattern. In addition varying amount of salt was also observed on the surfaces that might influence the ion/zeolite release. Furthermore, the zeolite filler caused remarkable changes in mechanical properties after the aging process, which could not be discerned.

Abstract: This work demonstrates particularly the basic properties of shape memory alloys and gives a brief review about their basic crystallographic processes. The attributes of shape memory alloys will be presented through the NiTi alloys. The crystallographic principles of three unique properties were investigated and the functional mechanism described. One of the three essential mechanisms, the one-way effect was demonstrated through an experiment. The change of length depending temperature was tested and documented. The hysteresis behavior of shape memory alloys was recorded.

Abstract: As part of our technology development program we started to prepare for introducing ceramic injection molding technology. The technology consists of the following steps: 1. feedstock preparation (mixing the ceramic powder with binding agent), 2. injection molding (green body production), 3. thermal or solvent debinding (brown body production), 4. sintering of the brown body. To make alumina ceramic parts essential to know the properties of all raw materials which are used during the PIM process. That is why this article is focused on the thermogravimetric studies of potential raw materials. These thermogravimetric studies helped to optimize the debinding experiments at specimens with high alumina content. First of all the measured curves of the feedstock were compared with calculated curves from the single raw materials. This comparison helped us to understand the processes in the feedstock during the sintering. Then thermogravimetric experiments in air atmosphere were made to optimize the sintering process. These experiments resulted good structural properties at the sintered parts.

Abstract: Aim of our experiments was to modify prosthetic material UHMWPE powder using sodium alginate. The sodium alginate has an important property that the appropriate chemical reagent could exchange its Na⁺ ions to Ca²⁺ ions. The Ca has important role in the healing process, so modifying this substance the UHMWPE material helps patients healing. In the first step we examined that the raw material UHMWPE powder is necessary to be treated in order to adhere alginate at the surface of the UHMWPE powder. In a second step, we examined that insoluble Ca alginate coating left at the surface of UHMWPE powder after the exchange of Na ions. The treated powders were analyzed by Fourier Transformed Infrared Spectroscopy and Diffential Scanning Calorymetry methods. SEM investigations were carried out on the prepared samples moreover energy-dispersive X-ray spectroscopy (EDAX) measurements were performed,-for detection of the presence of small amounts of Na and Ca ions. It has been found that the complex and complicated Caro’s acid chemical treatment is unnecessary in order to prepare alginate coated substrates. The best results were achieved by selecting the correct order of surface layer preparation; first coating the substrate with alginate solution then treating with aqueous CaCl₂.

Abstract: Specimens of austenitic stainless steel hardness changing were tested. The used hardening technology was a modified explosive treatment. During the hardening tests the explosive exploded different distance from surface. Same setup was tested with 2, 3 and 4 mm holder. The hardness improving and the plastic deformation were different as function of the holder size. The hardness was measured by Vickers hardness tester. The amount of strain induces martensite was detected magnetically. It can suppose that the microstructure changed during high rate strain. Results showed that the strain rate and result hardness depend on the holder size. We found that the bigger holder size in case of the tested setup provoke higher hardening. To determine the hardness properties it’s important to use an optional setup.

Abstract: This article shows two examination methods to measure the metal to artery ratio of stents. Our goal was to further develop the previously used measuring method in order to make it suitable for the integration into the quality control process of endovascular stent manufacture to provide more realistic data. The previous method was performed manually using rotating equipment under a stereomicroscope. The new method is an automatic method using an integrated scanner and a rotating engine. Both methods aimed at converting the cylindrical stent into a flattened two-dimensional image in order to enable the measurement of stent surface area by imaging software. From the image we can determine the cell sizes, the maximum achievable stent diameter, and the structure of the stent pattern. Each measurement process was tested on different types of stents. Our findings showed that the methods gave similar results, the largest differences are speed and accuracy.