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The use of polymeric materials to replace metal or wood has become increasingly popular lately in most fields of activity. Specific amounts of reinforcement materials have been included in the structure of these polymeric materials in order to improve their mechanical properties. The increasing popularity of these types of materials was accompanied by the development of different machinery and technologies designed to process them, so as to make them as productive as possible and to achieve inexpensive high performance parts. Natural polyamide 6.6 is a polymeric material noted for its high rigidity, hardness, impact resistance, etc. The reinforcement materials added improve the mechanical properties of this type of material. Our research consisted of a comparative study of the behavior of polyamide reinforced with glass fibers and glass microspheres when subject to different mechanical stresses. The test specimens were processed by injection and relied on an experimental Taguchi plan with six input parameters each of them with two levels. The materials employed to carry out the comparisons designed to determine the mechanical and tribological properties were natural polyamide 6.6 reinforced with 30% glass fibers and 1% furnace black, and natural polyamide 6.6 reinforced with 30% glass microspheres and 1% furnace black used to prevent microsphere agglomerations. Considering all these issues, the actual research was focused on tensile stress vs. tensile strain comparisons at 23oC and 60oC, and on determining the friction coefficient using disc rotation and oscillation, XRD analysis, Scanning Electron Microscopy (SEM) and EDAX analysis. As concerns tensile stresses, high values were recorded both on the 23°C and 60°C tests when polyamide was reinforced with glass fiber. This is also supported by the SEM structure for the two composite materials under survey. The mean value of the disc rotation friction coefficient was lower when glass fiber was used as reinforcement material. This was also the case with the disc oscillation friction coefficient. The diffraction study conducted on the two materials revealed that polyamide 6.6 reinforced with 30% glass fiber did not have an amorphous structure, given the high number of peaks resulted further to diffraction, whereas polyamide 6.6 reinforced with glass microspheres exhibited an amorphous structure and a structure-specific diffraction. The chemical elements spectrum (EDAX analysis) reveals high mass and atomic percentages of C, O, Ca for both composite materials under survey. Keywords: fibers, microspheres, glass, mechanical properties, tribology, spectrum

Waste rubber cause both health and environmental problems and this has forced governments to develop laws for recycling. Using particles of recycled rubber in the domain of soundproofing materials is of major importance from a technical, economical and ecological point of view. In this paper we determine the ability of sound absorption of each obtained material by measuring the sound absorption coefficient depending on frequency, using the impedance tubes. Materials, as composite materials prototype, were made from particles of recycled rubber and a polyurethane binder, in combination with other materials existent on the market (cork of fabric). Keywords: recycled rubber particles, acoustical materials, sound absorption coefficient

It was evaluated, in vitro, the effect of different artificial saliva on the mechanical properties of elastomeric ligatures. A total number of 160 elastomeric ligatures were divided in four groups (n=40 in each group). Three groups were exposed to three types of artificial saliva, (unmodified artificial saliva, with coca cola and with topical fluoride agent), for a period of 28 days. The fourth group (control group) remained unexposed. Tensile load at failure was determined by stretching the ligatures using an Instron Universal Testing Machine, until they fractured. The obtained data was statistically analyzed at a level of significance (p < 0.05). The two-way ANOVA showed significant statistical differences within groups (p < 0.001) and between time intervals (p < 0.005). There were a statistical significant interaction between groups and time on tensile load at failure (p < 0.005). Artificial saliva, Coke and Topical Fluoride seem to cause an increase in force decay of elastomeric ligatures, with a decrease in tensile load at failure over time. Keywords: elastomeric, orthodontics, tensile load

This work reports on a study concerning the behaviour of an elastic system subject to a periodic external excitation. Oscillatory movement is the most common type of mechanical movement found in nature and, of course, in technique. A system executing simple harmonic motion is called harmonic oscillator system. If the harmonic oscillator motion describes a path as the straight line, the harmonic oscillator is called linear harmonic oscillator. Such linear harmonic oscillator is considered an elastic system when the force acts upon it is an elastic one. If in the elastic system dissipative forces are involved then they have the effect of energy losses during oscillation, so that, after a while, the oscillator energy is lost in various forms. To compensate the energy losses of dissipative forces, the oscillator must be driven by a periodic external disturbing force that produces forced oscillations in the elastic systems. If external disturbing force is periodical, the oscillator will run a new type of oscillations called forced oscillations. In this case the period and frequency of forced oscillations of the elastic system will be the same as the period and frequency of disturbing force. In this situation there is a transfer of energy between the two systems. Studying forced vibrations, in terms of energy intake, through excitation forces, are overrun highlight the importance of phase shift between force and oscillator movement. Keywords: harmonic oscillator system, periodic external excitation, phase shift, energy, resonance phenomenon

This paper presents a procedure for the calculus and dimensional optimization using finite elements analysis of a polymeric retractable rod which replaces a metallic one. This rod is an element of the front auger embedded in a technological equipment. The mechanism is 3D modeled in SolidWorks. CosmosMotion is then used to simulate and analyze the motion of the mechanism and to calculate the loads acting on the rod during its movement. These loads are then exported in CosmosWorks – a finite elements analysis software – which is used here to perform stress analysis and to optimize the retractable rod’s dimensions. Keywords: polymers, optimization, finite elements analysis

The chitosan based nanofibers web is a biocompatible, biodegradable, antimicrobial and non-toxic structure which has both physical and chemical properties to effectively capture and neutralize toxic pollutants from air and liquid media. Despite such potentials, the mechanical properties of nanofibers web is very poor to use in filtration applications. To remedy this defect, nanofibers web could laminate into a strength structure. The purpose of this study is to consider the influence of laminating temperature on nanofibers web/multilayer structure properties. The nanofibers web morphology and multilayer cross-section was observed under an optical microscope and scanning electron microscope, respectively. Also, air permeability experiments were performed to examine the effect of laminating temperature on air transport properties of multilayer structures. Optical microscope images showed that the nanofiber web began to damage when laminating temperature was selected above melting point of adhesive layer. Air permeability decreased with increasing laminating temperature. It is also observed that the adhesive force between layers was increased by increasing laminating temperature. Keywords: chitosan, nanofibers web, filtration, lamination

Polymer materials for denture bases, with thermal or light polymerization are relatively fragile, being considered brittle materials from the Fracture Mechanics concepts point of view. This paper presents a comparative study on determination of fracture toughness for 2 types of resins used in complete dentures technology: heat-curing resin (Meliodent), and light-curing resin (Eclipse). The tests were performed on a static loading machine, model Zwick/Roell of 5kN. The results obtained by 2 methods differ no more than 10-15%. Both methods showed that Eclipse has a better resistance to fracture than Meliodent. Keywords: acrylic resins, complete dentures, fracture toughness

The paper presents a study on the waste polypropylene modification with styrene-isoprene block-copolymers in correlation with elastomers molecular weight. The modification of this polyolefin improves the mechanical properties, especially the impact strength. Keywords: styrene-isoprene block-copolymers, waste polypropylene, melt blending

Solid waste disposal is a significant to overhead in a shipyard environment. In many areas of Galati the disposal capacity is being reduced and the cost of disposal is continuing to climb. The study of the behaviour of bitumen mixtures is an old subject in the literature. Many specialists have been trying to replace the sand with recycled materials resulting from blasting ship parts. The main purpose of this study is obtaining a bitumen mixture with a good behaviour to long use. The grit is an abrasive blasting material (ABM), having an angular form, used in ship repair processes prior to the application of coatings. It is produced by the pulverization of molten steel, followed by a series of thermal and mechanical treatments in order to give the product its final characteristics. The shipyard in Galati generates annually thousands of tons of used blast grit and they dispose of it in landfills or directly into the Danube as a usual practice. We intend to find possibilities of disposing the wastes produced by shipyards, our research being focused on achieving the sustainable development requirements of the civil society. Environmentally speaking, recycling spent ABM has the potential to significantly reduce waste generation while saving money. Keywords: mix asphalt, grit, recycling, shipyard

In the present study we evaluated the applicability of laser Doppler line scanning in recording the gingival healing process after a surgical procedure followed by two types of plastic provisional restoration. The laser Doppler imaging is a non-invasive method for analyzing the perfusion map of a certain area and can be used in order to establish the health status of a certain region after surgical treatment. The two types of plastic temporaries had no negative influence on the healing process. Key words: composite materials, laser Doppler imaging, microcirculation, non-invasive diagnosis, real time imaging