Volume 49, Issue 3

Abstract: The paper presents, some experimental results obtained with different types and amounts of reinforcement in composite materials based on polypropylene matrix for automotive applications. There where characterized fourteen experimental samples. The reinforcing agents utilized were: particulate reinforcement (organic and biodegradable – powder wood and inorganic and non-biodegradable – talc powder) and fibrous reinforcement (organic biodegradable-short flax fibers). Keywords: composite, polypropylene, flax fibers

Abstract: Plastination as a means of preserving human biological tissues indefinitely, involves the use of reagents and polymers (S10, E12 and P40 ), with physical methods as vacuum, cold temperatures and photo polymerization. Invented over 30 years ago by the German pathologist Gunther von Hagens, plastination methods can be used successfully in over six areas of medicine and other specialties such as archeology or anthropology. The used of plastination of the oral tissues is directed towards the teaching and scientific research that implies microscopy and optical coherence tomography. Keywords: plastination, polymers, oral tissue, biotechnology, preservation

Abstract: A non invasive method as numerical simulation was employed to evaluate the periodontium comportment under the occlusal force appliances. Three types of periodontal support for a three elements metal polymeric fixed partial prosthesis were considered. The retractions trends of the periodontium were correlated with the occlusal conditions. Keywords: metal - polymeric fixed partial prosthesis, numerical simulation, periodontium

Abstract: A molecular rheological model for amorphous homopolymers filled with nanoparticles is presented. The fillers are non-agglomerated and interact energetically with the polymers. The model applies to situations in which the polymer-filler affinity is relatively weak. The essential physics represented in the model includes chain reptation, the slowing down of diffusion due to energetic interactions of polymers and fillers, chain stretch, and contour length fluctuations. The model is based on insight obtained from extensive simulations of the structure and dynamics of these systems. The chain population is composed of free, dangling and bridging chains, i.e. those that at given time do not contact fillers, contact one filler or multiple fillers, respectively. As the system evolves, a representative chain switches randomly between these categories. The representative chain reptates only when free, while contour length fluctuations are performed at all times. Relaxation is controlled by both tube renewal and the process of chain attachment/detachment to/from the filler surface. The second process modulates the first, leading to a relaxation with two characteristic times, in agreement with experimental observations. The parameters entering the model can be calibrated based on the rheology of the neat polymer and based on results from simulations of the respective filled system. Keywords: rheology of polymer nano-composites; reptation; contour length fluctuation; tube renewal

Abstract: We started this study considering the fact that, in our surgical clinic, the association of umbilical and inguinal hernias in cirrhotic patients was found in 47,6% of cases. Although this joined pathology is quite frequent, the data comparing surgical complications and long-term recurrence when using the two mesh procedures are limited. Keywords: mesh, polipropylen, umbilical, hernia, polyvinylidene, inguinal, cirrhosis

Abstract: In this paper, some aspects of electrospun nanofiber diameter measurement has been presented. The method was tested by a simulated image with known characteristics and a real web. The results show that this approach is successful in making fast, accurate automated measurements of electrospun fiber diameters. Keywords: transport properties, automated measurement, electrospinning, nanofiber diameter, image analysis

Abstract: In this article we present our work on the combination of two thermostats, motivated by our research on multiscaling molecular dynamics simulations. Molecular dynamics are used for studying the properties of polymers. Two schemes - global Berendsen and stochastic dynamics - are combined. A leap-frog algorithm was used for the calculation of kthermal. Simulation results on temperature, thermal rate, and diffusion for coarse-grained (MARTINI) water are discussed. Using these thermostats we observe no deviation from the reference temperature and show that the measured thermal relaxation rates agree well with theoretical predictions. Keywords: molecular dynamics, polymers, thermostats

Abstract: Manufacturing process of rubber parts have to take into consideration a set of parameters of production to accomplish the requirements of the quality standards, especially in the automotive industry. Starting from input data obtained from different rubber parts production process, this paper presents results and conclusion obtained with simulation software and specific application based on numerical methods, compared with measurements obtained in industrial process. Benefits of 3D simulations lead to important product development cycle time reduction, radical manufacturing cost reduction and possibility to optimize cycle times and product quality. Keywords: rubber injection process; Finite Element Analysis; numerical methods

Abstract: The rubber is widely used at railway infrastructure and rolling stock. Rubber plates are used at rail – sleeper fastening systems, rubber elements are used for primary suspension at electrical locomotives (in Romania and abroad) and metro (subway trains) as elastic elements in buffers, or as insertion plates at streetcar wheels etc. From those examples we can see that rubber elements are used as elements which are directly involved in circulation safety. Keywords: rubber plate, rail pad, K fastening, test, railway polyethylene

Abstract: The paper presents an experimental validation, through modal analysis, of some models of plates with discontinuities, made of plastic materials. The numerical study was undertaken using the Finite Element Method. The geometrical model was obtained with nondestructive evaluations using computer tomography, allowing thus to find the shape, position and dimensions of defects. The good agreement between the experimental and numerical results led to the validation of the investigated models. Key-words: defect, modal analysis, computer tomography, numerical analysis

Abstract: Records of pulpal blood flow obtained from human teeth with a laser Doppler flowmeter include a very large component derived from the periodontal tissue and other tissues outside the pulp. This contamination can be reduced by isolating the tooth from the surrounding tissues. The purpose of the present study was to show that polymers and resins make possible an optimal pulp vitality testing when used for fixing the laser probe, as well as for reducing the signals originating from the periodontium. Recordings were taken from 10 healthy, intact frontal upper teeth, in 8 individuals, ages between 20 - 40 years. Signals were recorded with the laser Doppler MoorLab and a straight optical probe, MP3b. Two consecutive determinations of the pulpal blood flow at a 5 minute interval where taken for each tooth using the following methods: 1 – a silicone impression combined with light curing periodontal liquid dam, and 2 – without periodontal isolation system. The data were processed using the statistical analysis software SPSS v16.0.1. The combination of the silicon impression with the Light curing periodontal resin isolation decreased significantly statistic the flux values (68.01% decrease) and was more effective in individualizing the pulpal blood flow than simple silicone impression. The presented technique is a viable method for determining pulp vitality, reproducible, easily applicable and shows a significant reduction in the intake of nonpulpar origin signals. Key words: condensation silicones, light curing periodontal liquid dam, laser Doppler flowmetry, pulp vitality

Abstract: The formation of the oxygen inhibition layer is examined on some commercial methacrylate resin based composite restorative materials: nano-filled Filtek Ultimate Universal Restorative and Filtek Supreme XT Universal Restorative and for comparison the microfilled Filtek Z250 Universal Restorative. Each material type is analyzed using scanning electron microscopy for microstructure and energy-dispersive X-ray spectroscopy for the chemical composition. Two polymerization lamps were used for various exposure times. It results an excellent chemical stability for Filtek Ultimate, while the percent of oxygen is increasing with the photo-polymerization time for the other two composites. From element mapping, the filler particles were identified and their volume percents and cluster particle size distributions were calculated. No correlation of these parameters with oxygen inhibition layer was found. Keywords: oxygen inhibition layer, chemical composition, dental restorative composites

Abstract: With increasing of electromagnetic pollution and wide use of commercial and military products, there is an increasing interest in electromagnetic interference (EMI) shielding. For EMI shielding materials, typical metals have been used. Electroless copper plating of polyester fabrics was demonstrated in the present investigation and compared to sample coated by Cu-Ni-P plated after five times washing and rubbing fastness test . In order to evaluate the residual copper after applying rubbing the surface of samples, SEM images and WDX analysis have been used. The evaluation of electrical conductivity after washing and rubbing tests shows high stability in spite of detaching of some part of coating which remarkably confirms the high stability in EMI shielding effectiveness. Keywords: electroless, copper-coating, polyester fabric, washing and rubbing tests, surface resistance

Abstract: The paper presents an algorithm to assess damages in composite structures, based on how natural frequencies of weak-axes bending vibration modes change due to damage. The authors have contrived a correlation between the strain energy stored in a segment of a beam-like structure and the frequency change for that mode if damage occurs on that segment. Finding that the dynamic behavior of composite structures can be best modeled using the share model, which consider the bending moment together with lateral displacement and share deformation, we worked out a relation which gives the frequency shift of all bending modes, involving one coefficient depending on the support type. To evaluate damages, we determine analytically the relative frequency shift as ratio between the frequency change and the natural frequency of the undamaged beam, for the more vibration modes, considering a large number of damage scenarios. Comparing these results with that obtained by measurements on the real structure, it is possible to detect and locate damages with high precision. The method was validated by numerous experiments. Keywords: composite materials, fiber reinforcement, damage detection, natural frequency

Abstract: The paper presents results on friction and wear, obtained from testing polybutylene terephthalate (PBT) against steel in a block-on-ring tribotester, for dry sliding. There were identified particular processes characterizing the friction couple and the test conditions. Tests were done for three sliding speeds: 0.25 m/s, 0.50 m/s and 0.75 m/s and for five normally applied loads: 1.0 N, 2.5 N, 5.0 N, 10.0 N and 20.0 N. The sliding distance was 7500 m. For comparing reason, there were also done tests for blocks made of PTFE. For PBT-steel couple, the friction coefficient remains in an acceptable range for forces above 2.5 N but it has higher value at the lowest tested values of the force (F=1.0...2.5 N). For evaluating the wear of PBT blocks, there was plotted a wear map using as wear parameter the linear wear intensity as a function of sliding speed and normal force. On this map, there were identified two zones with low values. There were indentified particular processes taking place on the PBT blocks and the steel rings that explain the good tribological behavior of this friction couple. The results of these tests recommend PBT for tribological applications that would function under similar dry regimes. Keywords: friction coefficient, wear, PBT, dry sliding, block-on-ring

Abstract: A biopsy sample that was taken from neurosurgery then introduced into the solution of formaldehyde was examined with Time Domain optical coherence tomography. The results are inconclusive and so that preserving was accomplished by plastination the tissue sample in which the degree of rigidity of the sample is controlled without destroying the tissue. Keywords: Plastination, Optical Coherence Tomography, nervous system

Abstract: The paper shows and analyzes the results of some researches on a plastic composite material as fiberglass reinforced polyester (FGRP) that is considered for being used for manufacturing the blades of small power wind turbines, such is the 5 kW wind turbine from Ciugud site in Alba County, Romania. During their operation the wind turbine blades are continuously subject to variable loadings developed by the stochastic and uncontrollable wind flow. Consequently has been performed mechanical strength researches done on a real blade, as well as, by lab testing on test specimens sampled from the original material of one blade tested at SC CLAGI Srl Company. The results of this research work came to confirm the quality of the FGRP used for blade fabrication, as well as, its capacity to bear well the loads and implicitly the structural stresses produced by the wind upon the wind turbine blades, although a metallic reinforcement included within the inner part enhances the whole mechanical strength of the blade structure. Keywords: fiberglass reinforced polyester (FGRP), wind turbine, aerodynamic forces, loads, stresses, mechanical strength

Abstract: This paper analyses the influence of the grind percentage on some mechanical properties of various injection-molded items in the automotive industry, which are made of acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6) and polyoxymethylene (POM). The specimens had the following compositions: new material 100%, new material 80% + grind 20%, new material 60% + grind 40%, new material 40% + grind 60%, new material 20% + grind 80% and grind 100%. The mechanical properties were measured using tensile tests, the Izod impact test and the Shore Durometer hardness test. It was observed that the hardness of the three tested polymers is not significantly influenced by the increase in grind percentage. The shock resistance of ABS and PA 6.6 decreases when the grind percentage is increased, while for POM the increase in grind percentage leads to an increase in shock resistance. The tensile strength at break decreases when the grind percentage is increased from 0% to 40% for ABS and POM. The further increase in grind leads to a slight increase in the tensile strength at break. In the case of PA 6.6 the tensile strength at break increases along with the increase in grind percentage. Keywords: acrylonitrile butadiene styrene (ABS), polyamide 6.6 (PA 6.6), polyoxymethylene (POM), tensile tests, the Izod impact test, the Shore Durometer hardness test

Abstract: This paper presents some morphological properties of polyamide 6 thin films obtained by spin-coating method. These properties were investigated by scanning electron microscopy and atomic force microscopy. It results that the thin film thickness is influenced both by rotation speed and solution concentration. Finally, some aspects between morphological and optical properties (structural colours) were considered. Key words: polyamide thin films, spin-coating method, scanning and atomic force microscopy, structural