Browse Articles

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

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

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

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

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

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

Two curing protocols were used to polymerize a difunctional benzoxazine monomer based on 4,4`-diamino diphenyl methane. The thermal degradation behaviour of both resulted materials (named PBZ_190 and PBZ_250) was investigated by thermogravimetric analysis coupled with mass spectrometry (TGA/MS), Fourier transform infrared spectroscopy (FT-IR) and X-Ray photoelectron spectroscopy (XPS). The dependence of activation energy on conversion was established using Kissinger-Akahira-Sunose isocoversional method. Degradation of PBZ_250 starts at lower temperatures compared with PBZ_190 but its residual char is higher than for PBZ_190. The degradation of PBZ_250 exhibits a lower activation energy at conversion a < 0.3, and higher values than PBZ_190 for a > 0.3. Keywords: polybenzoxazine, degradation kinetics, thermogravimetric analysis (TGA)

This paper refers to the electromechanical strain response of PDMS/TiO2/SiO2 composites as an electroactive polymer actuator. Lightweight electro-active polymers (EAPs) are ideal for control surface since they offer high strain rate, fast response, high elastic energy density and ease of manufacture [1,2]. We investigate the frequency response and vibrational modes of rectangular films with aluminum electrodes using Scanning Laser Doppler Vibrometry (SLDV) technique described elsewhere [3,4]. The results showed a similar behaviour with those of acrylic and silicone films coated with carbon-based compliant electrodes from literature. Field-induced vibrational strains decrease with frequency due to the increase in stiffness of sample and change of dielectric permittivity. These materials are possible candidates in polymer actuators for micro-pump and micro-valve applications in MEMS. Keywords: electroactive polymers, dielectric elastomers, non-destructive technique, frequency response, vibrational modes

This paper presents the maleinization study of linear styrene-butadiene block-copolymers carried out in solution by radical mechanism. The vinyl microstructure effect of the polybutadiene block on the kinetics reaction was established and the physical and mechanical properties were correlated with the maleinization degree of the elastomers. Keywords: styrene-butadiene block-copolymers, maleic anhydride, functionalized block-copolymers