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Base isolation systems are nowadays largely used to protect the build environment and to avoid loss of life. While the behaviour of natural rubber bearings NRB and lead rubber bearings LRB is well-known, hybrid devices incorporating a NRB and a LRB, due to their complex behaviour, are difficult to be modeled. The authors have developed a theoretical model able to describe with high accuracy the performance during earthquakes of hybrid isolation systems, meantime permitting to determine the equivalent stiffness for all levels of horizontal loads. At the end of the paper numerical simulations give an overview about the possibilities to control the structure response by fitting some parameters of the device. Finally comparison with the behaviour of “classical” devices is performed. Keywords: rubber, neoprene, composites, base isolation, earthquake

The development of resins represented a great step forward in dental technique, the first thermopolymerisable acrylic resins being developed in 1936. Due to their disadvantages, several new materials and their processing technologies, which promise better quality, were introduced on the market, among them diacrylic composite resins. Initially composites were elaborated as esthetic restorative materials, subsequently they developed very much, so nowadays are being used in many various fields of dentistry. Indications for diacrylic composite resins. (DCR) in dental technique include: esthetic veneering for mixed metal-polymeric fixed prosthetic restorations (FPR), unidental or temporary FPR, inlays, onlays, epitheses, repairing damaged porcelain veneers, artificial teeth, manufacturing the base of mobile and removable dentures, repairing and/or re-optimization of the mobile and removable dentures. The aim of this study is to bring into discussion the superior qualities of the the new generation, VITA VM LC (VITA) composite veneering resins. The laboratory steps to be followed in order to obtain a VITA VM LC veneered FPR are the usual ones. After completing the metallic frame, the following step is veneering with VITA VM LC. The VITA VM LC layering concept is oriented after the natural model and is clearly distinguishable from all the other stratification concepts. The natural fluorescence and opalescence reproduction possibility leads to individual results with an aesthetically impressive appearance. A layered restoration performed with VITA VM LC behaves like a natural tooth in different lighting conditions. The excellence in dentistry is often achieved by combining scientific principles with artistic creativity, while choosing the material and technique has a major importance. Keywords: diacrylic composite resin for veneering, VITA VM LC, layering concept, aesthetic results

Dielectric relaxation studies were carried out on unfilled and silica particle filled highly crosslinked PDMS samples, at temperatures above the calorimetric glass transition temperature. Our experiments suggest that the main a relaxation peak is preceded by a pre - a relaxation one, whose characteristics are not dependent in their nature on the presence of the reinforcing silica particles. This suggests that its presence may be characteristic of the high crosslink density PDMS. Keywords: highly crosslinked siloxane elastomers, silica filler, dielectric relaxation in the glass transition region, a-relaxation

Starting from the dynamic response of a sandwich beam with damping (which is in free vibration), is established a method used to determine the damping factor. We experimentally calculated the stiffness and damping factor per unit length and unit mass for beams with middle layer made of polystyrene and polypropylene honeycomb respectively; the external layers were made of epoxy resin reinforced with fiber-glass fabric and carbon-fiber fabric respectively. Keywords: sandwich beam, damping factor, polystyrene, polypropylene honeycomb, free vibrations

The dynamic behaviour of an orthotropic shaft leads to a nonlinear differential equation, Mathieu type, whose solving is quite difficult. Certain problems in theoretical physics lead to Mathieu equation, particularly the problem of the propagation of electromagnetic waves in a medium with a periodic structure, the problem of the electrons’ motion in a crystal lattice in the quantum theory of metals. The parametric equation was solved numerically for time history and was time integrated using Runge-Kutta method with initial boundary values. The results show a totally different dynamic behaviour of the shaft made of an orthotropic material compared with the one made of an isotropic material. Key-words: orthotropic material, shaft, orbit precession motion

It is a well-known fact that either pellets or granules used in sandblasting operations for cleaning/finishing metal surfaces of any kind, are subject over time to processes of either splitting or wear of the surface, thus diminishing their operational features, such as, for instance: the angularity and dimension. When being used in sandblasting operations, the granule size fractions that have lost their capacity of finishing surfaces are being sorted by sifting and eliminated. In industrial conditions, where very large surfaces are being sandblasted, the grit turns into a major problem, since it often requires large warehouse surface areas for storage. In that sense, this paperwork presents experimental data regarding the worn grit fractions management by using it in asphalt mixtures, conferring, beside an economic benefit, also that of environment protection, since those lightweight fractions oftentimes form very polluting air floating powder. By eliminating those fractions that are reusable in the process of sandblasting, on the remaining sort resulted from sifting through the 1.0 mm strainer granulation and bitumen behaviour studies were carried out. The analysis of proposed asphalt mixtures, holding a certain percentage of grit, highlighted the fact that the latter, by both the 0.4- 0.1 mm granule size and by the floatable particles of less than 0.2 mm granule size, allow for the replacement of natural quartz sand. The physical-mechanical features of studied mixtures were established on cylindrical probes made of bitumen, in which smashed silicone stone chippings were mixed, within standard required range of granule size, crushing sand and worn grit, in very well controlled mixing proportions. the results were compared to those derived from standard samples made of solely quartz crushing sand, alongside the other components that make up type BA8 asphalt mixtures, of a mere 6.5% bitumen of a 50/70 proportion, according to local standards. By comparing the two asphalt mixture type features (standard and experimental), it allowed for highlighting that worn grit may be very successfully used instead of crushed sand. Keywords: grit, asphalt mixture, recycling, exploitation, environmental protection

The study investigates the effect of several injection moulding parameters, such as the melt and mould temperature, on the adhesion obtained at the moulding of bi-component tensile test specimens. Mono- and bi-component specimens were subject to uniaxial tensile tests. The aim is to obtain a model analysis for the study of the mechanical behaviour of bi-component parts submitted to uniaxial tensile tests. The localised information on the state of stresses and strains at the interface between the two polymeric components is obtained through this analysis.The use of the G’Sell-Jonas model offers a good prediction regarding the mechanical behaviour of the two component tensile test specimens on both the elastic and the plastic regions. The simulation of the mono-component tensile test showed a good agreement between the experimental and the predicted results, with a correlation coefficient ranging between 0.9973 and 0.9998. High levels of confidence were obtained for the mono-component tensile test specimen results, further applied for FEA analysis of the two-component specimen (HDPE/LDPE). The necking effect observed in the experiments, at a 255°C melt temperature for the LDPE, was similar to the one revealed by the finite element analysis. Keywords: polymers, adhesion, tensile test, FEA

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

This article presents a new material obtained from a mix of waste of carbon fibre, sand and an epoxy resin. The obtained material values the reinforcement material waste that is accumulated in the process of production, of the companies that produce fibre-reinforced composite material. This new material obtained from the integral value of the carbon fibre waste is used as a material for the consolidation of the moulds made of composite material or in the domain of construction materials. The authors realize a study regarding the physico-mechanical characteristics of the morphology of the breaking surfaces and a chemical analysis of the EDAX constituents. The mechanical characteristics of this new material at compression, show us values doubled from the ones of a classic concrete and a density decreased with approximately 20 percent. Keywords: composite materials, carbon fibre, epoxy resin

Among the composition and morphological structure field of biomaterials, the biodegradable biocomposites based on, synthetic and natural polymers as biocompatible spongious matrices has been studied. The biodegradable synthetic polymers have good mechanical properties, low toxicity and a controlled degradation kinetic. However, these polymers are hydrophobic and do not exhibit adequate surface for cells attachment and proliferation because of receptors absence for cells recognition. The natural polymers show good cellular interaction and high hydrophilicity. The advantages of biocomposites made of both synthetic and natural polymers are holding both physico-chemical properties of synthetic polymers and biocompatibility, cellular adhesion properties and variety of biological interactions induced by the contact between cells and natural polymeric support. The aim of this study was the synthesis of biocompatible porous structures by compounding synthetic polymers - (poly(L-lactic acid) (PLLA), poly(D,L-lactic-co-glycolic acid) (PLGA) which are biocompatible, biodegradable but hydrophobic, with natural polymer – collagen, the main protein of extracelullar matrix. The biocomposites were prepared in a polymer: collagen ratio of 2:1 by adding synthetic polymer solution, solved in chloroform, to aqueous collagen gel. The synthesis of biocomposite matrices was achieved by lyophilizing of synthetic polymer/collagen blends after dialyse against 1M KCl. Both uncrosslinked and crosslinked samples were prepared. As standard sample the uncrosslinked and crosslinked collagen matrices were chosen. The morphology of biocomposite matrices PLLA/collagen, PLGA/collagen was characterized by SEM in order to investigate the macro-, micro and nanoporosity. Physico-chemical characterization was focused on thermal stability (DSC and TGA) and surface hydrophilic character by water vapours absorption, water vapours permeability and water absorption. Keywords: biocomposites, collagen, biodegradable synthetic polymers