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In this paper a modern multi-objective optimization of the pneumatic ejectors of the plastic injection mold is presented. For this Pareto multi-objective optimization, two objective functions (volume and efficiency of the ejector) and four genes were taken into consideration and a set of twelve constraints were formulated. In solving the optimization problem we used an original two-phase evolutionary algorithm (2PhEA) inspired from the concept of “punctuated equilibrium”. 2PhEA is implemented in Cambrian v.3.2 which is in operation at the Optimal Design Centre of the Technical University of Cluj-Napoca, Romania. The study on the individuals along the obtained Pareto front reveals some important conclusions useful in the design of the pneumatic ejectors. Keywords: optimal design, evolutionary algorithms, pneumatic ejector, injected part

The extraction of surface geothermal energy using heat pumps represents a recent topic in specialty literature. This paper presents a numerical model for modelling the thermal field around the heat exchangers mounted in the soil. The purpose of modelling is to reveal the dynamics of heat exchange between the soil and the polyethylene pipes and highlighting the variation in temperature field around the heat exchanger. Keywords: Geoexchange, heat pump, polyethylene, thermal field

In the recent years the utilization of polymeric materials increased due to their good mechanical properties and easy manufacturing. Starting from automotive industry up to food industry polymeric materials are used for obtaining components by molding or by machining. Taking into account the wide range of applications, it is important to know the mechanical behaviour of these materials in different loading conditions. Accordingly, this paper presents an experimental study to determine mechanical properties on 11 commercial polymeric materials. Tensile and shear static tests and impact tests on notched and un-notched specimens were performed. The results are presented comparatively, and two new parameters were introduced for material selection purpose. Keywords: mechanical testing, polymer materials, tensile strength, shear strength, impact strength

In the presented paper experimental results on welding polystyrene and optical elements are shown. On the basis of the obtained results on shearing-stretching and macroscopic analysis of the work pieces, conclusions are drawn regarding the weld when using ultrasonic welding process. Key words: ultrasounds, welding, plastic materials

Most of the problems of modern engineering are solved using numerical methods. In order to use a numerical method the first step that must be performed is to generate a numerical model that contains all the input data in terms of geometry, material data, boundary conditions (loads and support). Ideally a structure must be defined only using hexahedral elements that are capable to provide the best results. This paper presents a method for generation a fully hexahedral finite elements model using a grid based procedure. The method is a good support for the engineering involved in product design. An application to a plastic manufactured part is presented. The results obtained using the all hexahedral finite elements models are compared with the results obtained using a numerical model generated using conventional techniques. Keywords: numerical model, hexahedral finite elements, mesh generation method

This work paper proposes an elastic displacement field for a composite bar made of two constituents (phases). The deformation hypothesis described by this field is built in full respect of all the conditions of compatibility concerning deformation and strain-stress status of any kind. More else, the conditions of continuity concerning the surface separating the two constituents are also fully satisfied. Using this new displacement field we show that the tangent to each and every point of the characteristic curve built for this composite material depends only on the size of external charge (loading) and the longitudinal deformation of the composite bar. Based on these facts we also show that the constitutive equation of this composite material is a non-linear one: in fact it is a concave curve the way that the slope of the tangent to each and every point of the characteristic curve is decreasing as the deformation increases. We have released three sample groups with different arrangements of reinforcing fibers from one group to any other one and we have established the characteristic curve for each and every sample group. Using these curves we have obtained the longitudinal elasticity modulus, the tension at break, the elongation at break as well as the slope and the ordinate at the origin for the tangent to the breaking point of the characteristic curve. The characteristic curves have the shape (allure) suggested by the theoretically obtained results. We have shown that a certain parameter characterizing the non-linear behavior of the composite material is given by the ratio between the longitudinal elasticity modulus and the value of the slope of the tangent to the breaking point of the composite material characteristic curve. Keywords: composite materials, characteristic curve, elasticity modulus

The paper describes some aspects concerning the effects of the type of wood species on some mechanical characteristics of some hybrid composite materials reinforced with both E-glass woven fabric and wood flour. It also shows the effects of the moisture absorption on the mechanical behaviour in bending after immersion in two different environments: water and seawater. The specimens were manufactured by reinforcing a polyester resin Copoly 7233 with both E-glass woven fabric EWR145 and wood flour. Two kinds of wood flour, oak wood flour and fir wood flour were used to manufacture the two composite materials tested. The immersion time was approximately eight months. The quantity of the moisture absorbed was greater in case of the immersion in water than in case of the immersion in seawater. Then, the both dried specimens and the wet ones were subjected to flexural tests by using the method of the three points. Finally, the experimental results obtained were analysed in terms of the nature of the immersion environment. Moreover, it was analysed the effect of the immersion time on the changing of the mechanical characteristics in case of woven fabric / oak wood flour / polyester. Finally, the paper recommends the using of the oak wood flour in case of the parts made of composite material analysed, that works in humid environment excepting the case when its salt content is greater. Keywords: hybrid composite; wood flour; absorption; flexural test

Numerous studies have shown that the geometry of the femur and pelvis affects the distribution of the occurring tensions and movements. The study was performed on the 3D model (three dimensional), of the coxofemoral joint which was achieved through CT images (tomography computer). The results confirmed that the values of tensions and displacements slightly differ from those in the literature due to the geometry and the properties of the used material. Keywords: finite element analysis, hip joint, mechanical properties, modelling

Conducting polymer coating has been used to improve the surface performance of metallic materials, as Ti6Al7Nb alloy. Polypyrrole (PPy) was electrochemically deposited from 0,2 M oxalic acid aqueous monomer solutions by three different methods: potentiostatic, galvanostatic and potentiodynamic techniques. The stability of PPy / Ti-6Al-7Nb surface has been studied by electrochemical methods in Hank’s Balanced Salt Solution (HBSS) by Tafel tests and cycle voltammetry. The PPy / Ti-6Al-7Nb biofluid interface was analysed by electrochemical impedance spectroscopy (EIS) and the corresponding equivalent circuits were proposed. The structural infrared analysis and morphology of conducting polymer layer on titanium alloy have been evaluated. Keywords: Polypyrrole, Ti6Al7Nb alloy, stability properties, EIS, AFM

Epoxy-based composites with modified carbon nanotubes (CNTs) were synthesized using different types of CNTs. These were first modified by amidation of the carboxylic groups from the CNT’s surface and then embedded into the epoxy matrix. The modified CNTs and the corresponding composites were analyzed by FTIR, TGA, DMA and Raman Spectroscopy. The influences of CNT type and the nature of the organic modifier were pointed out in connection with the composites structure. Keywords: functionalization, carbon nanotubes, polymer nanocomposites, thermostability, Raman Spectroscopy