Browse Articles

This study refers to the obtaining of mortar plasters using perlite and polymer additives additions. The performed study has outlined the infuence of the polymeric additive nature and content as well as perlite addition on mortar plasters based on hydraulic binders characteristics. Keywords: mortar plasters, polymeric additive, perlite, redispersabile powders, cellulose ethers

The increasing of the field usage of high frequency (HF) welding joints technique of thermoplastic polymers gives advantages regarding productivity, quality of welded joints and high reproducibility of results. Base of experiments, this debate analyzes the main types of failure, the causes of the failure and the prevention method for HF welding of polyvinyl chloride PVC foils. Keywords: HF welding, polymers, failures

The paper proposes new structures to replace the polystyrene, which is well known to be a toxic and inflammable material, non-biodegradable, used on a large scale for residence and civil thermal insulation and for packaging. The proposed structures are intended to be light structures, easy to manipulate, easy to be cut at the sizes needed, compact enough to not be damaged during the transport or during the mounting time, easy to fix on the building walls and of course with similar thermal insulating properties as polystyrene. First agglomerated composites were proposed. The materials used in these structures are green and biodegradable, found as inserts of wood (flakes or fibers) and textiles (wool or jute) and binders as wheat flour, clay or ecological acrylic copolymers. The density and thermal conductivity coefficient were determined for each structure and compared with the expanded and extruded polystyrene values and finally the more appropriate structures were recommended. To some of the structures flakes of polyethylene were added, in order to constitute a steam barrier of the new product. The addition of the polyethylene proved to be a disadvantage for the thermal insulation property of the structure and also for its compactness and reliability. The agglomerated composites mentioned above were pressed at a normal temperature (20-22oC) and conditioned at a temperature of 40-50oC. Two other structures were also proposed in this paper for the same purpose: a sandwich one, obtained after pressing it at 200oC, containing jute, wood fibers and polyethylene granules for the core and beech wood veneers for the faces and a panelled board made of waste of polyethylene and jute core and fiberboard faces. Keywords: polystyrene, polyethylene, thermal insulation density, composites

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