Belgrade Polytechnic

Belgrade, Serbia

Belgrade Polytechnic

Belgrade, Serbia
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In numerous cases, metals and alloys traditionally used as structural materials in the process equipment can now be successfully replaced by nonmetallic composite materials. We study the influence of service solutions on the state of stress and tensile properties of glass-polyester pipes in the longitudinal and circumferential directions. These analyses are of great importance for the use of examined pipes in chemical industry. The pipes were produced by "Poliester" Corporation (Priboj). The influence of two solutions, methanol and ammonia, was studied. The samples were treated in solutions for three, seven and ten days. After this, the samples were subjected to tensile testing by the standard procedure. The stresses and strengths were determined both in the longitudinal direction (testing on flat test specimens) and in the circumferential direction (ring tests). The analysis of test results, according to the type of solution and the period of holding, was realized in comparison with the results obtained by testing intact pipes (not subjected to the influence of the solution). The micromechanical analysis of broken samples helped to determine the influence of the solution on the structure of composite pipes and determine the models and mechanisms responsible for the decrease in strength. © 2011 Springer Science+Business Media, Inc.

Stamenovic M.,Belgrade Polytechnic
Materials and Design | Year: 2011

The influence of liquids on the state of stresses and tensile strengths in the longitudinal and circumferential direction of glass-polyester pipes is the subject of this paper. The pipes were manufactured in Corporation " Poliester" Priboj, and had a definite structure and known fabrication process. These analyses are of great importance for the use of glass-polyester pipes in the chemical industry. The tensile properties were tested and determined for specimens cut out of the pipes; flat specimens for the tensile properties in the longitudinal direction and ring specimens for the tensile properties in the circumferential direction. First, the tension test was performed on virgin samples (without the influence of any liquid), to obtain knowledge about the original tensile properties of the studied composite material. Subsequently, the samples were treated by water, as well as alkaline and acidic solutions: sodium hydroxide (strong alkali), ammonium hydroxide (weak alkali), phosphoric acid (weak acid) and nitric acid (strong acid). The solutions were selected because of considerable differences in their pH values. The pipe segments were exposed to each liquid for 3, 10, 30 and 60. days, at room temperature. Then the specimens cut from these segments were subjected to tension testing by the standard procedure. A comparison of the results was made based on the pH values of the aggressive media in which the examined material had been soaked, as well as based on the original tensile properties and the number of days of treatment. Micromechanical analyses of specimen breakage helped in the elucidation of the influence of the liquids on the structure of the composite pipe and enabled models and mechanisms that produced the change of strength to be proposed. © 2010 Elsevier Ltd.

Pavlovic S.S.,Belgrade Polytechnic | Stankovic S.B.,University of Belgrade | Popovic D.M.,University of Belgrade | Poparic G.B.,University of Belgrade
Polymer Testing | Year: 2014

The thermal parameters that describe the transient response of cellulose textile fabrics due to the changes in physiological and environmental conditions were analyzed. Starting from the specific heat of the knitted fabrics determined by a new experimental method based on Newton's cooling rate law, and previously determined thermal conductivity of the knits, their thermal diffusivity and thermal effusivity (absorptivity) have been determined. According to the results obtained, it can be concluded that the structure of the knitted fabrics is responsible for their transient thermal response through thermal conductivity, whereas the composition of the knits influences their dynamic thermal behavior through specific heat. Hemp based textile fabrics are proved to be at a comparable level to other cellulose fabrics from the viewpoint of thermal behavior during the dynamic stage of heat transport. © 2014 Elsevier Ltd. All rights reserved.

Alivojvodic V.,Belgrade Polytechnic | Stanojevic M.,University of Belgrade | Antonijevic D.,Singidunum University
Environmental Engineering and Management Journal | Year: 2015

Establishing a management system for collecting and disposing the solid waste materials is of great importance in urban areas. Belgrade, the capital city of Serbia, is at its initial phase of managing this problem. Currently, landfill disposal is the main option for dealing with rapidly growing amounts of waste. This paper’s research goal is to estimate the landfill gas quantity at Belgrade’s only landfill site Vinca, and to estimate the potential for collection and utilization of methane. Considering that this landfill site has no gas collecting system, data from previous measurements of landfill gas were collected and analyzed. In addition to that, the globally acknowledged software for modeling landfill gas generation, LandGEM, was applied. © 2015, Gh. Asachi Technical University of Iasi. All rights reserved.

Stamenovic M.,Belgrade Polytechnic | Putic S.,University of Belgrade | Zrilic M.,University of Belgrade | Milovic L.J.,University of Belgrade | Pavlovic-Krstic J.,Otto Von Guericke University of Magdeburg
Metalurgija | Year: 2011

The experimental determination of energy of glass-polyester composite tubes static fracture is done. The tubes are of defined structure and known processes of fabrication. The aim was to determine the possibility of their usage as damping elements during impact. Two types of tubular samples with different diameters were tested until fracture under static (low speed) compressive loading. The applied forces and sample lengths were measured until complete destruction of samples. From the diagrams received directly from testing devices, certain energy values explained in the paper were determined.

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