High demand for part customization shifts industries toward AM technologies. Part customization in high-volume manufacturing is developed to its limits, whereas low-volume production using AM is ...still economically unjustified. FDM technology is quite common in low-volume AM production, but the main issue is poor printing parameter optimization which may result in insufficient final part quality. The subject of this paper is the experimental determination of the optimal parameters for the PLA polymer FDM parts, focusing on nozzle temperature and printing speed. Part geometry and mechanical properties are evaluated for the temperature range of 170–210 °C and speeds of 40, 80, and 120 mm/min. Roughness measurements for part geometrical accuracy assessment and tensile tests for mechanical property estimation have shown the clear advantage of 190 °C and 40 mm/min over the other parameter combinations. However, for higher FDM process productivity 80 mm/min speed may also be considered with 190 °C.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This paper contains a comparison of the flexural strength results of two different samples. Both samples were made using additive manufacturing, from ABS (acrylonitrile butadiene styrene) material ...with the inclusion of an unknown filler designated as X. They also have in common that they are divided into two groups, the first group with a material infill of 100 %, and the second group with a material infill of 50 %. In order to determine that the material infill really affects the flexural strength results, the samples are differentiated by their shape. The first sample consists of tiles, while the second sample consists of pipes. The samples are printed vertically, which doesn’t change the material’s inherent mechanical qualities but does change the amount of infill and the strength of the bond between the layers. The difference between the values of the stress at failure of the material in the tile group is approximately 20 %, while in the tube group this difference is approximately 6 %. We can conclude that filling with the material in the range of 50 to 100 % during the production of pipes has an insignificant effect on bending strength, while this is not the case with plate samples. Based on this, there definitely is a significant influence of geometry when determining flexural strength. The idea for further research should be to measure the influence of samples treated with acetone on their flexural strength.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Ten asphalt mixtures with partial substitution of natural aggregate by RCA produced.•The optimum bitumen content increases with increasing RCA content.•Volumetric compositions of asphalt mixtures ...meet relevant technical requirements.•The amount of used RCA has no significant influence on the rutting resistance.•Asphalt mixtures with RCA have a lower stiffness modulus.
The objective of this research was to assess the possibility of using recycled concrete aggregate (RCA) in asphalt mixtures. The experimental research included 10 asphalt mixtures with partial natural aggregate substitution by RCA, which ranged from 15% to 45% of fine (⩽4mm), coarse (4/22.4mm) and both fine and coarse aggregate. The optimum bitumen content increased with increasing RCA content. The use of RCA had no significant influence on the permanent deformation, while the stiffness modulus of asphalt mixtures with RCA was lower compared with the control mixture, especially at high frequencies. The results indicate that RCA can be successfully used in asphalt mixtures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Selective laser sintering (SLS) is one of the additive manufacturing technologies dedicated to the production of high-quality parts with complex geometries. Here, polyamide 12 (PA12) is a commonly ...used material, for manufacturing parts with sufficient mechanical and thermal properties. In SLS, many manufacturing parameters have an effect on the mechanical properties of final parts. Even the decision regarding the orientation of a part in a powder bed may have a significant effect on the mechanical properties. In this research, the influence of horizontal (H) and vertical (V) printing orientations on the ultimate tensile strength (UTS) of fabricated PA12 specimens are examined. Our research findings show that H specimens exhibit larger deformations and smaller UTS value scatter in comparison with V specimens. Also, worth pointing out is the fact that V-oriented specimens have a higher elastic modulus. One can assume that the sintering process is more effective in V specimens, due to a more uniform laser beam trajectory than in the H specimens’ case.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Small amounts (15%) of copper slag (CS) do not change optimal binder content.•The addition of 30% CS has almost no impact on mixture properties.•The coarse CS fraction reduces rutting resistance ...whereas the fine fraction reduces cracking resistance.•Leachates do not contain heavy metals.•CS has high potential to be used as an alternative to virgin aggregate in asphalt mixtures.
This study aims to assess the feasibility of using copper slag (CS) in asphalt mixtures in both the surface and base layers of road pavements. For this purpose, two sets of asphalt mixtures with different CS content (15 and 30%) and fraction sizes (0/8 and 0/16 mm) were prepared. The optimal binder content of each mixture was determined using the Marshall mix design method. Their laboratory performances were investigated and compared with the properties of reference asphalt mixtures, i.e. mixtures consisting exclusively of virgin materials. Test results showed that adding CS to the mixture for the surface layer improved stiffness and rutting resistance and had almost no negative impacts on the remaining properties apart from cracking resistance. Further, the addition of CS to the base-layer mixture improved cracking resistance, but negatively affected stiffness, rutting and fatigue resistance. In both cases, adding CS did not influence the strength, water sensitivity or freeze–thaw resistance. From a leaching perspective, the results showed that leachates gathered from the asphalt mixtures designed for the surface layer did not contain heavy metals. Overall, it can be concluded that CS has a potential to be used as an appropriate aggregate substitute for virgin aggregates in asphalt mixtures for both surface and base layers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper focuses on examining the quality and competitiveness of Serbian defense industry in the global market for weapons and military equipment, with the aim to perform a structural and ...functional analysis of the global market of weapons and military equipment, to review its characteristics and to determine the place and role of the defense industry of the Republic of Serbia on it. The Covid-19 pandemic along with active and intense armed conflicts between Russia and Ukraine, Armenia and Azerbaijan, in the Middle East, in the north of the African continent and in the Sahel contributed to the sale of weapons and military services reaching record amounts in 2020. The activities of the USA, China and India on the international political scene and in the development and improvement of defense technologies will influence them to be dominant forces on the market of weapons and military equipment by 2030. The paper also gives a review of the quality and competitiveness of the Serbian defense industry.
This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt ...Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Martial arts and fight sports are mostly based on exchanging the punches and kicks that often result with injuries of face, skull bones, and neck vertebrae. One of possibilities to reduce number of ...injuries in athletes who deal with martial arts is development of new materials and improvement of designs for helmets used in sport fights. In order to experimentally analyze impact forces and simulate conditions during different fight punches mechanical installment was made. Aramis system is used to measure the displacement fields and the distribution of deformations which occur on the neck over the entire analyzed area based on the correlation of digital images. On this manner better understanding of behavior of both materials and structures during the action of the impact forces and loading is obtained. This information can further be used in researches related to the development of helmets used in martial arts which would influence reduction of values of neck deformations in athletes.
This paper presents new methodology for determining the actual stress–strain diagram based on analytical equations, in combination with numerical and experimental data. The first step was to use the ...3D digital image correlation (DIC) to estimate true stress–strain diagram by replacing common analytical expression for contraction with measured values. Next step was to estimate the stress concentration by using a new methodology, based on recently introduced analytical expressions and numerical verification by the finite element method (FEM), to obtain actual stress–strain diagrams, as named in this paper. The essence of new methodology is to introduce stress concentration factor into the procedure of actual stress evaluation. New methodology is then applied to determine actual stress–strain diagrams for two undermatched welded joints with different rectangular cross-section and groove shapes, made of martensitic steels X10 CrMoVNb 9-1 and Armox 500T. Results indicated that new methodology is a general one, since it is not dependent on welded joint material and geometry.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A financial/economic crisis may have an adverse effect on transport public-private partnerships (PPPs) as both traffic demand is negatively influenced, and governments are further under pressure. ...However, research on awarded road PPP contracts over a 20-year period in the European Union (EU) and Latin America and the Caribbean (LAC) showed that the market slowdown is brief and followed by a re-bounce leading to an overall upward trend. The LAC region has experienced multiple financial setbacks with no significant change in the PPP market structure as opposed to the EU, where significant changes were observed concerning a shift in the remuneration schemes employed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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