Browse Articles

This paper had as special-purpose rendering the enhancing of WNR. 1.2083 steel’s properties by vacuum heat treatment, in protective atmosphere, in order to find adequate solutions for the improvement of the tools destined for the injection molding of PBT reinforced with up to 45% fiberglass, for the total cost of a mold production project divided per the total number of the resulted pieces from that project to reach its minimum value. For that purpose to be achieved, the use of high performance steels with special alloying concept and distinct production technique is mandatory. Although the electroslag remelting process ensures a smaller number of non-metallic inclusions and a homogenous structure characterized by isotropic properties, this has to be extended after heat treatment also. By identifying the problems involved in the injection process PBT reinforced with up to 45% fiberglass, the right characteristics of the WNR. 1.2083 steel were established. In order for those characteristics to be reached, the execution of the proper heat treatment in vacuum furnaces, with protected atmosphere, will be presented in this paper. Keywords: reinforced PBT, fiberglass, heat treatment, vacuum, low tempering, distortion

This work investigates the mechanical properties of polyurethane rigid foams by means of Dynamic Mechanical Analysis (DMA) tests and Impulse Excitation Technique (IET). DMA tests were performed in single cantilever with a sweep in temperature (from -50 °C to 100 °C) and frequency (from 1 Hz to 100 Hz), not determining glass-transition in the test parameter interval. IET tests were used to determine the dynamic modulus of elasticity, showing good accordance with DMA results Keywords: PUR foams, DMA tests, impulse excitation technique

The aim of the present study was to compare the retention rate and caries-preventive efficiency of two types of sealing materials : a glass ionomer cement (Ionofil plus) and a nano-hybrid resin sealant ( Grandio Seal) over a 2-year period. 84.78% with resin composite sealings and 7.39% of the glassionomer sealings were fully retained. New caries lesions were found in 7.82% of the glass ionomer sealed surfaces and 5.65% of the resin sealed surfaces. It can be concluded that Ionofil plus and Grandio Seal exhibit similar caries preventive effects. Keywords: dental sealing; Ionofil plus; Grandio Seal; retention rate; caries outcome

Severe plastic deformation (SPD) is a manufacturing technique for producing bulk ultrafine grained materials and nanomaterials, the advanced grain refinement obtained by SPD substantially improving structural and physico-mechanical characteristics for the processed material. Equal-channel angular pressing (ECAP), the main SPD technology, entails pressing test samples through a die containing two channels equal in cross section and intersecting at a certain angle. The billet theoretically deforms by simple shear and retains the same cross sectional area to allow repeated pressings for several cycles. A commercial Al-Mg-Si alloy (6063- T1) was investigated in this study. As-received 6063-T1 alloy was firstly analyzed in OES and XRD tests. The specimens were subsequently processed at ambient temperature for a number of passes up to nine (one, three, six and nine ECAP passes), using a die channel angle of 100°. After ECAP, samples were cut from each specimen (ECAP treated and as-received) and prepared for microstructural investigations (SEM) and mechanical testing (compression and microhardness tests, fracture surfaces analysis). Furthermore, multiple correlations between ECAP processing parameters and the resulting microstructure and mechanical properties for the ECAP treated 6063-T1 alloy were also determined. Keywords: ultrafine-grained materials, aluminum alloys, severe plastic deformation, equal-channel angular pressing

Hormones are chemical substances which transmit a message as a signal within a physiological system between the place where they are secreted and the place of their receptors where they have the biological action. In the last decades the number of studies on phytohormones has increased continuously. In this study, polyurethane microstructures with and without brassinolide were synthesized in order to assess the release rate. Two different types of drug carriers were obtained (ether- and ester-based microstructures) and the evaluations were done by using two different methods: the measurement of microstructures’ size and the determination of free brassinolide concentration. The results suggest that ester-based polyurethane microstructures degrade faster and the two methods present very similar results. Keywords: brassinolide, drug carrier, DSC, polyurethane, UV-Vis, zetasizer

An increasing number of railway vehicles are using rubber springs as suspension elastic elements. Rubber is a suitable material for suspension purposes due to of its intrinsic properties and due to of the variety of forms into which it can be made. The clouth-type rubber spring may be used in both primary and secondary suspension of the vehicle and it may ensure the desired characteristics by setting the shape of its metallic components. In the present paper, a finite element static analysis was performed regarding the deformation of the clouth spring rubber under the action of various loads: vertical, longitudinal and transversal. The simulations allowed determining the distribution of deformations within the rubber element, the magnitude and the location of the largest deformation. Keywords: rubber, railway vehicle, suspension, clouth-type spring

Polyester coating of copper alloys is part of the technological procedures meant to improve the performances of metallic parts in order to reduce the rate of premature removal from operation. The paper highlights the positive influence that copper alloys coating with polyester impregnated with 5 - 10% graphite has on the main mechanical characteristics, especially the wear resistance. The effects on the wear, fragility and structural modifications have been determined on Amsler testing machine by means of roller-roller type couplings: polyester coated copper alloy – treated copper alloy; treated copper alloy - treated copper alloy. The comparison revealed the positive influence of the thin layer of polyester as lubricating agent, thermal barrier, electrical insulator, damping layer, and stress dissipation medium it also established the temperature limit up to which it is recommended to use the polyester coating in industrial applications. Keywords: polyester, graphite, cooper alloys

The paper presents comparative analysis for different solutions for the body of an internal spur gear used in a ground movement system of a drone with aerial and terrestrial movement capability. The comparative analysis is made from natural frequencies perspective and the purpose of the analysis is to reduce the weight of the drone without affecting its mechanical resistance and vibrational characteristics. Keywords: internal spur gear, modal analysis, natural frequencies, drone

This paper presents the influence of subsequent pressure of high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), polycarbonate and acrylonitrile butadiene styrene blend (PC+ABS) on some mechanical properties when obtained through the injection of items from various industries. The HDPE samples were obtained at the following subsequent pressure: 800 bar, 900 bar, 1000 bar, 1100 bar, and 1200 bar. The PMMA samples were obtained at the following subsequent pressure: 450 bar, 550 bar, 650 bar, 750 bar, and 850 bar, and PC+ABS samples were obtained at the following subsequent pressure: 500 bar, 600 bar, 700 bar, 800 bar, and 900 bar. Determining the mechanical properties was made using determining methods of tensile properties, of Izod impact test, and Shore Durometer hardness test. It was observed in the case of the three analyzed polymers that increasing the subsequent pressure when injecting HDPE leads to a slight increase of hardness, and in the case of PMMA and PC+ABS blend, an increase in the subsequent pressure leads to a decrease in hardness. The Izod shock resistance for HDPE and PMMA decreases along with the increase of the subsequent pressure. In the case of PC+ABS, an increase of the subsequent pressure from 500 bar to 700 bar leads to a decrease in the shock resistance from 68.675 kJ/m² to 51.475 kJ/m². A further increase in the subsequent pressure to 900 bar leads to an increase in the shock resistance up to 63.900 kJ/m². The tensile strength at break is influenced by the subsequent pressure. An increase in the subsequent pressure in case of HDPE and PC+ABS blend leads to an increase in the resistance of the tensile strength at break, whereas in the case of PMMA, an increase in the subsequent pressure leads to a decrease in the resistance of the tensile strength at break. Keywords: high density polyethylene (HDPE), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene polycarbonate blend (PC+ABS), tensile tests, Izod impact test, Shore Durometer hardness test