Browse Articles

The main target of the study is to highlight, by means of numerical simulations, the advantages and possible drawbacks of using composite materials instead of the classical cast iron to equip the brake system of railway freight vehicles. The qualitative and quantitative evaluations refer mainly to the braking capacity by considering as main parameter the stopping distance, in various operational conditions. Results indicate that composite materials are more efficient in the braking process, but in the case of low speeds, the recommendation is to perform earlier and/or stronger braking actions than usual, in classical cast iron equipment on rolling stock.

This paper presents a study based on simulating the impact between a yarn (or a single fiber with greater dimensions) and a bullet, the impact velocity being 400 m/s. The characteristics of the involved materials are taken from literature. The yarn is considered isotrope, but the values of the characteristics are close to those of aramid fibers and cooper and lead alloys used for manufacturing the bullets. Analysing the yarn failure caused by a bullet, this FE model allows for identfying the stages in the failure process. First, the yarn is pushed by the bullet and the local elongation of the yarn is tacking place. The yarn rupture occurs in the “strangled” zones, caused by the stretch of the yarn directly supporting the impact. The breaking of the yarn in the thinned zone (more pronounced asymmetric breaking) and it is visible that the yarn elastic recoil starts next the bullet. The friction between the yarn and the bullet is only on the conical surface of the bullet in the tapered zone of the bullet. The yarn is detaching from the bullet (the contact zones between the bullet and the yarn in polymeric matrix become smaller, justifying a neglectable influence of the thermal effect). The yarn has no more contact with the bullet. This step is in the favor of the assumption that, in the actual multi-yarn impact, the other layers of yarns maintain the bullet and the first yarns in contact and this is why bunch of fibers (fragments of the failed yarns) are pressed against the bullet and remain on it. The simulation results were qualitatively validated by SEM investigations of fiber failure under the same conditions as the model.

Environmental problems occurring in isolated or hardly accessible inhabited areas can be adequately addressed using membranes and membrane processes.In the present paper, the recuperative separation of aluminum ion from the aluminum sulfate-treated water through permeation using capillary composite membranes, from polypropylene with ethylene propylene diene terpolymer sulfonic acid (PP / S-EPDM) inclusions is followed by the reaction of complexation with 8-hydroxy quinoline. The installation used for studying the permeation process provides a usable surface area of 1 m2, the source phase solution volume is 3 L, and the receiving phase is 300 mL. The two phases are recirculated through the outside of the membranes (SP) and respectively through membranes (RP), by means of individual peristaltic pump that can provide flow variations between 2 and 200 mL / min by varying the intensity of the power supply. The optimal operating parameters were determined: operating time, pH and receiving phase flow, thus achieving an ionic flux (IR) above 10-11 mol / cm 2. s and a recovery factor (RF) over 90%.

Percutaneous coronary revascularization (PCR) with polymer-coated drug-eluting stents (DES) or bare-metal stents (BMS) is considered the standard therapy in advanced ischemic heart disease (IHD). Despite revascularisation, many of these patients subsequently develop heart failure with reduced ejection fraction (HFrEF). We analysed 51 patients with IHD, treated by PCR and insertion of DES and/or BMS who later developed HFrEF. Patients with DES where more likely women, of younger age and a higher incidence of diabetes mellitus compared to patients with BMS who were generally men, of older age and had more frequently acute ST-elevation myocardial infarction (STEMI) as indication for PCR. Although patients with DES had more severe IHD, their EF was higher, possibly due to the benefits offered by the DES.

The pyrolysis can be an attractive way to reduce the plastic waste and, in the same time, to obtain alternative conventional fuels. In this respect, four polymers (low-density polyethylene, high-density polyethylene, propylene and polystyrene) were used in the pyrolysis process. The experiments were carried out by using an in-house plant, which allowed a maximum test temperature of 450 °C. The product oil and the derived gas from the pyrolysis process were evaluated using different techniques, such as elemental analysis (EA), calorimetry, gas chromatography (GC), gas chromatography coupled with mass spectrometry (GC-MS). Furthermore, for a comparative study two catalysts, zeolite and lignite, were also used for the pyrolysis process, in order to observe their influences on the final products. The higher heating value obtained for the oil was in the 40.17-45.35 MJ/kg range, acceptable for the use of these oil as an alternative fuel for diesel engine. Also, the sulphur content from the obtained oil does not cause environment problems, being lower than the allowed limits (10 mg/L). In addition, the pyrolysis derived gas was rich in hydrocarbons, conducting to a high calorific value, in the 73.42 – 121.18 MJ/kg range.

Some disadvantages of traditional metallic implants used in orthopedics and traumatology prompted the development of bioresorbable polymer devices.The aim of this experimental study is to emphasize the characteristics of INION® resorbable implants (regarding design and polymers compositions), as well as to evaluate the results when using these innovative implants in two trauma cases. The polymers used in manufacturing INION® devices (Trimethylene Carbonate/TMC; L-Polylactic acid/LPLA; D,L Polylactic acid/DLPLA; Polyglycolic acid/PGA) degrade in alpha-hydroxy acids, gradually losing their hardness in 18-36 weeks with a complete bioresorption of 2-4 years. The clinical cases demonstrated the advantages of INION® plates (adapted shape, low profile, polyaxial screws, acceptable strength) or pins (allowing the aligmment and fixation of fracture, no migration). Among our patients, we found excellent results concerning the maintaining of primary reduced fracture, active range of motion, minimal pain with improving everyday comfort, no tissue or implant complications. Bioresorbable fracture fixation INION® devices are a viable alternative to traditional metallic implants, offering same significant advantages over them: the avoidance of long-term interference with gliding structures, keeping their strength long enough to support bone healing, no need to remove the implants, less pain, radiolucency, elimination of stress shielding and a lower risk of complications.

The aim of this study is to compare two different methods used for obtaining printed dental models -intraoral scanning and extraoral scanning; the comparative analysis was made in correlation to the accuracy of the traditional plaster cast model. Nine dental models were obtained: three plaster cast ones, three printed after intraoral scanning and there printed after impression scanning. A total of 137 measurements (arch and tooth measurements) were done on the three types of models and a statistical evaluation was performed (t-test, Fisher Test). Our results highlighted that 3D printed dental models represent a reliable option for clinical application.

The application of plastic materials in various areas of contemporary technology can lead to improvements in the function, quality and performance of engineering components. When determining the field of use of these materials, it is necessary, in addition to knowing the physical and mechanical properties, information about their behavior in service under the influence of the operating and environment factors. Compared to metallic or ceramic materials, polymeric materials exhibit a wide range of scratching deformations in a narrow range of pressure, speed, temperature, lubrication etc.In this paper is proposed a penetration model of a flat surface (from polymeric material) with a rigid conical penetrator and the determination of the flat surface material response mode. The penetration method corresponds to the deformation produced by the asperities in practice.The comparison of the experimental and the theoretical results confirms the veracity of the model and corresponds with many of the experimental results obtained in the specialized works.Based on the proposed models, maps can be produced, that can illustrate the response of any polymeric surface in contact with an abrasive material.

Reduced graphene oxide (r-GO) was synthesized chemically and it was characterized using Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and X-Ray Diffraction (XRD). The results revealed that the product r-GO is nano-sheets with non-smooth surface; the size of the obtained nano-sheets ranged from 20 to 100 nm. The well characterized nano-sheets were subjected to cytotoxicity test; results demonstrated that the nano-sheets show low cytotoxicity on the human cell line compared with the chemical nematicide. The r-GO was tested against the nematode during their life span and it was observed that the r-GO is capable to reduce the nematode gall number and egg mass of 94% and 99%, respectively. Moreover, the toxicity of the r-GO against the Juvenile (J2) root-knot nematode (Meloidogyne incognita) was also examined either in laboratory or under the greenhouse conditions. On the other hand, the treatment with the r-GO under greenhouse conditions showed higher mortality of the J2 of 98.5% compared with nematicidal treatment of 96% in a soil infested with M. incognita. Also, the same treatment was sufficient in inducting the growth of tomato plants: fresh weight of the shoot system increased with 30% and of the root system increased up to 285%; dry weight of the shoot system increased with 128% and of the root system increased up to 480%. r-GO has a high nematicidal activity and it is safe for human. The r-Go could be used as safe nematocide because it is safe, cheep, could be produced at large scale, and it is a good additive for the soil.

This paper analyzes the indentation hardness and the indentation elastic modulus variation depending on the variation of the grind percentage of polymer, when the other factors that can influence the injection molding remain unchanged. The analyzed polymers were: acrylonitrile butadiene styrene ABS MAGNUM 3453, polyamide PA 6.6 TECHNYL AR218V30 Blak and polyoxymethylene POM EUROTAL C9 NAT. The samples that were studied had different compositions in new and grinding material. The G-Series Basic Hardness Modulus at a Depth method was used. The increase of the grind percentage of ABS (from 0 to 100 %) leads to insignificant changes in the indentation hardness, indentation modulus, and maximum force applied to samples of tested material. The maximum hardness (0.137 GPa) of PA 6.6 is recorded in the case of the sample with 80% grind content, and the maximum hardness of POM is recorded as well in the case of the sample with 80% grind content, as being 0.215 GPa. The variation of the grind content in the analyzed samples determines changes in the evaluated parameters, depending on the type of polymer. Combining the new material with grind in proportions experimentally established for each techno polymer leads to changes in their mechanical properties.