B. Trybuś, J. M. Olive, N. Lenoir and A. Zieliński
The investigations of high-temperature oxidation of zirconium alloys, applied for fuel pellets in nuclear power plants, are usually limited to oxidation kinetics, phase transformations and microstructural characterization. The purpose of this research was to characterize the degradation phenomena occurring within oxide layer and at the interface oxide/metal, on internal and external Zircaloy-2 tube surfaces, below and over crystalline transformation temperature of zirconium oxides. The commercial tubes were oxidized at 1273 K and 1373 K in calm air for 30 min and then examined with a technique novel for such purpose, namely a high-resolution X-ray computer tomography. The light microscopy was used to examine the cross-surfaces. The obtained results show that the form and intensity of oxide damage is significant and it is in a complicated way related to oxidation temperature and on whether external or internal tube surface is studied. The found oxide layer damage forms include surface cracks, the detachment of oxide layers, the appearance of voids, and nodular corrosion. The oxidation effects and damage appearance are discussed taking into account the processes such as formation of oxides, their phase transformation, stress-enhanced formation and propagation of cracks, diffusion of vacancies, formation of nitrides, diffusion of hydrogen into interface oxide-metal, incubation of cracks on second phase precipitates are taken into account to explain the observed phenomena.
M. Davarpanah, G. Somodi, L. Kovács and B. Vásárhelyi
Understanding the quality of intact rock is one of the most important parts of any engineering projects in the field of rock mechanics. The expression of correlations between the engineering properties of intact rock has always been the scope of experimental research, driven by the need to depict the actual behaviour of rock and to calculate most accurately the design parameters. To determine the behaviour of intact rock, the value of important mechanical parameters such as Young’s modulus (E), Poisson’s ratio (ν) and the strength of rock (σcd) was calculated. Recently, for modelling the behaviour of intact rock, the crack initiation stress (σci) is another important parameter, together with the strain (σ). The ratio of Young’s modulus and the strength of rock is the modulus ratio (MR), which can be used for calculations. These parameters are extensively used in rock engineering when the deformation of different structural elements of underground storage, caverns, tunnels or mining opening must be computed. The objective of this paper is to investigate the relationship between these parameters for Hungarian granitic rock samples. To achieve this goal, the modulus ratio (MR = E/σc) of 50 granitic rocks collected from Bátaapáti radioactive waste repository was examined. Fifty high-precision uniaxial compressive tests were conducted on strong (σc >100 MPa) rock samples, exhibiting the wide range of elastic modulus (E = 57.425–88.937 GPa), uniaxial compressive strength (σc = 133.34–213.04 MPa) and Poisson’s ratio (ν = 0.18–0.32). The observed value (MR = 326–597) and mean value of MR = 439.4 are compared with the results of similar previous researches. Moreover, the statistical analysis for all studied rocks was performed and the relationshipbetween MR and other mechanical parameters such as maximum axial strain for studied rocks was discussed.
Abdelmadjid Abdi, Khelifa Abbeche, Djamel Athmania and Mounir Bouassida
This paper presents the results obtained from an experimental programme and numerical investigations conducted on model tests of strip footing resting on reinforced and unreinforced sand slopes. The study focused on the determination of ultimate bearing capacity of strip footing subjected to eccentric load located either towards or opposite to the slope facing. Strip footing models were tested under different eccentricities of vertical load. The obtained results from tests conducted on unreinforced sand slope showed that the increase in eccentricity of applied load towards the slope facing decreases the ultimate bearing capacity of footing. Predictions of the ultimate bearing capacity obtained by the effective width rule are in good agreement with those proposed from the consideration of total width of footing subjected to eccentric load. The ultimate bearing capacity of an eccentrically loaded footing on a reinforced sand slope can be derived from that of axially loaded footing resting on horizontal sand ground when adopting the effective width rule and the coefficient of reduction due to the slope. When increasing the distance between the footing border to the slope crest, for unreinforced and reinforced ground slope by geogrids, the ultimate bearing capacity of footing is no more affected by the slope ground.
We show that the global non-linear stability threshold for convection in a double-diffusive couple-stress fluid saturating a porous medium is exactly the same as the linear instability boundary. The optimal result is important because it shows that linearized instability theory has captured completely the physics of the onset of convection. It is also found that couple-stress fluid saturating a porous medium is thermally more stable than the ordinary viscous fluid, and the effects of couple-stress parameter (F ) , solute gradient ( S f ) and Brinkman number ( D a ) on the onset of convection is also analyzed.
János Endre Maróti, Dávid Miklós Kemény and Dóra Károly
Additive manufacturing (AM) offers the possibility to produce complex parts without the design constraints of traditional manufacturing routes. Our aim was to determine different mechanical and corrosion properties of direct metal laser sintered austenitic stainless steel (X2CrNiMo17-12-2) material with tensile test, Charpy impact test, scanning electron microscopy and corrosion test. The measured values were evaluated, and our results compared with literary values, furthermore, we also examined how the printing direction affects the properties.
Attila Gergely, József Kántor, Enikő Bitay and Domokos Biró
The effective recycling of polymer materials remains unresolved to this day, and this has had a devastating effect on the environment. This study examines an alternative method to PET recycling that is the generation of polymer fibers and fiber mats for filtration applications. The electrospinning instrumentation used in this study had to be designed and built in order to carry out the research. We have managed to produce PET fibers with 200-600 nm diameter, and free-standing fiber mats that could potentially be used in filtration applications.
Digital product processing and the utilization of novel, tissue-friendly materials allow the use of fixed dentures for patients. Its basis is a titanium plate fixed to the cortical bone surface at given screw positions. A digital dental cast is created from the existing bone surface, and modelling and necessary statistical analyses are carried out in a virtual environment. Safety of the welded joint is evaluated with mechanical methods. When designing the fixing points, an idealized denture is used that was previously designed for the patient. The number and position of pillar elements used for screw fixation of the denture are determined by the complex geometry of the denture itself, and the location, direction, and articulating position of existing teeth. The additively manufactured implant and the machined pillar sleeves are joined with laser-welding at given nesting positions. Homogeneity of the metallic material structure at the welded joint zone of the product is examined with micro-CT. Due to this implementation method, surgical time decreases together with complication rates and post-operative problems.
Nowadays additive manufacturing continues to gain more and more space in industrial technology. In particular, FDM (fused deposition modelling) machines have become easily available to the public. Quality of parts is impacted by several factors. In this study we investigate layer thicknesses of a prototype manufactured from PLA, and we pay special attention to the thickness of sequentially deposited layers.
Ultrasonic welding is a very useful and simple welding process. It is suitable for establishing a joint between thin sheets and dissimilar metals with short preparation and finish work time . Some welding defects were detected due to less than optimal ultrasonic welding parameters. These defects were ruptures, surface colour change and unacceptable deformations. This article aims to identify these failures and their causes.
Krisztián Kun, János Kodácsy, Dániel Vaczkó and Zsolt Ferenc Kovács
The subject of this research is the machining of Ni-based super alloys using indexable end mills. The cutting ability of these materials is known to be difficult, even challenging with modern tools, so our goal is to create an efficient technology recommendation on an experimental basis. To this end, we have developed an experimental design from which results are used to determine the optimal technological parameters. This research took place at John Von Neumann University, Department of Vehicle Technology of GAMF Faculty.