Abstract
This paper comparatively investigates the cavitation erosion damage of two self-fluxing NiCrSiB hardfacings deposited via the oxy-acetylene powder welding method. Examinations were conducted ...according to the procedure given by ASTM G32 standard. In order to research cavitation erosion (CE), the vibratory apparatus was employed. The cavitation damaged surfaces were inspected using a scanning electron microscope, optical microscope and surface profilometer. The hardness of the A-NiCrSiB hardfacing equals 908HV while that of C-NiCrSiB amounts to 399HV. The research showed that the CE resistance of C-NiCrSiB is higher than that of A-NiCrSiB. The results demonstrate that in the case of multiphase materials, like the NiCrSiB hardfacings, hardness cannot be the key factor for cavitation erosion damage estimation whereas it is strongly subjected to material microstructure. In order to qualitatively recognise the cavitation erosion damage of the NiCrSiB self-fluxing hardfacings at a given exposure time, the following factors should be respected: physical and mechanical properties, material microstructure and also material loss and eroded surface morphology, both stated at specific testing time. The general idea for the cavitation erosion damage estimation of the NiCrSiB oxy-acetylene welds was presented.
Abstract
This work deals with a comparative numerical finite volume method of airflow for a 3D airframe model. The analyzed airframe model allowed 3-vector thrust directing while using the geometry ...of the inverted delta, which increases lift force area, allows for vertical take-off and landing, as well as full control of its flight using rotating propulsion nacelles and an airframe control system. The airframe model dimensions were 3900 x 3250 x 915 mm, enabling the installation of components of specific dimensions. CFD analysis using a four-equation transition SST model with automatic surface roughness and initial conditions: T = 288K, viscosity η= 1.7894∙ 10−5
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and was carried out in the FLUENT module of ANSYS 16.0. For each simulation, 2000 iterations were performed with the intention of achieving a convergence of all residuals below 1∙10
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using a calculation mesh consisting of 500,000 elements and 150,000 nodes. The model uses aerodynamic profile geometries: CLARK Y, NACA 6409, and NACA 2414, which are provided to obtain the optimal aerodynamic characteristics and determine the optimal range of angles of attack for the designed solution. Those angles of attack were in the range of α = 5 ÷ 10° in which the highest excellence coefficient of the carrier airfoil profile occurs. For those values of parameters optimal lift and drag forces were determined
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•Electrochemical detection of trace explosives at boron-doped diamond/graphene nanowall electrodes.•Determination of important nitroaromatic explosive compounds, e.g. TNT with LOD of ...73 ppb.•Detection of explosives in real liquid effluents like a wastewater and landfill leachates.
The study is devoted to the electrochemical detection of trace explosives on boron-doped diamond/graphene nanowall electrodes (B:DGNW). The electrodes were fabricated in a one-step growth process using chemical vapour deposition without any additional modifications. The electrochemical investigations were focused on the determination of the important nitroaromatic explosive compounds, 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitroanisole (TNA).
The distinct reduction peaks of both studied compounds were observed regardless of the pH value of the solution. The reduction peak currents were linearly related to the concentration of TNT and TNA in the range from 0.05–15 ppm. Nevertheless, two various linear trends were observed, attributed respectively to the adsorption processes at low concentrations up to the diffusional character of detection for larger contamination levels. The limit of detection of TNT and TNA is equal to 73 ppb and 270 ppb, respectively. Moreover, the proposed detection strategy has been applied under real conditions with a significant concentration of interfering compounds – in landfill leachates.
The proposed bare B:DGNW electrodes were revealed to have a high electroactive area towards the voltammetric determination of various nitroaromatic compounds with a high rate of repeatability, thus appearing to be an attractive nanocarbon surface for further applications.
Artificial neural networks (ANN) are commonly used to solve many industrial problems. However, their application for cavitation erosion evaluation is a quite new attempt. Thus, the aim of this work ...was to elaborate the neural model of the cavitation erosion process of 34CrNiMo6 steel. Cavitation erosion tests were conducted with a usage of the ultrasonic vibratory method with stationary specimen that relies on the ASMT G32 standard. The proceeding damage of marked steel surface area was observed by means of a scanning electron microscope. Wear was evaluated with profiler measurements, image analysis of cavitation worn surface areas and weighing done in stated time intervals. The cavitation erosion results were analysed with Matlab software by Neural Network Toolbox. The developed neural model of cavitation erosion process that combines exposure time, roughness, area fraction of worn surfaces, and mass loss gives promising results.
This paper presents the results of a numerical analysis of a two-stage forging process for producing a hollow part with an external flange. The numerical analysis was performed via the finite element ...method using Deform-2D/3D. The analysed case included a cold forming process. The billet was a tube made of a low alloy steel grade 42CrMo4 with its flow curve described by a constitutive equation. The forming process involved the use of two operations: extrusion and forging in a tapered die cavity. The objective of the study was to determine whether the proposed forming technique could be used for production of hollow flanged parts. The kinematics of material flow, distributions of effective strains and the Cockcroft-Latham ductile fracture criterion, as well as force parameters were examined. The conducted research confirmed the correctness of the proposed method.
The article presents a method of numerical modelling of the load on pre-stressed dies. Numerical modelling was performed in two stages. In the first stage, a simulation of the process of extruding ...with stiff tools was performed. In the second stage, load on the tools obtained in the first stage was implemented and strength tests of the dies were performed. Four construction variants of the tools made of steel and sintered carbide were analysed. In the first set of tools, a monolithic die with a container was used. In the second set, a die and a divided container were applied. In the third set, a die and a container stressed with a singular ring were used. In the last set, a die with a container stressed with two rings was analysed. As a result, distributions of reduced, radial, tangential, and axial stresses were presented for various construction variants. Die and container made of sintered carbide stressed with two rings ensure the necessary strength of tools and correct progression of the process.
The aim of the article is to build-up a simplified model of the effect of atmospheric plasma spraying process parameters on the deposits' functional properties. The artificial neural networks were ...employed to elaborate on the model and the Matlab software was used. The model is crucial to study the relationship between process parameters, such as stand-off distance and torch velocity, and the properties of Al2O3-13 wt% TiO2 ceramic coatings. During this study, the coatings morphology, as well as its properties such as Vickers microhardness, porosity, and cavitation erosion resistance were taken into consideration. The cavitation erosion tests were conducted according to the ASTM G32 standard. Moreover, the cavitation erosion wear mechanism was presented. The proposed neural model is essential for establishing the optimisation procedure for the selection of the spray process parameters to obtain the Al2O3-13 wt% TiO2 ceramic coatings with specified functional properties.
To improve the wear resistance of low-carbon steel and gray cast iron, TiC/Fe-type composite layers were fabricated using reactive casting coatings. The in situ synthesis reaction of titanium carbide ...(TiC) was initiated by the high temperature of the liquid alloy (SHS – self-propagating high-temperature synthesis). The structure, microstructure, hardness, and wear properties of the composite layers were investigated. Wear examinations were carried out in various environments: dry sliding, slurry abrasion, and cavitation erosion in slurry. An observation of the microstructure revealed the presence of TiC particles that were well-bonded with both types of matrices. The mechanical properties showed an almost three-fold increase in the hardness within the area of the composite layer as compared to the base alloy (1000HV1). These results were reflected in a slurry abrasion test that indicated less than half of the weight loss as compared to the monolithic matrix of the composite castings. The cavitation erosion wear mechanism of the composite layers was examined for the first time taking the surface of the sample into consideration (after polishing and as cast – casting skin). The polished surfaces were characterized by higher resistance to cavitation erosion than the as-cast samples. On the other hand, the casting skin acted beneficially as an extra coating that prevented the castings’ cores from cavitation erosion damage.
•Composite layers were fabricated in situ in cast steel and cast iron.•Hardness within area of composite zones reached more than 850 HV1.•Composite layers were testes by ball on disc method, Miller test and cavity erosion.•Composite layers were tested in as – cast state and after polishing process.
Abstract
This paper presents a numerical analysis of a new cold forming process for a hollow part with an external flange. The following techniques were used: forward extrusion, an unconventional ...method of extrusion with a moving sleeve, and upsetting in a tapered die cavity. The billet (42CrMo4 steel tube) was formed at ambient temperature. The study aimed to investigate the proposed method in terms of forged part accuracy. The following are examined and discussed: material flow, process force parameters in relation to tool strength, energy consumption of individual operations, as well as the distributions of strains, stresses, temperature and Cockcroft-Latham integrals in the produced part. The study has confirmed that hollow forged parts with external flanges of relatively large diameters and heights can be cold formed in several operations using different techniques.
The paper describes the analysis of crack surface morphology of S355J2 steel specimens after bending-torsion fatigue. These experimental investigations of the surface topography were carried out ...using the focus variation microscope, an optical 3D measurement device. Selected results of measured fracture surfaces for S355J2 steel were analysed according to the surface texture ISO 25178 standard. Differences in roughness values for different loadings were demonstrated. For profile Rx and areal Sx parameters, characteristic relationships of fracture zones have been demonstrated. It has been shown that roughness profile Ra for the rupture area is higher than for the propagation area, as well as increases after both the LCF and HCF tests and increases with the torsional loading level. However, Sa in the propagation area increases and the rupture area decreases.
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