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Vpliv izdelovalnih parametrov na lastnosti izdelkov iz Ti-6Al-4V, narejenih s selektivnim laserskim taljenjem in plastenje površine z bioaktivnim polimerom
Snehashis Pal, 2019, doctoral dissertation

Abstract: Technological parameters included in energy density (ED) are the more powerful tools in selective laser melting (SLM) technology which can be used in the time of fabrication to regulate chemical, metallurgical, and mechanical properties of a product. The volumetric Energy Density (ED) depends on the energy input employed by the laser power, scanning speed, hatch spacing, and the layer thickness. Density, microstructure, surface morphology, dimension accuracy, strength and porosity including the number of pores, place of the pore, size of a pore shape of a pore, inclusions of pores of an SLM product depends on the processing parameters. As the powder material fusion process is done by track by track and layer by layer, the architecture of the microstructure in a product is oriented as the direction of building up too. The research has emphasized on metallurgical properties, tensile properties, and producing the non-porous products from Ti-6Al-4V alloy powder and surface modification using bioactive polymer for orthopedic application. The research has followed four steps to study the metallurgical properties and finding out the combinations of technological parameters in producing non-porous products. The purpose of the first step of the study was to examine the effects of ED on the product properties and to obtain an optimum ED as well as the optimal range of scanning speed. The second step of the study has focused on the influences of laser power. The third step of the study has investigated the effect of amounts of track overlapping and hatch spacing. Almost a zero-porosity product has been able to produce by following these three steps of the ongoing research. The fourth step has studied the metallurgical properties emphasizing on re-melting of every layer. High-density products have been found in the fourth step where a small amount of very small sized pores are present as a result of keyhole effect and gaseous bubble entrapment mainly. Four buildup orientations have been selected for each ED in the first step of the study to examine the tensile properties of the products. The best buildup orientation has been seen in longitudinally vertical tensile specimens considering tensile properties. The tensile properties have also been studied in the second and third step of the study with best build up orientation of the tensile specimens. The alterations of metallurgical and tensile properties have also been investigated after heat-treatment of the specific samples. Dimensional accuracies were also invigilated on the cubic, and tensile specimens over the studies and consequently, inaccuracies have been noticed. The fifth step of the study has observed the pore properties, adhesion properties, the compressive strength of gelatin coating manufactured using unidirectional freezing and the freeze-drying process of three different gelatin concentrations on four different surfaced Ti-6Al-4V alloy substrates. The results indicate that the coating properties depend on the substrate’s surface texture as well as the concentration of gelatin. Above 80% of porosity, interconnected and well-aligned pores of 75-200 μm have been obtained which is required to stimulate bone ingrowth histologically.
Keywords: selective laser melting, unidirectional freezing, fabricating parameters, porosity, microstructure, mechanical strength
Published: 01.04.2019; Views: 950; Downloads: 105
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Growth performance, haematology and serum biochemistry of West African dwarf sheep fed cassava peel-oil palm leaf meal based diets in a hot humid tropics
Peter-Damian Chukwunomso Jiwuba, Lydia Chidimma Jiwuba, Moses Udoha Onyekwere, 2017, original scientific article

Abstract: The growth performance, haematological and serum biochemical characteristics of thirty-six West African Dwarf (WAD) sheep of about 10 - 12 months of age and averaged 8.53kg in weight were sourced from the College flock. Four dietary treatments designated as T1, T2, T3 and T4 were formulated to contain 0%, 10%, 20% and 30% oil palm leaf meal (OPLM) respectively were randomly assigned to the animals. The experimental animals were divided into four groups of nine animals each, with each group replicated thrice with three animals per replicate. Each group was allotted to one of the diets in a completely randomized design. The animals were weighed at the beginning of the trial and weekly subsequently and data for growth performance were generated. Blood samples were obtained from one animal in each replicate, and data generated were analyzed statistically. Average daily feed intake, total dry matter intake and average daily weight gain were significantly (P<0.05) influenced by the dietary treatment, with animals on T4 group having higher and better values. Feed conversion ratio (FCR) also differed significantly (P<0.05) with sheep on T3 and T4 (11.82 and 11.49 respectively) having the best FCR. The haematology showed that the packed cell volume (PCV), red blood cell (RBC), and mean cell haemoglobin concentration (MCV) were significantly (P < 0.05) improved at 10%, 20% and 30% inclusion levels of OPLM, respectively. Sheep in treatment groups had improved (P < 0.05) white blood cell (WBC) count than those on the control group. Serum biochemistry results showed that total protein, albumin and globulin were significantly influenced (P < 0.05) and tended to increase with increasing levels of test ingredient. Sheep in treatment groups had higher (P < 0.05) urea values than those on control. Creatinine values at 20% and 30% inclusion differed significantly (P < 0.05) with the control value. Cholesterol was significantly influenced (P < 0.05) and followed an irregular trend across the treatment groups. The results showed that inclusion of OPLM had a beneficial effect on the general performance of the WAD sheep. Therefore, 30% OPLM supplementation was recommended for optimum performance in WAD sheep.
Keywords: sheep, supplemental diets, proximate composition, oil palm leaf meal, casava peel, blood parameters
Published: 10.10.2018; Views: 732; Downloads: 243
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Use of a Perth sand penetrometer (PSP) device to determine the engineering parameters of sands
S. D. Mohammadi, 2016, original scientific article

Abstract: Determining the in-situ engineering parameters of sandy soils has always been a challenge for geotechnical engineers, resulting in several methods having been developed so far. The Perth Sand Penetrometer (PSP) test is one of the most versatile of these methods. It is a considerably faster and cheaper tool than boring equipment, especially when the depth of the exploration is moderate. In the present research, a methodology for the use of a PSP device to evaluate the engineering parameters of sandy soils in laboratory conditions is discussed and the repeatability of the test results is studied. First of all, the tests were performed on typical Tehran young alluvial deposits (poorly graded sandy soil, SP) consistently prepared to 5 densities using the sand raining or pluviation technique. Next, the normal and logNormal distributions of the test data using the Kolmogorov-Smirnov normality test were examined. After that, based on the obtained results, the relationship types between the dynamic point resistance index (qd) and other parameters, such as the relative density (Dr), the modulus of elasticity (E), the shear modulus (G) and the friction angle of the soil, were determined. The results show that the obtained relationships were semi-logarithmic and logarithmic, and most of the obtained experimental formulas had a high coefficient of determination (>90%). To evaluate the accuracy of the results, 95% confidence and prediction bands were also used and the results show that all the obtained experimental relationships were appropriate. Finally, the repeatability of the test results was evaluated by calculating the coefficient of variations, which was less than 30% for all the tests.
Keywords: dynamic-point resistance index (qd), engineering parameters, repeatability, statistical methods
Published: 18.06.2018; Views: 507; Downloads: 62
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Analysis of a dilatometer test in over-consolidated sediments, basin of the Duero river, Spain
Félix Escolano Sánchez, Manuel Bueno Aguado, 2015, original scientific article

Abstract: A dilatometer test is a useful method for in-situ geotechnical surveys. It can be compared with the results obtained using a mathematical model. The mathematical model of concentric rings shown in this article is governed by the constitutive equation of the “Hardening Soil Model”. A large number of tests made on the Dueñas Geological Facies, with a consistency ranging from firm clays to soft rocks, are compared to the model results. In this way, the “Hardening Soil Model” parameters are adjusted to the Dueñas Facies materials.
Keywords: Dueñas, geotechnical parameters, hardening soil model, soft rocks and clays deformation
Published: 14.06.2018; Views: 586; Downloads: 47
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Radon anomalies in soil gas caused by seismic activity
Boris Zmazek, Mladen Živčić, Ljupčo Todorovski, Sašo Džeroski, Janja Vaupotič, Ivan Kobal, 2004, original scientific article

Abstract: At the Orlica fault in the Krško basin, combined barasol detectors were buried in six boreholes, two along the fault itself and four on either side of it, to measure and record radon activity, temperature and pressure in soil gas every 60 minutes for four years. Data collected have been analysed in a manner aimed at distinguishing radon anomalies resulting from environmental parameters (air and soil temperature, barometric pressure, rainfall) from those caused solely by seismic events. The following approaches have been used to identify anomalies: (i) ± 2σ deviation of radon concentration from the seasonal average, (ii) correlation between time gradients of radon concentration and barometric pressure, and (iii) prediction with regression trees within a machine learning program. In this paper results obtained with regression trees are presented. A model has been built in which the program was taught to predict radon concentration from the data collected during the seismically inactive periods when radon is presumably influenced only by environmental parameters. A correlation coefficient of 0.83 between measured and predicted values was obtained. Then, the whole data time series was included and a significantly lowered correlation was observed during the seismically active periods. This reduced correlation is thus an indicator of seismic effect.
Keywords: radon in soil gas, environmental parameters, earthquakes, correlation, regression trees, forecasting
Published: 15.05.2018; Views: 887; Downloads: 58
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Chemometric characterization of Slovenian red wines
Milena Ivanović, Anja Petek, Maša Islamčević Razboršek, Mitja Kolar, 2017, original scientific article

Abstract: Total phenolic (TPC), flavonoid (TFC) and tannin (TTC) contents, total $SO_2$, total acids, pH, and reducing sugars were measured in twenty five Slovenian red wines from three key wine producing regions, Podravje, Posavje and Primorska. The results were chemometrically analysed and the wines were classified according to wine growing region and vine variety. Principal component analysis proved that TPC, TFC and TTC contents were primarily responsible for variation in the wines. Additionally, linear discriminant analysis (LDA) was performed and resulted in the satisfactory classification of samples by both vine variety and region.
Keywords: Slovenian red wines, quality parameters of wine, polyphenols, chemometric analysis
Published: 03.10.2017; Views: 839; Downloads: 299
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Comparison of different optimization and process control procedures
Marko Reibenschuh, Franc Čuš, Uroš Župerl, 2010, review article

Abstract: This paper includes a comparison of different optimization methods, used for optimizing the cutting conditions during milling. It includes also a part of using soft computer techniques in process control procedures. Milling is a cutting procedure dependent of a number of variables. These variables are dependent from each other in consequence, if we change one variable, the others change too. PSO and GA algorithm are applied to the CNC milling program to improve cutting conditions, improve end finishing, reduce tool wear and reduce the stress on the tool, the machine and the machined part. At the end a summary will be given of pasted and future researches.
Keywords: optimization, milling, cutting parameters, LENS
Published: 04.08.2017; Views: 628; Downloads: 285
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Analysis of neural network responses in calibration of microsimulation traffic model
Irena Ištoka Otković, Damir Varevac, Matjaž Šraml, 2015, original scientific article

Abstract: Microsimulation models are frequently used in traffic analysis. Various optimization methods are used in calibration, and the one method that has shown success is neural networks. This paper shows the responses of neural networks during calibration of a microsimulation traffic model. We analyzed two calibration methods by applying neural networks and comparing their neural network learning (according to their achieved correlation and the mean error of prediction) and their generalization ability (comparison of generalization results was analyzed in two steps). The best correlation between the microsimulation results and neural network prediction was 88.3%, achieved for the traveling time prediction, on which the first calibration method is based.
Keywords: microsimulation traffic models, calibration, response of neural networks, traveling time, queue parameters
Published: 02.08.2017; Views: 756; Downloads: 314
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Analysis of the influence of car-following input parameters on the modelled travelling time
Irena Ištoka Otković, Tomaž Tollazzi, Matjaž Šraml, 2013, short scientific article

Abstract: The calibration process is a basic condition of traffic model application in local conditions. The choice of input parameters, which are used in calibration process, influences the success of the calibration process itself; therefore, the goal is to choose parameters with a larger influence on the modelling process. This paper offers a detailed analysis of car-following input parameters and their influence on the modelled travelling time. The experimental basis was a one-lane roundabout, and the tool used for traffic simulation was the VISSIM microsimulation traffic model. The results show that the car-following input parameters should be a part of the set of input parameters, which will enter the process of calibration. The examined car-following input parameters affect the capacity of intersections and results show that it is necessary to revise the range of input values of one of the observed car-following input parameters.
Keywords: car-following input parameters, input parameters for the process of calibration, VISSIM
Published: 11.07.2017; Views: 717; Downloads: 104
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Factors influencing the yielding constraint by cracked welded components
Dražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, original scientific article

Abstract: The effect of strength mismatch for welded joints performed with different geometries on the yielding constraint has been investigated in the context of single-edged fracture-toughness specimens subjected to bending SE(B) using the finite-element method. The crack was located in the centre of the weld. Two geometri cal parameters have been identified as being the most important: the crack-Iength ratio a/W and the sIenderness of the welded joint (W-a)/H. They were systematically varied as follows: a/W = 0.1; 0.2; 0.3; 0.4; 0.5 and W = 2H, 4H, 8H, 16H, 24H. Basic equations and plane-strain finite-element solutions for the overmatched SE(B) specimen with all configuration combinations are given. The results are in good agreement with those in literature. This paper aims to establish yield-Ioad solutions for the same weldment configurations, but with materials dissimilarity present within the weld. This situation is usually encountered during repair welding. For this purpose, a practical combination of filler materials, with the same portion of overmatched part with M = 1.19 and undermatched part with M = 0.86, has been selected. Plane-strain solutions for the heterogeneous weld with the cracklocated in the overmatched half were obtained. The influence of the yielding-constraint key parameters has al so been evaluated. Yield-Ioad results for the specimens performed with different weld widths have the greatest scattering for the a/W = 0.5. The transition from the overmatched to the undermatched solution with increasing H is evident. On the other hand, the behaviour of the specimen with a shallow crack is dictated by the overmatch region ahead of the crack tip and depends very little on the weld slenderness. An approximated 3-D area of the yield-Ioad solutions depending ona/W and (W-a)lH has been proposed. Furthermore, the stress triaxility parameter h has been calculated using 2-D and 3-D finite-element analysis, and given as a field in the spec imen to get an insight into yielding-constraint regions. It was found that the 3-D yield-Ioad solutions are very close to the plane-strain solutions. Also, the effect of a/W on the yielding constraint is more significant than the effect of Mand (W-a)/H.
Keywords: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters
Published: 06.04.2017; Views: 935; Downloads: 79
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