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Data-driven prediction of fracture toughness size effect in ductile-to-brittle transition using Two-Step-Scaling procedure
No full textThe fracture properties of ferritic steels in transition temperature region are usually statistically treated by models that presuppose the existence of various forms of quenched disorder (critical cleavage triggers). In this study, the fracture toughness from the Euro fracture toughness dataset (stress intensity factor used in the master curve KJc) for reactor steel 22NiMoCr37 is used with the aim of outlining a methodology for using the recently proposed two-step scaling (2SS) method. Three widely different temperatures (−154 °C, −91 °C, and 0 °C), which cover the entire range from lower shelf to upper shelf fracture, are selected to demonstrate the accuracy of extrapolation and interpolation of the fracture toughness CDF (cumulative distribution function) and the pertinent issues related to the procedure application. The obtained predictions at the two lower temperatures are in good agreement with the experimental results and well within the inherent experimental data scatter, while 2SS method is shown not to be applicable in upper-shelf transition region. Special attention is devoted to the effect of statistical sample size on prediction accuracy/reliability along with the minimum sample size requirement. Moreover, the reduction in random sample size affects the Weibull parameters, which in turn impacts the accuracy of predictions, introducing a degree of uncertainty and highlighting limitations in the method
Ревитализација аутоклава намењеног за сушење сировог угља (лигнита)
No full textТехничко решење је применљиво (пре свега) у циљу санације опреме под притиском, конкретно аутоклава. Такође, техничко решење се може користити за репаратуру заваривањем/наваривањем оштећених делова опреме под притиском и сличних делова који су изложени сличним условима у току експлоатације. Репаратура посуде под притиском је поред свих техничких предности које су остварене, утицала и на остваривање велике економске добити, будући да је целокупна ревитализација изведена у погонима фирме наручиоца и са постојећим капацитетима. Такође, ово техничко решење се може применити у циљу елимисања оштећења, односно поправки и делова других грана индустрије који су изложени сличним радним условима у току експлоатације
Doping Mn Induced Modification on the Crystal Structure, Morphology and Optical Properties of Mechanically Activated SrTiO3 Powders
No full textMechanically activated strontium titanate (SrTiO3) powders with various manganese dioxide (MnO2) doping levels (1.5, 3 and 6 wt%) were prepared by solid state method. Due to the possibility of manganese ion incorporation in SrTiO3 at Ti4+ and/or Sr2+ sites a detailed analysis of the influence of dopants on the microstructure, morphology and optical properties of perovskite oxide was conducted. The investigation showed that manganese was incorporated into the lattice and surface layers of SrTiO3 particles with the presence of manganese segregation and inhomogeneities. Optical measurements indicated a shift of the absorption edge to higher values of wavelengths where the lowest value of the band gap (3.10 eV) was for the longest activation time (120 min) and the highest weight percentage of dopant (6 wt%). In the case of lower concentration (1.5 wt%), there was a significant relative contribution of the substitution of Sr2+ ions by Mn2+ ions, while the substitution of Ti4+ ions by Mn4+ ions dominated samples with an increased concentration
PROGRAMMING AND VERIFICATION OF THE MACHINING PROGRAM FOR A TEST WORKPIECE FOR A MACHINE WITH A HORIZONTAL ROTARY AXIS
No full textThis paper presents the testing of the working accuracy of a 3-axis CNC mill. The machine has two
translational axes and a horizontal rotary axis, with the structure A'OXZ. For this machine, a postprocessor was
developed utilizing the kinematic equations. In this study, a specialized test piece was designed and machined to verify
the accuracy and reliability of both the postprocessor and the machine. The test piece was designed with specific
geometric features intended to evaluate the performance of the machining system and the postprocessing program
under various operational scenarios. PTC Creo Parametric software was used for part design and toolpath generation
processes. The generated toolpath was tested in a virtual machining environment on a virtual machine using Vericut
software. The final test piece will be machined on the machine, ensuring an evaluation of the machining system's
performance
Influence of build orientation and different printing angles on impact toughness of carbon-reinforced PET-G FDM material
No full textCarbon-reinforced polyethylene terephthalate glycol (PET-G) material is used in additive manufacturing (AM) for the production of moderately loaded polyester-based parts. Scientific papers show that the mechanical properties of additively manufactured specimens are substantially influenced by their build orientation and printing direction angle. This paper explores the additional influence of short carbon fibers on the impact toughness of composite specimens. In this study, low-energy instrumented Charpy test was used as an experimental method for evaluating the impact behavior of material. Experimental evaluation of impact toughness in the case of AM composite specimens fabricated with different build orientations and printing angles was performed. The impact tests were carried out on 5 specimens per batch (a total of 30 specimens). The obtained results from an instrumented pendulum were compared between different specimen groups to have an insight into the influence of build orientation and printing angle on short carbon fiber reinforced PET-G material. It was confirmed that different build orientations and printing direction angles (0° and 90°) strongly influence the final mechanical properties of this material
Aspekti korišćenja biomase u cilju povećanja energetske efikasnosti i smanjenja emisije CO2
No full textБиомаса представља један од најзначајнијих обновљивих извора
енергије, пре свега због велике заступљености и разноврсности, као и значајног
енергетског садржаја. Осим шумске биомасе, велики део укупног потенцијала биомасе у Србији потиче од пољопривредне биомасе. Oд укупне количине
расположивог техничког потенцијала пољопривредне биомасе мали део се користи у енергетске сврхе. У индустрији прераде воћа и поврћа остају значајне
количине органског отпада, као што је воћни троп, који може представљати алтернативну сировину за добијање енергије, уз смањење емисијe гасова са ефектом стаклене баште. У овом раду извршено је истраживање оцене угљеничног
отиска животног циклуса на примеру органског отпада преосталог након процеса цеђења сока од јабуке (тзв. тропа), јер је јабука најкоришћеније воће за производњу сокова у Србији. Анализирани су енергетски, еколошки и економски
аспекти коришћења тропа јабуке као алтернативног енергента. Постоји значајан
потенцијал коришћења воћног тропа као еколошки прихватљивог горива за добијање топлотне енергије. Урађена је процена директног коришћења осушеног
тропа јабуке за повећање енергетске ефикасности реалног постројења за прераду воћа, као и индиректног коришћења за загревање пластеника. Коришћењем
тропа јабуке може се значајно смањити емисија еквивалентног CO2
(CO2
eq) у
односу на фосилна горива, као и трошкови снабдевања енергијом, с обзиром да
воћни троп представља нуспродукт процеса прераде воћа.Biomass represents one of the most important renewable energy sources
in Serbia, primarily due to its abundance and diversity and its high energy content. In addition to forest biomass, a very significant part of the total biomass
potential in Serbia comes from agricultural biomass. Currently, only a small part
of the available biomass potential is utilized as a renewable energy source. Large
amounts of organic waste are available from the fruit processing industry, such
as fruit pomace, which represents a promising raw material for obtaining energy while reducing greenhouse gas emissions. In this paper, the research was carried
out on the evaluation of the carbon footprint of the apple pomace life cycle since
the apple represents the most used raw material for juice production in Serbia.
The technical, energetic, ecological, and economic aspects of using apple pomace
as an alternative energy source were analyzed. The use of dried pomace was evaluated for improving energy efficiency of the existing industrial facility for fruit
processing and heating greenhouses. Using apple pomace can significantly affect
the reduction of CO2
(CO2eq) emission, compared to fossil fuels, as well as the reduction of energy costs, considering that the fruit pomace is a by-product in the
food processing industry
Averaged Nystr\" om interpolants for the solution of Fredholm integral equations of the second kind
No full textLongtime evolution and stationary response of a stochastic tumor-immune system with resting T cells
No full textIn this paper, we take the resting T cells into account and interpret the progression and
regression of tumors by a predator-prey like tumor-immune system. First, we construct an appropriate
Lyapunov function to prove the existence and uniqueness of the global positive solution to the system.
Then, by utilizing the stochastic comparison theorem, we prove the moment boundedness of tumor
cells and two types of T cells. Furthermore, we analyze the impact of stochastic perturbations on the
extinction and persistence of tumor cells and obtain the stationary probability density of the tumor cells
in the persistent state. The results indicate that when the noise intensity of tumor perturbation is low,
tumor cells remain in a persistent state. As this intensity gradually increases, the population of tumors
moves towards a lower level, and the stochastic bifurcation phenomena occurs. When it reaches a
certain threshold, instead the number of tumor cells eventually enter into an extinct state, and further
increasing of the noise intensity will accelerate this process
The Influence of Temperature Gradient on Thin Plates Bending
Get PDFWithin the theory of thermo-elasticity, the temperature field of thin plates
is commonly defined via two parameters: temperature in the mid-plane and
linear temperature gradient normal to the mid-plane. First, the paper
analytically proves the justification of that assumption in machine
structures. Then, in an analytical closed form, applying the integral
transformation method, the thin plate deflection caused by a constant
temperature gradient is defined. It is shown that, in that case, the plate
deflection does not depend on its thickness but only on the plate
dimensions in the mid-plane. Analytically defined values are compared to
corresponding values obtained by applying the thin plate finite element,
where the temperature field is described using the two mentioned
parameters. This finite element is defined and programmed within the
Komips program package. The influence of the temperature gradient on
the behavior of constructions mostly depends on the type of material. That
is why the behavior of some structural elements made of brass, steel, and
concrete is analyzed in this paper
Dimensional Accuracy of Compressive Specimens Obtained by SLS Technology
No full textThe objective of this study is to examine the accuracy of dimensional measurements for parts produced using Additive Manufacturing (AM) technology. The specific 3D printer employed in this research is Fuse 1 (FormLabs, Summerville, MA). The printer operates on the Selective Laser Sintering (SLS) method, enabling the simultaneous creation of objects with diverse shapes and sizes, as long as they are printed at a minimum separation distance of 5 mm. The printing process involved a layer thickness of 110 microns. To assess the dimensional accuracy, a particular type of specimen adhering to the ISO 604 standard for compressive specimens was analyzed. These compressive specimens possess dimensions of Ø10 × 20 mm. Four sets of specimens were fabricated, differing in their printing orientation (horizontal or vertical) and printing location (edge or middle of the powder bed). Polyamide (PA 12) was the chosen material for printing the specimens, known to exhibit compressive strength values of 13/24/55 MPa at 1%/2%/5% strain, respectively. After printing, the specimens were subjected to a 3D scanner Atos Core 200. The most significant deviations observed across all four series of specimens were primarily in terms of height, ranging from 0.1 to 0.15 mm. In the case of vertically printed specimens positioned in the middle of the powder bed, variations in the width of the specimens were also noted