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The influence of stainless steel particles reinforcement on the fracture toughness of glass-ceramic matrix composite
Get PDFThe fracture of engineering materials is always an undesirable phenomenon, which primarily can endanger human lives, create economic losses, and lead to downtime and unavailability of mechanical parts. The main drawback that still prevents the broader use of ceramic and glass-ceramic materials is the tendency to brittle fracture due to extremely low toughness. Due to the appearance of cracks, the mechanical properties and structure of the material degrade irreversibly, which can lead to catastrophic failure of the mechanical element or construction. This drawback can be overcome by synthesizing novel composite materials with glass-ceramic matrix and metal reinforcement with improved fracture toughness.
This research examined two materials: a glass-ceramic material and a composite material based on glass-ceramic-metal. The glass-ceramic material is obtained from andesite basalt powder, while the glass ceramic-metal composite is made from the glass-ceramic matrix of andesite basalt powder and a metal reinforcement of stainless steel powder in the content of 20 wt%. The aggregate of andesite basalt from Serbia was used as the starting natural raw material for obtaining the glass-ceramic matrix. The austenitic stainless steel powder of the commercial grade Surfit TM 316L was used as a reinforcement. Both materials were obtained using powder metallurgy, which consisted of the following phases: crushing of andesite basalt aggregate, sieving of the stainless steel powder, homogenization of powder and binder, cold uniaxial pressing of the powder, cold isostatic pressing of green compact and sintering as the final phase to obtain a high-density solid sample.
The andesite basalt, and 316L stainless steel powder were characterized using a scanning electron microscope and X-ray diffraction method. The sintered samples of glass-ceramic and glass-ceramic-metal were characterized with an optical light microscope, scanning electron microscope, and Vickers hardness test.
Based on the obtained results, it can bu concluded that the presence of metallic particles in the glass-ceramic matrix leads to a slight decrease in hardness while contributing to an increase in the materials fracture toughness by about 33% [1]. During crack propagation in the glass-ceramic matrix, different crack particle interactions were observed: crack stops, deflects, or bridgings when encountering the spherical metal particle. These interaction phenomena and mechanisms of crack propagation in the glass-ceramic-metal composite lead to an increase of crack propagation resistance
Calculation of wheel path for 3+2-axis grinding of brazed carbide profilemill cutters for wood and plastic
No full textBrazed carbide profile mill cutters are widely used in the machining of wood, wood materials, and plastic to form various functional and aesthetic surfaces. Tools of this kind are used in serial and mass production and they are built today using very costly 5-axis grinding machines supported by specialized CAM software that is very expensive too. The paper first developed the possible concept of 5-axis grinding of brazed profile mill cutters using universal diamond grinding wheel shapes. The developed concept of 5-axis grinding served as a basis for the developed approach for 3+2-axis grinding of the brazed formmill cutters which is the essence of this paper. Verification of this set approach of 3+2-axis grinding is performed on a developed functional prototype of a simple 3+2-axis grinder (Axes XYZ are CNC controlled, axes B and C are unpowered axes and have fixed positions during grinding). Based on the established 3+2 grinding strategy complete grinding of a complex profile has been performed on a developed functional prototype. Shape and measures of the cutting edge profile achieved by grinding are inspected on an optical measuring system and showed exceptional results. The established 3+2-axis method of grinding
is an economically successful alternative to costly 5-axis grinding machines, as well as to specialized software, presented in the paper through experimental and practical application
Residual life assessment of the historical road riveted bridges
No full textNumerous roads and railways network steel bridges exist with more than 100 years in service, often of great historical value. The in-service safety assessment of these structures is a complex problem which requires interdisciplinary approaches – from civil engineering application of Eurocodes or European recommendation for fatigue life estimation, up to an in-depth assessment by means of fracture mechanics. This article emphasizes the importance of rehabilitating the structure of existing steel bridges, considering the historical monument character of these structures, as well as the reuse of existing structures. Toward this aim, the study case for a historical riveted steel bridge build in the beginning of the twentieth century is presented, with an assessment method considering the structural integrity by means of fracture mechanics. Based on this case study, the paper is proposing an algorithm to assess historical steel bridges. The results of in-depth XFEM analysis with different crack size in the area of a riveted joint are also presented, in order to validate the algorithm
Multifunkcionalna i rekonfigurabilna mašina alatka za brzu izradu prototipova glodanjem, laserskom obradom i dodavanjem materijala u polarno cilindričnim koordinatama
Get PDFPronalazak se odnosi na multifunkcionalnu i rekonfigurabilnu mašinu alatku za brzu izradu prototipova koja predstavlja novi koncept 3-osne CNC mašine sa horizontalnom obrtnom osom, koja radi u polarno-cilindričnim koordinatama i omogućava jedinstvenu integraciju tri proizvodne tehnologije na jednoj mašini: glodanje, lasersku obradu i dodavanje materijala (3D štampanje). Mašina svoju rekonfigurabilnost ostvaruje zamenom završnih uređaja koji mogu biti glava za glodanje, laserska glava ili glava za 3D štampu, uz razvijeni rekonfigurabilni upravljački softver koji podržava sve tri tehnologije. Mašina se sastoji od nepokretne noseće strukture (1), na kojoj se nalaze horizontalne vođice (10) po kojima je klizno pomerljiv klizač (9) ose X na kome se nalaze vođice (12) po kojima je klizno pomerljiv klizač (11) ose Z, na koji se postavlja ili glavno vreteno (13A) ili laserska glava (13B) ili glava za 3D štampu (13C) kao završni uređaj. Noseća struktura (1) sadrži se i obrtnu osu A’ koju čine pogonski motor (3) koji pomoću kaišnog para (19) prenosi obrtni moment na obrtno vreteno (2), uležišteno nosačima (20) ležaja, sa steznom glavom (21) gde se postavlja obradak. Na nosećoj strukturi (1) se nalaze i vođice (15) po kojima je klizno pomerljiv nosač (14) zadnjeg šiljka koji se koristi kao dodatni oslonac pri stezanju dužih obradaka u cilju povećanja krutosti.Spis malog patenta 1805 U1
Link
http://pub.zis.gov.rs/rs-pubserver/document?PN=RS1805%20RS%201805&iDocId=104428&iPosition=0&iFormat=
Контекстуални адаптивни систем за митигацију ризика рада рударских машина
No full textТехничко решење решава проблем менаџмента ризиком рударских машина и омогућава одабир адекватне стратегије одржавања. Техничко решење представља искорак у односу на све постојеће концепције управљања ризиком и одржавања рударских машина, јер је засновано на моделу међузависности контекстуалних фактора описаном структурним једначинама (SEM). Примена техничког решења омогућава решавање следећих проблема тј. унапређења која директно омогућавају:
• Подизање нивоа безбедности и здравља на раду, и
• Подизање нивоа продуктивности,
а последично доводе до:
• Унапређења индустријске безбедности, и
• Смањења трошкова одржавања.
Предложена иновација може има утицај на развој свих индустријских грана у којима раде
рударске машине, и омогућава правовремено мапирање ризика без географског ограничења
примене
EXCAVATOR DOWNTIME’S DIFFERENCES BETWEEN TYPES AND COMPARISON WITH OTHER MINING EQUIPMENT
Get PDFMining equipment working time is critical for ensuring output and fulfilling mining project deadlines. In order to find trends and possible downtime minimization measures, this article analyses numerous types of excavators, dump trucks, loaders, backhoe loaders, bucket wheel excavators, and surface-top hammer drill rigs in Serbian mining sites. The study collects data on mechanical, electrical, technological, organizational, abuse and meteorological downtimes types with the aim to highlight efficient ways for minimizing non-operational periods, hence improving the overall productivity and safety of mining operations in the industry. Special emphasis is put on excavators whose role in the mining industry is pivotal, directly impacting project timelines and financial outcomes. The methodology includes analysing the duration and implications of different downtime categories. Collected data showed non-parametric features, according to the descriptive statistics. To compare the data, the non-parametric Mann-Whitney U-test is implemented. The results of the research showed that, in most cases, there is a difference in the duration of downtimes between different categories of excavators` downtimes. However, a comparison between excavator downtimes and other machinery downtimes has not shown any statistically significant differences. This analysis aims to contribute to the optimisation of mining equipment usage, offering valuable insights for mining industry stakeholders
COMPARING THE DURATION OF DIFFERENT TYPES OF EXCAVATOR DOWNTIME
No full textIn the mining industry, excavator uptime is crucial for maintaining productivity and meeting project deadlines.
Downtime, or periods when excavators are not operational, can significantly impact project costs and efficiency.
This paper examines various types of excavator downtime, including mechanical, electrical, technological,
organisational, and meteorological, to identify patterns and potential mitigating strategies. By comparing the
duration and implications of different downtime categories, this study seeks to highlight effective strategies for
minimising non-operational periods, thereby enhancing the overall productivity and safety of excavator
operations in the industry. The descriptive statistics indicated that the data exhibited non-parametric
characteristics. The non-parametric Mann-Whitney U-test was used to compare the data. The results of the
research showed that, in most cases, there is a difference in the duration of downtimes between different
categories of downtimes. This analysis aims to contribute to the optimisation of excavator use, offering valuable
insights for industry stakeholders
Simulation of a three-axis mechanism with parallel kinematics based on Chebyshev’s linkage
No full textU okviru ovog rada će biti prikazan konceptualni dizajn mehanizma sa paralelnom kinematikom koji poseduje tri stepena slobode kretanja. Novina u konstrukciji razmatranog mehanizma je primena Čebiševljevog mehanizma kao pasivnog translatorno-obrtnog zgloba. Razmatrani mehanizam kao predstavnik mehanizama sa paralelnom kinematikom je sačinjen od velikog broja spojki međusobno povezanih pasivnim zglobovima, te kao takav predstavlja kompleksnu konstrukciju sa velikim brojem posledičnih kretanja unutar konstrukcije. Kako bi se došlo do zaključaka po pitanju mobilnosti konstrukcije, nameće se potreba za simulacijom razmatranog mehanizma u nekom virtuelnom okruženju. U okviru ovog rada biće prikazana simulacija
razmatranog mehanizma u softverskom paketu PTC Creo Parametric.This paper presents the conceptual design of a mechanism with parallel kinematic capable to achieve three degrees of freedom. A novel feature of the proposed mechanism is the application of the Chebyshev's linkage as a passive translational-rotary joint. As a representative of parallel kinematic mechanisms, the proposed design consists of numerous linkages connected with passive joints, resulting in a complex structure with a high number of dependent motions within the system. To gain insights into the mobility and overall performance of the mechanism, a simulation of the design in a virtual environment is required. This paper includes a simulation of the mechanism using the PTC Creo Parametric software package.Za izdavača: Dekan, dr Vladimir Popović, red. prof.
Tehnički urednici:
Prof. dr Saša Živanović, Doc. dr Miloš Pjević , Doc. dr Dušan Nedeljković, Lazar Matijašević, mast. inž. maš.
Štampa: Planeta prin
Dynamic Behavior Analysis of the Stacker Superstructure as the Basis for Determination of Favorable Belt Velocities of the Discharge Conveyor
No full textA novel research on the impact of a key technical parameter – the velocity
of the belt of the discharge conveyor, which directly dictates the
theoretical capacity of the designed machine, on the dynamic response of
the superstructure, was conducted on a stacker machine in the design
stage. The analysis of the dynamic response to the excitation load, caused
by the eccentricity of the discharge pulley, was performed using a spatial
reduced dynamic model which allows for the variation of the geometric
configuration of the superstructure, i.e. continuous variation of the
inclination angle of the discharge boom. The velocity of the belt was varied
over the domain defined by values commonly used on this type of
machines, for the purpose of identifying unfavorable belt velocities, i.e.
values that would lead to the appearance of negative dynamic effects.
Results of the modal analysis, on their own, have discarded a total of
37.1% of the spectrum of considered belt velocities, due to the possibility
of appearance of a resonance for some operational configurations of the
superstructure. In similar fashion, results of analysis of the dynamic
response have eliminated 46.6% of the initial spectrum of belt velocities.
Finally, taking into account the inevitable slippage of the belt conveyor on
the drive pulley in the operating conditions, which can reduce the nominal
belt velocity by up to 5%, only 29.3% of the initially-considered spectrum
of belt velocities will not result in the appearance of negative dynamic
effects
The use of metadiscourse markers in achieving persuasion in short advertisements written by ESP students
No full textThe paper focuses on the metadiscourse markers used with the aim of
persuasion in ESP student writing. The corpus consisted of 66 short advertisements
(8,611 tokens) written by the first-year students of the Faculty of Mechanical
Engineering, University of Belgrade as part of their ESP course. Based on Hyland’s
model of metadiscourse, we analyse the frequency of use and different types of
metadiscourse markers in students’ advertisements. The aim is to explore whether ESP
students use MD markers to persuade the audience to try out a new welding technique.
The most frequently used markers overall were engagement markers, followed by
attitude markers, whereas the least frequent were frame markers and code glosses.
Interactional metadiscourse categories are used much more than the interactive ones,
both in the body of the advertisement and the slogans. Based on the obtained findings
on the use of MD markers in student-written advertisements, it can be concluded that
some students successfully kept up with the trends found in similar research of
advertisements written by experienced copywriters.U radu se bavimo metadiskursnim markerima koji se koriste sa ciljem ubeđivanja u esejima
studenata koji uče engleski jezik struke. Korpus na kome je izvršena analiza obuhvatio je 66 kratkih
reklamnih oglasa (8611 reči) koje su pisali studenti prve godine Mašinskog fakulteta Univerziteta u
Beogradu u okviru kursa engleskog jezika. Koristeći Hajlandov model metadiskursa, analizirali
smo učestalost upotrebe i različite tipove metadiskursnih markera u ovim reklamnim oglasima. Cilj
je bio da se istraži da li studenti koriste metadiskursne markere da ubede publiku da isproba novu
tehniku zavarivanja. Generalno gledano, najčešće korišćeni markeri bili su markeri angažovanja, a
za njima markeri stava, dok su najređi bili okvirni markeri i objašnjivači. Interakcioni metadiskurs
se koristi mnogo više od interaktivnog, kako u glavnom delu oglasa, tako i u sloganima. Na osnovu
dobijenih nalaza o upotrebi metadiskursnih markera u reklamnim oglasima koje su pisali studenti
koji uče engleski jezik struke, može se zaključiti da su neki studenti uspešno ispratili „trendove“
uočene u sličnim istraživanjima reklamnih oglasa koje su pisali iskusni pisci reklamnih tekstova