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Assessment of the Drone Arm’s Plastic–Metal Joint Mechanical Resistance Following Natural and Artificial Aging of the 3D-Printed Plastic Component
No full textAs drone technologies advance, there is an increasing need for structural components
that are lightweight, durable, and easily replaceable. Additive manufacturing (AM)
with PLA offers a cost-effective solution to improve mechanical performance, especially
when enhanced with embedded metal inserts. However, the long-term durability of PLA–
metal joints under environmental aging conditions remains underexplored. This study
evaluates the mechanical integrity of 3D-printed PLA drone arms produced with reduced
infill density with embedded brass inserts. To replicate realistic service conditions, the samples
underwent natural aging and five artificial aging protocols involving thermal cycling,
humidity, UV/IR exposure, and freeze–thaw cycles. Mechanical performance was assessed
through pull-out and tensile strength testing, supported by FTIR spectroscopy, colorimetric,
wettability analysis, and finite element modeling. Notably, to our knowledge, wettability
analysis has not previously been applied to this type of material, and metal–plastic contact
zones have not been tested under such comprehensive aging protocols. Results showed
a 70% reduction in pull-out strength under harsh conditions, though the joints remained
functional. Numerical modeling confirmed that stress concentration begins on the inner
side of the arm. With optimal print settings, the arm can support a 2.31 kg payload (20%
confidence), while the metal inserts withstand up to 17.9 kg
From raw clay to ceramics: Evaluating the suitability of raw materials through compositional analysis
No full textRaw clay has been an essential material for thousands of years, valued for its distinctive
properties and versatility, particularly in ceramic production. Thus, this study seeks to systematically
classify raw clays based on their suitability for manufacturing ceramic building
materials. Key indicators such as 0.063 mm sieve residue and chemical composition were
evaluated to enable a preliminary and rapid assessment. The 50 raw clays from Serbia were
grouped using Principal Components Analysis (PCA) according to compositional similarities,
and these classifications were subsequently compared against industrial samples. Further
analysis through mineralogical composition and behavior during heating within these
groups provided a comprehensive understanding of their physical behavior. The results
demonstrate that PCA effectively distinguishes raw clays based on their chemical composition,
paving the way for a reliable classification for ceramic production. This system enables
manufacturers to optimize materials for diverse applications, including common bricks and
blocks, roof tiles and clay ceilings, ceramic tiles, and refractory products. Key findings reveal
that raw clays containing 15-20% Ah03, 3-9% Fe20 3, and at least 2% fluxing oxides are wellsuited
for heavy clay products. For ceramic tile production, optimal clay batches should
contain no more than 1.5% Fe203, 1.0% Ti02, and less than 0.2% organic carbon. Meanwhile,
refractory clays must exhibit a minimum of 15-20% and up to over 42% Ah03, with constraints
on Si02 (below 76%), Fe203 (3.7%), Na20 and K20 (3.7%), and CaO (1.0%) after firing.
Through this classification framework, manufacturers can more effectively select and refine
raw clays to meet the stringent demands of ceramic production, ensuring both efficiency
and performance in industrial application
Rezidualna čvrstoća smicanja neproduktivnih sredina sa PK Drmno
No full textOva doktorska disertacija istražuje rezidualnu čvrstoću smicanja neproduktivnih (jalovinskih) sredina sa površinskog kopa Drmno, sa ciljem poboljšanja razumevanja stabilnosti kosina u površinskim kopovima. Ispitivanja su fokusirana na definisanje rezidualnih parametara čvrstoće smicanja (kohezija i ugao unutrašnjeg trenja) različitih tipova tla (pesak, alevrit, siva glina i peskovita prašina) korišćenjem dva tipa aparata: aparata za direktno smicanje i aparata za kružno smicanje.
Eksperimentalni deo disertacije obuhvata rezultate laboratorijskih ispitivanja fizičkih i mehaničkih svojstava tla, korišćenjem Bromhead-ovog aparata za kružno smicanje i aparata za direktno smicanje sa konstantnom brzinom deformacije. Ispitivanja su izvršena pri konstantnoj brzini smicanja od 0,02 mm/min i sa različitim vertikalnim opterećenjem (50, 100, 200 i 400 kPa). Poređenje rezultata dobijenih iz ova dva aparata, pokazuje jasne razlike u vrednostima rezidualnih parametara, naročito kod glinovitih tipova tla. Na primer, kod sive gline, rezidualni ugao unutrašnjeg trenja određen aparatom za kružno smicanje bio je u proseku 1,7 - 2,3° niži nego kod direktnog smicanja, što ukazuje na veću pouzdanost aparata za kružno smicanje u definisanju rezidualne čvrstoće u ovakvim uslovima. Slično, kod alevrita su razlike bile manje izražene (1,2 - 1,9°). Za peskovite prašine razlika je bila od 1,6 - 2,6° između rezultata dobijenih ova dva aparata. Ovakve razlike ukazuju na uticaj veličine horizontalne deformacije uzorka na dobijene vrednosti rezidualnih parametara i naglašavaju značaj izbora odgovarajuće metode ispitivanja u zavisnosti od tipa tla.
U disertaciji su sprovedene detaljne korelacione analize između rezidualnih uglova unutrašnjeg trenja i sadržaja glinovitih (R² = 0,758-0,898) i peskovitih (R² = 0,979 - 0,993) frakcija, zatim indeksa plastičnosti (R² = 0,767- 0,921), granica tečenja (R² = 0,816 - 0,823) i kombinovanog indeksa CALIP (R² = 0,798-933). Rezultati pokazuju postojanje jakih (R² > 0,7) korelacija između ovih parametara, što omogućava pouzdanu procenu rezidualne čvrstoće tla na osnovu indetifikaciono klasifikacionih ispitivanja i indeksnih vrednosti.
Verifikacija dobijenih rezultata je izvedena poređenjem sa podacima iz literature i analizom stabilnosti kosina na površinskom kopu Drmno koristeći Bišopovu metodu granične ravnoteže. Rezultati analize ukazuju na zadovoljavajuću saglasnost između faktora sigurnosti dobijenih korišćenjem rezidualnih parametara iz aparata za direktno i kružno smicanje. Rezultati ovog istraživanja doprinose boljem razumevanju ponašanja različitih tipova tla pri velikim deformacijama, pružajući smernice za precizniju procenu stabilnosti kosina u inženjerskoj geotehnici
Reconstruction of the enigmatic pre-Variscan paleogeographic configuration of the western peri-Moesian realm (Carpathian-Balkans, eastern Serbia): An insight into Devonian small-scale continental and paleo-oceanic units
No full textThe Carpathian-Balkans provide insight into how two distinct but limited-sized north Gondwanan ribbon-shaped paleocontinents interacted prior to the Variscan Devonian collisional onset: (i) the drifted “Carpathian-Balkan microcontinent” (Serbo-Macedonian/Supragetic/Getic(Kuˇcaj)) and (ii) the already amalgamated Avalonian Danubian-Moesian basement fragment with its Devonian suture elements. These two crustal fragments were separated by the intervening Rheic Ocean during the Devonian. Despite the investigated eastern Variscan collisional assembly being stacked near the overprinted promontory of the East European Craton, its sliced basement segments and their Devonian record are well exposed in eastern Serbia. The synthesis reveals that the sliced Carpathian-Balkan inliers play a crucial role in understanding the lithospheric-scale movement of smaller continental terranes from north Gondwana and their suturing modes related to the surrounding Paleozoic oceans. An analysis of geochemical, paleogeographic, and regional geological data reveals that continental and oceanic paleoenvironments existed prior to and during the Devonian period, merging with the already amalgamated Danubian block and the Moesian microplate. Nonetheless, despite the well-preserved Devonian record found in eastern Serbia, the Romanian South Carpathians, and western Bulgaria, only a limited number of reconstructions clarify the pre-Variscan tectono-paleogeographic setting. After a few rift-drift cycles connecting north Gondwana and southern Laurussia, the tectonic transport of Cadomian to Cenerian peripheral terranes from northern Gondwana begun with the post-Ordovician rifting off. The rifting led to the formation of narrow, elongated crustal segments. The outboard Lower Paleozoic ribbon-shaped paleocontinent, including its Carpathian-Balkan continental fragment, occupied a position between two principal Paleozoic oceans. On the southern flank of the exotic narrow Lower Paleozoic microcontinent, we demonstrate for the first time the presence of a continental extension of Devonian age, likely associated with the adjacent Paleotethyan Ocean. The synthesis further demonstrates that the volcano-sedimentary protoliths of Devonian-aged greenschist facies rocks, which traverse the continental Serbo-Macedonian/Supragetic/Getic Devonian microcontinent, serve as markers of Early Devonian (back-arc) rifting. On its opposite Eurasian flank towards Danubian/Moesia, following the accumulation of Silurian–Early Devonian deep-water sediments, the Kučaj(Getic) turbidites, along with the expanding Middle to Late Devonian oceanic crust (Danubian ophiolites), belonged to the Rheic Ocean. The geochemical modeling of Devonian ophiolites reveals that this Balkan-Carpathian ocean displays both mid-ocean ridge basaltic (Tisovita Iuti, Deli Jovan) and volcanic arc/ back-arc signatures (Zaglavak, Tcherni Vrah). The extracted petrographic and regional geological constraints confirm the short transport of eroded material from the eroded Serbo-Macedonian/Supragetic narrow elongated landmass into the Late Devonian (Carboniferous) Kuˇcaj(Getic) trench turbidites. Geochemical signatures outline the intraoceanic character of this frontal pre-Variscan subduction-driven active margin. The proposed new Devonian reconstruction updates the existing paleogeographic constraints on the opposite Avalonian block, revealing that the narrow Devonian ocean and its subduction beneath the Avalonian “micro-terranes” (Danubian/Moesia) produced an epicontinental basin with Devonian volcanism assigned to the Hanseatic-type rifting off processes
Clays in transition: Addressing resource challenges and sustainable innovations in the construction sector
No full textThis review examines the reintegration of lower-grade clays into industrial applications,
with a focus on ceramics, cementitious binders, and infrastructure materials as key sectors
for sustainable transformation. It compiles current research and experimental
insights to understand how such materials, often overlooked due to variable composition
or limited reactivity, can be adapted to meet sector-specific performance requirements.
In ceramic tile production, low-grade clays demonstrate varying degrees of
sintering efficiency and thermal shrinkage, compared to traditional kaolin, offering viable
paths for cost reduction. In cement applications, contrasts between kaolinite-based and
limestone calcinated clay (LC3) reveal trade-offs in strength development, shrinkage behavior,
durability, and CO2 emissions. The review critically examines technical constraints,
including mix variability, curing sensitivity, and activation thresholds, while emphasizing the need for regulatory adaptation and economic feasibility. In infrastructure applications,
lower-grade clays have demonstrated promising adaptability for use in road base stabilization,
where their plasticity and compaction behavior outweigh the demands for high purity.
Their mineralogical variability influences moisture sensitivity and load-bearing performance,
yet tailored mix designs and hybrid systems can mitigate these effects. The review underscores
that while durability and regulatory compliance remain key challenges, these clays
offer viable alternatives for low-carbon construction in regions with abundant local deposits.
Through a synthesis of empirical findings and methodological analysis, this work contributes
to the strategic valorization of underutilized clay sources and supports the advancement of
resource-efficient material design
Experimental and analytical study of lightweight foamed concrete reinforced with sugarcane bagasse fiber
No full textGrowing environmental concerns have intensified research into sustainable construction materials,
such as natural fiber-reinforced concrete. Among these, lightweight foamed concrete (LFC) stands
out for its reduced material consumption, improved thermal insulation, and lower environmental
footprint. The integration of natural fibers, such as sugarcane bagasse fiber (SBF), into LFC has the
potential to further enhance its performance. This study investigates the influence of varying SBF
weight fractions (0%, 1%, 2%, 3%, 4%, and 5%) on the physical, mechanical, and durability properties
of LFC with a target density of 1000 kg/m3. The primary objective was to determine the optimal SBF
content for achieving superior material characteristics. Experimental results revealed that the inclusion
of 4% SBF provided the best overall performance, improving compressive strength by 53%, increasing
ultrasonic pulse velocity (UPV) by 17%, and reducing drying shrinkage by 58% compared to the control
mix. Additionally, slump flow decreased progressively with higher fiber content, indicating enhanced
cohesion. Water absorption and porosity were significantly reduced with increasing SBF, with the 5%
mix showing up to a 19% decrease in water absorption. Thermal conductivity also declined slightly,
suggesting improved insulation properties. Microstructural analysis confirmed better fiber-matrix
bonding at the optimal fiber content, contributing to the observed improvements in performance. This
study offers valuable insights into the mechanical, thermal, and durability characteristics of LFC-SBF
composites, highlighting their potential as sustainable construction materials
Quality management and comparative analysis in wind turbine generator piles testing
No full textThe paper presents a methodology for quality management in pile testing and analyzes the results of pile tests for wind turbine foundations. Quality control was carried out in accordance with ISO/IEC 17025 for Static Load Tests (SLT) and Dynamic Load Tests (DLT), alongside the introduction of a new technical document – the Pile Testing Project, which defines, implements, and supervises the entire testing process. Tests were performed using both reaction and autonomous hydraulic loading systems. The study found that most DLT results fall within the mean value and standard deviation range, noting that DLTs were performed in foundation pits on service piles, whereas SLTs were conducted outside the pits on test piles
Design and Development of Sustainable Geopolymers Based on Fly Ash, Slag, and Diatomaceous Earth: A Chemometric Approach
No full textThe burning of coal in thermal power plants throughout Serbia produces significant amounts of industrial waste, primarily in the form of fly ash, boiler ash, and slag. Given their annual production, availability, and fine grain structure, it is necessary that sus-tainable strategies are developed for their reuse, instead of depositing them directly in landfills. In this research, the possibility of using fly ash, slag, and diatomaceous earth as raw materials for the synthesis of geopolymers at low temperatures was examined, in order to replace cement in construction materials, with the aim of reducing carbon dioxide emissions. Special emphasis was put on the effect of addition of organic macromole-cules—polyvinyl alcohol (PVA), chitosan, and starch—upon the structure and mechanical properties of the obtained materials. In addition, the behavior of the materials with regard to the leaching of heavy metals in different environmental conditions was examined. Chemometric methods of multivariate analysis were used to examine the correlations between the obtained physical–chemical parameters, while the dependence of me-chanical properties on the composition of the raw mixture was analyzed using the Mixture Design of Experiments method. The results obtained indicate that the examined waste materials have potential to be used as an environmentally friendly alternative to cement. The addition of PVA and chitosan had a positive effect on the mechanical properties of the geopolymers, with the highest strength achieved in formulations based solely on fly ash, containing 2.5% PVA, which reached 12.6 MPa. It was also shown that the addition of 30% diatomaceous earth increases the density and compressive strength of the material, while reducing the number of microcracks present in its structure, with a compressive strength of 13 MPa
Poboljšanje izolacije od vazdušnog zvuka masivnog zida od giter bloka dodavanjem lakih sistema sa gips-kartonskim pločama
No full textU Laboratoriji za akustiku i vibracije Instituta IMS u laboratorijskim uslovima sprovedena
su ispitivanja na masivnom zidu od giter bloka i istog zida dodavanjem lakih obloga od mineralne
vune i gips-kartonskih ploča sa jedne i sa obe strane masivnog zida. Ispitivanja su sprovedena u
serijama prilikom instalacije svake od obloga kako bi se pratile merodavne vrednosti izolacionih
moći u različitim fazama instalacije, a sve u cilju da se vidi koliko je poboljšanje zvučne izolacije
dodavanjem lakih obloga na masivni zid
Uticaj drobljene reciklirane gume na otpornost betona na dejstvo mraza
No full textU radu je analizirana mogućnost primene betona sa 2.5%, 5% i 7.5% zapreminske zamene sitnog agregata sa drobljenom recikliranom gumom (CRC – 2.5%, CRC – 5% i CRC – 7.5%), primenjenim vodocementnim odnosima W/C = 0.55, 0.50, 0.45 i 0.40 u odnosu na običan (referentni) beton (OPC) i beton sa hemijskim dodatkom aeranta (AER), sa aspekta primene u svežem betonu koji je praćen kroz vreme od 10, 30 i 60 minuta od momenta dodavanja vode u betonsku mešavinu i dobijenih fizičko-mehaničkih svojstava očvrslog betona. Dat je pregled i analiza aktuelnih istraživanja iz oblasti primene zrna drobljene reciklirane gume, različitih veličina, na osnovu čega je formirana baza podataka pomoću koje je definisan program sopstvenog eksperimentalnog istraživanja. Istraživanje uticaja zapreminske zamene sitnog agregata drobljenom recikliranom gumom je zasnovano na komparativnoj analizi 20 betonskih mešavina u kojima je variran zapreminski sadržaj drobljene gume u vrednostima od 2.5%, 5% i 7.5% kojim je zamenjen deo sitne frakcije agregata. Izvršena su ispitivanja svežeg i očvrslog betona. Kod svih betona praćeno je ponašanje sveže betonske mešavine kroz vreme (nakon 10, 30 i 60 minuta) od momenta dodavanja vode u betonsku mešavinu. Izvršena su ispitivanja svežeg betona: konzistencija metodom sleganja, sadržaj vazduha i zapreminska masa. Na očvrslom betonu izvršena su ispitivanja: zapreminska masa, čvrstoća pri pritisku, vodonepropustljivost, otpornost betona na dejstvo mraza, otpornost betona na dejstvo mraza uz prisustvo soli za odmrzavanje, karakterizacij vazdušnih pora u očvrslom betonu, dinamički modul elastičnosti nakon ciklusa zamrzavanja/odmrzavanja, koeficijent migracije hlorida, statički modul elastičnosti i skupljanje usled sušenja. Ukupan broj uzoraka koji je ispitan iznosi 650, a za njihovu izradu bilo je potrebno napraviti cca 2.5 m³ betona. Analizirani su betoni sa različitim procentom zapreminske zamene sitnog agregata drobljenom gumom (CRC), te sa različitim vodocementnim odnosima (W/C = 0.55, 0.50, 0.45 i 0.40). Na osnovu komparativne analize zaključeno je da zapreminska zamena sitnog agregata drobljenom gumom bitno utiče na svojstva betona u svežem i očvrslom stanju u odnosu na običan (referentni) beton. Pokazano je da se zamenom sitnog agregata drobljenom recikliranom gumom (CRC) u količini do 7.5% mogu dobiti konstrukcijski betoni, odnosno betoni sa zadovoljavajućim fizičkim i mehaničkim karakteristikama