Repository of the Institute for Material Testing (RIMS)
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Frost resistance of heavyweight self-compacting concrete
Get PDFSelf-compacting concrete (SCC), a non-shaped composite building material, has
improved microstructure packing, strength, and durability thanks to the use of fly ash, a
highly effective mineral additive. Performances of SCC with fly ash and conventional
SCC with limestone filler were compared. Additional experimental self-compacting
concretes were made and adjusted with various types of fine aggregates, fillers, and
unique additives to increase freeze-thaw resistance. The relationship between the
proportion of barite sand and additives and the properties of SCC was investigated and
discussed. Tests of freeze-thaw resistance with and without de-icing salts are the main
focus of these articles
The Influence of Parameters of Sand Soil on States PH 2D Frame on Seismic Response
Get PDFDuring earthquakes that exceed the designed level of the structure, the structure gets damaged. Here, the structure-foundation-soil is considered as a system, and the effect of the soil on the piles can be replaced by nonlinear p-y curves. Work on this topic began as early as 1957, based on the analogy between the triaxial test and the form of soil failure, and during the 1970’s, a number of researchers made significant progress in the development of appropriate models for different types of soil. Eurocode 8 pays special attention to the selection of earthquakes as a set of accelerograms. For areas within a radius of several hundred kilometers from central Romania and its southern part, the Vrancea hypocenter has a significant influence. In North Serbia and its surroundings, other sources of earthquakes are also possible, but when choosing accelerogram, the response spectra of several Vrancea records should also be used. The SSI model itself, where the soil is replaced by p-y curves, even though it might look complicated, it is significantly simpler and leads to faster results than integral 3D models. By using adequate soil parameters, fairly reliable data can be obtained on the degree and distribution of damage to the SSI system, like plastic hinges. In soil models used for clean sand, the curves used seem significantly more reliable than clayey ones, but here too caution is needed because the degree of compaction (relative density) has a significant effect, and the way of determining it is still not reliable
The design of cementitious composites with advanced thermal properties
No full textThe phyllosilicate mineral pyrophyllite can be utilized in cementitious composites design to replace quartz powder and boost workability, early strengths, and refractoriness. Employed as a mineral additive or microfiller, pyrophyllite is stable at high temperatures owing to its thermal conversion into mullite.
In this study, mortar samples were prepared using andalusite as aggregate, high-alumina cement as a binder, and pyrophyllite as an additive (15%, 25%, and 35%). Compressive and flexural strengths, both at normal and elevated temperatures (samples were thermally treated at 1000°C) were tested on the samples, along with the refractoriness. The effects of pyrophyllite addition on the mineral composition, microstructure, and bonding and sintering mechanisms were studied using instrumental analytical techniques. Pyrophyllite acted as additional pozzolana during cement hydration as it formed microreinforcement
in the shape of crystalline folia within the microstructure, which improved the
compressive strengths of mortars. The differential thermal analysis highlighted that pyrophyllite did not negatively interfere with the cement hydration route; moreover, this mineral additive behaved as pozzolana. The investigation demonstrated that pyrophyllite additions of up to 25% can be used in cementitious composites without affecting their performance
Mathematical modeling and experimental investigation of a composite beam failure - Case study
No full textComposite materials have been extensively employed in the aviation industry in recent years. The application of new materials enables significant weight savings with improved mechanical characteristics. This is also very important in the field of development of unmanned aerial vehicles (UAV). In the design phases, it is necessary to perceive all the aspects that are important for the structure and consider different load cases. The relationship between weight and strength proved to be important. This means that detailed strength analyses of each structural part are indispensable. In particular, primary load-bearing structures must sustain all types of loads without fail. Failure of the structure can affect the motion of the UAV during the mission or lead to a crash and significant losses. This paper presents the research performed on the failure analysis of a composite beam of a novel UAV. During the testing phase, under an unpredictable load condition followed by a crash landing, failure of the structure occurred on a beam element. The study was performed to determine the cause of the failure of certain layers of the composite laminate, because the previous calculation showed that it met the criteria for which it was dimensioned. Based on the telemetry data and the impact load that was registered, a complementary numerical and experimental analyses were performed to determine what happened and why. Composite test specimens were extracted from the beam and subjected to standard tensile tests, in order to determine the actual mechanical characteristics of the layered material. The paper presents in detail the comparison of the results as well as the methodology used in this research
Reliability of main fan coal mining plants
No full textIn this paper, a mathematical model for determining the reliability of ventilation plants was given and said ventilation plant was checked using a specific example for two types of fans operating in different modes due to the difference in the age of the fans. Within the framework of the paper, the principles of arrangement of ventilation systems of mines are stated, after which the mathematical model for determining the probability of reliability of ventilation systems is presented. For checking and proving the given mathematical model, coal mines in Serbia have been selected. The experimental part presents the basic characteristics of the main fan plants of active underground coal mines in Serbia, and based on the given mathematical model and collected data on downtime in the operation of the main fan plants at coal mines, the reliability of their operation is calculated. The paper confirms that the proposed method of determining the mathematical probability of reliability of ventilation systems can be used as an initial indicator of ventilation systems, where regular plant maintenance and application of this mathematical model could predict and prevent the operation of ventilation systems, and thus extend their lifespan. By processing the data on the operation of ventilation plants, the appropriate empirical dependence of the reliability parameters was obtained with the corresponding dependence, which enables application in practice
Parameter programs for 3D modeling in the function of nondestructive testing and determination of the lifetime of pressure vessels
Get PDFPreparation for non-destructive testing (NDT), preparation of test reports, as well as control
calculation of a pressure vessel (PV) using the finite element method (FEM), with or without
identified irregularities, requires the use of commercial programs for parametric modeling,
which allow the rapid creation of three-dimensional (3D) model of the test object. 3D modeling
programs enable the determination of one or more rappers in order to orient the test object,
accurately define the established irregularity or error after NDT, as well as the most critical
part of the PV construction after FEM calculation with the possibility of optimization.
Programs for 3D modeling also enable modeling of determined irregularities after performed
tests that occurred during the construction, calculation, production or exploitation of the PV
construction itself. Irregularities are reflected in the form of improperly performed welded
joints, cracks, corrosion, erosion or cavitation of materials, and are used for the preparation of
test reports and control calculations of the PV structure with and/or without established
irregularities and errors, with the aim of making the correct decision on the continuation of
exploitation construction of PV or about its degree of rehabilitatio
Influence of recycled rubber on properties of concrete
Get PDFGlobal warming and the emission of CO2 into the atmosphere is becoming a bigger
problem in the world every year. The desire for a global increase in production and the
ever-increasing development of industry are the cause of the increased amount of waste
in landfills and environmental pollution. Concrete is the most used construction material
in the world, and the production of its main ingredient, cement, is responsible for about
7% of CO2 emissions in the world. Application of waste materials and by-products that
end up as waste during some industrial process in production can find further
application in concrete. Such materials can be used as mineral additives or as aggregate
fillers, for partial or complete replacement of natural stone aggregate and/or cement. In
this work, volume replacement of the fine fraction with 2.5 and 7.5 % crushed rubber
was performed. Based on the test results of fresh concrete, in concrete with rubber
addition, the slump consistency and bulk density decrease, and the air content
increases. A drop in compressive strength of concrete was observed with an increase in
the rubber content of 7.5%
How bad volcano-clastic badlands actually are?
No full textEight sediments samples, four from Đavolja varoš and four from Kazár badland have been compared from the perspective of mineralogical composition, petrographic characterization, particle size distribution, pH, electrical conductivity (EC), and the sodium adsorption ratio (SAR)
Fatigue crack growth rate of a low carbon microalloyed steel for high temperatures
No full textThe influence of temperature on the fatigue crack growth parameter, was analyzed by testing chromium-molybdenum steel of the new generation additionally alloyed with vanadium, designed for high temperatures application. The paper presents a comparison of the fatigue threshold value ΔKth and the fatigue crack growth rate da/dN of the specimens taken from the pipe made of virgin steel, tested at room (RT) and operating (HT) temperatures of 540 °C. The influence of the location of the notch and crack initiation, as well as the test temperature, have a decisive effect on the fatigue threshold values ΔKth of the chromium-molybdenum alloyed steel of the new generation additionally alloyed with vanadium for high temperatures application
Razvoj modela upravljanja kvalitetom ispitivanja šipova
Get PDFU radu je ukazano na postojeće probleme koji se pojavljuju prilikom planiranja, u toku i
nakon ispitivanja šipova. U tom smislu, na osnovu iskustava autora rada, predloženi su modeli
upravljanja kvalitetom ispitivanja šipova kojima se efikasnije planiraju i rešavaju sve aktivnosti
ispitivanja šipova i utiče na donošenje odluka koje se u praksi neadekvatno rešavaju. Posebno je
naglašeno uvođenje i primena Elaborata ispitivanja šipova kao nova forma dokumenta u kojem bi
se celokupna aktivnost planiranja, ispitivanja i donošenja odluka nakon ispitivnaja adekvatno
ispratili