Repository of the Institute for Material Testing (RIMS)
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Prototyping of a Wall-climbing Robot for the Inspection of Concrete Bridges
No full textThe inevitable process of reduction in the structural resistance of concrete bridges,
which keeps pace with the aging of the structure, can be slowed to certain extent by proper
asset management. If regular detailed inspections of bridges are carried out as part of asset
management, proactive rehabilitation can be planned in a timely manner. This type of inspection
requires efficient execution. In addition, the inspection often requires specialized equipment to
reach certain bridge areas, which can put the inspector at risk. Both challenges can be
overcome by developing a robotic system for inspection. This paper presents different
prototypes of a wall-climbing robot for concrete bridge inspection, developed by our research
group within the project ASAP. The paper also addresses the challenges of integrating these
devices into the wall-climbing robotic system
An analysis of impact testing of high strength low-alloy steels used in ship construction
Get PDFBrittle damages have been examined widely since welding became common practice when it comes to carrying out robust structures. Welded structure of the ship hull has to be continuous. Brittle damages that occur on hull structures have always been examined thoroughly. Cracks are most commonly initiated at locations where stress concentrators exist. These concentrators can originate due to flaws that occur during the design phase or due to mistakes that occur during the assembly of the structure. When it comes to failures and damages that occur at ship structures, it has been noticed that damages due to brittleness practically always happen at low temperatures. Impact test analysis is significant due to the fact that it replicates the ductile to brittle transition of steel in practically identical range of temperatures for all ship structures. Impact of ductile-brittle transition temperature is an important factor especially because there have been many ship failures and damages in history. In ship structures made of welded joints of high strength low-alloy (HSLA) steels with their segments (parent metal, weld metal and heat-affected- zone), the toughness test determines the tendency of steel to brittle fracture, respectively the tendency to increase brittleness during exploitation. Parameters obtained by testing the properties of plasticity are the fundamental for the composition of ship structures with the aim of realize strengths under tested load. The test results of high strength low-alloy steel toughness assessment at different test temperatures show that temperature significantly affects the impact toughness of steels and their alloys
Diabase from Drača open pit mine in central Serbia - Quality assessment for building stone purposes
Get PDFVast masses of basic rocks are present as tectonic blocks and slices along the Eastern deep fault of the Vardar zone of Serbia. They are predominantly comprised of gabbro, with smaller part made up of diabase, and occurrences of granite, aplite and pegmatite dykes. Basic rock masses are trending along the line Kragujevac (Ždraljica)-Velika Pčelica-Bogalinac ∼8 km west of Rekovac. A significantly smaller diabase massif is present along the same tectonic line, further toward SE, at Prevešt village by Kalenicka River, approximately 13 km south of Rekovac. Drača open pit mine is situated in this diabase massif. Geologic explorative works have confirmed the reserves of 1 846 695 t of stone mass for building purposes. For over a decade, Draca mine has been producing various types of building stone, mainly graded stone aggregate with favourable physico-mechanical properties for road-construction works. Chemical analyses and petrographic study have shown typical composition and fabric for this type of rock. Main constituents are plagioclase and pyroxene, with opaque minerals as accessory and varying secondary minerals - chlorite, calcite, in some places epidote and limonite. Pyrite enrichment is visible in some areas of the massif. Chlorite, calcite, epidote and pyrite are the products of propylitic alteration. Although products of alteration are present throughout the rock mass with variable intensity, as is typical for the basic rocks of the former ocean floor sequences, petrologic properties are favourable for building stone purposes. Physico-mechanical properties of diabase have favourable values and varying scattering degrees. Dry state uniaxial compressive strength average values from seven analyses vary in the range 130-169 MPa. Resistance to abrasion average values vary in the range 9.04-17.07 cm3/50cm2. Apparent density varies within the span 2759-2926 g/cm3 and real density 2804-2951 g/cm3. Water absorption values 0.08-1.04 %. Resistance to weathering through testing of stability using Sodium-sulphate values vary from 0.00 to 0.15 % and through frost resistance from 0.00 to 0.04 %. Porosity values are almost constant at 0.8 %. In more altered parts of the rock mass, porosity reaches 1.6 %. Graded crushed aggregate has favourable values of Los Angeles coefficient 14.2 and 14.3 % for gradation B. Taking into consideration all performed tests and analyses, it is concluded that diabase from Drača mine can be used as a building stone for production of aggregate for use in concrete and for road-construction (asphalt paving mixtures for moderate, light and very light traffic load as a top wearing layer; for lower and upper bearing layers; for classic and modern road foundations); for production of crushed and hewn stone for building; crushed stone for railroad ballast. Also, it can be and is used as a raw material for production of stone wool for thermal insulation purposes
Application of Artificial Neural Networks in performance prediction of cement mortars with various mineral additives
No full textPrediction of physico-mechanical and thermo-mechanical properties of cement mortars with different mineral additives based on materials’ starting compositions by means of machine learning models is an essential feature in contemporary civil engineering. In this study, the prediction of performances of seventeen mortar mixtures based on Portland cement (CEM I 42.5R) with mineral additives and subsequent comparison with properties of mortars in which various cement types were used as binders was conducted using artificial neural network (ANN) modeling. Analytical model comprised discrimination based on similarities and differences between composite mortars and mortars based on 6 different cement types (without additives). The employed cements were: ordinary Portland cement, moderate heat hydration cement, high early strength cement, low heath hydration cement, high sulphate resistant cement, calcium aluminate cement, and high alumina cement. The mineral additives used were: fly ash, bottom ash, zeolite, bentonite, perlite, vermiculite, pyrophyllite, micro silica, silica fume, spinel, chamotte, calcinated clay, kaoline clay, alumina, limestone, talc, and copper slag. This investigation designates the impacts of various process parameters, such as the concentration of SiO2 , Al 2 O3 , Fe 2 O3 , CaO, MgO, K2 O, Na 2 O, TiO2 , SO3 , and LoI, and their effects on the quality of mortars with additives. The characteristics of mortars were evaluated regarding the dependent parameters such as: pozzolanic activity, heath of hydration, setting time, compressive strength, split tensile strength, compressive and split tensile strength under various temperatures up to 1000 °C, refractoriness, and sulphate resistence. Cluster Analysis and Principal Component Analysis were used for estimating the effect of ascertained process parameters on the quality of cements and additives. Artificial neural network model was employed to foresee the quality of cement mortars with additives of discovered outputs and its results show the high suitability level of anticipation: 0.999 during the training period, which can be regarded appropriately enough to correctly predict the observed outputs in a wide range of processing parameters. The developed ANN model displayed high predictive accuracy and it can be used in civil engineering for prediction of properties of novel mineral additives if their chemical composition is known
Zaštita od korozije brodskih konstrukcija
Get PDFHull maintenance is one of the most important aspect in ships lifetime. Ship maintenance represents
prevention of ship system failures, dealing with them and extending ships lifetime. Corrosion has
been a common cause of damage in ships for years. The most widely used method for protecting
ship structures is application of coatings. Ships age, size and navigation area all influence in
choosing the right protective coating system. Hull protective coating can be applied either during
navigation or during ship repair works in shipyard
Primena kalcinisane gline za dobijanje savremenih cementnih kompozita / reparaturnih maltera
No full textKorisnik tehničkog rešenja: Maxima d.o.o., Dragiše Mišovića 16, 32240 Lučani
godina početka primene tehničkog rešenja: 2020. god;
Verifikacija tehničkog rešenja od strane Matičnog naučnog odbora za saobraćaj, urbanizam i građevinarstvo sprovedena je na sednici održanoj 29.12.2020. godin
A Theoretical Model for Vibro-Impact Dynamics of Spur Gears with Tooth Flanks Wear
No full textThe main performance of involute gears operation leads to the appearance of nonlinear dynamic behavior and impact. In this chapter the influence of mild wear of the tooth flanks of gears without machine finishing and surface hardening on the vibro-impact behavior is considered. For this purpose, a new theoretical model for vibro-impact dynamics of spur gears with mild wear on tooth flanks is developed and described. The developed theoretical model is based on the main postulates of a model of the central centric collision of two fictive rolling disks with radii equal to the radii of kinematic diameters of the pinion and the wheel, as well as on a combined analytical/numerical approach used finite element analysis for the calculation of contact deformations, contact pressure, and wear on tooth flanks surfaces. A particular gear pair for earth moving machine is used for presenting the developed model. The conclusions about the influence of mild wear on the vibroimpact oscillations during running-in period are described
Nonlinear Dynamics as a Tool in Selection of Working Conditions for Radial Ball Bearing
No full textThis paper contains elements of a comprehensive research devoted to the dynamic behavior of radial ball bearings in real working conditions. The general motivation for this topic comes from the requirements for high performance operation of bearings within complex mechanical systems, defined in many industrial branches during the last decades. The discussion of the fundamental postulates of the approach used for analyzing the vibration response of rolling ball bearings in order to select the optimal working conditions is given. The certain simplifications and reductions used for analyzing the radial ball bearings are explained. The developed procedure can be used for research of influence of different damages and variable operation conditions on the rolling bearings dynamics. The detail analyses of the dynamic behavior of rolling bearings are performed for particular types of radial ball bearings in two case studies: For the damaged outer raceway surface in accordance with real fatigue damage shapes and dimensions and, for variable working temperature. Obtained results are shown by comparative diagrams of vibration and phase plane portraits. Presented results could be a base for more widely research of nonlinear dynamics of radial ball bearings with different damages and for the application of phase plane analysis in order to choose the optimal operation conditions
Cavitation erosion resistance of basalt
No full textThe cavitation erosion resistance of the basalt samples from Vrelo, Kopaonik deposit was investigated. The cavitation erosion test was performed using an ultrasonic vibratory cavitation testing method in accordance to the ASTM G32 standard. To measure the cavitation resistance, a change in the sample mass in function of the cavitation time was monitored. The alternations of the samples’ surface morphology with the passing time were analyzed by scanning electron microscopy. The level of the surface degradation was quantified using image analysis software. The results indicate that basalt posses a good cavitation resistance, which implicates that this raw material can be utilized in extreme exploitation environment
