Papers by Keyword: Resistance

Abstract: This paper presents a type of Ag/polydimethylsiloxane (Ag/PDMS) nanocomposite material for use in strain gauge element applications. In these elements, the Ag nanoparticles work as conductive elements by electron tunneling and the PDMS forms the tunneling dielectricstructure. In our experiments, the piezoresistance and piezocapacitance characteristics of these Ag/PDMS composites have been studiedunder applied rain/stress. From the results, the gauge factors for piezoresistance and piezocapacitance can reach up to 153 and 224, respectively. Also, when acting as strain elements, the Ag/PDMS composites show fine levels of repeatability and stability. The results given here prove that the material can be used to form anew type of high-sensitivity element for sensor applications. The detectionmethod used for the sensor signals also offersdiversity by including both piezoresistance and piezocapacitance.

Abstract: This study is to investigate the curing of silver conductive ink tracks on fabrics using a combination of direct light projector (DLP) and hot plate since conventional curing process using laser and oven suffer from several weaknesses mainly costly process and warping defect. The fabrics used are made from nylon and polyester while silver conductive inks were used for the entire study. Samples were made by coating the fabrics with rubber dye inks using silkscreen process and conductive inks were manually laid out on top of the rubber dye according to the designated pattern. A Microsoft power point slide is used to shape the light image on top of the hot plate where the sample is located. Variation of curing time and temperature with constant curing distance were investigated. Several mechanical and electrical tests were conducted to determine the cure, hardness, adhesion and resistance level of the ink tracks. The results obtained were as expected which the longer curing time taken and a higher temperature used, a lower resistance is produced. It is proven that a combination of projector and hot plate is capable of curing the ink tracks properly, a cheap process and easy to handle.

Abstract: An assessment was performed to estimate ecological and biological effects of metallic and binary NPs of various chemical nature and structural characteristics. Application of rapid toxicity tests using hydrobionts of various trophic levels (E. coli, Сhlorella v. B., Paramecium c., Daphnia m. S., Danio r.) allowed to determine resistance range to NPs Ni, Pt, ZnO and CeO2. It was established that test reaction to contamination of water with NPs and development of adverse effects to phyto- and zooplankton is contingent on NPs physicochemical properties and sensitivity of hydrobionts. Concentrations of NPs not causing observed change of test reactions were determined. Chlorella v. B. was established to be the most vulnerable to contamination of medium with NPs; photosynthetic pigment quantity was determined to be the most sensitive parameter: nCeO₂ L(E)С₁₀ = 0.0007 mg/l, nNi L(E)С₁₀ = 0.0015 mg/l, nZnO L(E)С₁₀ = 0.0048 mg/l, nPt L(E)С₁₀ = 0.033 mg/l. The highest resistance (L(E)С₁₀ > 100 mg/l) to contamination shown by: E. Coli, Daphnia m. S., Danio r. to nPt ; Danio r. to NNi and nZnO, E. Coli, Paramecium c. to nCeO2; and Danior r. by the parameter ‘embryotoxicity’. The most vulnerable chains of trophic structure of communities were revealed as well as ways of disrupting food pyramid of an aquatic system. Range of resistance or range of concentrations within which biota retains resistance was shown to be an integral characteristic of NPs effects on ecosystems.

Abstract: Thispaper presents the results of the studies of the combined influence of properties of carbide substrate and composite coatings on tool wear resistance in machining of chromium-based heat-resistant alloys. It was established that the efficiency of carbide tools with coatings is determined by a combination of the properties of the carbide substrate and the coating itself. For carbides with relatively low strength and crack resistance, the efficiency of coatings appeared to be unsatisfactory because of brittle fracture of the substrate and thus intensive failure of coating. High heat resistance of cobalt-rhenium alloy is not realized during deposition of coating because of blocking of the most important property of heat-resistant Co/Re binder, i.e. the ability to hold carbide grains under significant deterioration of carbide matrix even at a high temperature in the cutting zone.The maximum efficiency of the coating in machining of chromium-based heat-resistant alloy is provided withcarbide tools made with a balanced ratio of hardness, heat resistance and strength.

Abstract: Structure and properties of cement composite are time-varying characteristics, depending among others on environmental conditions. The key idea is a struggle for complex research of joint effect of physical, chemical and dynamic loads on the internal structure [1] of cement composite and understanding the correlation between changes in microstructure and macro-scale properties [2, 3]. During the experimental program, specimens will be exposed to combined influence of freeze-thaw cycles [4,5,6], aggressive chemical agents [7] and dynamic loading [8]. The aim is to create a theoretical basis for design of effective cement composites meant to be used in severe environmental conditions.

Abstract: Rapid freeze–thaw cycle experiments were carried out on concrete specimens with 0.4, 0.5, and 0.6 water–cement (w/c) ratio in 0% (tap water), 1%, and 5% Na₂SO₄ solutions, respectively, to study the performance of ordinary concrete resistance to sulfate freeze–thaw cycle. The specimens underwent visual inspection, and mass losses and relative dynamic elastic modulus (RDEM) were measured regularly. Scanning electron microscope observation and X-ray diffraction analysis were conducted on partial specimens after the freeze–thaw cycle experiment. Research results show that due to the coupling effects of freeze–thaw cycle and sulfate corrosion, freeze–thaw cycles of concrete in Na₂SO₄ solution caused more damages than in tap water. Higher Na₂SO₄ concentration produced severe damages. Concrete with different w/c ratios exhibit different sulfate freeze–thaw cycle resistances, and concrete with lower w/c ratio usually produces stronger resistance. RDEM loss is considered the control index to determine concrete failure. The corrosion products in Na₂SO₄ solution freeze–thaw cycle are mainly ettringite and gypsum. With the increase in Na₂SO₄ concentration, ettringite formation gradually decreases and gypsum formation gradually increases.

Abstract: The paper deals with the tribological properties of investigated types of hard-faced materials at erosive wear process. Influence of inclination angle of elements on friction resistance and microhardness changes of hard-faced layer were investigated too. From quantitative aspect were hard-faced layers evaluated on the base of weight loses. From achieved results follow that inclination angle is one from determining factors on to material’s wear measure.

Abstract: Experimental verification of global reliability of slender reinforced concrete columns from the regular concrete C45/55 and high performance concrete C70/85 was realized within the applied research of the Faculty of Civil Engineering at Slovak University of Technology in Bratislava (SUT). Production of test columns and samples was in cooperation with ZIPP Bratislava Ltd. Columns are designed in the way to collapse due to stability before the resistance of the critical cross-section is reached. The relative compression of concrete was scheduled about 1,5 ‰. For performed experimentally verified slender columns, the reliability of simplified and nonlinear design methods according to European standards was compared.

Abstract: The use of non-linear methods for design of slender concrete columns by European standards. For the verification of non-linear design methods it is important to compare their results with results of experiments. Within the applied research of the Faculty of Civil Engineering at Slovak University of Technology in Bratislava in cooperation with the company ZIPP Bratislava LTD the experimental verification of the slender reinforced concrete columns was realized. In the paper the authors present the preparation and process one of three series of slender reinforced concrete columns, which were made to verify the reliability of various design methods. Columns of planned second series were designed from high performance concrete C100/115, but the material tests showed that the strength class of concrete was C70/85. The columns, subjected to axial force and bending moment were designed to fail due to loss of stability before the resistance of the critical cross-section is reached. The expected compressive strain in concrete was 1,5 ‰.

Abstract: Pure SnO₂ and Pt doped SnO₂ (0≤Pt≤10wt.%) ceramics have been successfully fabricated in the form of pellet by sintering at 1000 °C for 3 h. The resistance of the samples in air and in reducing gases (200 ppm H₂ and 200 ppm CO) was determined by measuring current – voltage (I-V) characteristics via two-probe method between 150 to 450 °C. All samples show a decrease in resistance with an increase in temperature both in air and in gases. However, the values of resistance in gases are lower compared when the same samples were in air, due to gas molecules reactions with surface oxygen species which affect potential barrier to decrease and causes resistance to reduce. The resistance of the doped samples also increased by 279 - 1226% with an increase in Pt doping in SnO₂, due to Pt surface states density.