Papers by Keyword: Shear

Abstract: This paper is focused on testing in mode II. In this article there is presented the double-edge notched specimen based on the theory of the infinite plate to determine the critical factor K_II. There are three approaches to this testing here. Firstly, the real test documented by photos and measured data to determine the value of the critical stress intensity was carried out. Secondly, the real test evaluated by the digital image correlation and finally the numerical model in Adina was made. The success of the testing was lower than has been expected (only 24 %). All three prescriptions were used for all 55 specimens. The highest value of K_II is reached with the prescription without fly ash.

Abstract: Bearings of small turbo machines support high speed rotors rotating with the frequency over 1 [kHz]. Such bearings are often supported with O-rings made of soft materials like rubber to attenuate high frequency oscillations. Dynamic properties of rubber supporters have been measured experimentally for individual dimensions, but the universal prediction of dynamic properties for various frequencies is difficult not only because rubbers exhibit nonlinearity against its strain, but because O-ring supporters deform heterogeneously. For the precise prediction, it is necessary to investigate the viscoelasticity of rubber under various deformations and frequencies. Such properties can be measured by the standard shear vibration non-response method of ISO 6721-6 (JIS K 7244-6). However this is applicable only to low frequency range under 100 [Hz] because of the limitation of resonance frequency of the load cell. In this research, based on BERM (Base Excitation Resonant Mass) method, a new method was developed to measure the complex shear modulus at high frequencies up to 1 [kHz] of rubber sheets under homogeneous shear deformations. In the presented method, the force is calculated from the acceleration of the mass instead of the direct measurement by a load cell. Hence accurate measurement became possible even in the range beyond the resonance frequency of a load cell. The measured shear storage modulus G’ and shear loss modulus G” of deformed rubber were presented.

Abstract: Based on the analysis of the development trends of modern transport equipment the prospect of structural composite materials usage, for example CFRP structural, is shown. In this regard, the expediency of conducting research to improve the strength characteristics of these materials is established. It is shown that, despite the large amount of scientific publications on the application of electro-technological methods and microwave technologies for modification of composite materials, applied to heterogeneous materials, such as carbon fiber, in Russia and abroad there are still some unsolved theoretical and practical questions. The studies of the effect of microwave electromagnetic field power density on different physical and mechanical characteristics of laminated composite materials in order to establish the opportunities to improve their performance, in particular their strength, were made. The example of carbon is used to show that the microwave electromagnetic field power density of 17.5 W/cm³ at a frequency of 2450 MHz exposure time of 2 minutes causes an increase in the shear strength of 38 – 40 % and an increase in the duration of the construction operation of carbon under the action of the peak load of 1.5 up to 4.5 times, wherein the change in flexural strength and modulus of elasticity was 2.6 %.

Abstract: As a key component of high-voltage power lines, aluminium clad steel reinforced (ACSR) conductors must have adequate mechanical properties that ensure running safety. This paper presents the results of experimental and theoretical analysis of spiral stranded conductors that consist of a core with two layers of steel wires and three layers of aluminium wires. Tests were performed using two ACSR conductors of the same type, one new and the other 40-year-old, used for a 220 kV power lines. In service, the conductors can be subjected to additional stresses, which may lead to accelerated deterioration and premature failure. In order to provide reliable results, the tests were performed in similar conditions and using the same equipment for both strands. Comparison of results highlighted the influence of the service time on the mechanical properties.On the other hand, the degradation was decisively influenced by the position of the layer. The mechanical properties of the aged conductor are adequate even after 40 years in service. The most advanced degradations are near the clamping area, therefore intensive inspection and maintenance are recommended.

Abstract: The shear capacity of reinforced concrete beams strengthened with cement based composite materials (FRCM system) was investigated in this paper. The analysis refers to PBO-FRCM system made by PBO fibres (p-Phenylene Benzobis Oxazole) and cement based mortar. The use of cement mortar is connected with the slip phenomenon that occurs between the matrix layer and the fibres. This phenomenon leads to premature debonding of the ends of the composite and the loss of the shear capacity. To prevent this, designed end-anchorage systems is needed. Therefore, the laboratory tests on reinforced concrete beams strengthened in a shear with PBO-FRCM system were conducted. At this aim tests on three strengthened RC beams with different end-anchorages systems have been preformed and obtained results discussed. The experimental results revealed that the use of FRCM composites increased the shear capacity and construction of end-anchorage of composite had an impact on shear capacity.

Abstract: This article presents the results of experimental research focused on the shear strengthening of reinforced concrete beams with one of the latest and most promising method: NSM - Near surface mounted reinforcement. In recent years, research in this area focuses on combination of epoxy and FRP (fiber reinforced polymer) materials suitable for strengthening concrete elements. A traditional material: stainless steel was also used in this study but in non-traditional T-cross section in terms of strengthening of concrete members. Structural epoxy adhesives offer excellent properties but are very sensitive to elevated temperatures. Effect of increasing temperature gradually degrade their properties and subsequently decreased bond strength, whereas during cooling may acquire significant parts of the original strength. The influences of these factors were investigated in shear resistance of NSM strengthened concrete beams under four point bending at ambient temperature, at elevated temperature and after cooling to ambient temperature.

Abstract: The best way how to test fracture mode II and determinate the critical factor K_II of cement paste beams is investigated. Several methods are presented and the test based on a theory of the double-edge notched infinite plate is described in detail and will be carry out.

Abstract: The molecular dynamics simulation method in two-dimensional case is presented for the simulation of grain refinement and can be applied to the investigation of grain boundary sliding and defects movement under severe plastic deformation. Nanopolycrystalline system is shown as the example of the application of the method proposed. Atomistic details of structure formation and grain growth (refinement) are shown by the example of change of loading scheme. It was shown that elongated grains which appear under plastic deformation can grow up even larger or be destroyed, depending on the direction of the applied maximal shear stresses.

Abstract: The aim of the work was to assess the safety margin of reinforced rectangular concrete cross-sections subjected to shear. In the performed analyses models of shear resistance based on concrete tension strength was taken into account. Assessment was performed with use of Monte Carlo method. Utilized models of shear resistance were taken from formerly used Polish standards: PN-84/B-03264, PN-B-03264:2002 and the European standard EN-1992-1-1:2004. From the same standard necessary assumptions related with the models were taken. The safety margin and influence of the differences in assumptions on the obtained results were analyzed. The selected models was also evaluated in terms of their “sensitivity” to changes of basic parameters of distribution functions of selected random variables. Results showed that average shear resistance differs about 3 times depending of assumed model of the shear resistance and the reliability level, measured with the partial reliability exponent Δ_R, differs 4-7 times.

Abstract: We studied basic structural elements of a deformation relief formed on lateral faces of nickel single crystals under compression. We correlated deformation heterogeneity with the type of structural elements of the relief. It was revealed that deformation heterogeneity did not depend on the type of a relief element or its scale. In addition, some studies were carried out to define ways of the deformation process in slip bands, mesa-and macrobands of deformation as well as in folds. It was found that a slip developed in separate slip bands resulted in their merging into micropackets with a slip occurring concurrently in several parallel planes. It led to the formation of a mesa-or macroscopic element of the deformation relief. We observed both intrusion and extrusion in the material in macrobands of [111]-single crystals as well as the formation of folding areas discussed.