RESEARCH OF CONCRETE OF REINFORCED CONCRETE SLEEPERS, WHICH DECIDED DAMAGE DURING OPERATION

Purpose. On the railways of Ukraine in some areas there is an intensive premature exit sleepers due to the formation of defects that can affect the safety of trains and cause significant material losses due to a single replacement of a significant number of sleepers. The purpose of the study is to establish the causes of damage reinforced concrete sleepers on a characteristic section of the railway with their intense premature exit. Methodology. The condition of reinforced concrete sleepers of SB3 type under unlined substrate fastenings on 324-332 km of the pair track of the Odnorobivka-Bukine section of the Southern Railway was studied, where since 2007 their intensive output was observed due to defects. Findings. It is established that for 15 years of operation, as 236.3 million tons were put into operation, about 2.8 % of sleepers were replaced due to defects (44 pieces per 1 km of track). Typical defects (damages), due to which the sleepers were removed from the track, were mainly 13.2 and 13.2 according to the classification of CP-0150 – cracks and fractures of sleepers, including ones with crushing concrete. These defects were preceded by the formation of a network of thin cracks on the visible surfaces of sleepers. 3 sleepers with an initial compressive strength of 68…77 MPa produced by the Korosten Reinforced Concrete Sleeper Plant and the Gnivan Special Reinforced Concrete Plant, removed from the track due to characteristic defects, were selected and investigated. Samples were selected from the sleepers, with the help of which there was determined the final strength of concrete and microscopic examinations, including luminescence flaw detection method, were performed. It was found that the network of cracks in sleepers is spatial, mostly developed mostly beneath their top edge, the least developed above the bottom edge, and causes a decrease in compressive strength of concrete by 47…72 %. It is noted that the destruction of concrete during loading occurred behind these cracks. On the inner surfaces of the cracks there are individual grains of aggregates, which have signs of active silica content, that together with the nature of the cracks may indicate that the cause of their formation is corrosion of concrete from the interaction of cement alkali with reactive aggregates. On the surfaces of the cracks in the lower part of the sleepers leaching products were found, apparently leached by electro migration, which may indicate that corrosion processes were promoted by leakage currents on electrified DC tracks. Originality Thus, in the study area, the main cause of defects, which caused the replacement of the sleepers – was the corrosion of concrete due to the interaction of cement alkali with reactive aggregates, promoted by leakage currents, as well as a small diagram of sleepers and the use of unlined anchor intermediate rail fasteners. Practical value. The results of the study allow to establish the causes of cracks and other damage in reinforced concrete sleepers during operation and, in turn, reduce the losses of fasteners manufacturers and sleepers from defects and complaints, optimize the total cost of track repairs and subsequent track maintenance due to rational purpose of track construction, reduction of damage and replacement of sleepers during track operation.

Based on The Gate Bottom Edge Structures Specific Numerical Simulation of Flow Pattern of Gate

The bottom edge structure is a key factor affecting the flow pattern under the gate. The reasonable selection of bottom edge configuration plays an important role in the safe and stable operation of the gate. RNG k-ɛ model is used to simulate the gate water area. Through numerical simulation, the pressure cloud map and pressure data of monitoring points of water area under the gate are fully simulated. Influence of bottom edge structure on flow pattern. The results show that only the flat bottom gate always has negative pressure zone directly below the bottom edge, and the other three structures have no obvious negative pressure zone and move around the downward inclination Angle with time. According to the analysis of the characteristics of upper support and suction, it can be concluded that the upper support force increases with the increase of the front rake angle, and the upper support force of the flat-bottom gate is negative, showing the characteristics of suction.

One size fits all?: Modeling face-mask fit on population-based faces

The use of face masks by the general population during viral outbreaks such as the COVID-19 pandemic, although at times controversial, has been effective in slowing down the spread of the virus. The fit of simple cloth masks on the face as well as the resulting perimeter leakage and face mask efficacy are expected to be highly dependent on the type of mask and facial topology. However, this effect has to date, not been examined and quantified. Here, we study the leakage of a rectangular cloth mask on a large virtual population of subjects with diverse facial features, using computational mechanics modeling. The effect of weight, age, gender, and height on the leakage is studied. The Centers for Disease Control and Prevention (CDC) recommended mask size was used as a basis for comparison and was found not to be the most effective design for all subjects. Thin, feminine, and young faces benefit from mask sizes smaller than that recommended by the CDC. The results show that side-edge tuck-in of the masks could lead to a larger localized gap opening in many face categories, and is therefore not recommended for all. The perimeter leakage from the face mask worn by thin/feminine faces is mostly from the leakage area along the bottom edge of the mask and therefore, a tuck-in of the bottom edge of the mask or a mask smaller than the CDC recommended mask size are proposed as a more effective design. The leakage from the top edge of the mask is determined to be largely unaffected by mask size and tuck-in ratio, meaning that other mechanical alterations such as a nose wire strip are necessary to reduce the leakage at this site.

Guided Wave Propagation for Monitoring the Rail Base

In order to monitor the rail base, the dispersion characteristics and propagation properties of the guided wave are studied. Firstly, two modes named as Modes V1 and V2 are selected by the semianalytical finite element method (SAFE). The region at the bottom edge can be monitored by Mode V1, while the junction of the base edge and the flange can be detected by Mode V2. Then, the characteristics in the propagation process are analyzed using the finite element method (FEM). The two modes can be separated about 0.6 ms after they are excited. Thirdly, a wave attenuation algorithm based on mean is proposed to quantify the wave attenuation. Both waves can have weak attenuation and be detected within 5 m. Finally, a mode-identified experiment is performed to validate the aforementioned analysis. And a defect detection experiment is performed to demonstrate the excellent monitoring characteristics using Mode V2. These results can be used to monitor the rail base in practice engineering.

Liquid Impingement Flow and Heat Transfer of a Cone Heat Sink With Filet Profiles

Jet impingement is a technique for removing heat efficiently. A liquid jet impingement on a cone heat sink was investigated numerically to explore the effect of filet profiles at the top and bottom edge of conical protuberances on fluid flow and heat transfer. An adopted turbulence model was validated through an experiment as described in the literature. Numerical results of pressure coefficient and Nusselt number were obtained for cases with and without filet profiles for variable jet Reynolds numbers and conical angles. Results showed that the flow and heat transfer of conical protuberances with small tip filet profiles are similar to that of the original cone. Pressure coefficient curves are similar to that of convex surfaces, and the average heat transfer slightly increases when the radius of the tip filet profiles exceeds 1 mm. A small filet profile of a conical bottom edge can improve the average Nusselt number. A secondary jet that enhanced the overall heat transfer was demonstrated, and the heat transfers of convex surfaces, as the comparison, with small angles were enhanced in most cases.

The Analytical Aspect of Pressure Dependence and the Change of Edge Crack Propagation of Horizontal Layer

The receiving of plain problem by analytical appearance with horizontal edges on the endless layer of propagation of the vertical crack and the dependence of the inner pressure of crack is observed. It supposed that the bottom edge of the layer is fixed to absolutely hard semi-flatness, but the upper edge is free. In this respect, we have tried to get the propagation measure of the opening and the analytical aspect of pressure change dependence acting inside it, by method of local modifications using the received solutions. The corresponding methods of approximate illustration of functional dependence are used. In the environment of the opening and the received measure of crack propagation the analytical expressions of distribution of stresses give the full image of peculiarities of those dependences for that immeasurable domain and correspond to the received results by method of modifications. The received formulas may be applied by solving concrete applicable problems and in studies of opportunities of cracks’ propagation for environment of fragile material. Those opportunities are increasing moreover if we take into account that the solutions are received for immeasurable environment.

Numerical study of liquid jet impingement flow and heat transfer of a cone heat sink

Purpose The purpose of this paper is to explore the flow and heat transfer characteristics of the jet impingement onto a conical heat sink and evaluate the ability of heat transfer enhancement. Design/methodology/approach A numerical study of the flow and heat transfer of liquid impingement on cone heat sinks was conducted, and transition SST turbulence model was validated and adopted. The flow and thermal performances were investigated with the Reynolds number that ranges from 5,000 to 23,000 and cone angle that ranges from 0° to 70° in four regions. Findings Local Nusselt numbers are large, and pressure coefficients drop rapidly near the stagnation point. In the conical bottom edge, a secondary inclined jet was observed, thereby introducing a horseshoe vortex that causes drastic fluctuations in the curves of the flow and heat transfer. The average Nusselt numbers are higher in a conical protuberance than in flat plates in most cases, thus indicating that the heat transfer performance of jet impingement can be improved by a cone heat sink. The maximum increase is 13.6 per cent when the cone angle is 60°, and the Reynolds number is 23,000. Originality/value The flow and heat transfer behavior at the bottom edge of the cone heat sink is supplemented. The average heat transfer capacity of different heat transfer radii was evaluated, which provided a basis for the study of cone arrays.