Electrical and Optical Investigation of an Electric Arc in Hydrogen for short gaps

Hydrogen or mixtures containing hydrogen represent attractive gases for low-voltage switching devices because of increased arc quenching behaviour. However, fundamental electrical properties of arcs in hydrogen are still not well known. In this paper, first results of a study of a DC switching arc in pure hydrogen at 1 bar between graphite electrodes are presented for low currents of 8 and 16 A. The arc voltage and current are measured during contact separation. High-speed images of the arc are processed to determine the arc length considering the high arc dynamics with erratic elongations and jumps of the electrode attachment. The arc voltage dependence on the length results in a typical sheath voltage of approximately 23 V and mean electric fields in the arc column of 18.7 V/mm at 8 A and 10.8 V/mm at 16A

FRICTION TEST AND PARAMETER ANALYSIS OF PRESTRESSED CONCRETE CONTINUOUS BEAM BRIDGE

The prestressed ducts of prestressed concrete continuous girder bridges are usually three-dimensionally distributed and long in length. The control of prestress loss during construction is very important. In order to ensure the effect of prestress tensioning, the test and analysis of friction parameters of prestressed ducts are particularly important. Based on the tension process of a prestressed concrete continuous beam bridge, the initial tension stress, loading time and channel friction parameters of the prestressed concrete continuous beam bridge are tested by field tests. Combined with the measured friction parameters, the finite element software Midas / Civil is used to analyse the influence of friction parameters on the mechanical properties of prestressed concrete continuous beam bridge. The results show that when the prestressed steel with bending angle not more than 40° and length not more than 70 m is stretched, the initial tension stress is suggested to be set as 20 % of the tension control force and the loading time is 5 min. The measured tunnel friction parameters are larger than the standard value, and the tension control force should be adjusted during the formal tension construction；The deflection of the key section of the main beam increases with the increase of the friction parameters, and the roof stress decreases with the increase of the friction parameters. The change of channel deviation coefficient has a greater impact on the deflection and roof stress than the change of friction coefficient

The influence of lithium water glass on the durability of concrete

The aim of the research is to verify the effect of lithium water glass on the durability and reduction of concrete absorption. For this purpose, the absorption test was made and the influence of the impregnation agent on durability when the test specimens are exposed to cyclic freezing and thawing was verified. Finally, the permeability of the test specimens was measured before and after impregnation. On the basis of the tests carried out, the effect of the impregnation agent was determined by comparing impregnated test specimens with reference specimens

Dependence of mechanical and thermal properties on the composition of lightweight gypsum composites

One of the ways to use the treated gypsum waste is in gypsum mixtures for the production of gypsum blocks. Gypsum blocks can be used in standard interior as well as exterior applications and are made of gypsum, water, PP microfibres and are lightened with foam, which is created from a foaming additive and water. Above all, the amount of foam significantly influences the bulk density of the resulting material, and the bulk density then has a major influence on the mechanical and thermal properties. The use of PP microfibres had a positive effect on the overall stability of the foamed structure, which resulted in an increase in compressive strength while maintaining good thermal insulation properties

Mechanical properties of basalt: a study on compressive loading at different strain rates using SHPB

This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200–600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others

Exact solutions for time-dependent complex symmetric potential well

Using the pseudo-invariant operator method, we investigate the model of a particle with a time-dependent mass in a complex time-dependent symmetric potential well V (x, t) = if (t) |x|. The problem is exactly solvable and the analytic expressions of the Schrödinger wavefunctions are given in terms of the Airy function. Indeed, with an appropriate choice of the time-dependent metric operators and the unitary transformations, for each region, the two corresponding pseudo-Hermitian invariants transform into a well-known time-independent Hermitian invariant which is the Hamiltonian of a particle confined in a symmetric linear potential well. The eigenfunctions of the last invariant are the Airy functions. Then, the phases obtained are real for both regions and the general solution to the problem is deduced

ANALYSIS AND OPTIMIZATION OF WIND RESISTANCE PARAMETERS FOR LATTICE-TYPE HIGH-MODULUS SUPPORTS BASED ON THE OPTIMAL CRITERIA METHOD

Lattice high-molded support can generally be used for cast-in-place support for bridges, but for more than 50 meters of lattice high support, due to the wind, load and other factors, due to the support length and slenderness of the relatively large, relatively light and flexible structure and other characteristics of the role of the wind load is very sensitive. When the lattice high-molded stent construction is used in the typhoon area, it is easy to be damaged by the typhoon, and the structural design of the lattice high-molded stent and the construction of that technology are facing great challenges. In this paper, based on the new construction of a special bridge in Fujian, finite element analysis of four-legged and six-legged lattice bracing is carried out by ANSYS, and the effects of steel pipe diameter, number of columns, longitudinal and transversal spacing of bracing, and diagonal bracing structural parameters on structural performance are analyzed by using the coefficients of buckling stability and the coefficients of critical loading. The results of the study show that the main design variable for displacement sensitivity is the diameter of vertical rod; the main design variable for stress sensitivity is the diameter of diagonal rod; the main design variable for overall stability sensitivity is the diameter of diagonal rod; and the main design variable for overall stability sensitivity of total volume is the diameter of diagonal rod. And the optimal wind resistance parameters are: 4 lattice high-braced columns are selected, the section length should be controlled within 15m, and the total height should not be more than 70m, and the spacing of the columns is controlled between 7m and 8m. This study proposes a set of optimized design process method for wind-resistant lattice structure under the constraints of stiffness, strength and critical load factor, which improves the economy and ensures the reasonableness of the design, and can be used for the design of high-modular lattice bracket in typhoon area

The influence of the construction of tram fronts on the consequences of accidents with passenger cars

In recent years, there has been a large increase in passenger and public transport in cities. An increase in traffic flow results in an increasing risk of accidents. Manufacturers and operators of trams are increasingly subject to higher requirements for ensuring the safety of vehicles. Vehicle safety can be divided into two groups: active and passive safety. Systems and elements of active safety are intended to reduce the risk of accidents. Systems and elements of passive safety are intended to minimize the consequences of accidents. The requirements for the passive safety of newly designed railway vehicles are described in standard EN 15227. Standard EN 15227 was created due to the effort to protect passengers and crew inside railway vehicles in the event of an accident, so it is a so-called self-protection. The standard EN 15227 does not stipulate any requirements for so-called partner protection. Partner protection means an approach in which the vehicle protects passengers inside and outside the vehicle with its deformation elements.This article deals with the issue of how the construction of the front of tram vehicles designed according to the requirements of the standard EN 15227 will affect the consequences of tram´s accidents with passenger cars. The first part of the article describes the requirements of the standard EN 15227 for newly designed trams. Than it describes the creation and evaluation of tram accident statistics in the Czech Republic for the years 2016 to 2018 with regard to the types of collision vehicles, collision directions and consequences of accidents. From the results of the evaluation of the accident statistics, a collision scenario was determined, in which the passengers inside cars were most often injured. The last part of the article is devoted to the creation of simulation models of accidents of three trams with a car and evaluation of simulation calculations with regard to the risk of injury to car´s driver in an accident with trams using human biomechanical criteria

Collapse potential and ultrasonic pulse velocity of loess soils after treatment with expanded perlite and metakaolin

Collapsible soils, including loess, can support heavy loads at their natural humidity but then collapse rapidly and lose a substantial volume when the humidity increases. Soil collapse potential at different immersion stresses was investigated according to ASTM D5333. Different immersion stresses, including 100, 200, 300, 400, and 500 kPa, were used to evaluate the stress-strain behavior of soils before and after saturation. The results indicated that soil collapse potential rose with a raising of immersion stress, resulting in the highest soil collapse potential at 500 kPa immersion stress. Furthermore, the effectiveness of expanded perlite and metakaolin in treating loess soils was examined. The results revealed that the soil collapse potential reduced with an increase in perlite and metakaolin up to 8 %. Also, perlite had a more significant impact on the soil collapse potential than metakaolin. The interlocking force between soil particles was enhanced as the perlite quantity rose, and perlite prohibited soil particles from slipping on each other. Metakaolin decreased the soil collapsibility due to the pozzolanic and chemical reactions which increased particle bonding. The ultrasonic pulse velocity of soils decreased as the percentage of perlite increased. Because the perlite was not spread homogeneously, and the waves can be stuck in the heterogeneities, Metakaolin acted as a filler and increased the ultrasonic pulse velocity of the soils

Modelling of laminated glass interlayer by fractional viscoelasticity

Fractional calculus, i.e. the theory of derivatives and integrals of non-integer order, can be efficiently used for the theoretical modelling of viscoelastic materials. Our research is focused on the polyvinyl butyral which is used as an interlayer for the laminated glass. Polyvinyl butyral can be classified as a viscoelastic material and the introduction of the fractional viscoelasticity seems to be appropriate tool for its description. This paper briefly introduces the springpot element and its connection into more complex theoretical models. We mainly consider the generalized Maxwell model in its standard and fractional form and show their application by fitting the data obtained by experimental analysis