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A steel pipe-rubber friction damper (FRD) is proposed for the purpose of achieving greater cost-efficiency. The theoretical calculation formula of yield load was deduced based on generalized Hooke's law, and in order to investigate the behaviour of the proposed damper quasi-static cyclic tests were carried out on 7 specimens. Besides, a numerical finite element analysis (FEA) was carried out on ten dampers. Furthermore the mechanical property of FRD was proposed. Tests and finite element analysis results show that: Hysteretic curve of the steel pipe-rubber friction damper is slippery. The seismic energy dissipation capability is stable which related to load amplitude rather than loading rate. The results of finite element analysis fit well with the test curve. The differences of yield load between the theoretical value, FEA value and experimental data are small. The simulating hysteretic curve with ideal elastoplastic model is identical to the test data, and it is feasible to adopt the ideal elastoplastic model to simulate the damper element in the analysis of a structure with the steel pipe-rubber friction damper.

To recycle the thermoset phenolic foam (PF) wastes, a new flame-retardant panel was developed using milled PF particles and natural wood fibers (WB). PF particles were smashed into three particle size, pre-modified and blended with the sizing fibers in five wt% contents (0, 10, 20, 30, 40%). Each type of mixtures was hot-pressed at same temperature. Physical, mechanical and flame-retardant properties of WB-PF composites were investigated. The mechanical properties of WB-PF composites were found to be rapidly declined with the increasing proportion and size of PF particles. There was also a progressive decrease in thickness swelling for the boards with increasing addition of PF particles. The ultimate fire-retardant property of the boards was remarkably enhanced with more addition and smaller size of PF particles. Among the WB-PF composites, panel with 30 wt% of PF particles had optimum results. The final board with good physical-mechanical and fire-retardant properties can find application in fields like muti-functional furniture, construction, house ware, etc.

The experiments of multi-cycle detonation were carried out based on a direct-connected pulse detonation engine (PDE) and an air-breathing PDE. The ignition energy was less than 50 mJ generated by a spark plug. The gasoline and air were used as the fuel and oxidizer. The pressure variation along the length of the direct-connected PDE and air-breathing PDE at several different operating frequencies was measured by the piezoelectric pressure sensors. The temperature of the exhaust plume from the PDEs was measured by the temperature and water vapor concentration instrument based on infrared spectrum measurement principle. Meanwhile, the average thrust of the air-breathing PDE with three different nozzles, including convergent nozzle, divergent nozzle, and convergent-divergent nozzle was measured by the force sensor. The experimental results indicated that there was a reflected shock wave propagating upstream when the detonation wave reached the convergent nozzle, while there was no reflected shock wave for the divergent nozzle. The exhaust plume temperature increased slightly with the increasing operating frequency. The exhaust plume temperature of the PDE with the convergent nozzle was lower than that of the divergent nozzle and convergent-divergent nozzle, while the PDE with divergent nozzle obtained the highest exhaust plume temperature. Analogously, the average thrust of PDE with the convergent nozzle was the largest while the PDE with the divergent nozzle obtained the minimum average thrust. The spontaneous flow field of the exhaust plume under the condition of multi-cycle was observed by a high speed camera. Several Mach disks looked like diamonds were generated at the center of exhaust plume and the flow was supersonic for a while. The flow field was similar to that of the supersonic unexpanded free jet.

C6F12O has the potential to be used in gas-insulated equipment because of its excellent insulation performance and low global warming potential value. In order to study the effect of O2 on the decomposition characteristics of the C6F12O/CO2 gas mixture, power frequency breakdown experiments were conducted on a C6F12O/O2/CO2 gas mixture with different O2 mixing ratios. The decomposition products of the C6F12O gas mixture after multiple breakdowns were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry. The effects of the O2 mixing ratio, breakdown times, and effective gas production rate on the decomposition characteristics of the gas mixture were investigated. The results show that the main decomposition products are CF4, C2F6, C3F6, C3F8, C4F10, C5F12, C3F7H, and CF2O, and the addition of O2 will promote the formation of the above several decomposition products. Except for C3F6, the concentrations of other decomposition products tend to increase and then decrease with the increase in the O2 mixing ratio. The concentrations of CF4, C2F6, C3F6, and C3F8 increase with the times of breakdowns. The effective gas production rates of CF4, C2F6, and C3F8 show a trend of increasing and then decreasing in the process of adding O2 to the C6F12O/O2/CO2 gas mixture. This study provides a reference for the industrial application of the C6F12O/O2/CO2 gas mixture.

From laboratory experiments it was shown that the flashover voltage of the wet contaminated insulator was significantly influenced by the parameters of the local arc. An integrated optical and electrical diagnostic platform was designed in this paper, which was used to acquire the emission spectrum and electrical parameters of the AC local arc over the wet contaminated surface. The analysis of thermodynamic and electric results showed that AC local arc had a “static time-varying” feature. Hence, a new characterization method of volt–ampere characteristics of the AC local arc was proposed, and a time constant was introduced to describe the time required for the AC local arc to reach the stable state from the beginning. The relationship between the voltage gradient of the AC local arc and the leakage current amplitude was obtained for flashover voltage calculation. Special attention was also paid to the influence of environmental factors, such as air pressure and ambient temperature, on the arc characteristic. This work can enrich the investigation of the parameters of the local arc over the wet contaminated insulation surface and may provide useful parameters for flashover voltage calculation of insulators in service.

In this paper, an efficient boundary condition is applied to solve the photoionization rate, and a two-dimensional numerical simulation is carried out for the development and propagation of an air streamer at low temperature and sub-atmospheric pressure. The results show that the new boundary condition improves the calculation accuracy, but the influence of photoionization on the streamer discharge process is not obvious. The discharge current in the development of streamer discharge is defined, and the corresponding expression of the positive and negative streamer discharge current is given. The influence of the electric field exceeding the threshold value on the discharge process is preliminarily introduced. In the process of discharge, only the propagation velocity of the streamer is obviously higher than that of normal temperature and pressure, and the trend of the other parameters is basically the same as that described in the previous paper. The above results give us a deeper understanding of the discharge characteristics under low temperature and sub-atmospheric pressure, which has certain significance for the development of aviation and high voltage engineering.

Dry-coupling ultrasonic technology is applied to detecting oil-level of oil-filled equipment in power grid. Vinyl silicone rubber is used to substitute liquid coupling agent to fabricate dry-coupling ultrasonic probe, which makes the ultrasonic directly enter the oil-filled equipment through the special structure of dry-coupling probe and detect oil-level of oil-filled equipment accurately and rapidly. Omitting the step that smearing liquid coupling agent on the probe can avoid the contamination on the surface of equipment and significantly improve the detection efficiency.

Probing the decomposition products of Sulfur hexafluoride (SF6) under partial discharge provides important information for fault diagnosis of Gas Insulated Switchgear (GIS). Here, the effects of discharging time, gas pressure, and discharging voltage on SF6 decomposition products have been investigated by Fourier transform infrared (FTIR) spectroscopy. The infrared spectra of decomposition products such as CF4, SOF2, and SO2F2 have been obtained. It can be found that the CF4, SOF2, and SO2F2 concentrations increase over increased discharging time up to 96 hours. The SO2F2 concentration increases while the discharging voltage is raised from 20 kV to 46 kV, due to the rapid deceleration to the lower energy of electron capture and dissociative attachment. The SO2F2 concentration is reduced while the gas pressure is increased from 0.3 MPa to 0.4 MPa. The present results about the SF6 decomposition can be useful for electrical fault diagnosis.Probing the decomposition products of Sulfur hexafluoride (SF6) under partial discharge provides important information for fault diagnosis of Gas Insulated Switchgear (GIS). Here, the effects of discharging time, gas pressure, and discharging voltage on SF6 decomposition products have been investigated by Fourier transform infrared (FTIR) spectroscopy. The infrared spectra of decomposition products such as CF4, SOF2, and SO2F2 have been obtained. It can be found that the CF4, SOF2, and SO2F2 concentrations increase over increased discharging time up to 96 hours. The SO2F2 concentration increases while the discharging voltage is raised from 20 kV to 46 kV, due to the rapid deceleration to the lower energy of electron capture and dissociative attachment. The SO2F2 concentration is reduced while the gas pressure is increased from 0.3 MPa to 0.4 MPa. The present results about the SF6 decomposition can be useful for electrical fault diagnosis.

As a widely used gas insulator, sulfur hexafluoride (SF6) has a large cross section for electron absorption, which may make the molecule ionized to the -1 charge state in the high-voltage environment. Using ab initio calculations, we show that the absorbed electron is located averagely on the six F atoms, occupying the antibonding level of the s-p σ bonds and increasing the S-F bond length. The ionized SF6- molecule decreases its decomposition energy to only 1.5 eV, much lower than that of the neutral molecule (4.8 eV), which can be understood according to the occupying of the antibonding orbital and thus weakening of the s-p σ bonds. The weakening of the bonds results in an obvious red shift in the vibrational modes of the ionized SF6- molecule by 120-270 cm-1, compared to those of the neutral molecule. The detailed origin of these vibrational modes is analyzed. Since the appearance of the ionized SF6- molecules is before the decomposition reaction of the SF6- molecule into low-fluoride sulfides, this method may improve the sensitivity of the defection of the partial discharge and save more time for the prevention of the insulation failure in advance.

Serrated grain boundaries in conventional cast nickel base superalloys can enhance high temperature mechanical properties of the alloy due to a large number of precipitates arranged in grain boundaries,which effectively inhibited the movement of dislocations.During service at elevated temperatures,the ripening,coalescence or degeneration process may occur in these precipitates,resulting in the coarsening of grain boundaries with time.This paper aims to investigate the coarsening kinetics and microstructure evolution of serrated grain boundaries in a conventional nickel base superalloy during long term aging.After solution and aging heat treatment,a long term aging treatment at 900°C for 3000 h was carried out on a cast K480 nickel base superalloy.The microstructure of grain boundaries(GBs) was observed using OM and SEM respectively,and phase composition was measured using EDS.The results showed that the GBs of K480 alloy were the irregular serrated GBs composed of carbide GBs andγ' GBs respectively,both of which coarsened with aging time.During the course of aging,the MC carbides in the carbide GB were decomposed with the formation of new phases of M_6C carbide and n phase;the discontinuous large-sizedγ' particles in theγ' GB were coalesced with each other along the GB direction with aging time andγ' bands formed after aging treatment.The coarsening ratio of the carbide GB was higher than that ofγ' GB at the beginning of aging treatment and the difference in these two values became larger with increase in aging time.A Johnson-MehlAvrami-Kolmogorov (JMAK) type of function was employed to quantify the evolution of coarsening behaviors of the two kinds of GBs with aging time.The good agreement between calculated results and experimental data indicated that the coarsening behaviors of carbide GB andγ' GB in the serrated GB were evolved as a JMAK type of function of aging time in K480 nickel base superalloy long term aged at 900℃.

The yield strength, corresponding to 0.2% plastic deformation, of superalloy single crystal DD407 with 22 different orientations were measured at 760 to investigate the orientation dependence of yield strength for this superalloy. The facets of fractured specimens were observed by scanning electron microscopy and their crystallographic characters were identified with the aid of X-ray diffractometer. The results indicated that specimens near (111) were deformed by cubic slip systems, and the rests were deformed with octahedral slip systems. The orientation dependence of yield strength was established and analyzed by an LCP-model. It showed that the yield strength of DD407 specimens deformed by octahedral slip accorded with LCP-model, whereas those deformed by cubic slip, such as (111) crystals, deviated from LCP-model. A close inspection of the LCP parameters suggests that, in dual-phase / ' crystals, the effect of matrix must be responsible for the positive sign of b2 term which is negative in mono-phasecrystals.