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Modified Hopkinson pressure bar apparatus is widely used to investigate the dynamic fracture behavior of materials at higher rate loading. While using a small sample for fracture toughness testing, plane strain conditions are compromised. In the current work, a large diameter two-bar/ three-point bend fracture setup is used to analyze stress wave propagation behavior within a larger cracked specimen. The experimental setup model consists of striker, incident bar, loading pin, cracked three-point specimen, span and transmission bar. The model is prepared using ANSYS software and the transient dynamic analysis technique is used to simulate the dynamic load. The effects of increased transient time on the stress wave propagation behavior within the cracked sample and the stress and strain values at the crack tip of the three-point bend specimen are analyzed. In addition, the effects of the hollow striker, the hollow incident bar and the specimen span are studied. It is found that during large specimen testing, an increase in the transient time results in the lower stress and strain values in the specimen crack-tip. The relationship of the specimen span, the striker and the incident bars with the strain values in the specimen is analyzed and a method for the three-point bend specimen testing at the higher strain rates is also proposed.

Symbol synchronization offset of orthogonal frequency division multiplexing (OFDM) communication system will cause the rotation of data constellation at receiver even if such offset falls in the range of the appended cyclic prefix. When OFDM modulation is combined with spread spectrum technique, e.g., OFDM code division multiple access (OFDM-CDMA), the problem becomes more serious since OFDM-CDMA communication system generally works under very low signal-to-noise ratio. This paper focuses on symbol timing synchronization of OFDM-CDMA communication system and proposes an effective sequence structure on the basis of circular conjugate-symmetric properties of discrete Fourier transform. The proposed frequency-domain sequence not only can generate real time-domain signal to reduce calculation complexity, but also can resist peak-to-average power ratio of OFDM modulation by exploiting suitable computer search algorithm. The simulation results show a sharp cross-correlation peak can be obtained, which is quite helpful for accurate symbol timing synchronization of OFDM-CDMA communication system.

The physicochemical characteristics of a new composite oxygenated fuel named oligomeric polyoxymethylene dimethyl ether and DMM10 (the blend of this fuel and conventional diesel oil with 10% in volume) were analyzed. The power performance, fuel economy, combustion characteristics and exhaust gas emission of a four strokes, direct injection, turbocharged and intercooled diesel engine fuelled with DMM10 and diesel fuel were analyzed and compared. The results show that in comparison to original diesel engine, when the engine fuelled with DMM10 blend fuel, the power performance remains unchanged; BSEC decrease slightly, smoke emission decreases obviously and its decrease rate is up to 72%.

The author puts forward the core system design scheme of kilowatt aluminum-air battery on the basis of its chemistry characteristics and calculated function parameters of cell stack, and introduces the component functions, including control design, functional electrolyte circulation, air transport, DC / AC inverter system and other modules.

Hopkinson pressure bar apparatus is extensively used for the measurement of the dynamic fracture properties. For accurate measurement of the dynamic fracture properties we need to understand concepts and principles associated with the test setup. The understanding of stress wave in the bar and specimen is also very important. In the current work, ANSYS LS-DYNA software is used to simulate the propagation behavior of the time based loading and generation of stress wave. The stress and strain plots in the specimen and the incident bar are obtained as an output of the analysis. The analysis of the plots suggest that, for the same time duration the rising trend is observed for the plots of stress and strain of incident bar whereas a sine wave trend is observed for the plots in the specimen.

For the Comprehension of the dynamic mechanical properties of the materials under the dynamic loading, Hopkinson pressure bar apparatus is used. During the compression testing of the low impedance materials the use of the hollow transmission bar is common. In the current work, the analysis is performed to analyze the effects of hollow transmission and incident bars on the specimen testing for the large diameter compression setup. Complete model of the setup is prepared using the ANSYS software and the simulation of loading is done using the LS-DYNA software. The results of analysis indicate that for the large compression testing setup, solid bars can be replaced with hollow bars. By using the hollow transmission bar the objective of high strain rate testing is also obtained.

In order to study the feasibility and practicality, the hydrological forecasting model are established respectively by the traditional method and the new methods, BP network and projection pursuit. The result shows that the accuracy of the BP model is within 10%, has better forecasting effect and more practical value than the others.

One-step process of poly(styrene-co-maleic acid)(PS-PMA) nanofibers/QCM combination system was proposed as a novel ammonia detection in this study. Nano-sized PS-PMA fibers were deposited on the QCM electrodes via electrospinning technique directly, which can retain the original high specific surface area of PS-PMA nanofibers, and simplify NH3detection process significantly. Experimental results showed that this new PS-PMA nanofibers/QCM sensor exhibited excellent ammonia sensing performances, such as rapid response and good reproducibility. Moreover, the carboxyl content on the surface of PS-PMA membranes was also determined as well as the specific surface area in order to study the structure-properties relationships.

This report has shown that the dye of Methyl Orange (MO) in water can be decolorized effectively in the presence of KIO3 under UV irradiation. Decolorisation efficiency of MO increases as the loading of KIO3 increases and has no an optimal amount of KIO3 in this case. The kinetic result shows that the decolorisation reaction is a pseudo first-order reaction when the concentration of MO is below 10 mgL-1. The influences of the pH value and hydroxyl radical scavengers on the decolorisation reaction were investigated in detailed. Several observations indicate that the mechanism is not the attack of hydroxyl radicals in MO decolorisation with KIO3 under UV irradiation. More considerations should be focused on the underlying possible decolorisation mechanism of MO with KIO3 under UV irradiation.

In this paper, a KIC gradient composite plate was designed and prepared by changing material prescriptions to make the KIC gradient change along the thickness direction. The expression of fracture toughness at any point within the gradient composites was derived, and the crack propagation behavior was examined by drop-weight impact test. The test results show that under impacting, the macro-crack propagates rapidly in the layer with lower KIC value because of the structure of this gradient composite material, but the high crack propagation resistance in the thickness direction of the plate observed.

This document explained and demonstrated the crack growth of unidirectional glass fiber-reinforced composites (UD-GFRP) using the fracture mechanics theory during the process of machining. The models of fracture mechanics were established at antidromic cutting and direct cutting. The result is obtained that mode-I crack and mode-II crack transform each other during cutting and the complex crack is come into being. The propagation of complex crack makes the material fracture. The quality of machined surface at direct cutting is better than the quality at antidromic cutting.

Nano-Cr2O3 was added to vitrified bond CBN grinding tools to improve their properties. Effects of nano-Cr2O3 on properties and microstructures of vitrified bond CBN grinding tools were investigated. The samples were characterized by differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and related detecting techniques. Results show that the refractoriness of vitrified bond firstly decreases and then increases with the addition of nano-Cr2O3, but the fluidity has the opposite change. Compared with basic vitrified bond, the refractoriness and fluidity of vitrified bond (4 wt.% nano-Cr2O3) are reduced by 25°C and increased by 5.4%, respectively. The bending strength of CBN grinding tools can be enhanced obviously with the addition of nano-Cr2O3, and it has the maximum bending strength (59.27MPa) when adding 4 wt.% nano-Cr2O3. SEM result shows that CBN grinding tool has the most dense structure and the least pore when adding 4 wt.% nano-Cr2O3.

The mechanical properties and microstructure of Mn-series bainitic steel as 5Mn2SiNbTi after air cooling and tempering have been investigated in this paper. The results show that the investigated steel show high strength (tensile strength up to 671MPa), low toughness (20J at -30°C) after hot rolling (final rolling at 1050°C) and air cooling. Medium temperature tempering can improve the toughness, without sacrificing strength of the steel. After tempering at 450°C for 1h, the steel obtained 632MPa tensile strength, 467MPa yield strength, 140J impact energy at -30°C, remaining 25.0% elongation. It is indicated that the tested steel can gain excellent combination of strength and toughness without precious alloy adding, control rolling and control cooling.

In the paper, a non-API tubing connection’s sealing structure is analyzed through numerical simulation. It is very important for sealing integrity to maintain intimate and usually high contact stress of mating metal surfaces under different loading. First, the contact pressure of main sealing surface and torque shoulder surface generated by interference fit after make-up procedure is analyzed. Then, the variation of contact pressure of sealing system during the load envelope test consisting of the axial loads and internal pressure is analyzed. The analysis results can be used to optimum design and operational suitability test of non-API tubing connections.

As a lightweight, fast, airtight, flexible foundation pit supporting structure, lasson steel sheet pile has obvious advantages of short-cycle and low-cost during the construction of double track railway abutment. However, the influence of insertion and extraction of steel sheet pile to original lines is also very big. Therefore, timely backfill grouting, settlement displacement observation and propermaintenance are needed.