In this work, the (Y0.5Nb0.5)xTi1−xO2 (x = 0.001, 0.01, 0.02, 0.04, 0.06 and 0.1) ceramics (as called YNTO) were fabricated by synthesized through a standard solid-state reaction. As revealed by the X-ray diffraction (XRD) spectra, the YNTOs exhibit tetragonal rutile structure. Meanwhile, the grain size of YNTO ceramics increased and then decreased with the increase of x value, and the largest value reached when x = 0.02. All the YNTO samples display colossal permittivity (~102–105) over a wide temperature and frequency range. Moreover, the optimal ceramic, (Y0.5Nb0.5)0.02Ti0.98O2, exhibits high performance over a broad temperature range from 20 °C to 180 °C; specifically, at 1 kHz, the dielectric constant and dielectric loss are 6.55 × 104 and 0.22 at room temperature, and they are 1.03 × 105 and 0.11 at 180 °C, respectively.

A series of flexible composites with a carbon black (CB) filled silicone rubber matrix were made by an improved process in this work. A low percolation threshold with a mass ratio of 2.99% CB was achieved. The piezoresistive behavior of CB/silicone composites above the critical value, with the mass ratio of carbon black to the silicone rubber ranging from 0.01 to 0.2, was studied. The piezoresistive behavior was different from each other for the composites with different CB contents. But, the composites show an excellent repeatability of piezoresistivity under cyclic compression, no matter with low filler content or with high filler content. The most interesting phenomena were that the plots of gauge factor versus strain of the composites with different CB contents constructed a master curve and the curve could be well fitted by a function. It was showed that the gauge factor of the composites was strain-controlled showing a promising prospect of application.

No abstract

Short single‐wall carbon nanotubes (SWCNTs)/epoxy composites were fabricated by a procedure of cutting and functionalizing SWCNTs, dispersion and curing, with a very low weight ratio of SWCNTs from 0.03% to 0.5%. It was found that the tensile fracture strength of composites increases with increasing SWCNT content initially, then reaches a maximum at 0.05 wt% and finally decreases with further increasing the SWCNT content. The fracture strength of the composite with 0.05 wt% SWCNTs (78.46 MPa) is ~160% of that of pure epoxy sample (48.64 MPa). A model analysis based on the competition of local matrix fracture and the debonding of short SWCNT was proposed. It revealed that there is a transition from local matrix fracture to the debonding of SWCNT when the SWCNT content increases, this transition leads to the decrease in the tensile strength. Further analyses indicated that the content of carbon nanotubes (CNTs) at the transition depends on their radius and length. Considering the effect of surface cracks on the fracture strength of pure epoxy sample, the theoretical analyses are qualitatively in agreement with the experimental results. The present study partly explains why the fracture strength of CNT reinforced composites has various results for a similar CNT loading in previous works.

No abstract

In order to explore the contra-rotating axial flow pump design method and analysis its hydrodynamic performance, the inlet and outlet velocity triangle of front rotor and rear rotor was analysed, then, a high specific speed contra-rotating axial flow pump was designed using three dimensional method based on the condition of the front rotor outlet circulation equal to the inlet circulation of the rear rotor. At last, the performance of the pump is calculated by using RANS simulation. The results show that: the efficiency of the pump reaches 80.2% on the mass flow design point, namely, the average efficiency of the front rotor and rear rotor is up to 89%. At the same time, the efficiency will decrease rapidly when the mass flow is greater than the design flow. The efficiency of contra-rotating axial flow pump can be maintain higher than 80% by changing the rear rotor speed when the mass flow is in the range of 0.68 d Q~1.07 d Q , which verifies changing rear rotor speed can effectively expand the operation range of pump's high efficiency.

No abstract

Based on the B/S architecture, a design scheme was proposed to develop a data management system of ordnance support work with certification. Containing such hardware components as printing and attendance devices, the system could not only realize the management of the ordnance support work with certification, but also support the immediate production of a work pass in the form of IC card, and realize the daily attendance management of technical support personnel. An information-based solution was therefore given for the problems of work with certification encountered by the ordnance support forces.