Optimization Study of C/SiC Threaded Joints

The influences of fiber preform structure and thread engagement length on the mechanical properties of Carbon fiber reinforced silicon carbide matrix (C/SiC) threaded joints were studied. The results show that stacking 3K carbon fiber cloth followed by stitching is a good preform for preparing a C/SiC nut because of its high bearing ability. Stacking 1K carbon fiber cloth followed by stitching is a preferred preform to prepare a C/SiC bolt, and its minimum thread engagement length resulting in bolt rupture instead of thread spalling failure is 4 mm, which is obviously smaller than those of other bolts.     

Effects of fiber preform structures on the mechanical properties of C/SiC nuts and bolts

Carbon fiber-reinforced silicon carbide (C/SiC) nuts and bolts (M8) with different fiber preform structures were prepared by precursor infiltration and pyrolysis. The influences of fiber preform structures on the mechanical properties of C/SiC nuts and bolts, as well as the failure behaviors of threaded joints were studied. A C/SiC nut, which was fabricated by using the preform prepared by stacking 3K carbon fiber cloth followed by stitching, had the highest shearing strength (64.5 MPa). The bolt with the preform prepared by alternatively stacking 3 K carbon fiber cloth and unidirectional layer of carbon fiber tows followed by stitching had the highest extreme tensile strength (243.2 MPa) and shearing strength (106.3 MPa), but low thread tooth bearing ability (3.5 kN) and critical thread engagement length (9 mm). It is suitable for applications emphasizing the extreme tensile or shearing strengths of threaded joints or possessing enough thread engagement length to ensure bolt rupture as the failure mode. The bolt with the perform prepared by stacking 1K carbon fiber cloth followed by stitching had the highest thread tooth bearing ability (5.0 kN) and the lowest critical thread engagement length (6 mm), as well as moderate extreme tensile strength (163.0 MPa) and shearing strength (82.1 MPa). It works effectively for applications concerning thread tooth strength or possessing limited thread engagement length. Therefore, the preform for preparing a C/SiC bolt should be selected according to its application requirements.     

玻璃纤维无捻粗纱布纬纱位移问题的探讨

分析了玻璃纤维无捻粗纱布纬纱位移形成的原因,介绍了不同后道工序与纬纱位移的关系,以及产品卷长、幅宽、织物组织对纬纱位移的影响,提出了预防和纠正纬纱位移的措施,从而解决了玻璃纤维无捻粗纱布纬纱位移这一生产难题,提升了玻璃纤维无捻粗纱布产品质量。     

Compacting of the weft thread on a shuttleless loom

Methods which increase the reliability of the technological process and the reproducibility and quality of the fabrics are proposed for joining the pick to the shed and compacting the weft thread on a shutteless loom. It was shown that these methods of forming cloth can be successfully used in further developing the capabilities of shuttleless looms.Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 43–45, January–February, 1993.     

Resistance of cloth barriers made of high-modulus fibres to ballistic impact

The following conclusions can be drawn: the bending and shear strength in cloth made of high-modulus thread does not affect the protective power of cloth packs of traditional structure; the corresponding mechanical characteristics of the yarn cannot be taken into consideration in planning such barriers; the bending strength can be used for increasing the energy capacity of a barrier based on a cloth pack by using a structure that ensures combined deformation of the pack layers but retains the freedom of shear strains and independent stretching of warp and weft in layers.St. Petersburg State University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 34–36, May–June, 1995.     

新型剑杆织机在玻纤行业的应用研究

详细分析了各种不同种类的玻纤织物特性;根据各种织物的不同特性进行了门幅、车速、引纬打纬系统、开口系统、送经系统、卷取系统、纬纱张力控制系统等各项设计,并研制了适合各种织物的WL450-BQ剑杆织机。     

Device for measuring the length of the warp wound on the warp beam or warp shaft of a sectional or high-speed warping machine

A measuring device is developed to replace obsolete similar devices in order to more accurately measure warp length during winding and make the operation of warping machines more reliable. The article examines an algorithm for determining the length of warp being wound on a warp beam or shaft. The counter that is used to track the length in meters stores the count, which allows the machine operator to assess the wound length of the warp. The counter is reset to zero by throwing a “reset” switch to generate a signal. The signal is removed to restore the count. The measurement error in tests performed on warping machines is no greater than ±0.3-0.5 m.     

Use of a predictive colour model for managing the colour appearance of two‐colour woven fabrics

The aim of this study was to implement a two‐dimensional colour appearance model for prediction of the colour values of weft threads when the optical mixing of a two‐colour woven structure had to match the colour appearance of a single‐colour reference woven fabric. Five single‐colour woven fabrics were woven from five threads of similar hue. One of the samples was chosen as a reference, for which the colour appearance was the goal to be achieved in the two‐colour woven fabrics prepared with the other available warp threads and newly dyed weft threads. The colour values of dyed weft threads were predicted by a two‐dimensional colour appearance model. With dyed weft threads, managing the colour appearance of the two‐colour woven fabric was enabled to achieve the colour values of the reference. In the results, colour deviations between the predicted and measured colour values of weft threads revealed some limitations to the colour appearance model and performance of the dyeing process. After the production of the two‐colour woven fabric, the colour appearance matched the appearance of the reference, resulting in deviations of ΔE_CMC(2:1) = 1.2‐7.8. Moreover, the differences between theoretically predicted and measured colour values of the two‐colour woven fabric were evaluated as small, ranging from ΔE_CMC(2:1) = 1.5‐1.9. The results demonstrated the efficiency of implementing the colour appearance model and the dyeing process of weft threads as an approach to achieve the defined colour appearance of two‐colour woven fabrics, which with small colour deviations matches the colour of a single‐colour reference.     

Effect of the structure of glass fibres on their physicomechanical properties

It was found that the critical twisting of glass fibres is within the limits of 250–300 turns/m. In fabrication of some types of glass cloth and thread-sewn cloth, it is expedient to use complex glass fibres with low twisting —within the limits of 0 to 30 turns/m. Moscow State Textile Academy. Translated fromKhimicheskie Volokna, No. 3, pp. 52–54, May–June, 1999.     

Decoration of carbon cloth by manganese oxides for flexible asymmetric supercapacitors

Here we describe the production of carbon cloth coated with MnO₂ nanosheets or MnOOH nanorods through a normal temperature reaction or a hydrothermal approach, respectively. Of note, the electrochemical performance of MnO₂-coated carbon cloth was better (429.2 F g⁻¹) than that of MnOOH-coated carbon cloth. When the MnO₂-coated carbon cloth is introduced as the positive electrode and the Fe₂O₃-coated carbon cloth as the negative electrode, a flexible asymmetric supercapacitor was obtained with an energy density of 22.8 Wh kg⁻¹ and a power density of 159.4 W kg⁻¹. Therefore, such a hierarchical MnO₂-coated carbon cloth nanocomposite is a promising high-performance electrode for flexible supercapacitors.     

The effects of transient heat release rate and crosswind on flame length and tilt angle of flames at different positions in the spread of fire over a diesel pool

The spread of fire over liquid fuel is a common phenomenon, and it has been demonstrated experimentally that the flame length and tilt angle change with the transient heat release rate and different positions of the flame. The coupling relationship between these factors is studied in this paper. The experiments are composed of a rectangular pool with dimensions of 80 cm × 6 cm × 5 cm and crosswind with speeds of 0.8 to 2.4 m/s. Diesel is used as the fuel, and a new method is applied to ensure that the initial temperature of the diesel is constant during ignition. The results show that the traditional method of luminous flame intermittency may not be suitable for studying the geometric characteristics of the spread of fire over a pool, and a new method is proposed. In addition, the transient variation of flame length in different positions of the pool is shown to fluctuate around a mean flame length. The evolution of flame tilt angle along the longitudinal direction of the pool exhibits a U‐shaped curve. Moreover, the multivariate nonlinear relationships of mean flame length and tilt angle among the heat release rate, fire position, and wind speed are established, and relevant coefficients are determined.     

DC and RF performance of surface channel MESFETs on H-terminated polycrystalline diamond

DC and RF performance of submicron gate-length metal–semiconductor field effect transistors (MESFETs) fabricated on hydrogen-terminated polycrystalline diamond is investigated in detail for different material electronic quality (grain size in the range 100–200 µm) and device geometry (drain-source channel length in the range 1–3 µm). DC characteristics appear almost independent of both properties, giving maximum drain-source current values in the range 120–140 mA/mm in MESFETs having same gate length (0.2 µm) and gate width (25 µm). The layer properties underneath the hydrogenated surface seem then to affect the DC behaviour to a lesser extent when the same hydrogenation procedure is used. At variance, the electronic quality of diamond layers employed for MESFETs realization largely affects the RF performance, resulting into a low oscillation frequency f_max for a MESFET realized by a self-aligned process (1 µm drain-source channel length) onto low quality diamond polycrystalline film. Such a performance improves to f_max = 35 GHz for devices realized onto large grain polycrystalline diamond, although fabricated without self-aligned gate procedure (3 µm drain-source channel length). These findings are discussed in terms of different roles played by surface hydrogenation, device geometry detail and electronic quality of the polycrystalline diamond substrate for MESFET realization.     

Power from marine sediment fuel cells: the influence of anode material

The effect of anode material on the performance of microbial fuel cells (MFC), which utilise oxidisable carbon compounds and other components present in sediments on ocean floors, estuaries and other similar environments is reported. The MFC anode materials were carbon sponge, carbon cloth, carbon fibre, and reticulated vitreous carbon (RVC). Power was produced through the microbial activity at the anode in conjunction with, principally, oxygen reduction at a graphite cloth cathode. After a period of stabilisation, open circuit voltages up to 700 mV were observed for most cells. Steady state polarisations gave maximum power densities of 55 mW m⁻² using carbon sponge as the anode; which was nearly twice that achieved with carbon cloth. The latter material typically gave power densities of around 20 mW m⁻². The performance of the cell was reduced by operation at a low temperature of 5 °C. Generally, for cells which were capable of generating power at current densities of 100 mA m⁻² and greater, mass transport was found to limit both the anode and the cathode performance, due primarily to the low concentrations of electro-active species present or generated in cells.     

玻纤机织工艺特性研究及机构创新

深入分析了玻纤织物的结构和织造特性,研究了用剑杆织机织造玻纤织物的工艺特征。通过对玻纤织物纬向移位、剪切困难、布面起皱、退解张力控制困难等现象的研究,提炼织物经纬向的受力特征,寻找解决方法。通过机构创新,解决玻纤机织物的织造难题。     

Temperature measurement performance of thin-film thermocouple cutting tool in turning titanium alloy

The measurement of cutting temperature is one of the most important research topics in the field of cutting. Traditional technology for cutting temperature measurement has limitations because it cannot accurately measure the real transient temperature change in the cutting area. In this study, a thin-film thermocouple sensor with high temperature measurement accuracy and rapid response was positioned near the cutting tool tip to prepare a thin-film thermocouple temperature-measurement tool. Its Seebeck coefficient was 48.13 μV/°C, and the highest temperature difference measured between cold and heat regions was 600 °C. The cutting temperature of a TC4 titanium alloy was measured using an infrared thermal imager and the proposed thin-film thermocouple temperature measurement tool in an orthogonal turning test. The test results were analysed to verify the reliability, accuracy, and repeatability of cutting temperature measurements. The cutting length could extend beyond 1500 m.     

A thermoelectric generator comprising selenium-doped bismuth telluride on flexible carbon cloth with n-type thermoelectric properties

Carbon cloth was used as a flexible substrate for bismuth telluride (Bi₂Te₃) particles to provide flexibility and improve the overall thermoelectric performance. Bi₂Te₃ on carbon cloth (Bi₂Te₃/CC) was synthesized via a hydrothermal reaction with various reaction times. After over 12 h, the Bi₂Te₃ particles showed a clear hexagonal shape and were evenly adhered to the carbon cloth. Selenium (Se) atoms were doped into the Bi₂Te₃ structure to improve its thermoelectric performance. The electrical conductivity increased with increasing Se-dopant content until 40% Se was added. Moreover, the maximum power factor was 1300 μW/mK² at 473 K for the 30% Se-doped sample. The carbon cloth substrate maintained its electrical resistivity and flexibility after 2000 bending cycles. A flexible thermoelectric generator (TEG) fabricated using the five pairs of 30% Se-doped sample showed an open-circuit voltage of 17.4 mV and maximum power output of 850 nW at temperature difference ΔT = 30 K. This work offers a promising approach for providing flexibility and improving the thermoelectric performance of inorganic thermoelectric materials for wearable device applications using flexible carbon cloth substrate for low temperature range application.     

Wall surface effects on particle-wall friction factor in upward gas-solid flows

The variation of the particle-wall friction factor along the riser is investigated in an Internal Circulating Fluidized Bed (ICFB) riser 1 m in length and 0.052 m in diameter. The results obtained are based on calculating the normal and the shear forces at the wall under dynamic conditions rather than the static ones usually obtained in shear box experiments.The strength of the method used resides in the measurement technique applied to measure the particle velocity field in the riser. The radioactive particle tracking program was developed for coaxial systems and is used to build dynamic pictures of particle trajectories in the vicinity of the wall of the ICFB riser.The experiments were conducted using sand (d_p = 250 µm) and alumina (d_p = 170 µm) materials in the gas velocity range between 2 and 12 m/s. The most common correlations for calculating the particle-wall friction factor are reviewed and compared to the results obtained in this work. The data obtained demonstrates that the particle-wall friction factor is not a constant value but changes along the riser and with change in the gas superficial velocity. The results also show the effect of the roughness of the wall surface and define the particle-wall friction factor area.     

Drag reduction by DNA-grafting for single microspheres in a dilute λ-DNA solution

The fluid resistance of single micrometre-sized blank and DNA-grafted polystyrene microspheres under shear flow is compared in purified water and dilute λ-DNA solutions by means of optical tweezers experiments with a high spatial (±4 nm) and temporal (±0.2 ms) resolution. The measurement results show that the drag experienced by a colloid in a dilute λ-DNA solution (molecular weight of 48,502 bp per molecule, radius of gyration of 0.5 μm) is significantly decreased if the microsphere bears a grafted DNA brush. This newly discovered drag reduction effect is studied for different parameters, comprising the molecular weight of the grafted DNA molecules (250 bp, 1000 bp and 4000 bp), the concentration of the λ-DNA solution (11, 17 and 23 μg ml^?1, all being significantly smaller than the critical entanglement concentration c¹), the microsphere core diameter (2 μm, 3 μm and 6 μm) as well as the flow speed of the medium (10–50 μm s^?1). The maximum extent of the drag reduction is found to amount to (60 ± 20)% compared to the λ-DNA-induced contribution on the drag acting on blank colloids. We propose a theoretical explanation of this effect based on the combination of the dynamic density functional theory of Rauscher and co-workers [Rauscher M. J. Phys.: Condens. Matter 2010;22:364109] and the stagnation length theory of polymer brushes, as it was established by Kim, Lobaskin et al. [Kim et al. Macromolecules 2008;42(10):3650–3655]. In particular, the solution of the Stokes equation (i.e., the Navier–Stokes equation for creeping flow) for the studied system yields a numerical prediction that is found to be in full accord with our experimental results within measurement uncertainty.     

Low-velocity pneumatic conveying of coarse particles in a horizontal pipe

Slug flow was studied for air velocities less than 8 m/s with polyethylene pellets in a straight pipe 32 mm in diameter and 5.5 m in length, and was classified into 2 regimes: successive slug flow and solitary slug flow. A settled layer of particles did not form in the latter and high air pressure was required to push the slug as compared with the former. Successive slug flow was found in the low-velocity region where the power consumption reaches a minimum, a minimum that is lower than the minimum of the suspension flow region.     

从材料角度探讨影响玻璃钢拉伸性能的诸因素

玻璃钢拉伸强度主要取决于玻璃布经纬向的玻璃纤维和基全树脂的性能以及两者之间的组合状态。本文就组成玻璃钢的三种主要材料；玻璃纤维增强材料、基体树脂浸润分别进行讨论。