Damage characterization of 3D braided composites using carbon nanotube-based in situ sensing

Carbon nanotubes (CNTs) were used as an in situ sensor to detect the initiation of micro-cracks and their accumulation in fiber-reinforced polymer composites. The breakage of the electrically conductive networks formed by CNTs throughout the polymer matrix when dispersed in composites enables the micro-cracks to be sensed. This methodology was applied to three-dimensional (3D) braided composites with the aim of investigating the feasibility of detecting their matrix failure and analyzing their damage behavior. Tensile specimens were prepared using 3D braided ultra-high molecular weight polyethylene (UHMWPE) preforms and vinyl ester containing multi-walled CNTs (0.5 wt%) via vacuum-assisted resin transfer molding (VARTM). The electrical resistance of the composites was then measured during tensile testing, while their internal structures were analyzed using X-ray computer tomography (CT), demonstrating that the CNTs dispersed in the matrix enable micro-cracks to be sensed and the damage modes of the 3D braided composites to be analyzed. Finally, four critical strain levels that can classify the damage modes were identified from the change of the electrical resistance of the 3D braided composites.     

大型磨盘座的铸造工艺优化与实践

通过对磨盘座的工艺优化,解决了冒口根部清理过程产生的裂纹及加工周期长等诸多问题,满足了用户质量及进度的要求。     

逆合成孔径成像激光雷达低信噪比稀疏多孔径成像方法研究

受目标非合作特性的影响,逆合成孔径成像激光雷达(ISAIL)回波存在缺失;同时受大气衰减和自然背景光等因素的影响,ISAIL回波信号信噪比较低,因此,常规的稀疏多孔径成像方法不再适用。针对上述问题,该文提出了一种结合压缩感知(CS)和权矩阵的稀疏多孔径成像方法。首先,通过基于CS的稀疏多孔径成像方法对原始数据处理,得到目标像的支撑域;然后,据此建立权矩阵,优化采用CS重构时的代价函数,对稀疏多孔径ISAIL原始数据进行成像处理,利用不完整的回波信号获得高分辨目标像。此算法具有较好的抗噪能力。采用室内ISAIL系统实测数据验证了算法的有效性。     

Elaboration,characterization and study of a novel affinity membrane made from electrospun hybrid chitosan/nylon-6 nanofibers for papain purification

Electrospun hybrid chitosan/nylon-6 nanofibrous mats with fiber diameters in the range of 80–310 nm were successfully fabricated using an electrospinning method. Nanofibrous membranes were prepared by nucleophilic reaction of the chitosan’s hydroxyl and amidocyanogen with the triazinyl chloride of Cibacron Blue F3GA (CB) ligand. This system was used to study the purification of papain. Physical and chemical properties of the affinity membrane were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), contact angle (CA) and element analysis (EA). The equilibrium adsorption capacity (from Langmuir isotherm data) for papain was 93.46 mg/g affinity membrane. Fifteen layers of the composite affinity membrane were packed into a spin column to separate papain from raw material. Significant amount of the adsorbed papain (about 90.4%) was eluted by 1.0 M NaSCN at pH 9.0, and 4.8-fold purification was achieved in a single step. Experiments on regeneration and dynamic adsorption were also performed. It is shown that this system has the potential to be developed for the industrial purification of the papain.     

High piezoelectric d33 coefficient in (Ba1 − xCax)(Ti0.98Zr0.02)O3 lead-free ceramics with relative high Curie temperature

Lead-free (Ba_1 − xCa_x)(Ti_0.98Zr_0.02)O₃ (x = 0-0.04) ceramics were prepared successfully using a solid-state reaction technique. The polymorphic phase transitions (PPT) from orthorhombic to tetragonal phase around room temperature were identified in the composition range of 0 < x < 0.03. High piezoelectric coefficient of d₃₃ = 375 pC/N and planar electromechanical coupling factor of k_p = 44.1% were obtained for the samples at x = 0.01. With the increase of Ca content, the orthorhombic-tetragonal phase transitions shifted towards room temperature, while relative high Curie temperature (T_C) was still maintained about 115 °C.     

平沟煤矿瓦斯治理中采空区埋管抽放技术的应用

详细分析了采煤过程中瓦斯涌出量增大的原因,概述了采空区埋管抽放技术的工作原理。该技术成功地对平沟煤矿0908综采工作面采煤过程中产生的瓦斯进行了有效地治理,保证了采煤工作面安全、稳定、高效的生产。     

金属矿山冒顶片帮的事故树分析

针对金属矿山冒顶片帮事故频发这一现状,运用事故树分析法,对引发冒顶片帮事故的各种因素进行了定性分析,并提出了相应的预防措施。对实现金属矿山安全生产,提高经济效益和社会效益,具有重要的现实意义。     

Tracking formulas and strategies for a receiver oriented dual-axis tracking toroidal heliostat

A 4 m × 4 m toroidal heliostat with receiver oriented dual-axis tracking, also called spinning-elevation tracking, was developed as an auxiliary heat source for a hydrogen production system. A series of spinning-elevation tracking formulas have been derived for this heliostat. This included basic tracking formulas, a formula for the elevation angle for heliostat with a mirror-pivot offset, and a more general formula for the biased elevation angle. This paper presents the new tracking formulas in detail and analyzes the accuracy of applying a simplifying approximation. The numerical results show these receiver oriented dual-axis tracking formula approximations are accurate to within 2.5 × 10⁻⁶ m in image plane. Some practical tracking strategies are discussed briefly. Solar images from the toroidal heliostat at selected times are also presented.     

应用正交码组信号的传统雷达距离旁瓣抑制方法

为了抑制传统雷达的距离旁瓣和提高传统雷达抗欺骗式干扰性能,该文提出一种传统雷达随机发射一组正交信号的信号发射策略。给定一组正交性好且距离旁瓣低的相位编码信号,雷达在每次发射时从这组波形中随机选取一个波形进行发射,接收端已知该发射信号波形并基于该波形对接收信号进行脉冲压缩,最后对多次相邻脉冲的回波信号进行相干积累。理论分析和仿真结果均表明,距离主瓣信号能够有效积累,而距离旁瓣信号近似白化,因而脉冲积累后可明显降低系统的最大距离旁瓣电平。     

非连续性旋转导向钻具组合的广义纵横弯曲法

旋转导向系统底部钻具组合的三维力学分析是导向工具设计和井眼轨道控制的基础。结合有限元单元划分思想和纵横弯曲法梁理论,提出了广义纵横弯曲法。将钻柱分解为若干单元,以节点处的弯矩、转角、挠度和到钻头的曲线长度作为广义坐标,以井眼轴线作为参考构型,采用梁理论建立单元受力变形方程,同时补充节点边界条件和特殊连接边界条件,组装单元方程和边界方程得到系统方程组,选取牛顿迭代法进行数值求解。与经典算例进行了比对,计算结果相吻合;以某型非连续性旋转导向钻具组合为例研究了井斜角、造斜率和钻头侧向力的关系,分析了造斜能力并给出了最大造斜率,论证和演示了广义纵横弯曲法的正确性和实用性。