选区激光熔化工艺参数对气雾化316L不锈钢粉末成形制品性能的影响

本研究系统考察了激光功率和扫描速度对316L不锈钢粉末选区激光熔化工艺成形熔道、制品微观组织及力学性能的影响,并分析了各类缺陷的形成原因。研究结果表明:在低激光功率和高扫描速度条件下,熔道中出现了大量球状颗粒,这些颗粒之间的空隙恶化了下一层粉末的熔化条件,这正是成形制品中熔道分布混乱以及孔洞、裂纹产生的根本原因,进而导致成形制品力学性能降低;在高激光功率和低扫描速度条件下,熔池快速升温/冷却的热应力作用增强,使得成形制品的熔道交界处也存在孔洞和裂纹等缺陷。在本研究实验条件下,激光功率为350 W,扫描速度为1750 mm/s时,SLM成形制品的力学性能最为优异,其中抗拉强度为731 MPa、屈服强度为638 MPa、断后伸长率为40.0%,致密度为96.27%。     

基于新型光纤的传输技术探讨

随着互联网的高速发展，引发了网络流量、电信骨干网流量急速增长，使得网络容量的提升迫在眉睫。目前，100G 系统已经商用，超100G系统能够更有效地解决流量和网络带宽持续增长带来的压力，本文主要介绍新型单模光纤的特性以及探讨基于新型单模光纤的传输技术。     

基于改进雷达图的配电系统电能质量评估方法

本文针对配电系统电能质量综合评估存在的评估指标权重分配过于主观或客观的问题,提出一种基于改进雷达图法的配电系统电能质量评估方法。该方法利用最小偏差组合权重法计算各评估指标的最优组合权重。并在传统雷达图的基础上对各指标轴间夹角值的确定和特征向量的选取两方面做了进一步的改进。首先采用扇形区域取代原始的三角形区域,并利用最小偏差组合权重法计算各指标轴间夹角值。其次选择新的特征向量构造评估函数对配电系统电能质量进行综合评估。最后通过对某钢铁厂棒材变电站10kV配电系统电能质量进行综合评估,验证了该方法的可行性和合理性。较传统雷达图而言,改进雷达图法解决了传统雷达图法中各指标间信息共用以及评估结果不唯一的问题,使评估结果更加准确合理。     

Stabilizing temperature-capacitance dependence of (Sr,Pb, Bi)TiO3-Bi4Ti3O12 solutions for energy storage

(1-x)Sr_0.7Pb_0.15Bi_0.1TiO₃-xBi₄Ti₃O₁₂ ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm³, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 10⁸ W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.     

Challenges and new methods for designing reliability experiments

Abstract

Engineers use reliability experiments to determine the factors that drive product reliability, build robust products, and predict reliability under use conditions. This article uses recent testing of a howitzer to illustrate the challenges in designing reliability experiments for complex, repairable systems. We review research in complex system reliability models, failure-time experiments, and experimental design principles. We highlight the need for reliability experiments that account for various intended uses and environments. We leverage lessons learned from current research and propose methods for designing an experiment for a complex, repairable system.     

组合轮径差对地铁车辆动力学性能的影响

为了研究各种轮径差组合形式对地铁车辆动力学性能的影响,基于车辆系统动力学和赫兹非线性接触理论,建立地铁动车非线性动力学模型,分析各种轮径差组合工况下地铁车辆的临界速度、平稳性、安全性和磨耗功率及其变化规律。结果表明:在多种轮径差组合工况下,轮径差增大会使地铁车辆的临界速度有较大幅度降低,会使地铁车辆的横向平稳性和磨耗功率明显增大;轮径差对地铁车辆的垂向平稳性、轮轴横向力、轮轨垂向力、脱轨系数和轮重减载率影响较小;通过左、右曲线时,轮径差对磨耗功率增幅的影响存在差异,但变化规律一致。     

Drag Power Loss Investigation in Cylindrical Roller Bearings Using CFD Approach

In high-speed rolling element bearings, the drag forces can be prominent and it is demonstrated in this investigation that the classical models may not be appropriate for correctly estimating this power loss contribution. A modification of the models is thus proposed, including the usual drag forces formulation relying upon the drag coefficient to be evaluated from a numerical computational fluid dynamics (CFD) approach. A three-dimensional approach that considers both the rings and the cylinder ends seems the only adequate approach to be used because a two-dimensional approach predicts a drag coefficient value that is too low. When using the former computed drag coefficient for the evaluation of the total power losses, high values of oil volume fraction must be employed to recover the measured power losses.     

Study of MW-scale biogas-fed SOFC-WGS-TSA-PEMFC hybrid power technology as distributed energy system: Thermodynamic,exergetic and thermo-economic evaluation

Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW).     

核电厂电气设备陶瓷部件受风生飞射物的冲击破坏

为研究沿海台风中的风生飞射物对核电厂电气设备的冲击破坏，以核电厂户外高压电气设备的陶瓷绝缘材料为研究对象，基于LS-DYNA和HyperMesh，分析陶瓷部件在小球和钢管打击下的破坏情况。结果表明：在受到钢管垂直打击时，陶瓷部件很容易发生破坏；在受到小球冲击时，陶瓷部件局部表面发生破坏。进一步计算得到小球对陶瓷部件的临界破坏冲击速度，可为后续设计和研究提供参考。     

菱铁矿直接还原-低阶煤提质一体化扩大试验

摘要：菱铁矿作为中国重要的铁矿资源，因具有“贫、细、杂”的特点，常规选矿工艺无法对其进行有效分选；此外，中国低阶煤通常被用作低级燃料直接燃烧使用，导致大气污染严重。因此，开发复杂难选铁矿石及低阶煤资源高效清洁利用新技术，将具有重要现实意义。以难选的低品位菱铁矿和难利用低阶煤为对象，开展菱铁矿直接还原与低阶煤提质一体化扩大试验研究。以神府烟煤为还原剂，在直接还原温度为1050℃，时间为120min，C/Fe质量比为250，脱硫剂配比为6%，干式磁选磁场强度为015 T，一段磨矿细度小于0074mm占50%左右，湿式磁选磁场强度为008 T，二段磨矿细度小于0074mm占90%左右，磁选磁场强度为0043 T的条件下，可获得直接还原铁（DRI）粉铁品位9103%、铁总回收率8133%的良好指标；同时每吨DRI固定碳质量分数为7611%的半焦产品产出率为1340kg，其质量达到工业及民用燃料兰炭Ⅰ级品标准。在煤基直接还原工艺中一步成功实现低阶煤半焦化提质和铁矿直接还原，不仅可制备电炉炼钢原料，还可以生产新型的清洁燃料半焦。