关键词： 摩擦纳米发电机   介电层   砂纸模板   微结构   CNT  

摘要： 针对目前摩擦纳米发电机介电层表面微结构制作方法存在工艺流程复杂,成本高的问题,提出在聚二甲基硅氧烷(PDMS)中掺杂碳纳米管(CNT)提高介电常数,并以砂纸为模板快速在PDMS表面成型微结构,实现微结构CNT/PDMS弹性体膜摩擦纳米发电机介电层的制备。研究不同目数砂纸下PDMS表面微结构、CNT掺杂质量分数及载荷作用对摩擦纳米发电机性能输出的影响,测试发电机输出功率及耐久性。结果表明:表面微结构制作方法可增加介电层表面积提高发电机输出电压及电流,800目砂纸成型微结构时,摩擦纳米发电机输出最大;掺杂CNT可提高介电层电容值,CNT质量分数为1%时,电容值达到最大24.2 pF;制备的摩擦纳米发电机可产生最大瞬时功率密度1.23×10^(-3) W/m^(3),且经10000次工作循环,表现出较好的耐久性。

关键词： 损伤   层裂强度   微结构   加载特征  

摘要： 鉴于冲击载荷下金属材料的变形损伤具有微结构和加载特征的依赖性,对国内外有关层裂现象的研究进展进行了简要梳理与总结。概述了晶粒尺寸、织构、晶界类型、相界和元素偏析带等结构对金属材料变形损伤的影响,重点阐述了脉冲宽度、应变率和峰值应力等加载特征对金属材料层裂强度的耦合作用,为了解冲击载荷下金属材料微结构、加载特征与变形损伤行为之间的关系提供参考。

关键词： 碳纳米管/聚丙烯   复合材料   稀释母料   微结构   性能  

摘要： 采用稀释母料的熔融共混方式制备碳纳米管/聚丙烯复合材料(CNTs/PP)并加工出微结构面板。研究不同含量CNTs的复合材料的结晶行为、力学性能以及流变性能,得到CNTs对聚合物的增强机理,开拓CNTs复合材料在微结构制品方面的应用。结果表明:采用稀释母粒的方式,CNTs在PP基体中分散相对均匀;CNTs的加入会抑制β晶的形成,降低在(040)晶面取向度;同时也会使复合材料的结晶度从60.36%降低到53.17%。随着CNTs含量的增加,CNTs/PP复合材料的弹性模量可以提高近43%,拉伸强度可以提高近26%。CNTs含量为1wt%时,其冲击强度最高。在低剪切速率下CNTs能显著提高复数粘度,剪切速率越高,复数黏度对CNTs含量的依赖性越低。在纯PP中添加CNTs后,剪切应力明显提高,且随剪切速率的增大呈同步变化趋势。综合结果分析,选择CNTs含量低于3%进行微结构加工较为适宜。

关键词： 叶尖   抗冲蚀   微结构设计   非本征强韧化机制   离子束技术  

摘要： 从叶尖工况及损伤机理、涂层结构、研究现状、制备工艺等4个方面,综述了近年来国内外学者对于叶尖抗冲蚀涂层技术的研究进展。首先,介绍了压气机叶尖的实际工况及砂尘冲蚀损伤机理,如低入射角的微切削理论和高入射角的二次冲蚀理论。其次,着重强调了抗冲蚀涂层的硬韧匹配、材料与结构设计。对纳米多层结构、纳米复合结构和单相固溶体结构的微观结构进行了深入阐述,对其非本征强韧化机制和结构设计准则进行了详细归纳。随后,介绍了抗冲蚀领域的最新研究进展。最后,深入对比了4种国际主流的离子束沉积技术在涂层微结构设计、成分调控等方面的技术特点。发现磁过滤阴极真空弧技术在制备叶尖抗冲蚀涂层方面具有传统涂层制备技术不可替代的优势。本着优化涂层性能和促进实践应用的目的,对磁过滤阴极真空弧技术精细定制化制备的叶尖抗冲蚀涂层的应用前景及工业化生产进行了展望,为该技术在叶尖防护领域的推广提供参考。

关键词： biofabrication   extracellular matrix   immunomodulation   macrophages   melt electrofibrillation   melt electrowriting  

摘要： Supplement-free induction of cellular differentiation and polarization solely through the topography of materials is an auspicious strategy but has so far significantly lagged behind the efficiency and intensity of media-supplementation-based protocols. Consistent with the idea that 3D structural motifs in the extracellular matrix possess immunomodulatory capacity as part of the natural healing process, it is found in this study that human-monocyte-derived macrophages show a strong M2a-like prohealing polarization when cultured on type I rat-tail collagen fibers but not on collagen I films. Therefore, it is hypothesized that highly aligned nanofibrils also of synthetic polymers, if packed into larger bundles in 3D topographical biomimetic similarity to native collagen I, would induce a localized macrophage polarization. For the automated fabrication of such bundles in a 3D printing manner, the strategy of "melt electrofibrillation" is pioneered by the integration of flow-directed polymer phase separation into melt electrowriting and subsequent selective dissolution of the matrix polymer postprocessing. This process yields nanofiber bundles with a remarkable structural similarity to native collagen I fibers, particularly for medical-grade poly(epsilon-caprolactone). These biomimetic fibrillar structures indeed induce a pronounced elongation of human-monocyte-derived macrophages and unprecedentedly trigger their M2-like polarization similar in efficacy as interleukin-4 treatment.

关键词： functionally gradient material   mechanical properties   microstructure   nickel-based superalloy   stainless steel   wire arc additive manufacturing  

摘要： The additively fabricated functionally gradient structures can be a potential replacement for conventionally manufactured structures via fusion welding techniques. A SS321/Inconel 625 functionally gradient material was processed by wire arc additive manufacturing (WAAM) process. The WAAM-formed SS321 comprises of equiaxed and columnar structures, while the Inconel 625 consists of dendritic structures. It can be concluded that a very narrow interface was formed between the additively manufactured SS321/Inconel 625 FGM without forming cracks or fissures. Energy-dispersive x-ray spectroscopy (EDS) element maps show a smooth transition of elements at the interface without much segregation while EDS point scan confirmed the presence of laves phase. The electron backscatter diffraction results at the interface region revealed continuous crystallographic growth with large elongated grains in the orientation. Tensile properties were better for SS321 and comparable for Inconel 625 than the wrought alloys, while the interface FGM sample failed on the SS321 side. The micro-hardness steadily changed from 226-195 HV and 272-236 HV in SS321 and Inconel 625, respectively. The WAAM process demonstrates that successful FGM components can be fabricated with multi-material and controlled properties.

关键词： Directed energy deposition   Multi-material structures   Compositionally graded materials   Superalloys  

摘要： Varying material properties are required for components designed to withstand harsh environments with simultaneous thermal and mechanical loading. This has been traditionally achieved by using multiple materials fabricated by traditional processes, followed by permanent or non-permanent joining techniques to realize a full, multi-material and multi-functional component. A potential simpler approach to this is to develop multi-material structures fabricated using additive manufacturing (AM). Additionally, many existing structures in can also be simplified by incorporating multi-material and multi-functional structures. Laser directed energy deposition (laser-DED) AM technique is suitable for fabricating multi-material structures using powdered feedstock material with high material flexibility. However, the fabrication of multi-material structures requires careful investigation into the compatibility and behavior of the constituent material systems. This remains a crucial task for multimaterial deposition because there is relatively less knowledge available currently on the optimal multimaterial mixtures for achieving adequate structural integrity and mechanical performance. In this study, multi-material structures of stainless steel 420 (SS420) and Inconel 718 (IN718) alloys were studied. These alloys were chose due to their applications in gas turbine components such as shaft assemblies, exhaust components and in the energy industry for fabricating various high strength, corrosion resistant devices. The specific compositions of the multi-materials structures investigated were: 100% SS420, 100% IN718, 75% SS420 + 25% IN718, 50% SS420 + 50% IN718 and 75% IN718 + 25% SS420. These samples were characterized for their microstructural, phase, and mechanical properties in the as-fabricated condition and compared with conventionally fabricated alloys. Significant differences in the microstructure and properties were observed between the laser-DED fabricated 100% alloys and

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关键词： Mixtures  

摘要： Warm-mixed reclaimed asphalt pavement technology, as an environmental recycling method to reuse waste materials, has been widely investigated around the world. However, the skeleton of the reclaimed asphalt mixture is unstable due to the existence of the reclaimed materials. Semiflexible pavement has been successfully used in heavy traffic area due to its high rutting resistance. For combination with these two methods, a warm-mixed reclaimed semiflexible pavement material was proposed in this study. In order to investigate the interfacial weakening effect of the warm-mixed reclaimed semiflexible pavement material in a microstructural perspective, an image-based two-dimensional microstructural finite element model was presented. Results show that the maximum compressive stress of the new and RAP aggregates and cement mortar with interface is greater than that without interface and the compressive stress of the material increases when considering the interface. Besides, the maximum compressive strain of the material with interface is greater than that without interface and the strain values in the models with interface at all three positions are greater than those without interface.

关键词： 柔性压力传感器   微结构设计   仿生结构   多级结构   人机交互   3D打印   激光直写  

摘要： 对电阻型柔性压力传感器的材料、制备和应用场景进行了简单阐述,重点介绍了通过引入微结构提升电阻型压力传感器性能的设计理念,分别评述了国内外研究中,天然表面微结构、仿生微结构和多孔结构对器件压阻灵敏度的提升,以及跨尺度结构、多级结构和多层结构对测量范围的进一步拓展。简单介绍了本征导电和填充型导电两种材料类型,进一步针对表面微结构和多孔结构的制造原理和工艺方法,重点阐述了倒模成形、3D打印、激光直写、气溶胶喷印等工艺。总结了近年来电阻型柔性压力传感器在人机交互、医疗健康监测及电子皮肤等场景的应用进展,最后结合应用需求对该领域未来研究方向进行了展望。