多层界面相对SiCf/SiC复合材料综合性能的影响

界面相的存在对于SiCf/SiC复合材料的力学性能和抗氧化性能有重要影响,选择合适的界面相对于复合材料本身性能至关重要。本工作采用化学气相渗透工艺制备了具有三种不同界面的SiCf/SiC复合材料,即：SiCf/BN/SiC;SiCf/(BN-SiC)/SiC和SiCf/(BN-SiC-BN)/SiC,研究了多层界面相对材料本身力学性能和抗氧化性能影响。结果表明,界面相的存在有利于维持并提高材料本身的力学性能和抗氧化性能,并且在三种复合材料中,SiCf/(BN-SiC-BN)/SiC复合材料在1200 ℃高温有氧环境强度保有率最高约为95%,并且呈现出更好的自愈合能力。     

基于微纳层叠技术的聚合物纳米纤维制备及应用研究进展

简述了微纳层叠共挤技术的发展;总结了近些年来基于微纳层叠技术制备纳米纤维的研究进展,包括聚合物参数,制备方法和成纤机理;对目前几种典型微纳层叠成纤方法进行了分类和对比,并对纤维的性能进行了阐述;对微纳层叠纳米纤维的应用进行了介绍。最后针对微纳层叠技术用于纳米纤维制备的发展方向和应对的挑战进行了浅析。     

极紫外宽带多层膜反射镜离散化膜系的设计与制备

极紫外(EUV)宽带多层膜的光谱性能对膜厚控制精度要求较高,仅由时间控制膜厚的镀膜系统难以满足其精度控制要求。本文提出了基于进化算法的宽带EUV多层膜离散化膜系设计方法,与传统膜系设计相比,离散化膜系所制备多层膜具有更为优良的EUV反射光谱性能。为验证离散化膜系设计在宽带EUV多层膜研制中的优越性,采用磁控溅射方法对具有离散化膜系的宽带多层膜反射镜进行了制备和测试。测试结果表明:研制的宽角度多层膜反射镜可实现入射角带宽为0°～17°,高于41%的反射率;研制的堆栈宽角度多层膜反射镜可实现入射角带宽为0°～18.5°,高于35%的反射率;研制的宽光谱多层膜反射镜可实现波长带宽为12.9～14.9 nm,高于21%的反射率。     

Modelling photovoltaic modules with neural networks using angle of incidence and clearness index

A neural network for modelling photovoltaic modules using angle of incidence and clearness index is proposed. Engineers require methods to estimate the output of a photovoltaic plant depending on meteorological conditions. Therefore, models for the grid inverter and the generator must be provided, and their outputs must be combined. The connection between both models is related to the maximum power point of the generator and how it is tracked by the inverter. That maximum power point under specific conditions of irradiance and module temperature is determined by the I–V curve of the module, which must be simulated under those conditions. Algebraic procedures were used to simulate the I–V curve. Recently, neural networks have been used for the same purpose. Previous methods only take into account the irradiance and the module temperature. The model proposed is based on neural networks, and it uses not only the irradiance and the module temperature but also the angle of incidence and the instantaneous clearness index as additional inputs. The normalised clearness replaces the standard clearness index because it allows the removal of the hourly trend found in this last index. This new model improves the results obtained with previous ones as it can distinguish amongst samples with the same solar irradiance and temperature values but with different angle of incidence and instantaneous clearness index. Results show that this model could be used to improve the accuracy of the tools used to forecast the output of photovoltaic plants. Copyright © 2014 John Wiley & Sons, Ltd.     

On-site experimental estimation of thermal conductivities and heat capacities in multilayer walls under arbitrary transient conditions using explicit and implicit finite difference schemes

It is often required to estimate the thermal properties of the layers of a multilayer wall, which is already part of an existing building. Such cases are encountered when an ex post check is required in order to find out if the design specifications have been followed, or if air conditioning loads have to be calculated in old buildings, the walls of which are composed of layers of unknown materials and thermal properties. In the present study, a method is proposed for estimating the thermal conductivities and heat capacities of the layers a multilayer wall is composed of. The method is based on explicit and implicit finite difference schemes and uses on-site temperature measurements at various locations within the wall. It is applicable to multilayer walls which are already parts of buildings. The outdoor and indoor conditions may be arbitrary, i.e. transient, nonperiodic, with solar radiation. The accuracy of the method, which has been verified by numerical and experimental applications, depends on the available number of temperature values in space. For example, in a 10-cm thick wall layer, measurement at five locations gives satisfactory accuracy, which is considerably improved by increasing the number of values in space using fourth-order polynomial interpolation.     

溅射法制备Al/Pb金属多层膜

通过直流二极溅射法制备了具有不同调制波长和周期的Al／Pb金属多层膜。分别通过扫描电镜、X-射线衍射试验以及能谱对多层膜的表面形貌、断面形貌、结构和组成进行了分析。结果表明,所制备的Al／Pb纳米多层膜既无新相生成也无非晶相产生;在亚微米尺寸范围内,铝和铅的微粒分布均匀;在纳米尺寸范围内,形成了Pb对Al的包覆。     

多层陶瓷外壳的失效分析和可靠性设计

文章对多层陶瓷外壳的失效模式,包括陶瓷底座断裂失效、绝缘电阻失效、断路和短路失效、外引线和无引线外壳引出端焊盘与外电路连接失效、电镀层锈蚀失效、密封失效、键合和芯片剪切失效和使用不当造成失效等进行讨论,并对这些失效的失效机理进行了分析,根据以上的失效模式及其失效机理分析,对多层陶瓷外壳的可靠性设计进行了探讨。     

最小膜层厚度对X射线非周期多层膜光学性能的影响

选用能制备小周期的钨/硅(W/S i)作为膜层材料对,着重研究最小膜层厚度对X射线非周期多层膜光学性能的影响。基于矩阵法计算多层膜反射率和单纯形数值优化方法,设计了入射光子能量为8.0keV,掠入射角的宽度分别为0.85°~1.10°,1.40°~1.70°的X射线超反射镜。结合实际实验制备技术,考虑了W/S i两种膜层材料的最小成膜厚度,确定了膜堆中最小膜层厚度为0.5nm~1.0nm。通过改变最小膜层厚度的值,优化设计了上述条件下的非周期多层膜并对其光学性能进行比较。结果表明:同一个工作波长下,随着多层膜工作角度(掠入射)的增加,膜堆中膜层的厚度减小,最小膜层厚度对其光学性能的影响增加,其光学性能变差。     

Improved properties of low-carbon MgO-C refractories with the addition of multilayer graphene/MgAl2O4 composite powders

The paper investigated the effects of different amounts (0%, 3%, 6%, 9%) of in situ multilayer graphene/MgAl₂O₄ composite powders on the slag resistance, thermal shock resistance, and oxidation resistance of low-carbon MgO-C refractories. Comparing with commercial MgAl₂O₄, the MgAl₂O₄ in in situ multilayer graphene/MgAl₂O₄ composite powders has higher lattice strain of crystal, which can trap more Mn and Fe ions, resulting in the better slag resistance. The oxidation decarbonation layer of MgO-C specimen with 3% composite powders is 9.71 mm, which is lower than not only the specimen with other contents but also specimen containing carbon black/MgAl₂O₄ powders. Moreover, the residual strength ratio of the specimen C/MA-3 was 47.47%, which is 28.5% and 8.08% higher than specimens with no additive and with carbon black/MgAl₂O₄ powders, respectively. Both improving thermal shock and oxidation resistance properties are related with the unique nano structure, multilayer graphene in situ formed between MgAl₂O₄ grains, of added composite powders. The former is due to higher strain energy consumed by multi-deflection of cracks inside the multilayer graphene/MgAl₂O₄ composite powders. And the latter is due to the higher energy of oxidation activation of multilayer graphene/MgAl₂O₄ composite powders due to effective protection of multilayer graphene by MgAl₂O₄.     

界面约束作用下Ti/Al多层复合材料的力学性能和冲压成形性能

采用热压+热轧复合法在500 ℃制备了3层、5层和7层配置的Ti/Al多层复合材料（LMCs）,研究了拉伸和埃里克森杯突试验过程中复合板的裂纹萌生和扩展行为,分析了界面约束效应对复合板力学性能和冲压成形性能的影响机理。结果表明,复合板界面具有微米级厚度的金属间相,导致其具有较强的界面结合。随复合板层数的增加,其屈服强度（YS）和极限抗拉强度（UTS）增加,延伸率（EL）和韧性降低,且由于热轧形成了强基面织构,复合板力学性能的各向异性明显增加。同时,复合板的加工硬化指数（n）和塑性应变比（r）均降低,屈强比（σ_s/σ_b）增大,这些均导致了复合板的冲压成形性能变差。对于层数较少的复合板,在断裂过程中界面脱粘起了主要作用。由于界面结合不佳,界面易发生分层,通过抑制裂纹萌生、促进裂纹偏转和钝化、降低裂纹扩展的驱动力,有效地延缓了复合板的断裂失效。