Experimental and Numerical Crashworthiness Investigation of the Empty and Foam‐Filled Conical Tube with Shallow Spherical Caps

This paper experimentally investigates the crash responses of the empty and polyurethane foam‐filled conical tubes with shallow spherical caps under quasi‐static axial loading. To find more details about the energy absorption mechanism, finite element methods is used to simulate the crush process. In terms of finding more efficient and lighter crash absorbers particularly, the energy absorption and specific energy absorption and load ratio have been considered. The influences of the tube geometrical and material parameters such as radius of spherical region, wall thickness, length, semi‐apical angle and foam density on the energy absorption mechanism have been investigated. This study provides practical information for the use of thin‐walled tubes with shallow spherical caps as energy absorbers in aerospace applications to design reentry of sounding rocket based on foam‐filled conical tube with shallow spherical caps.     

Joining Technologies for Al‐Foam—Al‐Sheet Compound Structures

The present paper reviews various conventional joining techniques which can be applied for foam‐sheet structures, i.e., riveting, screwing, welding, gluing, and soldering. Additionally, the combined application of riveting and gluing is presented. The properties of the joints are investigated with the help of model structures in bending and tensile shear tests. Finally, the transferability of the utilized joining methods to component like parts is shown with the corresponding properties of the compound structures in torsion and dynamic bending tests.     

Ultralarge Bending Strain and Fracture‐Resistance Investigation of Tungsten Carbide Nanowires

Hard tungsten carbide (WC) with brittle behavior is frequently applied for mechanical purposes. Here, ultralarge elastic bending deformation is reported in defect‐rare WC [0001] nanowires; the tested bending strain reaches a maximum of 20% ± 3.33%, which challenges the traditional understanding of this material. The lattice analysis indicates that the dislocations are confined to the inner part of the WC nanowires. First, the high Peierls–Nabarro barrier hinders the movement of the locally formed dislocations, which causes rapid dislocation aggregation and hinders long‐range glide, resulting in a dense distribution of the dislocation network. In this case, the loading is dispersed along multiple points, which is then balanced by the complex internal mechanical field. In the compressive part, the possible dislocations predominantly emerge in the (0001) plane and mainly slip along the axial direction. The disordered shell first forms at the tensile side and prevents the generation of nanocracks at the surface. The novel lattice kinetics make WC nanowires capable of substantial bending strain resistance. Analytical results of the force–displacement (F–d) curves based on the double‐clamped beam model exhibit an obvious nonlinear elastic characteristic, which originates fundamentally from the lattice anharmonicity under moderate stress.     

Crash Behavior of Foam‐based Components: Validation of Numerical Simulations

An extensive experimental database has been established for the structural behaviour of aluminium foam and aluminium foam‐based components (foam‐filled extrusions). The database is divided into three levels: 1) foam material calibration tests, 2) foam material validation tests and finally 3) structural interaction tests where the foam interacts with aluminium extrusions. This division makes it possible to validate constitutive models applicable to aluminium foam for a wide spectrum of loading configurations. To illustrate the use of the database, four existing material models for foams in the explicit, non‐linear finite element code LS‐DYNA have been calibrated and evaluated against configurations in the database.     

Dynamic Behaviors of Liquid in Partially Filled Tank in Short-term Microgravity

The oscillation of liquid/gas free surface in a partially filled storage tank caused by an abrupt drop of gravity level is of critical importance for the fluids management in space. In present study we investigate the dynamic behavior of free surface in tank models (tubes) using water as the working medium utilizing the Drop Tower Beijing, which can provide a 3.6s short-term microgravity condition. Meanwhile, the corresponding numerical simulation using volume of fluids (VOF) methods was carried out. It is shown that the dynamic behavior of free surface, which belongs to the typical phenomenon of capillary flow, is affected by the properties of working medium and the geometry and surface properties of the storage tank (especially the contact angle) jointly. The numerical simulation could capture the major characteristic oscillation frequency of free surface revealed by experiment. The oscillation frequency of free surface increases with the increasing air fraction and remains nearly constant at large air fraction. For the same air fraction, the oscillation frequency significantly increases with the decreasing tank diameter.     

Self‐Assembled 3D Foam‐Like NiCo2O4 as Efficient Catalyst for Lithium Oxygen Batteries

A self‐assembled 3D foam‐like NiCo₂O₄ catalyst has been synthesized via a simple and environmental friendly approach, wherein starch acts as the template to form the unique 3D architecture. Interestingly, when employed as a cathode for lithium oxygen batteries, it demonstrates superior bifunctional electrocatalytic activities toward both the oxygen reduction reaction and the oxygen evolution reaction, with a relatively high round‐trip efficiency of 70% and high discharge capacity of 10 137 mAh g^?1 at a current density of 200 mA g^?1, which is much higher than those in previously reported results. Meanwhile, rotating disk electrode measurements in both aqueous and nonaqueous electrolyte are also employed to confirm the electrocatalytic activity for the first time. This excellent performance is attributed to the synergistic benefits of the unique 3D foam‐like structure and the intrinsically high catalytic activity of NiCo₂O₄.     

Bending strength dependence of load‐to‐annual ring direction

The bending strength was studied for load‐to‐grain direction at angle of 90° and load‐to‐annual tree ring direction at angle of 45° of almost 700 years old subfossil elm wood from Sava riverbed. Elm wood is widely used because it is solid and hard regarding its weight. However, due to the Elm Dutch disease and mass drying of elm trees in 1950s, nowadays it is almost impossible to find in natural forest stands of south‐eastern Europe a tree of reproductive age. The value and uniqueness of the studied material lies also in the fact that the subfossil elm wood is even rarer than the recent one, and is highly appreciated for its aesthetic and mechanical qualities. Bending strength has been determined by a three‐point bending test. The mean bending strength value is within the limits for recent elm wood. This investigation has shown that such load‐to‐annual ring direction has almost 20 % higher value for bending strength than for loads applied to the longitudinal‐tangential surface (angle of 0°) and to the longitudinal‐radial surface (angle of 90°). This proves that the ring orientation plays an important role in the measurement of mechanical properties of elm wood and that the measurement of the angle of 45° should always be considered for investigation of bending strength.The coefficient of determination of Weibull functions has been close to value of 1, so it has been concluded that the measured bending strength follows Weibull distribution.     

瓦楞原纸环压强度测量不确定度评定

目的为提高瓦楞原纸的检测水平,研究瓦楞原纸环压强度测量的不确定度评定方法。方法根据JJF 1059.1—2012《测量不确定度评定与表示》,对瓦楞原纸进行抽样,分析其环压强度不确定的主要来源并对其量化,对检测结果进行评定。结果瓦楞原纸环压强度测量的扩展不确定度为78.78,置信概率为95%,包含因子为2。结论检测结果可用于瓦楞原纸环压强度的合格判断,对于其他性能如耐破度、戳穿强度的不确定评定具有参考价值。     

Compound‐Droplet‐Pairs‐Filled Hydrogel Microfiber for Electric‐Field‐Induced Selective Release

The separate co‐encapsulation and selective controlled release of multiple encapsulants in a predetermined sequence has potentially important applications for drug delivery and tissue engineering. However, the selective controlled release of distinct contents upon one triggering event for most existing microcarriers still remains challenging. Here, novel microfluidic fabrication of compound‐droplet‐pairs‐filled hydrogel microfibers (C‐Fibers) is presented for two‐step selective controlled release under AC electric field. The parallel arranged compound droplets enable the separate co‐encapsulation of distinct contents in a single microfiber, and the release sequence is guaranteed by the discrepancy of the shell thickness or core conductivity of the encapsulated droplets. This is demonstrated by using a high‐frequency electric field to trigger the first burst release of droplets with higher conductivity or thinner shell, followed by the second release of the other droplets under low‐frequency electric field. The reported C‐Fibers provide novel multidelivery system for a wide range of applications that require controlled release of multiple ingredients in a prescribed sequence.     

部分充液悬臂柔性转子系统不稳定特性的实验研究

从实验上详细地观察和研究了部分充液柔性转子系统不稳定产生的过程、失稳过程中转子系统的动力特性以及充液量对转子系统振动和稳定性的影响。结果表明部分充液转子系统的不稳定特性与转子系统中其它失稳因素引起的不稳定特性之间存在着明显的差异。部分充液转子系统失稳的门坎转速在充液转子的一阶临界转速之上，并且在空转子系统的一阶临界转速附近。转子在不稳定区内的涡动频率既不是一个固定的频率，也不是转子系统的某阶固有频率，转子的涡动频率随转速的增大而增大，随充液量的增大而减小。     

Magnetization Dynamics of an Individual Single‐Crystalline Fe‐Filled Carbon Nanotube

The magnetization dynamics of individual Fe‐filled multiwall carbon‐nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single‐crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin‐wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single‐crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin‐wave transport in magnonic applications.     

典型木塑制品抗弯性能的研究

以3种典型木塑制品结构为研究对象,进行抗弯性能试验研究,通过建立各结构的有限元模型,施加特定载荷和约束条件,模拟试验条件下的实际受载情况,实施有限元分析。研究结果表明,利用模拟分析结果中的特定指标来评价典型结构基本性能,具有较高的精度和可行性,可以简化型材的结构设计,对木塑型材结构的研究设计具有很好的指导意义。     

AB型瓦楞纸箱边压强度测量不确定度评估

根据GB/T 6546-1998,对一批AB型瓦楞纸箱进行边压强度的测试,并根据标准JJF 1059-1999对其进行了不确定度的评估。其不确定度主要来源是重复性测量、仪器自身示值准确度、数值修约。这批AB型瓦楞纸箱边压强度测量扩展不确定度为78.26 N。