Influence of Low‐Intensity Repeated Impacts on Energy Absorption and Vibration Transmissibility of Honeycomb Paperboard

Packaging products in logistics typically will receive multiple low‐intensity repeated impacts, fewer moderate to high‐intensity impacts and vibration. As a result of low‐intensity repeated impacts, local buckling and fold will be formed in honeycomb paperboard, and its cushioning performance will be weakened. This paper investigates the influence of low‐intensity repeated impacts on the cushioning performance of honeycomb paperboard. The low‐intensity repeated impacts with dropping height 5 cm were conducted at first. Then, the moderate‐intensity impact with dropping height 80 cm and vibration experiment were, respectively, conducted. The results show: (a) honeycomb paperboard absorbs the energy produced by low‐intensity repeated impacts through layer upon layer folding of honeycomb structure. The highest buckling peak turns up in low‐intensity impact, followed by a series of buckling in intact honeycomb paperboard. However, the buckling is not obvious in repeated impacts; (b) the load carrying capacity of honeycomb paperboard after low‐intensity repeated impacts declines significantly. Three deformation stages are observed in the load–displacement curve. Most of impact energy is absorbed in the plateau stage. The absorbed energy of damaged honeycomb paperboard under moderate‐intensity impact decreases with the increasing of low‐intensity impact repetitions; and (c) the low‐intensity repeated impacts have an obvious influence on the resonance frequency of packaging product and stiffness of honeycomb paperboard. To confirm vibration properties of product using honeycomb paperboard cushioning, it should be considered in a designing process that honeycomb paperboard changes soften more in logistics. Copyright © 2016 John Wiley & Sons, Ltd.     

具有非线性滞回特性的振动系统的稳定性及分叉行为研究

本文研究了具有非线性滞回特性的振动系统的稳定性及分叉行为,讨论了系统微分方程的非临界情形,分析了系统具有单零和一对纯虚数特征值的分叉行为,得到了滞回系统的具有7阶精度的中心流形及Hopf分叉必要条件。     

Estimation of the Dynamic Properties of Non‐linear Packaging Materials Using a Reverse Multiple Input/Single Output Based Approach

During the distribution phase, packaged consignments are exposed to a variety of environmental hazards (such as vibrations) that, if excessively severe, may cause damage to or even destroy the product. Structural deterioration can be tracked by monitoring variations in the packaging system's modal parameters, particularly its natural frequency (stiffness). Natural frequency estimates are often extracted using a least‐squares regression curve fit, applied to an estimate of the system's frequency response function (FRF). FRF estimates are generally obtained using the Fourier transform with a single input and single output (SISO). This approach is suitable for many applications; however, as the non‐linearity of the system under analysis increases, the ability of this technique to accurately monitor changes in the system will decrease. In addition, when the excitation to the non‐linear system is varied (increased or decreased amplitude), a SISO‐based approach may indicate a shift in natural frequency (as a result of the varied input) even though no change in the condition of the system has occurred. This paper discusses an approach that is designed to separate the linear component of the system's FRF using a reverse multiple input/single output (RMISO) algorithm. Such separation will allow traditional modal parameter extraction (curve fitting) techniques to be used to monitor the condition of non‐linear systems. The paper presents the results of experiments in which expanded polystyrene samples were subjected to broad‐band random base excitation with a free‐moving load placed atop the cushion sample. Continuous acceleration measurements of the vibration table and the free‐moving load were used to compute the FRFs of the cushions, and the differences between a conventional (SISO) approach and the proposed RMISO‐based parameter extraction technique were evaluated. Copyright © 2014 John Wiley & Sons, Ltd.     

转子-轴承-密封系统的非线性动力学研究

将非线性油膜力模型Muszynska密封力模型相结合，综合研究转子一轴承一密封耦合系统在不平衡量激励下的非线性动力学特征。针对转速对耦合系统动态响应的影响进行了仿真计算，并利用系统轨迹图、Poincare映射和分叉图分析了耦合系统的非线性动力学特征。数值仿真表明，随着转速的变化，耦合系统呈现出复杂的动力学行为，产生了包括周期、倍周期、拟周期等丰富的振动现象，具有很强的非线性特征。     

裂纹转子的弯扭耦合振动分析

以水平Jeffcott裂纹转子为研究对象,建立了弯扭耦合振动的运动方程,分析其动态特性。数值分析表明：使用三种不同的模型,裂纹转子弯曲振动响应中均出现1X、2X、3X…分量;并发生了数次共振现象,考虑变扭耦合振动后,转子弯曲振动响应中出现一些新的频率成分。U值的变化影响裂纹转子的中心轨迹形状,并且随着U的增大,裂纹转子的轴心轨迹变得不稳定。β的变化主要影响1X分量的大小,对别的分量影响不大,并且随着β从0到π增大时,1X分量越来越小。     

Monitoring the Condition of Non‐linear Packaging Materials Subject to Varying Excitation Levels Using a Reverse Multiple Input/Single Output Based Approach

During transportation, protective packaging is subjected to random dynamic compressive loads that arise from random vibrations generated by the vehicle. The ability of the protective packaging to withstand these dynamic compressive loads depends on the environmental vibration levels, the nominal stresses and the material's characteristics. Previous research has shown that cumulative damage, in the packaging system under random dynamic compression, will result in a change in the overall stiffness of the system. This change is manifested as a shift in the system's fundamental resonant frequency. Natural frequency estimates are often extracted using a least squares regression curve fit applied to an estimate of the system's frequency response function. Frequency response function estimates are generally obtained using the Fourier transform with a single input/single output (SISO). This approach is suitable for many applications; however, it is not well suited to non‐linear systems subjected to non‐stationary excitation where the vibration level (overall root‐mean‐square value) can vary. This paper investigates the use of an optimised reverse multiple input/single output algorithm for reliably tracking variations in the condition of packaging elements subjected to excitation with varying magnitude (root‐mean‐square). Results are presented from the analysis of physical experiments performed on expanded polystyrene cushions as well as empty corrugated paperboard containers. The experiments performed using the polystyrene samples were designed to limit natural variation in the system's natural frequency; whereas the paperboard samples were allowed to naturally damage under dynamic loading. Copyright © 2015 John Wiley & Sons, Ltd.     

柴油机各缸负荷不均衡对轴系扭转振动特性影响的研究

本文从能量的观点出发，通过对多缸机气体激励功的分析研究，引入柴油机气缸负荷不均衡工部下的相对振幅矢量和概念，揭示各缸负荷不均衡对柴油机轴系扭转振动影响的机理。并以相对振幅矢量和作为目标函数进行最大化分析，确定“最差”的气缸不均衡系数排列，并进一步据此，通过强迫振动实例计算表明其影响程度。同时提出了主动调节各缸负荷不均衡作为减振措施的思路。     

A Study on the Reliability of a Large Vibration Machine

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拖曳声纳阵隔振模块性能实验分析

在现代反潜、海洋水文和资源勘探测量中，拖曳线列阵声纳得到了越来越广泛的应用。为了进一步提高拖曳式声纳的工作性能，必须在声阵模块前、后插人性能优良的隔振模块。本文对隔振模块在水下的隔振性能进行了测量。结果表明：隔振模块的隔振性能与其长度、所受到的拉力及激振力的频率和幅值有关。其中隔振模块的长度和激振力的频率是影响隔振效果的主要因素。随着隔振模块长度的增加，其隔振效果将变得越来越好。在长度、激振力相同的情况下，拉力小时隔振效果较好。在其他条件相同时，激励频率越大，隔振效果越好。在相同拉力和激振力作用下，隔振模块的隔振效果的起始频率随隔振模块的长度增加而减小。     

Label‐Free Tracking of Single Organelle Transportation in Cells with Nanometer Precision Using a Plasmonic Imaging Technique

Imaging and tracking of nano‐ and micrometer‐sized organelles in cells with nanometer precision is crucial for understanding cellular behaviors at the molecular scale. Because of the fast intracellular dynamic processes, the imaging and tracking method must also be fast. In addition, to ensure that the observed dynamics is relevant to the native functions, it is critical to keep the cells under their native states. Here, a plasmonics‐based imaging technique is demonstrated for studying the dynamics of organelles in 3D with high localization precision (5 nm) and temporal (10 ms) resolution. The technique is label‐free and can track subcellular structures in the native state of the cells. Using the technique, nanometer steps of organelle (e.g., mitochondria) transportation are observed along neurite microtubules in primary neurons, and the 3D structure of neurite microtubule bundles is reconstructed at the nanometer scale from the tracks of the moving organelles.     

基于振动分析的无桨混合机中物料运行规律研究

在现场对无桨混合机中混合物的形态进行观察,搭建振动测试系统,采集混合机转轴上的振动信号,并提取各阶段频谱特征。针对频谱特征的变化分析振动变化的原因,得出生产过程中各阶段物料在无桨混合机中流动形态变化的规律。     

轧机主传动系统扭振盲测点测量模型的研究

为解决轧机主传动系统实际测试中不可测点处物理参数测取的难题,构造了一类连续轴段质量扭振分析模型,并推导出轴段上盲测点处的扭振参数计算公式。通过把实测点的测试数据代入盲测点计算公式,可计算盲测点的振动参数。轧机实际现场扭矩测试和数据分析处理结果验证了理论推导的正确性。这为轧机现场监测中一些不易布置传感器关键点处的物理量测取提供了理论依据和技术支持,通过编制程序可以实现轧机在线系统监测和故障分析,从而确保轧机正常平稳运行。     

N2‐Plasma‐Assisted One‐Step Alignment and Patterning of Graphene Oxide on a SiO2/Si Substrate Via the Langmuir–Blodgett Technique

Precise control of the placement and patterning of graphene on various substrates has tremendous impact in many fields, such as nanoscale electronics, multifunctional optoelectronic devices, and molecular sensing. A one‐step facile technique involving N₂‐plasma promotes surface modification and enhances the surface wettability of the substrate. The technique is employed to create partially hydrophilic surfaces on SiO₂/Si substrate with the aid of various templates, enabling the selective deposition, alignment, and formation of patterns comprising monolayer graphene oxide (GO) sheets; it successfully uses the Langmuir–Blodgett (LB) deposition technique over a large area without the need of any sophisticated equipment. Various characterization techniques are carried out in order to understand the possible mechanism behind the pinning of the GO on the partially treated areas. It is a relatively easy and swift process that can reliably accomplish specific surface modification with high bonding strength between GO and the substrate. This technique allows the creation of patterns with controllable dimensions. For example, the thickness of the GO sheets can be controlled; this is particularly important in creating arrays and devices at wafer‐scale. Being simple yet effective and inexpensive, this technique holds tremendous potential that can be exploited for numerous applications in the field of bio‐nanoelectronics.     

飞行器内碰摩转子模型的光滑处理及非线性研究

利用一无穷次可微且可无限逼近阶跃函数的实函数对不连续的Jeffcott转子碰摩系统进行了光滑处理，建立了机动飞行的飞行器内碰摩转子系统的力学模型，光滑处理后的系统成为连续的非线性系统。数值研究结果表明：(1)由于机动飞行所引起飞行器倾角变化的影响．碰摩转子系统的非线性响应形态会发生变化，可能在周期解、拟周期解、浑沌解之间相互转变；(2)飞行器加速时，转子系统响应中会出现新的频率成分，而且随着加速时间的延长．这些暂态频率会迁移并逐渐减弱甚至消失；(3)飞行器的加速还会使振幅增加．从而使原未碰摩的转子系统可能发生碰摩，或使原来的碰摩加剧；(4)飞行器的加速可能改变转子系统的稳定性。     

Study of EDL effect on 3‐D developing flow in microchannel with Poisson–Boltzmann and Nernst–Planck models

Microchannels have been suggested to be a very effective heat transfer device. However, the electrical double layer (EDL) effect in a microchannel is anticipated to be significant. In this paper, two EDL models coupled with Navier–Stokes equations were used to compute a 3‐D developing microchannel flow. The Poisson–Boltzmann model (PBM) has been proven to be a promising tool in studying the EDL effect for developed microchannel flow, with respect to its accuracy and efficiency. However, it was commended that the assumption of Boltzmann distribution in PBM, for electric ion concentration distribution in particular was questionable in the developing flow. Nernst–Planck model (NPM), with its two extra partial differential equations (PDEs) to predict the ion concentration distribution, was reported to be a more appropriate model for developing microchannel flow though increased RAM and CPU were needed as compared to the PBM. The governing equations for both models were discretized for developing rectangular microchannel flows in Cartesians co‐ordinate. An additional source term, related to the electric potential, resulting from the EDL effect was introduced in the conventional z‐axis momentum equation as a body force, thereby modifying the flow characteristics. A finite‐volume scheme was used to solve the PDEs. The discrepancy in the results predicted by the two models was more dominant in the near‐wall region and not in the mainstream region. However, the performance of the microchannel was significantly affected by the EDL effect. An increase in Schmidt number will lead to decrease in friction coefficient. For the effect of aspect ratios (ARs), the discrepancy of f Re and Nu values for different ARs was obvious. Therefore, a 3‐D analysis was concluded to be important and necessary for investigating the EDL effect in microchannels. Copyright © 2006 John Wiley & Sons, Ltd.     

Preparation of Microcellular Epoxy Foams through a Limited‐Foaming Process: A Contradiction with the Time–Temperature–Transformation Cure Diagram

3D cross‐linking networks are generated through chemical reactions between thermosetting epoxy resin and hardener during curing. The curing degree of epoxy material can be increased by increasing curing temperature and/or time. The epoxy material must then be fully cured through a postcuring process to optimize its material characteristics. Here, a limited‐foaming method is introduced for the preparation of microcellular epoxy foams (Lim‐foams) with improved cell morphology, high thermal expansion coefficient, and good compressive properties. Lim‐foams exhibit a lower glass transition temperature (T_g) and curing degree than epoxy foams fabricated through free‐foaming process (Fre‐foams). Surprisingly, however, the T_g of Lim‐foams is unaffected by postcuring temperature and time. This phenomenon, which is related to high gas pressure in the bubbles, contradicts that indicated by the time–temperature–transformation cure diagram. High bubble pressure promotes the movement of molecular chains under heating at low temperature and simultaneously suppresses the etherification cross‐linking reaction during post‐curing.     

Effects on Oxygen‐barrier Properties of Pretreating Paperboard with a Starch–Poly(Vinyl Alcohol) Blend before Polyethylene Extrusion

Polyethylene (PE) extrusion coating was performed on paperboard pre‐coated with water‐borne barrier coatings based on starch–poly(vinyl) (PVOH)–plasticizer blends in order to investigate that how the addition of a plasticizer to the pre‐coating affects the oxygen‐barrier properties of the board after PE extrusion coating. The plasticizers used were glycerol, polyethylene glycol (PEG) and citric acid (CA). Photomicrographs showed that the barrier coating layers were rather smooth, but defects were observed in the starch–PVOH layers when a plasticizer was added. Starch–PVOH layers had oxygen‐barrier properties similar to those of pure PVOH without plasticizers. When a sufficient number of layers (four layers) were applied to cover defects, the starch–PVOH layers containing CA showed oxygen transmission rate (OTR) values similar to those of starch–PVOH layers without plasticizer. The adhesion of PE to pre‐coated paperboard decreased when a plasticizer was added to the pre‐coating recipes. PE extrusion coating resulted in a reduction in the OTR in the case of pre‐coating formulations containing plasticizers. A lower OTR after polyethylene extrusion was observed with PEG as plasticizer than with CA as plasticizer. This could be explained by the increase in brittleness due to cross‐linking under the high temperature load during the extrusion process. Dynamic mechanical analysis of the films showed a substantial increase in storage modulus between 100°C and 200°C for CA‐containing starch–PVOH films. The contact angle of diiodomethane on the pre‐coating layer decreased when a plasticizer was added to the coating recipe indicating an increase in wetting of the PE melt. Addition of PEG to the pre‐coating led to a greater wetting than the addition of CA, and this may have sealed some defects in the pre‐coating leading to lower OTR values.     

变动电流作用下焊接熔池谐振现象的研究

本文在固定点 TIG 焊接电弧下,利用在直流焊接电流上叠加正弦波电流的方法,通过计算机对电弧电压变化量采样处理,对薄钢板焊接熔池在变动电流作用下产生的谐振现象做了初步实验研究,结果表明,熔池金属谐振频率与熔池尺寸之间有严格对应关系,利用此方法可以一定程度地解决薄钢板焊接熔透控制问题。