Improved one-dimensional beam model for unbalanced composite single-lap joint

An analytical nonlinear solution was provided for unbalanced composite single-lap joint (CSLJ) using an improved one-dimensional beam model, which incorporated the effect of bending–tension coupling. The bending–tension coupling stiffness was introduced to characterize the coupling bending and tension behavior induced by the un-symmetric stacking sequence of composite laminates. The governing differential equations captured the bending–tension coupling behavior and the geometrically nonlinear features were constructed based on the displacement compatibility conditions of flexible interface. The transverse deformation in overlap region, edge moment factors and adhesive stress distributions for the unbalanced CSLJ with inflexible, intermediate flexibility and flexible adhesive can be determined by the present one-dimensional beam model. The accuracy of the present model was validated by the comparison with nonlinear finite element model. The effect of bending–tension coupling on edge moment factors and peak values of adhesive stresses was shed light on with the present model.     

碳酸钙改性聚苯乙烯的初步选择性激光烧结实验

针对选择性激光烧结(SLS)成型的高分子粉末烧结件尺寸精度差、强度低的问题,以聚苯乙烯(PS)为基体粉末,探讨了不同扫描速度下铝酸酯偶联剂处理前后的碳酸钙对PS粉末烧结性能的影响。结果表明,随扫描速度的增加,烧结件的尺寸精度提高、弯曲强度降低;未经处理的碳酸钙对PS烧结件的尺寸精度没有影响,反而降低了弯曲强度;经铝酸酯处理的碳酸钙在一定程度上提高了PS烧结件的尺寸精度和弯曲强度,当扫描速度为1 500 mm/s时,添加质量分数为2%的经铝酸酯处理的碳酸钙,PS烧结件的Z向高度相对误差为4.25%,较纯PS烧结件减少了48.5%,弯曲强度达到6.32 MPa,比纯PS烧结件提高了18.4%,但当扫描速度提高到1 800,2 000 mm/s时,两者之间的弯曲强度差异变小。     

Electro-mechanical analysis of composite and sandwich multilayered structures by shell elements with node-dependent kinematics

ABSTRACT

In this work, a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed. The main idea of models coupling is developed by presenting the concept of nodal dependent kinematics where the same finite element can present at each node a different approximation of the main unknowns by setting a node-wise through-the-thickness approximation base. In a global/local approach scenario, the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states, and their electro-mechanical coupling present a complex distribution. Several numerical investigations are carried out to validate the accuracy and efficiency of the present shell element. An accurate representation of mechanical stresses and electric displacements in localized zones is possible with reduction of the computational costs if an accurate distribution of the higher-order kinematic capabilities is performed. On the contrary, the accuracy of the solution in terms of mechanical displacements and electric potential values depends on the global approximation over the whole structure. The efficacy of the present node-dependent variable kinematic models, thus, depends on the characteristics of the problem under consideration as well as on the required analysis type.     

Hysteresis in bending electrostriction of polyurethane films

This report presents the mechanism and unique features of hysteresis in bending electrostriction of polyurethane films. The films were made of segmented polyester–polyurethanes and coated with a thin gold electrode on both surfaces. The application of a 2‐MV/m electric field to the 0.2‐mm‐thick film caused a bending deformation, which showed hysteresis. The hysteresis was closely related to the absorption current, suggesting that its origin is ionic polarization attributed to ionic impurities in the polyurethane. The existence of ionic polarization after the removal of the electric field was shown by measuring a thermally stimulated discharge current. In addition, a couple of unique features of the hysteresis in the bending deformation are described. One of the features is that the prior application of an electric field significantly improves the bending speed in the successive application. The other is that the prior application also controls the bending direction in the subsequent application of an electric field of opposite polarity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1121–1126, 2001     

Periodic crazing on polymethylmethacrylate film by localized bending

Crazing was induced on a polymethylmethacrylate film using an original, low‐cost, simple process in which the film was bent using a wedge‐shaped plate (referred to herein as a crazing edge, or an edge). In this process, stress concentration and stress opening occur spontaneously by feeding the film past the edge, and crazing is periodically induced (periodic craze). The craze interval, width, and depth depend on the localized bending conditions at the tip of the edge. Two different types of crazing mechanism were suggested. It was assumed that the films were either crazed by bending along the tip of the edge or by bending according to the curvature induced by the three‐point bending system. The calculated maximum stress determined by the three‐point bending process and the experimental values of the craze interval and width showed similar tendencies. These results suggested that the craze depth could be determined using this bending process and known mechanical properties and crazing conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Valve metal behaviour of bismuth in NaOH

Galvanostatic anodization of bismuth in different media indicates that the formation of the oxide film depends simultaneously on both pH and the anions present in the anodization medium. Dissolution of these films in NaOH supports this observation. The film is formed of two layers. Open circuit impedance and potential measurements in NaOH indicate film growth. The anodic film formed in NaOH dissolves, however, in NaOH solutions following a zero order mechanism. A number of factors including formation voltage, NaOH concentration, current density and temperature are investigated. The activation energy of the oxide film dissolution is calculated. It may be concluded that the outer layer, in addition to being of a more defective structure, is probably of a higher oxidation state than the inner layer.     

Bending electrostriction in polyurethane films doped with electron acceptors

The effect of electron acceptors as dopants on the bending electrostriction of polyurethane (PU) films was studied. The PU films (ca 0.3 mm thick) doped with 0.5 wt% 7,7,8,8‐tetracyanoquinodimethane (TCNQ) were bent by application of a 1 MV m^?1 electric field. The bending deformation of the TCNQ‐doped film was more than 30 times greater than that of the undoped film. The current and the charge distribution in the films during the application of the field were also measured. Based on these measurements, the mechanism of the doping effect is discussed. Copyright © 2007 Society of Chemical Industry     

Impedance and transient study of aluminium barrier-type oxide films

The effect of the passivation potential on the properties of the barrier films formed on high purity aluminium has been examined. The current-time responses were recorded, the charge used during formation of the barrier film was determined, and the steady-state currents were discussed. Impedance measurements provided an insight into the characteristic sizes of barrier films. Equivalent circuits which illustrate the examined aluminium/oxide film/electrolyte systems were proposed and individual circuit elements were defined. The resistance and thickness of the barrier film were shown to increase linearly with increase in the passivation potential, while increase in solution pH caused a marked decrease in the total system impedance. The paper also defines current efficiency in the formation of the barrier film. The value of 20% indicates that the formation of barrier films on aluminium is a process that takes place with considerable current losses. The mechanism of barrier film growth has been examined within the framework of two models suggested by different authors. Both agreements with and differences from the theories proposed have been indicated.     

Self‐Powered Flexible Sensor Based on the Graphene Modified P(VDF‐TrFE) Electrospun Fibers for Pressure Detection

Polymer P(VDF‐TrFE) has been extensively applied in modern flexible electronics, such as nanogenerators and pressure sensors. In this study, a repolarization method is proposed to exploit the piezoelectric properties of the P(VDF‐TrFE) electrospinning film modified by the reduced graphene oxide (rGO). Then, the repolarized composite film is applied as the self‐powered flexible pressure sensor. Notably, the piezoelectric output voltage and current of the repolarized composite film are up to 1.5 V and 0.125 µA, respectively. Typically, the piezoelectric voltage of the composite film is three times as high as that of the pure spinning film. Meanwhile, this composite film also exhibits piezoresistive effect, which is ascribed to the 3D network structure of the electrospun nanofibers. In addition, the highest piezoresistive sensitivity of the pressure sensor is 0.072 kPa^?1. To sum up, the pressure sensor fabricated in this study allows to simultaneously detect the static and dynamic pressure loads, which thereby has great application potentials in electronic skins (e‐skins) for human motion monitoring, such as motion state and finger bending.     

Bending‐electrostrictive response of polyurethane films subjected to a reversed electric field

This study dealt with the bending‐electrostrictive response of a polyurethane film, which was a promising candidate for a material to be used in polymer actuators. The film bent under an electric field (2.5 MV/m). However, when the field polarity was reversed, the bending direction curiously did not change. To clarify the mechanism of this behavior, we measured the space charge distribution in the film. The measurement showed a pair of charges (induced charge on an electrode and space charge in the film) on one side of the film during the application of the field. However, when the field polarity was reversed, the location of the charges did not change. The charges were assumed to be the cause of the bending. Therefore, we concluded that the bending direction did not change despite the reversed field because the location of the charges did not change. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3644–3650, 2004     

The effect of molding conditions on mechanical and morphological properties at the interface of film insert injection molded polypropylene‐film/polypropylene matrix

An extensive study on the peel strength between a polypropylene (PP) film and PP substrate fabricated using film insert injection molding technique was carried out through a 180° peel test. Injection molding conditions such as barrel temperature, injection speed and holding pressure were varied to gauge their effects on the mechanical and morphological properties. Morphological observations were made at the film‐substrate interfacial regions by means of transmission electron microscopy (TEM). The injection molded products, with the films still attached, were subjected to bending and impact tests to determine if there is any relationship between film‐substrate adhesion and bulk properties. Observation of the load‐displacement curves during the peel test revealed three unique and interesting curves, corresponding to different peeling and film fracture mechanisms. Increases in injection speed, barrel temperature and holding pressure lead to increased bonding between the film and substrate surfaces. The enhancement of bonding between these two polymer surfaces could be attributed to polymer‐polymer interdiffusion. Substantiating evidence from TEM, which shows the fading of the interface as the bond strengthens, further boosts the accuracy of this assumption. The hope that the films could contribute to enhancing bulk properties has been diminished since the bending properties appeared to be similar with or without the film attached. Polym. Eng. Sci. 44:2327–2334, 2004. © 2004 Society of Plastics Engineers.     

端面锥形参数对锥-孔组合型机械密封性能的影响

给出新型锥-孔组合型端面密封,考虑液膜压场的变化规律与环受力变形的相互作用关系,构建机械密封3D流、固耦合数学模型,并给出相关的数值计算方法,获得了膜压分布规律及端面变形情况,分析锥面结构参数在各工况下对密封性能的影响规律。结果表明：由菱形孔所引起的动压效应可使端面产生周向和径向波状变形,而静压效应随锥度Ф和锥宽比γ的变化,在端面区域范围内所起作用也发生相应变化;对压强较低和低、中转速设备,应选取Ф=5~6或Ф=2~4的收敛锥面密封,且γ=0.8~1.0。对高压和高速设备,应选用Ф=2~3的收敛锥面密封,且γ=1.0或γ=0.2;通过改变锥面结构可有效改变机械密封的特性参数,实现密封运行中的自动调节,特别适合变工况条件。另外,由于锥面结构的变化所引起平衡系数B和膜厚h的变化,低速时可弥补动压效应较小的缺陷,获得较大开启力,也可在大h下工作,故可降低密封端面对平整度和光洁度的要求。     

Electrodeposition of cohesive carbon films on aluminum in a LiCl–KCl–K2CO3 melt

Electrodeposition of carbon on an aluminum electrode was studied in a LiCl–KCl–K₂CO₃ melt. A cyclic voltammogram for an aluminum electrode indicates that the cathodic current is due to the reduction of CO₃ ^2– ions. Carbon films on aluminum substrates were obtained by potentiostatic electrolysis, and the cohesiveness of the films depended on the potential. SEM observations showed that the morphology of the deposited carbon film depends on the electrolytic conditions. Raman spectroscopy, XPS and XAES measurement showed that the film consisted of carbon in the sp² state.     

Effect of counter current gas phase on liquid film

Liquid film flow is very important in many industrial applications. However, there are few reports about its characteristics on structured packings. Therefore, in this paper, liquid film phenomena were investigated experimentally to exploit new approaches for intensifying the performance of the structured packings. All experiments were performed at room temperature. Water and air were the working fluids. The effect of counter current gas phase on the liquid film was taken into consideration. A high speed camera, a non-intrusive measurement technique, was used. It is shown that both liquid and gas phases have strong effects on film characteristics. In the present work, liquid film width increased by 57% because of increasing liquid flow rate, while it decreased by 25% resulting from the counter current gas phase.     

静电场中极板表面液膜蒸发特性研究

以静电场中水分子的极化和受力特性为基础,对热干烟气中极板表面液膜内水分子输运过程进行分析。考察了电场特征、液膜物性对静态高压电场中液膜蒸发特性的影响并提出了蒸发模型;同时研究了多场（温度、速度和静电）耦合作用下液膜蒸发过程中的主导作用机制。结果表明：离子风为静态高压电场中液膜蒸发的主要动力,蒸发速率是自然蒸发的6.7倍（25 kV）。液膜蒸发为等速过程,蒸发速率与电场强度呈正相关关系;液膜加入溶质,蒸发过程受抑制,蒸发模型变为等速和降速两个过程,最终液膜表面析出溶质;流场耦合静电场作用下,液膜蒸发速率随电压升高先缓慢上升（U＜20 kV）后快速上升（U＞20 kV）,流速和电压分别是这两阶段的主要影响因素;温度场耦合静电场作用下,蒸发速率大于单场叠加数值。研究结果为热干烟气中极板表面稳定成膜、系统水耗及空间电场中温湿度分布等问题的研究提供理论支撑。     

HDPE及增韧HDPE的力学性能与测试条件的关系

于23℃时,研究了拉伸、弯曲速度及试样缺口剩余宽度对高密度聚乙烯(HDPE)、HDPE/弹性体、HDPE/E型增韧母料(E-TMB)的拉伸、弯曲及冲击强度等力学性能的影响。结果表明,所研究的测试条件对这三种材料力学性能影响的程度不同:对于这三种材料,均是拉伸速度对拉伸屈服应力、弹性模量影响的程度较小,对断裂伸长率影响的程度较大,弯曲速度对弯曲弹性模量、弯曲强度影响的程度较大;三种材料中,拉伸速度对断裂伸长率影响程度最大的是HDPE/弹性体,最小的是HDPE/E-TMB,弯曲速度对弯曲弹性模量、弯曲强度影响程度最大的是HDPE/E-TMB,最小的是HDPE/弹性体;随外力作用速度增大性能并非匀速变化,对不同的材料、不同的性能有相应的敏感区;试样缺口剩余宽度对HDPE/E-TMB的悬臂梁缺口冲击强度影响程度较大,而且缺口剩余宽度由7.8mm增加到8.0mm是影响的敏感区,对HDPE、HDPE/弹性体的影响的程度很小。     

Residual stresses in chemical vapour deposited diamond films

In this paper we report the determination of residual stresses in diamond films grown on Si(100) using a plate bending theory and a bi-metal theory combined with micro-Raman spectroscopy. Raman spectra show that with an increase in the film thickness, the characteristic diamond line shifts from higher wave numbers (>1332 cm⁻¹) to lower (<1332 cm⁻¹), indicating a change of compressive to tensile bi-axial stress with increase in the film thickness. A plate bending theory and a bi-metal theory are used to determine the distribution of the stress induced by the thermal mismatch. The modelled results show that the bi-axial stress decreases linearly along the film growth direction and the stress at the film/substrate interface decreases when the film becomes thicker. The difference from the Raman results is attributed to intrinsic stress.