Analysis of a rotation‐free 4‐node shell element

In this paper, a shell element for small and large deformations is presented based on the extension of the methodology to derive triangular shell element without rotational degrees of freedom (so‐called rotation‐free). As in our original triangular S3 element, the curvatures are computed resorting to the surrounding elements. However, the extension to a quadrilateral element requires internal curvatures in order to avoid singular bending stiffness. The quadrilateral area co‐ordinates interpolation is used to establish the required expressions between the rigid‐body modes of normal nodal translations and the normal through thickness bending strains at mid‐side. In order to propose an attractive low‐cost shell element, the one‐point quadrature is achieved at the centre for the membrane strains, which are superposed to the bending strains in the centred co‐rotational local frame. The membrane hourglass control is obtained by the perturbation stabilization procedure. Free, simply supported and clamped edges are considered without introducing virtual nodes or elements. Several numerical examples with regular and irregular meshes are performed to show the convergence, accuracy and the reasonable little sensitivity to geometric distortion. Based on an updated Lagrangian formulation and Newton iterations, the large displacements of the pinched hemispherical shell show the effectiveness of the proposed simplified element (S4). Finally, the deep drawing of a square box including large plastic strains with contact and friction completes the ability of the rotation‐free quadrilateral element for sheet‐metal‐forming simulations. Copyright © 2005 John Wiley & Sons, Ltd.     

Low‐cycle fatigue behavior of a newly developed cast aluminum alloy for automotive applications

The drive for increasing fuel efficiency and decreasing anthropogenic greenhouse effect via lightweighting leads to the development of several new Al alloys. The effect of Mn and Fe addition on the microstructure of Al‐Mg‐Si alloy in as‐cast condition was investigated. The mechanical properties including strain‐controlled low‐cycle fatigue characteristics were evaluated. The microstructure of the as‐cast alloy consisted of globular primary α‐Al phase and characteristic Mg₂Si‐containing eutectic structure, along with Al₈(Fe,Mn)₂Si particles randomly distributed in the matrix. Relative to several commercial alloys including A319 cast alloy, the present alloy exhibited superior tensile properties without trade‐off in elongation and improved fatigue life due to the unique microstructure with fine grains and random textures. The as‐cast alloy possessed yield stress, ultimate tensile strength, and elongation of about 185 MPa, 304 MPa, and 6.3%, respectively. The stress‐strain hysteresis loops were symmetrical and approximately followed Masing behavior. The fatigue life of the as‐cast alloy was attained to be higher than that of several commercial cast and wrought Al alloys. Cyclic hardening occurred at higher strain amplitudes from 0.3% to 0.8%, while cyclic stabilization sustained at lower strain amplitudes of ≤0.2%. Examination of fractured surfaces revealed that fatigue crack initiated from the specimen surface/near‐surface, and crack propagation occurred mainly in the formation of fatigue striations.     

Structural and optical properties of nitrogen‐iron co‐doped titanium dioxide films prepared via sol‐gel dip‐coating: Effect of urea and iron nitrate concentration in the sol

In this study, nitrogen‐iron co‐doped titanium dioxide films were prepared via sol‐gel dip‐coating method using urea and iron nitrate as nitrogen and iron source, respectively. Nonmetal doping of TiO₂ have some disadvantages such as massive charge carrier recombination and losing the photo‐catalytic capability. Three different nitrogen‐iron co‐doped titanium dioxide sols with different urea and iron nitrate concentration were prepared. The resulting sols were homogeneous and transparent, and no precipitation was observed in any of them. It was observed that the film prepared with middle urea‐iron nitrate concentration sol got opaque in a short time after the dip‐coating process. All prepared films were characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, confocal microscopy and ultraviolet–visible (UV‐Vis) spectroscopy. It was found that the concentration of the urea and iron nitrate in the sol had an effect on the crystal structure, microstructure, surface morphology and optical properties of the resulting films. Samples with middle concentrations had amorphous structure and bigger particle size. It was seen that sample with higher iron amount has lower band‐gap. It is concluded that we can prepare transparent anatase, transparent amorphous and opaque amorphous titanium dioxide films by changing the urea and iron nitrate concentration in the sol.     

The Design and Synthesis of Hollow Micro‐/Nanostructures: Present and Future Trends

Hollow micro‐/nanostructures have attracted tremendous interest owing to their intriguing structure‐induced physicochemical properties and great potential for widespread applications. With the development of modern synthetic methodology and analytical instruments, a rapid structural/compositional evolution of hollow structures from simple to complex has occurred in recent decades. Here, an updated overview of research progress made in the synthesis of hollow structures is provided. After an introduction of definition and classification, achievements in synthetic approaches for these delicate hollow architectures are presented in detail. According to formation mechanisms, these strategies can be categorized into four different types, including hard‐templating, soft‐templating, self‐templated, and template‐free methods. In particular, the rationales and emerging innovations in conventional templating syntheses are in focus. The development of burgeoning self‐templating strategies based on controlled etching, outward diffusion, and heterogeneous contraction is also summarized. In addition, a brief overview of template‐free methods and recent advances on combined mechanisms is provided. Notably, the strengths and weaknesses of each category are discussed in detail. In conclusion, a perspective on future trends in the research of hollow micro‐/nanostructures is given.     

Effect of As,Cu and Sb impurities on performance of Pb‐Ca‐Sn grids of lead‐acid batteries

The performance of Pb‐Ca‐Sn grids of lead‐acid batteries made from recycled lead in 4 M H₂SO₄ in the absence and presence of traces of Cu, As and Sb, as potential impurities in the recycling process at 0.1% level, is investigated by electrochemical methods. The study includes the effect of each impurity and impurities combined on the alloy corrodibility, the efficiency of PbO₂ formation, the rate of the self‐discharge and the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The results show that individual impurity enhances the corrosion resistance but increases the anode corrosion and the self‐discharge rate. Impurities play opposite effects on hydrogen evolution reaction and oxygen evolution reaction either individually or combined. Concerning water loss problem, the harmful effect of individual impurity on increasing oxygen evolution reaction is compensated by their suppression of hydrogen evolution reaction. The impurities combined suppress effectively both hydrogen evolution reaction and oxygen evolution reaction relative to alloy without any impurity. Sb has the highest harmful effects on oxygen evolution reaction and the self‐discharge but it is the best in the suppression of hydrogen evolution reaction. The impurities combined relatively improve the general corrosion resistance, the anode corrosion resistance and the self‐discharge. The study supports higher tolerance levels of Cu, As and Sb in Pb‐Ca‐Sn grids, especially when present combined, than the recommended levels in the industry standards.     

Multifunctional POSS‐Based Nano‐Photo‐Initiator for Overcoming the Oxygen Inhibition of Photo‐Polymerization and for Creating Self‐Wrinkled Patterns

Oxygen inhibition remains a challenge in photo‐curing technology despite the expenditure of considerable effort in developing a convenient, efficient, and low‐cost prevention method. Here, a novel strategy to prevent oxygen inhibition is presented; it is based on the self‐assembly of multifunctional nano‐photo‐initiators (F₂‐POSS‐(SH)₄‐TX/EDB) at the interface of air and the liquid monomer. These nano‐photo‐initiators consist of a thiol‐containing polyhedral oligomeric silsesquioxane (POSS) skeleton onto which fluorocarbon chains and thioxanthone and dimethylaminobenzoate (TX/EDB) photo‐initiator moieties are grafted. Real‐time Fourier‐transform infrared spectroscopy (FT‐IR) is used to investigate the photo‐polymerization of various acrylate monomers that are initiated by F₂‐POSS‐(SH)₄‐TX/EDB and its model analogues in air and in N₂. FT‐IR results show that F₂‐POSS‐(SH)₄‐TX/EDB decreases the effects of oxygen inhibition. X‐ray photo‐electron spectroscopy and atomic force microscopy reveal that the self‐assembly of F₂‐POSS‐(SH)₄‐TX/EDB at the air/(liquid monomer) interface forms a cross‐linked top layer via thiol–ene polymerization; this layer acts as a physical barrier against the diffusion of oxygen from the surface into the bulk layer. A mismatch in the shrinkage between the top and bulk layers arise as a result of the different types of photo‐cross‐linking reactions. Subsequently, the surface develops a wrinkled pattern with a low surface energy. This strategy exhibits considerable potential for preventing oxygen inhibition, and the wrinkled pattern may prove very useful in photo‐curing technology.     

A non‐linear interface element for 3D mesoscale analysis of brick‐masonry structures

This paper presents a novel interface element for the geometric and material non‐linear analysis of unreinforced brick‐masonry structures. In the proposed modelling approach, the blocks are modelled using 3D continuum solid elements, whereas the mortar and brick–mortar interfaces are modelled by means of the 2D non‐linear interface element. This enables the representation of any 3D arrangement for brick‐masonry, accounting for the in‐plane stacking mode and the through‐thickness geometry, and importantly it allows the investigation of both the in‐plane and the out‐of‐plane responses of unreinforced masonry panels. A co‐rotational approach is employed for the interface element, which shifts the treatment of geometric non‐linearity to the level of discrete entities, and enables the consideration of material non‐linearity within a simplified local framework employing first‐order kinematics. In this respect, the internal interface forces are modelled by means of elasto‐plastic material laws based on work‐softening plasticity and employing multi‐surface plasticity concepts. Following the presentation of the interface element formulation details, several experimental–numerical comparisons are provided for the in‐plane and out‐of‐plane static behaviours of brick‐masonry panels. The favourable results achieved demonstrate the accuracy and the significant potential of using the developed interface element for the non‐linear analysis of brick‐masonry structures under extreme loading conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

The influence of defect and temperature on the fatigue behaviours of Al‐Si‐Cu‐Mg‐Ni alloy

High‐cycle fatigue (HCF) properties of two Al‐Si‐Cu‐Mg‐Ni alloys with different defect sizes named as alloys A (smaller ones) and B (bigger ones) were investigated at 350°C and 425°C, respectively. The results indicate that fatigue strengths of both alloys decrease as the temperature increases. Fatigue cracks originated from pores and oxide films at both temperatures. They propagated preferentially through cracked matrix at 350°C and debonded interface and grain boundary at 425°C. Alloy A exhibits higher fatigue life and fatigue strength than alloy B at 350°C due to its smaller pore sizes. However, it has slightly worse fatigue properties than alloy B at 425°C because the fatigue crack initiation is controlled by oxide film at this temperature and is not affected by its size. This indicates that there is a transition of predominant initiation site from pores to oxide films when the temperature increases. The fatigue strength estimated through defect size is consistent with the experimental results at 350°C, while unsuitable at 425°C.     

Improved estimation of residual capacity of batteries for electric vehicles

Abstract

This paper proposes an improved means of estimation for the residual capacity of lead‐acid batteries used in electric vehicles. The residual capacity of batteries in commercial products is usually indicated by the state of charge (SOC) of the battery set, in terms of the measurement of amp‐hours, or roughly an instant voltage. More practical and accurate SOC in the operation of electric vehicles must consider the original capacity when the battery is first installed, capacity deficiency due to high discharge rate, capacity dissipated in internal resistance, and correcting parameters for the battery aging process. The proposed estimation techniques include the amp‐hours measurement weighted by a correction function of various discharge rates, the transient open‐circuit voltage measurement to compensate for the energy dissipation from internal resistance, and the reset of parameters in the linear function of SOC and open‐circuit voltage for the aging effect. A monitoring circuit with a programmable logic chip is implemented, and the experimental results show that a more accurate indication of SOC is achieved using the modified estimation techniques, namely a weighted ampere‐hour measurement with transient open‐circuit voltage combined with the aging effect.     

Addressable Microfluidic Polymer Chip for DNA‐Directed Immobilization of Oligonucleotide‐Tagged Compounds

A microfluidic polymer chip for the self‐assembly of DNA conjugates through DNA‐directed immobilization is developed. The chip is fabricated from two parts, one of which contains a microfluidic channel produced from poly(dimethylsiloxane) (PDMS) by replica‐casting technique using a mold prepared by photolithographic techniques. The microfluidic part is sealed by covalent bonding with a chemically activated glass slide containing a DNA oligonucleotide microarray. The dimension of the PDMS–glass microfluidic chip is equivalent to standard microscope slides (76 × 26 mm²). The DNA microarray surface inside the microfluidic channels is configured through conventional spotting, and the resulting DNA patches can be conveniently addressed with compounds containing complementary DNA tags. To demonstrate the utility of the addressable surface within the microfluidic channel, DNA‐directed immobilization (DDI) of DNA‐modified gold nanoparticles (AuNPs) and DNA‐conjugates of the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) are carried out. DDI of AuNPs is used to demonstrate site selectivity and reversibility of the surface‐modification process. In the case of the DNA–enzyme conjugates, the patterned assembly of the two enzymes allows the establishment and investigation of the coupled reaction of GOx and HRP, with particular emphasis on surface coverage and lateral flow rates. The results demonstrate that this addressable chip is well suited for the generation of fluidically coupled multi‐enzyme microreactors.     

The dynamic characteristics of taper seals

Abstract

The dynamic characteristics of taper seal has been investigated. The approach is similar to Black's analysis; the stiffness and damping coefficients are derived. The results showed that the taper seals presented more stable characteristics comparing with plain seals. The practical application of this theory is increasingly used in industry.