Local buckling resistances of cold-formed high-strength steel SHS and RHS with varying corner radius

This paper reports an experimental and numerical study of the cross-sectional behaviour of cold-formed high-strength steel (HSS) square and rectangular hollow section (SHS and RHS) members. Six stub column tests, six 3-point and three 4-point bending tests have been carried out, followed by the development of accurate finite element (FE) models and a parametric study. Based on the test and FE results, the design rules for slender cross-sections in European, American, Australian and Chinese standards and the GSRM method have been assessed via reliability analyses. A new equation for deriving the cross-sectional slenderness of SHS and RHS considering the influence of corner radius and new area reduction factors for designing slender cold-formed S900 (and above) SHS and RHS have also been propose

Ferroelectric Polymer Thin Films for Organic Electronics

The considerable investigations of ferroelectric polymer thin films have explored new functional devices for flexible electronics industry. Polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene (TrFE) are the most commonly used polymer ferroelectric due to their well-defined ferroelectric properties and ease of fabrication into thin films. In this study, we review the recent advances of thin ferroelectric polymer films for organic electronic applications. Initially the properties of ferroelectric polymer and fabrication methods of thin films are briefly described. Then the theoretical polarization switching models for ferroelectric polymer films are summarized and the switching mechanisms are discussed. Lastly the emerging ferroelectric devices based on P(VDF-TrFE) films are addressed. Conclusions are drawn regarding future work on materials and devices

Defect-Structure-Related Ferroelectric Properties of K0.5Na0.5NbO3 Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric ceramics K0.5Na0.5NbO3 (KNN) doped with Cu, Fe, and Ni have been prepared by a conventional ceramic process. The results reveal that Cu-doped KNN ceramic exhibits double-loop-like characteristics, while Fe & Ni-doped KNN ceramics show normal single loops. EPR spectra verified the formation of irreversible defect complex (DC1) and (DC2) in Cu-doped ceramics, while defect complexes were observed in Fe-doped ceramics and very small defect complex signal in Ni-doped ceramics. The experimental results show that the ferroelectric properties of KNN ceramics are strongly related to these defect structures

Bond stress-slip relationship in concrete-filled square stainless steel tubes

The application of stainless steel tubes in concrete-filled steel tube systems can significantly improve their corrosion resistance in comparison with those that employ carbon steel tubes. In this paper, a series of push-out tests were carried out to investigate the bond stress-slip behavior between stainless steel tubes and concrete. A total of 14 concrete-filled square stainless steel tube specimens were tested, covering two cross-sectional width-thickness ratios (B/t = 30 and 50), two concrete strength (fcu = 44 and 76 MPa), three rib stiffener types (ordinary, saw-shaped and perfobond leister) and two stainless steel grades (austenitic and duplex). The test results indicate that B/t, fcu and stainless steel grade have noticeable influences on the ultimate bond stress (τu) in concrete-filled square stainless steel tube and the addition of rib stiffeners significantly improves the bond behavior. The bond mechanism at different stages of loading and the effect of various parameters on τu are discussed. Based on the test results, an idealized bond stress-slip strain (τ-εS) curve was proposed, where good agreement between the test and the proposed model has been achieved.</p

Bond stress-slip relationship in concrete-filled square stainless steel tubes

The application of stainless steel tubes in concrete-filled steel tube systems can significantly improve their corrosion resistance in comparison with those that employ carbon steel tubes. In this paper, a series of push-out tests were carried out to investigate the bond stress-slip behavior between stainless steel tubes and concrete. A total of 14 concrete-filled square stainless steel tube specimens were tested, covering two cross-sectional width-thickness ratios (B/t = 30 and 50), two concrete strength (fcu = 44 and 76 MPa), three rib stiffener types (ordinary, saw-shaped and perfobond leister) and two stainless steel grades (austenitic and duplex). The test results indicate that B/t, fcu and stainless steel grade have noticeable influences on the ultimate bond stress (τu) in concrete-filled square stainless steel tube and the addition of rib stiffeners significantly improves the bond behavior. The bond mechanism at different stages of loading and the effect of various parameters on τu are discussed. Based on the test results, an idealized bond stress-slip strain (τ-εS) curve was proposed, where good agreement between the test and the proposed model has been achieved.</p

Preparation and Performance of Polypyrrole Film with Micro-Antennal Morphology for Medical Biology

PPy film with micro-antennal morphology was prepared by potentio-static method without any templates directly onto the Surfaces of iron, platinum and gold-plated plastic sheets, respectively. Morphology of PPy film was observed with scanning electron microscopy, and its electrochemical properties were determined by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Attention was paid to the influence of reaction time, potential value, types of substrates, types and conconcentrations of electrolyte on the morphology and electrochemical properties of PPy film. Stable PPy film with thriftily long antennae was obtained on different substrates with good electrochemical properties. The film was applied for a prototype of biosensor, in which bioactive substance of glucose oxidase was immobilized