Defects or flaws in highly loaded structures have a significant impact on the structural integrity. Early inspection of faults can reduce the likelihood of occurrence of potential disasters and limit the damaging effects of destructions. According to our previous work, a novel approach called as Quantitative Detection of Fourier Transform (QDFT) using guided ultrasonic waves is developed in this paper for efficiently detecting defects in pipeline structures. Details of this fast method consist of three steps: First, an in-house finite element code has been developed to calculate reflection coefficients of guided waves travelling in the pipe. Then, based on boundary integral equations and Fourier transform of space-wavenumber domain, theoretical formulations of the quantitative detection are derived as a function of wavenumber using Born approximation. This lays a solid foundation for QDFT method, in which a reference model in a problem with a known defect is utilized to effectively evaluate the unknown defects. Finally, the location and shape of the unknown defect are reconstructed using signal processing for noise removal. Several examples are presented to demonstrate the correctness and efficiency of the proposed methodology. It is concluded that the general two-dimensional surface defects can be detected with high level of accuracy by this fast approach.
Aiming to the treatment of skin burns, a new wound dressing, nanofiber mats with metal or metal oxide nanoparticles (Ag, CuO and ZnO) , was fabricated by the electrospinning technique. During the therapeutic process, the antibacterial ability and bio-compatibility of a new dressing material are of major concerns. To expound the characteristics of EVOH nanofiber mats encapsulated with the metal or metal oxide nanoparticles, notated as Ag-EVOH, CuO-EVOH and ZnO-EVOH, respectively, for possible use as the new wound dressing materials, we have investigated the suitable processing parameters to fabricate these materials, such as the voltage, the tip-to-collector distance, the concentration of the solution, and the effect of environmental temperature. The antibacterial abilities and the bio-compatibilities of Ag-EVOH, CuO-EVOH and ZnO-EVOH were then tested and quantified. The outcomes show that the most suitable temperature for fabrication of the materials is 40℃(±3℃). Antibacterial experimental results indicate that 0.08g/ml of metal/metallic oxide shows the highest antibacterial ability on Staphylococcus aureus. And the largest diameters of bacteriastatic loops of the three kinds of nanofiber mats, ie., Ag-EVOH, CuO-EVOH and ZnO-EVOH, are 5.89mm, 5.21mm and 4.12mm, respectively. Fially, the cell proliferation of the three nanofiber mats show a similar growth trend.
Purpose Quantitatively detecting surface defects in a circular annulus with high levels of accuracy and efficiency has been paid more attention by researchers. The purpose of this study is to investigate the theoretical dispersion equations for circumferential guided waves and then develop an efficient technique for accurate reconstruction of defects in pipes. Design/methodology/approach The methodology applied to determine defects in pipelines includes four steps. First, the theoretical work is carried out by developing the appropriate dispersion equations for circumferential guided waves in a pipe. In this phase, formulations of strain-displacement relations are derived in a general equidistant surface coordinate. Following that, a semi-analytical finite element method (SAFEM) is applied to solve the dispersion equations. Then, the scattered fields in a circular annulus are calculated using the developed hybrid finite element method and simulation results are in accord with the law of conservation of energy. Finally, the quantitative detection of Fourier transform (QDFT) approach is further enhanced to efficiently reconstruct the defects in the circular annuli, which have been widely used for engineering applications. Findings Results obtained from four numerical examples of flaw detection problems demonstrate the correctness of the developed QDFT approach in terms of accuracy and efficiency. Reconstruction of circumferential surface defects using the extended QDFT method can be performed without involving the analytical formulations. Therefore, the streamlined process of inspecting surface defects is well established and this leads to the reduced time in practical engineering tests. Originality/value In this paper, the general dispersion equations for circumferential ultrasonic guided waves have been derived using an equidistant surface coordinate and solved by the SAFEM technique to discover the relationship between wavenumber of a wave and its frequency. To reconstruct defects with high levels of accuracy and efficiency, the QDFT approach has been further enhanced to inspect defects in the annular structure.
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