Analytical and numerical studies of approximate phase velocity matching based nonlinear S0 mode Lamb waves for the detection of evenly distributed microstructural changes View the table of contents for this issue, or go to the journal homepage for more 2016 Smart Mater. Struct. 25 045023

Based on experimental observations and theoretical explanation of the streamer spatial extension for an inhomogeneous field gap in SF6, a new model is developed, taking into account the probability of the appearance of an efficient electron. The model, which can help one to better understand the breakdown characteristics of the impulse-steepness dependence, relates the spatial extension of the streamer corona in an inhomogeneous field gap in SF6 gas to the steepness of applied positive impulses.

This paper describes the mechanism of discharge development in non-uniform field gap in SF 6 under positive impulses with different rising steepness. Based on theoretical consideration, an expression of the transition delay time from streamer to leader is presented, which can help to better understand the process of streamer to leader transition under impulses with different rising steepness in SF 6 . Also, the calculated results of the proposed expression for the transition delay time are quite in agreement with the experimental ones.

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To solve existing problems of current processing methods for flanged cylinders with a large diameter-thickness ratio, a double-roller clamping spinning (DRCS) process is proposed as a novel flanging process on a cylinder. Finite-element (FE) numerical simulation is used to research the DRCS process. First, on the basis of non-linear FE analysis software Abaqus/ Explicit, an FE model for the DRCS process is established. Second, some key problems in FE modelling of DRCS are solved, for example, the definition of contact, the treatment of meshing, the load curves applied on the rollers, the optimal clamping position, and the bending point on the defined initial workpiece. Then, the reliability of the FE model is verified using the energyconservation principle and experimental results. Finally, the DRCS process of the flange is simulated using the verified FE model, and the equivalent stress field, equivalent strain field, and wall-thickness distribution on the flange during the whole forming process are obtained. The FE model established in this study can be used to explore and develop the DRCS process.