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Blends of compatibilized polyoxymethylene (POM)/ethylene butylacrylate copolymer (EBA)/ethylene‐methyl acrylate‐glycidyl methacrylate copolymer (EMA‐GMA) and uncompatibilized POM/EBA were investigated. The notched impact strength of the compatibilized blends was higher than that of their uncompatibilized counterparts. The toughness of the POM blends was improved obviously with relatively low loading of EBA. Fourier transform infrared spectroscopy (FTIR) spectra of EMA‐GMA, pure POM, and POM/EBA/EMA‐GMA blends indicated that epoxy groups of EMA‐GMA reacted with terminal hydroxyl groups of POM molecular chains. The glass‐transition temperature (Tg) values of the POM matrix and the EBA phase were observed shifted to each other in the presence of EMA‐GMA compatibilizer indicating that the compatibilized blends had better compatibility than their uncompatibilized counterparts. With the addition of EBA to POM, both the compatibilized and uncompatibilized blends showed higher onset degradation temperature (Td) than that of pure POM and the Td values of the compatibilized blends were higher than those of their uncompatibilized counterparts. The scanning electron microscopy showed better EBA particles distribution state in the compatibilized system than in the uncompatibilized one. The compatibilized blend with an obvious rougher impact fracture surface indicated the ductile fracture mode. POLYM. ENG. SCI., 58:1127–1134, 2018. © 2017 Society of Plastics Engineers

This paper describes the design and development of the Dove, a flapping-wing micro air vehicle (FWMAV), which was developed in Northwestern Polytechnical University. FWMAVs have attracted international attentions since the past two decades. Since some achievements have been obtained, such as the capability of supporting an air vehicle to fly, our research goal was to design an FWMAV that has the ability to accomplish a task. Main investigations were presented in this paper, including the flexible wing design, the flapping mechanism design, and the on-board avionics development. The current Dove has a mass of 220 g, a wingspan of 50 cm, and the ability of operating fully autonomously, flying lasts half an hour, and transmitting live stabilized color video to a ground station over 4 km away.

The flexibility of flapping-wing strongly affects the aerodynamic performance of Flapping-wing Micro Air Vehicle (FMAV), and the deformations in span-wise and chord-wise directions are coupled together in flight. In this study, the flexible deformation is formulated in span-wise and chord-wise separately in order to analyze its effects on aerodynamic behavior. The preconditioned Navier-Stokes equations based on chimera grid are used in the computational fluid dynamics method to study the aerodynamic effects caused by flexible deformation, and the simulation results are compared with experimental test to illustrate the capability of above method. Based on our results, it is clearly showed that the span-wise flexible deformation should be limited in a small range to achieve higher aerodynamic performance and the chord-wise deformation could enhance the aerodynamic performance. The results also suggest that FMAV designers should design the flapping-wing with high stiffness leading edge to limit the span-wise deformation, and more flexible chord ribs to keep chord-wise deformation in suitable range.FMAV, flexible flapping-wing, Navier-Stokes equations, chimera grid, span-wise deformation, chord-wise deformation Citation:Yang W Q, Song B F, Song W P, et al. The effects of span-wise and chord-wise flexibility on the aerodynamic performance of micro flapping-wing.

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Sea-island polyurethane (PU)/polycarbonate (PC) composite nanofibers were obtained through electrospinning of partially miscible PU and PC in 3 : 7 (v/v) N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were influenced by composition ratio in the binary mixtures. The pure PC nanofiber was brittle and easy to break. With increasing the PU content in the PU/PC composite nanofibers, PU component not only facilitated the electrospinning of PC but improved the mechanical properties of PU/PC nanofibrous mats. In a series of nanofibrous mats with varied PU/PC composition ratios, PU/PC 70/30 showed excellent tensile strength of 9.60 Mpa and Young's modulus of 55 Mpa. After selective removal of PC component in PU/PC composite nanofibers by washing with acetone, the residual PU maintained fiber morphology. However, the residual PU nanofiber became irregular and contained elongated indents and ridges along the fiber surface. PU/PC composite fibers showed sea-island nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. At PC content below 30%, the PC domains were small and evenly dispersed in the composite nanofibers. As PC content was over 50%, the PC phases became large elongated aggregates dispersed in the composite nanofibers.

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Ternary polyoxymethylene (POM) blends comprising methacrylate‐butadiene‐styrene (MBS) copolymer and thermoplastic polyurethanes (TPU) in different weight percentages are prepared by a two‐step melt extrusion technique. The synergistic toughening effect of polyoxymethylene by MBS as the impact modifier and TPU as the compatibilizer is investigated. The thermal behaviors of the prepared POM/MBS/TPU blends are analyzed. The notched impact resistance of the modified POM (POM/MBS/TPU 80 wt%/15 wt%/10 wt%) reached 40.83 kJ m−2. The enhanced toughness of the POM/MBS blends with the incorporation of TPU indicates the significance of TPU as a compatibilizer. Although the TPU compatibilizer enhances the interfacial adhesion between POM and MBS and decreases the size of MBS particles, serious agglomeration phenomenon is observed at higher TPU contents (more than 10 wt%) and caused slightly reduced tensile strength and the elongation at break for the sample with both loadings of MBS and TPU at 15 wt%. Instead, further increase of the notched impact strength is noted resulting from the compatibilizer TPU and an effective impact modifier MBS on the POM blend system to achieve a “super‐tough” effect. These “super‐tough” polyoxymethylene blends can be applied as the host matrix for preparing various multifunctional nanocomposites.