This study proposes producing sandwich composites that have functionalities in addition to good mechanical properties. Flexible polyurethane (FPU) foam is used as the core, whereas nonwoven fabrics are used as the top and bottom panels. The functionalities, including flame‐retardant (FR) efficacy, acoustic absorption, and electromagnetic shielding effectiveness (EMSE), help in expanding the application fields. In this study, FR agent is added to FPU foam to form the core, while the low‐melting point polyethylene terephthalate (LPET) nonwoven fabric with/without carbon fiber (CF) fabric is used as panels. One‐step molding and hot pressing are used to make these materials into LPET/FPU and CF‐LPET/FPU sandwich composites. The cell structure of the FPU foam is examined, after which the limit oxygen index (LOI), the compression modulus, and heat insulation efficacy of LPET/FPU sandwich composites are examined, thereby examine the influence of FR agent. The test results show that the mechanical properties of sandwich composites are dependent on the amount of FR agent. Using 50 wt %, FR agent provides LPET/FPU sandwich composites with an optimal LOI of 28. In addition, the combination of CF fabric further provides CF‐LPET/FPU composite sandwich with the maximum acoustic absorption coefficient of 0.90376 and an optimal EMSE of 50 dB. The proposed sandwich composites have functionalities of FR efficacy, acoustic absorption, heat insulation, and EMSE and thus are qualified for protective partitions used in karaoke and kindergartens. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46871.

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Exposure to prolonged or excessive noise has been shown to cause a range of health problems. In this study, flexible sandwich composites (FSCs) with excellent sound absorption and mechanical properties were designed and fabricated by a one-step foaming process. The compound fabric as composite panel and fabric sequence contacted with PU foam has been designed and optimized for excellent cushioning and sound absorption properties. In comparisons of three processing methods for fabricating compound fabrics as reinforced panels of FSCs, punching/hot pressing was found to be the most effective method. Through experiments, the L (low-melting polyethylene terephthalate nonwoven fabric, LPNF) -W (warp-knitted spacer fabric, WKSF) -F (flexible polyurethane foam, FPF) composites had the best performance, reaching the sound absorption coefficient of 0.997 (1000 Hz), 107.77 KPa in compression modulus, 6541 N in maximum impact contact force and 44.68% in impact energy absorption. Morphological study revealed that the transition region formed by FPF and WKSF played a vital role in the L-W-F structure. In that region, small cavities and complex porous paths were observed that effectively improved the sound absorption and cushioning properties by dissipating the stress wave and sound wave level-to-level.

Aiming at the problem of premature failure of organic material polyimide film in the afterburner fuel distributor of a turbofan engine, the material parameters of polyimide film and the temperature and the fluctuation amplitude of the film during use were obtained based on previous investigation. The finite element simulation model of polyimide film was established in ANSYS software to study the Mises stress distribution and weak area distribution of the film when the film fails in the form of fracture. Based on the fatigue life calculation theory of probabilistic fracture mechanics, the fatigue life cycle times and their variation rules of the film under different reliability were obtained. The results show that there is stress concentration in the film, and the stress con-centration and weak area of the film occur at the outer edge of the film clamping. The fatigue life cycle times of the film under different reliability are calculated, and the fatigue life cycle times decrease with the increase of reliability.