| The lightweight,high-strength,sound-absorbing sandwich composite material is a promising choice for the future acoustic stealth structure that replaces the traditional anechoic structure.In order to meet the requirements of pressure resistance,sound absorption and lightweight,this paper carried out the research on the preparation and pressure/sound absorption performance of stitch-reinforced foam sandwich composite materials.The stitch-reinforced foam sandwich composite materials are prepared by vacuum infiltration molding process to investigate the effect of stitching distance,stitched fiber-column diameter and foam density on the properties of the sandwich structure composites.The main contents as following:(1)The vertical stitching reinforcement form was selected by theoretical analysis and finite element simulation method.The influencing factors of the flat compressive and flexural properties of the sandwich composite structure are analyzed.The results show that the flat compression modulus of sandwich structure with vertical stitching is twice as much as that with 45 degree stitching.(2)The processing problems of the stitch-reinforced foam sandwich composites prepared by VIMP are analyzed to investigate the effect of stitching process on the processing quality.The results show that when the fiber volume fraction of the stitched fiber-column in the range of 45%?47%,the resin is well infiltrated with the fibers in the foam pores with the least defects.(3)The effects of different stitching parameters on the overall flat compressive properties are investigated.The results show that,the flat compressive modulus and strength of the stitched sandwich composite reduced by 65.7% and 54.3% respectively,as the suture spacing is doubled.The flat-compressive modulus and the flat-compressive strength of the increase significantly with the increasing of the stitched fiber-column diameter,and the flat-compressive modulus positively correlated with the square of the fiber-column diameter.After the stitching is strengthened,the maximum flat-compressive modulus is increased by 9.2 times,and the maximum flat-compressive strength is increased by 3.9 times,after stitched reinforcement.The failure of stitch-reinforced foam sandwich structure depends on the stitching method,which is mainly consists of two failure modes: Foam cracking failure and fiber-column failure.(4)The sound-absorption coefficient of the stitched reinforced foam sandwich structure under 1atm air pressure and 2MPa pressure conditions are tested.The results show that the average sound-absorption coefficient of the stitched samples at atmospheric pressure is 0.49,while that of the unstitched samples is 0.12.The sound-absorption coefficient of the stitch-reinforced sample under 2MPa pressure is 0.75,while that of the unstitched samples is 0.49.It indicates that the stitching reinforcement can effectively enhance the sound-absorption properties of the sandwich composite structures.The finite element simulation by ANSYS is used to analyze the variation of the sound-absorption coefficient with frequency.The results show that the simulation results are in agreement with the experimental data. |
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