| With the rapid development of modern technology,electromagnetic waves are increasingly used in commercial,military and civilian applications,especially in the military field.In order to improve the survivability and penetration ability of weapons,a new generation of stealth materials requires a comprehensive performance of “light,thin,wide and strong”.The structural absorbing material combines the bearing and absorbing microwave to reduce the structural weight and improve the absorbing performance.The traditional structural absorbing material is incorporated an absorbent in a high performance fiber reinforced resin matrix to improve the absorbing properties of the material.The type and content of the absorbent have certain effects on the mechanical and absorbing properties of the composite.The application of frequency selective surfaces in stealth materials breaks the limitations of traditional stealth material preparation and provides new ideas for the design of a new generation of stealth materials.It is a research hotpot in the field of absorbing microwave to introduce the periodic structure into the composite material to improve the absorbing properties of the material.The main research contents and results in this paper are as follows:The hot pressing forming process of the composite material with the optimum mechanical properties was obtained by exploring the key parameters of the process,such as pressure point,pressure,curing temperature and curing time.Fiber reinforced resin based absorbing composites incorporated with magnetic loss absorber were prepared by hot pressing with nano-Strontium ferrite and carbonyl iron powder as absorbents,respectively.The cross-sectional characteristics of the stress fracture of the absorbent-incorporated composite material with different contents were observed.The distribution of carbonyl iron powder in the form of flakes and spheres in the composite was studied.The mechanical properties of the composites under different contents of absorbent were tested.And the influence of the change of the absorbent content on the electromagnetic properties and the absorbing properties of the composite was studied through the calculation of the reflectivity.For the nano-Strontium ferrite incorporated fiber reinforced resin matrix composite,when the content of the absorbent was 20 wt%,the bending strength of the composite increased by 9.7% compared with the composite without absorbent.But even if the nano ferrite content increased to a high level,the absorbing properties of the composite material was still very poor.For the carbonyl iron powder incorporated fiber reinforced resin matrix composites,the mechanical properties of the flake carbonyl iron powder incorporated composites were better than that of spherical carbonyl iron powder incorporated composites.For the flake like carbonyl iron powder composite,when the material was thinner,the corresponding peaks of reflection loss were in X and Ku bands.As the thickness increased,the reflection loss peak value of the composite shifted to the left.The absorbing properties of the material could be adjusted by adjusting the thickness of the composite.Carbon black,nano-graphite sheet,micron and nano-sizedBarium titanate and SiC fiber two-dimensional woven fabric were used as absorbents to prepare fiber reinforced resin based absorbing composites incorporated with electric loss absorbent by hot pressing method.The distribution of absorbents in the resin matrix were observed.The influence of the change of absorbent content on the mechanical properties of the composites was analyzed.The electromagnetic properties of the materials were analyzed,and the mechanism of the absorbent to improve the absorbing properties was described.When the carbon black content was 8 wt%,the flexural strength of the composite reached a maximum of 705 MPa.As the absorbent content increased to 10 wt%,the complex permittivity of the composite at 8.2 GHz increased to 6.7-j 4.1.The absorbing property of the composite was the best when the content of absorbent was 10 wt% and the thickness of the composite was 3 mm.For the carbon black-incorporated fiber reinforced resin matrix composites,The carbon black-incorporated composites with a content of 5 wt% were subjected to a constant temperature 230 ? heat aging test.The mechanical properties of the composites after heat aging for 1000 h were reduced by 32.4%,and the electromagnetic properties were basically unchanged.The results showed that the composites were in 230 ? can show better stability under constant temperature and heat aging.The tensile properties and bending properties of 5 wt% carbon black incorporated composites at 200 ? and 250 ? were tested.The results showed that the flexural strength and tensile strength of the composites at 200 ? and 250 ? were reduced by56.4% and 43.8%,respectively,and 72.2% and 72% at 250 ?,respectively.With the increase of absorbent content from 1 wt% to 5 wt%,the complex permittivity of the composite in 8.2 GHz increased from 4.69-j 0.4 to 7.48-j 2.53 for the fiber reinforced resin matrix composites incorporated with nano-graphite sheets.The carbon black and nano-graphite sheet incorporated composites with absorbing content of 5 wt%,the nano-graphite incorporated composites had better absorbing properties in X band than that of carbon black at the thickness of 3 mm.Comparing the mechanical and absorbing properties of micron and nano-sizedBarium titanate incorporated composites,it was found that the mechanical and absorbing properties of nano-sizedBarium titanate incorporated composites were better than those of micro-sizedBarium titanate incorporated composites.The nanometerization of the absorbent scale was advantageous for the improvement of the absorbing properties.As an absorbent,SiC fiber could solve the problem of uneven dispersion of absorbent in materials.However,SiC fiber reinforced composite materials could hardly meet the two basic principles that ideal absorbing material must meet,so it did not achieve a good absorbing effect.For absorbing composites containing a single layer periodic structure,the influence of the position of the periodic structure in the composite,the unit size of the periodic structure,the side length of the square patch,the surface resistance and the thickness of the square patch,and the content absorbent of the matrix were investigated by simulation.The law of the influence of the change of the factors on the absorbing property of the composite was found out.The multi-layer periodic structure can improve the absorbing bandwidth of the composite by the coupling between multiple layers of FSS.Therefore,the absorbing properties of the composite with multi-layer periodic structure were studied,and the accuracy of the simulation was verified by experiments.When the periodic structure was increased from the bottom layer to the surface layer to 13 layers,the simulated composite had a bandwidth of 6.6 GHz with reflection loss less than-8 dB.The experimental results showed that the reflection loss of the composite less than-8 dB was from 9.6 to 15.6 GHz,with the bandwidth of 7 GHz.There was good consistency between simulation and experiment. |
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