| Honeycomb absorbing structure is a kind of structural absorbing material with excellent comprehensive properties,and is widely used in aviation,aerospace and shipping due to its light weight,good load-bearing properties and excellent absorbing properties.However,the excellent mechanical properties of the honeycomb absorbing structure are only displayed in the out-of-plane,and its in-plane mechanical properties are poor.Usually,the out-of-plane mechanical properties are dozens of times better than those in-plane.In practice,it is easy to cause failure and bring very serious consequences when it is subjected to in-plane forces.To solve these problems,thesis designs a modified polyurethane foam filled honeycomb structure,which mainly improves the in-plane mechanical properties of the honeycomb structure,and at the same time gives consideration to the electromagnetic properties,thus effectively expanding its application fields.The main research and conclusions of thesis are as follows:1)A method for preparing modified polyurethane foam was invented and its mechanical properties were studied.A modified polyurethane foam was prepared through formula design and optimization of the foaming process,and conductive carbon black was introduced to realize the preparation of modified polyurethane wave-absorbing foam.The results of the mechanical experiments show that the addition of conductive carbon black will affect the foaming process,increasing the number of foam's holes and reducing the density by more than 10 Kg/m3,which makes the elastic modulus and energy absorption properties reduced to some extent compared with the structure without carbon black.2)Based on experiments and simulations,the mechanical properties of foam-filled honeycomb structures are systematically studied.The mechanical properties and deformation modes of the structure were explored through quasi-static compression experiments and compared with the honeycomb structure.The failure mode of the honeycomb structure during out-of-plane compression is layer-by-layer folding,and the failure mode after foam filling is uniform deformation;and the yield strength of the 1.83pore honeycomb increased by 83.2%and the 2.75-pore honeycomb increased by 91.1%after foam filling.During in-plane compression,the filling of foam makes the folding band basically disappear,which can significantly improve the fluctuation of the plateau phase of the displacement-load curve.The plateau force in the L direction can be increased by up to 1111.3%,in the W direction can be increased by 695.7%.Based on ABAQUS simulation software,the vibration properties of the honeycomb structure before and after the foam filling is investigated.The results show that the foam filling does not change the vibration mode of the original honeycomb in the low-order mode,but its natural frequency can be increased by more than 300%.3)The electromagnetic properties of the foam-filled honeycomb absorbing structure are studied through experimental.Cyanate ester and modified polyurethane foam were used to fill the honeycomb structure respectively,and their electromagnetic properties were studied.The dielectric constant of cyanate ester and self-made foam was evaluated by coaxial test system and free space method.It was found that the cyanate ester foam would make the electromagnetic properties of the original honeycomb absorbing structure worse,while the real part of the dielectric constant of self-made foam was close to the optimal value of 1.4 obtained by the simulation experiment.After that,the absorbing properties of honeycomb absorbing structure filled with modified polyurethane foam was tested.The results show that a composite structure that does not affect the absorbing properties of the honeycomb structure can be obtained under a specific ratio,and the electromagnetic properties of the honeycomb structure can be further improved by suitable conductive carbon black,with a maximum enhancement of 17.3dB at 15 GHz. |
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