## 6 Conclusions and Discussion  
In the present analysis, the buckling load of a honeycomb reinforced laminated structure filled with viscoelastic material is examined by employing the equivalent stiffness parameters obtained through asymptotic methods and the Halpin-Tsai model. The geometrical and physical parameters that influence the composite laminate's buckling loads are qualitatively and quantitatively discussed and compared through an analysis. The following conclusions can be obtained from this research:  
1. The physical parameters, such as the elastic modulus and shear modulus of the viscoelastic material, are affected by the load's frequencies; accordingly, the buckling loads of the composite structure are influenced by the load's frequency. The trend of the buckling loads affected by the loading frequency is the same as the composite structure's dynamic equivalent effective stiffness, and the original phenomenon can be traced back to the behaviors of viscoelastic materials.
2. Buckling loads are affected by the geometry parameters of the composite sandwich structure directly. The buckling load is significantly increased by increasing by the width of the composite structure, but it is decreased sharply by increasing the length of the sandwich structure. This phenomenon shows the same results as those of the buckling analysis of classical beams and plates.
3. The composite structure's buckling load is influenced by the honeycomb reinforcement layer's thickness and the honeycomb's width. The main reason is that the equivalent stiffness of the composite sandwich structure is changed by the honeycomb reinforcement's width and height. It should be noted that, by comparing it to the honeycomb reinforcement layer's thickness, the honeycomb's width affects the structure's buckling loads to a relatively smaller degree.  
The moisture and temperature of the environment as well as the loading amplitude influence the viscoelastic material's physical parameters as well, which is the same as the frequency-dependent properties. The background temperature in the research is considered to be 20 \({}^{\circ}\)C, the loading frequency ranges from 1 to 1000 Hz and the moisture effect on the viscoelastic material is neglected. Moreover, the loading amplitude properties on the viscoelastic material are not taken into consideration. In further research, those factors will be introduced.  
D.Q.: Conceptualization, Investigation, Methodology, Writing--original draft preparation. Q.S.: Methodology, Writing--review and editing. S.Z.: Conceptualization, Methodology, Writing--review and editing. Y.W.: Writing--reviewing and editing, Supervision, Funding acquisition. X.Z.: Writing--reviewing and editing, Methodology, Funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Key Research and Development Program of China under Grant No. 2018 YFD0700604 and by the Fundamental Research Funds for the Central Universities under Grant No. 2019 kfyXJJS192.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.