Analysis Of Bending Mechanical Properties Of Honeycomb Sandwich Structure With Defects

Recently, metal honeycomb sandwich structures are widely used in aerospace field because of its specific advantages. However, there are some inevitable technical defects in the metal cellular structure. Some defects won’t affect the mechanical performance, but some are seriously harmful to the safety in use. Based on the problem, surface and honeycomb de-soldering defects which will seriously affect mechanical properties of honeycomb sandwich structure are analyzed in this paper. Because the honeycomb sandwich structure is usually used to bear the bending load as external panel, the bending performance is also discussed in this paper.First of all, the FEM is used to calculate equivalent stiffness matrix of the honeycomb sandwich structure. A single unit model of the structure is built, and periodic displacement boundary conditions of single unit modeling are derived theoretically. In the whole calculation, the internal structure is taken into account. The usage of single unit to obtain the whole stiffness matrix can save the computation time enormously. The result demonstrates that surface and honeycomb de-soldering defects can influence the bending performance of the structure greatly.Then, three point bending test is performed to analyze bending performance of the honeycomb sandwich structure with defects. In the test, two defect dimensions are designed, different test pieces are chosen, which are the long and short beams, thick and thin covering beams. NDT is conducted before bending test with infrared and supersonic method to make sure specimens with the design defects. Short beam experiment is used to determine shear strength(modulus) of the structure. Long beam experiment is used to obtain the bending strength. Overhanging beam test is used to measure the elastic modulus of the structure and shear modulus of the honeycomb core.Finally, the bending performance of honeycomb sandwich structure with different defects under various conditions is analyzed by numerical simulation. Numerical method is used to simulate and analyze the bending performance of honeycomb core structure with defects, which is also verified in comparison with the test results. Bending test of honeycomb structure in different thickness under room temperature and high temperature is conducted, respectively. It is found that with the thickness of surface panel, the honeycomb core thickness remains constant. Therefore, it is less influence on the bending performance by the defects. In addition, two de-soldering conditions are simulated. The results show that when defects exist on upper or under panel, the specimen will be destroyed quickly if the defects dimension reaches a certain value.