Investigation On Plastic Deformation Mode Of The NOMEX Honeycomb Structure Subjected To Low-speed Loads

This paper investigate the plastic deformation mode of the honeycomb sandwich structures to quasi-static compression load, impact load and falling load.First, the quasi-static uniaxial compression load is applied on the NOMEX honeycomb structure and aluminium honeycomb structure and the mode of plastic deformation is studied. Experimental study and theoretical analysis are two aspects of the system work, and obtained the following results:Experimental study found that the plastic deformation is buckling overlap drape deformation of the 4.76 mm diameter size NOMEX honeycomb structure and the same aperture size of aluminium honeycomb structure under the quasi-static uniaxial compression load. The reason is that section moment in gradually increasing, until the moment is equal to the biggest moment, then a plastic hinge appear. Along with the load is increasing, the plastic hinge moving along the honeycomb cellular wall produces the buckling overlap drape deformation. The deformation of the honeycomb structure with 3.18mm aperture size is completely different. It lost the carrying capacity because of the overall unstable. The causes of this phenomenon for this structure are aperture size decreased, and density increased, stiffness increased, and structure holistic enhanced.Parameter study (including cellular structure density, cellular materials) indicated that density can change stress and deformation performance.3.18 mm aperture size NOMEX honeycomb structure only has elastic stage, but 4.76 mm aperture size NOMEX honeycomb's force-displacement curve has three stages, especially the platform area is obvious. The force-displacement curves of the honeycomb structure with the same aperture size and different materials are same. The difference is the peak stress and stability of the platform area. The difference between the honeycomb structure and the honeycomb sandwich structure are the peak stress and the yield stress. This phenomenon show that the honeycomb sandwich structure not only have high strength, also have the good energy-absorption efficiency, perfect inherited the good performance of two kinds of material.Furthermore, the deformation modes of the NOMEX honeycomb sandwich structures subjected to impact loading and falling loading are studied.Projectiles were used to provide different impulses to the NOMEX honeycomb sandwich beams and laser displacement sensor was used to research the back face deformation displacement of specimens. Deformation mode of the front face is mainly indenting in the region of impacting mixed with the overall deformation, and the failure mode is indenting. The regions of the deformation of the core are divided into fold area, part fold area and not fold area. The failure is the shear failure between fold area and not fold area. Deformation mode of the back face is the overall deformation and arched shape. Parameter study (Including the impulse of the projectiles and the thickness of the face) indicated that the displacement of the back face of the structure which have the same material parameters increasing with the impulse increasing. In the condition of the material and the thickness of the core are same, the thickness of the face is increasing, and the ability to resist impact is increasing, and the displacement of the back face is reducing. This paper calculated and analyzed the absorption of the energy. 50%--90% energy is absorbed by the core in the impact process. And impulse is increased, the more energy absorbed by the core. The results indicate that the sandwich beams can be effectively improved the ability to resist deformation by increasing the face thickness.The research content includes studied that the plastic deformation modal of the glass fiber reinforced honeycomb sandwich structures under the low-speed impact loading applied by DWTT loading experiment machine and the relationship between the DWTT energy and the depth of the DWTT pressed into the specimens. The deformation of the upper face under the falling load with the hollow, solid edge support conditions is mainly indenting in the region of the DWTT and the failure mode is fiber fracture. The regions of the deformation of the core are divided into fold area, part fold area and not fold area. The failure is the shear failure between fold area and not fold area. Deformation mode of the lower face is the overall deformation and arched shape. The deformation of the upper face under the falling load with the rigid, solid edge support conditions is mainly indenting in the region of the DWTT and the failure mode is also fiber fracture. But the regions of the deformation are only divided into fold area and not fold area. That is say, the deformation of the core only in the DWTT region. And the lower face has no deformation. The specimens have different thicknesses of the face, the abilities of resistant load are different. The thickness of the upper face is increasing, and the ability is increasing. Analyzing the results found that the relationship of the energy of the DWTT and the displacement is linear relationship.