Investigation On Compression Strength Of Honeycomb Sandwkh Structure With Closing Frame

Honeycomb sandwich structure is widely used in aerospace and other fields because of its high specific stiffness,high specific strength,light specific mass,sound insulation,heat protection and fatigue resistance.There is a transition zone with sloping external enclosure frame when honeycomb sandwich structure transits to thin plate.In order to explore the static mechanical properties of the honeycomb sandwich structure with enclosed edge frames and the effect of core debonding on the whole structure on the transition zone slope,the honeycomb sandwich structure with enclosed edge frames composed of aluminium alloy panel and Nomex honeycomb core is studied in this paper.Three basic elastic mechanical parameters of Nomex honeycomb core were measured and the failure process was analyzed.The critical strain energy release rate of surface-core interface cracking of honeycomb sandwich panel was measured and calculated by double cantilever beam(DCB)test and single limb bending(SLB)test.In DCB and SLB experiments,it is found that the separation of panel and honeycomb core is caused by the fracture of honeycomb core wall in contact with adhesive layer,and the crack surface propagates along the adhesive layer and honeycomb core interface.The failure process of honeycomb sandwich structures with enclosed frames under in-plane compressive loads is simulated by using interface elements.The influence of the inclined plane core bonding(intact and debonding)in the transition zone of sandwich structures on the failure load is discussed.It is found that the failure of the specimens under both bonding conditions occurs in the transition zone.The outer panel is the main load-bearing object,and the maximum stress and dangerous area are at the four corners of the outer panel.In the transition zone,the core debonding on the top of the slope has a greater impact on the stress of the inner panel,which is 49% lower than the maximum stress of the inner panel in the bonding model.The in-plane compression strength of honeycomb sandwich structure with enclosed frames was tested by compression test.The influence of inclined core bonding(intact and debonding)in transition zone of sandwich structure on failure load was compared.The experimental results show that for the materials studied,the compressive failure is characterized by the local instability of the outer version of the transition zone,and the failure strength of the debonded specimens is 2.2% lower than that of the specimens with good bonding.The results of finite element calculation and test for the failure load and failure mode of the two bonding cases are in good agreement,which indicates the validity of using interface element to simulate the interface between face and core in finite element analysis.