Research On Damage And Scarf Repair Of Edge Closed Honeycomb Sandwich Panels

Composite honeycomb panels are one of the most effective structural forms to improve the bending specific stiffness of the structure.Honeycomb panels whose joints are tapered or closed is widely used in aerospace structures.However,in the process of manufacturing and maintenance of composite honeycomb panels,defects such as cracks,debond and delamination are inevitably caused,resulting in a decrease in structural load carrying capacity.Therefore,it is of great significance to conduct strength analysis,damage assessment and repair research on edge closed composite honeycomb panels.The main work of this paper is as follows:(1)A progressive damage UMAT subroutine containing equivalent stiffness of honeycomb core,Besant criterion and direct stiffness reduction scheme was prepared.The comparison between the finite element calculation results of compressive/shearing examples about the honeycomb panel and the literature test results proves that the subroutine can reasonably predict the ultimate strength and failure mechanism of the honeycomb panel under compressive/shearing conditions.(2)The finite element models of the edge-closed honeycomb panel without defects and with surface/core debonding defects were established.The effects of different debonding defect sizes on buckling load and buckling mode under compressive and shearing load were analyzed.According to the analysis results,40 mm and 80 mm were selected as the typical debonding defect size.(3)The compressive and shearing tests of perfect honeycomb panels and the compression test of honeycomb panel with typical prefabricated defects were carried out.The test results agree with the simulative results,and the reliability of the established analytical model is verified.(4)The finite element model of the stepped repair about honeycomb panels is established.The shearing ultimate strength prediction and damage expansion analysis of the edge-closed repair structure are carried out.After the repair,the ultimate strength of the intact structure is almost restored.The effectiveness of the repair method was verified.The effect of patch width and additional layer patch diameter on recovery strength was analyzed.