Study On Damage Mechanism Of Composite Honeycomb Panel Bonded Repair Structure

Composite structure is widely used as the main raw material of civil aircraft load-bearing parts because of its advantages of high strength and high specific stiffness.Structural parts may be damaged and need to be repaired under complex working conditions.The damage mechanism and ultimate bearing capacity prediction of repaired composite honeycomb sandwich panels have become an urgent problem to be solved in the study of composite strength evaluation because of the different degrees and types of damage in each component after damage repair.In this paper,the progressive damage model of composite honeycomb sandwich panel and its typical bonded repair structure is established,and the structural bearing capacity and damage mechanism are studied.The progressive damage model of composite laminate bonded repair structure considering the influence of slope is established.The mixed failure criterion combining Hashin failure criterion and maximum principal stress criterion is selected as the damage criterion,and the appropriate stiffness degradation model is selected as the stiffness reduction scheme after material failure.By compiling the VUMAT subroutine,the failure criterion and stiffness degradation model are added to the finite element analysis.The influence of different inclinations on the bearing capacity of glued repair structure under tensile load was studied.The simulation results show that the repair efficiency increases linearly with the slope decreasing,and the increase of ultimate bearing strength is not obvious when the slope is 1:20and 1:25.Therefore,for the repair parts with high tensile load-bearing requirements,the slope of 1:20 is more appropriate in the bonding repair process of laminates.A progressive damage model of composite honeycomb sandwich bonded repair structure considering the influence of temperature is established.The model not only considers the influence of temperature on the constitutive equation,but also considers the influence of temperature on the basic properties of composite materials.Considering the complexity of the model and the highly nonlinear problem,ABAQUS / explicit solver is selected to solve the problem.The influence of temperature on the ultimate strength and damage mechanism of composite honeycomb sandwich repair structure under bending load was studied.The results show that with the increase of temperature,the material properties are damaged,and the debonding coefficient is reduced accordingly,and the ultimate bending capacity is reduced.The temperature rise and debonding of the adhesive layer will aggravate the separation between the patch and the damaged part,and destroy the stability of the repaired structure.Finally,according to the verified progressive damage model of honeycomb sandwich repair structure,the parameter optimization analysis is carried out.The effects of different inclination and temperature on the ultimate bearing strength,failure displacement and repair rate of composite honeycomb sandwich bonded repair structure were studied.The progressive damage results show that the stepped bonding repair can effectively improve the ultimate bearing capacity of the damaged structure,and is superior to the patching bonding method.In the repaired structure,the adhesive layer is most affected by temperature.The strength and shear stress bearing capacity of the adhesive layer are related to the stability of the repaired structure.The two progressive damage models established in this paper can effectively predict the ultimate bearing capacity and damage propagation mode of repaired composite structures,which is of great significance to the study of damage mechanism of repaired composite structures.