Simulation And Experimental Research On Damage Failure Of Connecting Interface Of Stiffener And Skin Of Aircraft Door

Composite materials are more and more widely used in the aviation field because of their superior mechanical properties and economic benefits.At present,the composite material structure in the aviation field has transitioned from some secondary load-bearing structures to main load-bearing structures.The stiffener skin connection structure is the basic component of the composite stiffened panels.The strength of the connection interface between the stiffener and the skin is lower than the composite material itself.When the structure is subjected to external load,the interface damage failure is likely to occur first,which affects the overall structure’s load-bearing performance.Therefore,the performance of the connection interface plays a vital role in the overall performance of the structure,and it is related to the safety life of the overall composites structure.Analysis of the failure process and failure mechanism of the connection interface between the stiffener and the skin of the composite stiffened panels is very important for the application of aerospace composite material structure,and helps to develop the potential of composite materials.In this paper,based on the engineering and technical requirements,taking the typical stiffener skin structure of aircraft carbon fiber reinforced composite cabin door as the research object,aiming at the typical failure mode of interface delamination,the load bearing characteristics,failure process and failure mechanism under specific load are researched by experiment and finite element analysis.The research content of this paper is as follows:In this paper,the pull-off performance of the I-stiffener skin structure of the aircraft door was researched.Through the pull-off experiment research,the pull-off loadbearing characteristics of the structure were obtained,and it was found that the structure pull-off failure mode is the delamination of the interlayer interface in the outer edge of the long stringer.A three-dimensional finite element model of pull-off based on cohesive elements was established.The simulation results are in good agreement with the experiment,verifying the validity of the model,and reveals the interface failure process and failure mechanism of the structure’s pull-off failure.The finite element model takes into account the characteristics of higher interface strength due to the co-curing process,and analyzes the tearing problem of the ply in the pulloff experiment.At the same time,the difference between the delamination near the filling area in the finite element results and the experimental results was discussed in detail.It is considered that the difference is due to the manufacturing process defects and the complexity of the filling area structure.This paper also carried out the research on the side bending performance of the I-stiffener skin structure of the aircraft door.Through the side bending experiment research,the side bending load bearing characteristics of the structure were obtained.It is found that the failure mode of the structure is delamination at the interface of the tension side chamfer of the stiffener web.At the same time,the delamination will be accompanied by the delamination transition phenomenon because of the thin composite layer.Using the model parameters verified in the pull-off performance research,and considering the possible multi group interface delamination behavior of the tensile side layup of the structural under the side bending load,based on the cohesive element,a three-dimensional side bending finite element model was established.The simulation results are in good agreement with the experiment,verifying the validity of the model,simulating the failure process of each interface,revealing the interface failure process and failure mechanism of the structure’s side bending failure,and discussing the position of the structure’s side bending layer.The research results of this paper can provide theoretical basis and experimental reference for the design and engineering application of the stiffener skin structure of the composite stiffened panels,and can provide simulation ideas and methods for the finite element analysis of the structure.