Stress Distribution Around Countersunk Hole In Carbon Fiber/Epoxy Composite Laminates

At present,with the automotive lightweight technology in the automotive industry is widely used,automotive lightweight materials-carbon fiber composite materials are also a large number of applications in the automotive industry,the application prospects are bright.Application of unavoidable composite material connection problems,especially in the mechanical connection hole will inevitably lead to hole stress concentration,there may be hole defects,buried for the safety of the car.In this paper,the stress distribution of the countersunk hole in the carbon fiber composite laminates and the related problems of the stress concentration in the hole are studied.The application of the lightweight technology of the carbon fiber composite body and the design and optimization of the lightweight structure of the vehicle body are provided support.This article has done the following work:Firstly,an analytical model of composite laminates with countersunk holes was established.The model analysis method(P-C model analysis)was established by combining the progressive damage model with the cohesive element model,and the analysis method was verified.Compared with the literature experiment,the bearing capacity is predicted to be accurate and the error is within 1%.The failure mode is consistent with the failure shape of the specimen.Secondly,the factors influencing the stress concentration of the countersunk hole are analyzed,such as plate width,plate thickness,the radius of the hole,countersunk angle,the depth of the countersunk and the laminate ply angles.By means of factorial analysis and multivariable nonlinear fitting method,the effective and accurate stress concentration equation of the countersunk head of composite laminates was obtained and verified.Based on the FEA results of the countersink,it was found that the maximum stress concentration Kt occurred in the transition area between the countersink and the straight hole.Finally,the stress concentration of the countersunk hole of the composite laminates can lead to higher interlaminar stress,resulting in secondary expansion of the slight delamination damage.The delamination initiation and growth of the composite laminates structure with the countersunk hole in the bolt pre-loading process are also investigated.When there is an embedded delamination at the transition area of countersunk hole,the delamination in the bolt pre-loading process is easy to expand.The delamination factor,the plate countersunk angle and the delamination depth of the plate thickness have a significant effect on the delamination initiation and growth behavior of the composite laminate.