Research On Static Compression Deformation Of Nomex Honeycomb Core In Automatic Fiber Placement Process

The Automatic fiber placement technology is one of the important technologies for the future production of aerospace composite components,and it can significantly reduce the manufacturing cost of composite materials and improve the molding efficiency.Nomex honeycomb sandwich composite materials skin is mainly made by hand lay-up molding process,which has problems such as low accuracy,high labor intensity,low material utilization rate and poor-quality stability.In order to obtain a good molding quality of the Nomex honeycomb sandwich composite materials,the automatic fiber placement of Nomex honeycomb sandwich composites has been studied at home and abroad.However,there is no in-depth study on the selection and influence of the laying pressure during in the automatic fiber placement process.This paper takes the regular hexagonal Nomex honeycomb core as the research object,and focuses on the static compression deformation of Nomex honeycomb core in the automatic fiber placement process.It provides a reference and basis for the extensive application of automatic fiber placement technology in honeycomb sandwich members.The main research work of this paper includes:(1)The static compression deformation process of Nomex honeycomb core in the automatic fiber placement process was systematically analyzed,and two influencing factors were obtained: laying pressure and Nomex honeycomb core structure parameters.Based on the analysis of the Nomex honeycomb core’s typical compressive stress-strain curve,the critical buckling load value of Nomex honeycomb core is defined as the maximum contact stress between the Nomex honeycomb core and the laying roller.Based on the rectangular thin plates theory of four-sided simply supported and unidirectionally compressed,the basic equation of the critical buckling load of the outside Nomex honeycomb core surface is established,and the ratio of the honeycomb core thickness to the core length has the most significant influence on the critical buckling load.(2)The unit cell Nomex honeycomb core finite element model was established and verified.The critical buckling load values and ultimate load values obtained by finite element linear buckling(eigenvalue method)and nonlinear buckling(arc length method)analysis,and are compared with the Nomex honeycomb core static compression test data.The research shows that the eigenvalue method is more accurate than the arc length method for the critical buckling load value of the Nomex honeycomb core,and the arc length method can better simulate the post-buckling behavior of the Nomex honeycomb core under static compression deformation.(3)Based on Gaussian statistical theory,the silicone rubber pressure roller was taken as the research object,combined with the quasi-static compression test of silicone rubber,the elastic modulus of silicone rubber was determined to be 1.22MPa;Classical Hertz contact theory was validated by experimental method can be applied to the elastic contact process between flexible silicone rubber roller and Nomex honeycomb core.The contact cores number of different core side lengths Nomex honeycomb core and flexible silicone rubber roller was calculated.The maximum contact stress of Nomex honeycomb core was obtained by multiplying the critical buckling load of the unit cell Nomex honeycomb core with the number of contact cores.(4)Based on the analysis of the elastic contact process between the flexible press roll and the Nomex honeycomb core,and the maximum deposition pressure corresponding to the Hertzian contact stress does not exceed the critical buckling load of the Nomex honeycomb core is defined as the allowable deposition pressure.The influence of thickness and core length on Nomex honeycomb core allowable placement pressure is analyzed.Research Results Shows: when the automatic placing pressure is between 100N~900N,the Nomex honeycomb core thickness has no significant effect on the allowable placing pressure;the side length of core lattice has obvious influence on allowable laying pressure.It is determined that the side length of the core is between 3.8mm~4.0mm,the allowable laying pressure of the Nomex honeycomb core is 800N;the side length of the core is between 4.0mm~4.2mm,and the allowable laying pressure of the Nomex honeycomb core is 500 N.