Study On The Stability Of Liner Of Composite Overwrapped Pressure Vessels

Compared with traditional metal pressure vessels,metal-lined composite pressure vessels can not only reduce the weight but also meet the strength requirements.It has been favored by aerospace systems,as well as energy storage devices and automobile engineering.Composite pressure vessels need autofrettage in the production process,so that the excellent properties of the fibers can be fully deployed,thereby significantly increasing the overall load capacity of the pressure vessel.However,due to the mismatch of plastic deformation between metal liner and composite material,metal liner will produce irreversible plastic deformation during autofrettage while composite material is still within the elastic range.After unloading the autofrettage pressure,a compressive stress exists between the liner and the composite material,and the metal liner is prone to instability under high compressive stress,which significantly affects the service life of the pressure vessels.However,most of the researches on composite pressure vessels only focus on the strength analysis and material failure,and there is a lack of researches on the stability of the liners.This thesis summarizes the existing studies on the buckling problem of pipeline liner and finds that the buckling problem of fiber-wound composite pressure liner is related to the shrinkage buckling problem of the pipeline.Both are liner buckling caused by the inward shrinkage of the outer layer.However,the existing liner buckling model can only be used to solve the elastic buckling analysis based on the two-dimensional plane strain assumption.The depression and buckling deformation of the liner of the composite pressure vessel are complexthree-dimensional problems,and it cannot be simplified by the traditional two-dimensional plane strain model.Considering many factors of material nonlinearity and geometric nonlinearity,it is difficult to derive the critical buckling load by analytically analysis.The thesis established a finite element model of liner buckling based on the assumption of two-dimensional plane strain.The numerical simulation results are in good agreement with the Vasilikis simulation results,which verifies the rationality of the finite element analysis in the buckling loading prediction.Then the two-dimensional model is extended to a three-dimensional model,and the three-dimensional concave defects are introduced into the finite element model by modifying the coordinates of the element nodes.The stability of the liner was analyzed by using the nonlinear finite element analysis technique,considering the factors such as large deformation,initial geometrical defects,contact nonlinearity and material nonlinearity.To sum up,the local buckling analysis model of the composite material pressure vessel liner is established in this thesis,considering the influence of the autofrettage.The influence of some factors on the critical buckling load was studied,including the initial depression depth,axial dimension,hoop dimension,and axial stress and hoop stress ratio of the pressure vessel.The research shows that the critical buckling load of the local buckling of the composite pressure vessel has a strong sensitivity to the geometric defects.