Buckling Analysis Of Carbon Fiber Composite Cylindrical Shells Under External Pressure

Submersibles are important equipment for the exploration and development of marine resources.As one of the important components of the submersible,the pressure shell plays a role in ensuring the safety of the internal operators and the normal work of various equipment.The performance of the pressure shells is affected by various factors,including material properties,structural form,load and environment.Among them,material properties are a prerequisite for optimizing overall performance,and designers must consider a combination of factors,such as strength,stiffness,fatigue and corrosion resistance,when selecting materials.Due to their advantages of small weight,high strength,corrosion resistance and strong machinability,carbon fiber composites have good application and development potential in underwater pressure-resistant components;thus,an in-depth study on the bucking characteristics of carbon fiber composite cylindrical shells was performed.The main research contents are as follows:(1)Based on the experimental and numerical analysis methods,the buckling characteristics of carbon fiber composite cylindrical shells under uniform external pressure were studied,and a nonlinear analysis method was established to accurately calculate the buckling load of carbon fiber composite cylindrical shells.Eight carbon fiber composite cylindrical shells with different length-to-diameter ratios(L/d)and ply angles θ were designed and manufactured.The geometry,wall thickness,inner diameter and length of each cylindrical shell,as well as the material properties of the corresponding plates,were measured.Then,a hydrostatic test was performed.According to the measured data,the linear and nonlinear buckling analysis of carbon fiber composite cylindrical shells with real geometric defects was effectively performed,and the error of the test and numerical analysis results was within 7%.(2)The effects of the length-to-diameter ratio,ply angle and geometric defects on the buckling characteristics of carbon fiber composite cylindrical shells with positive and negative symmetric alternating padding and asymmetric alternating padding were discussed.The influence trends of the positive and negative symmetrical alternating padding and asymmetric alternating padding were basically the same,and the buckling bearing capacity of the cylindrical shell decreased with increasing length-to-diameter ratio.The ply angle had a great influence on the buckling characteristics of carbon fiber composite cylindrical shells,and the influence of the ply angle varied with the length-to-diameter ratio.Moreover,the carbon fiber composite cylindrical shell was a defect-sensitive structure,and the introduction of initial geometric defects reduced the bearing capacity of the shell.With the increase in the geometric defect coefficient,the influence of defects on the bearing capacity of the shell gradually decreased.(3)The BP neural network optimized by the sparrow search algorithm(SSA)was established to predict the critical buckling load of carbon fiber composite cylindrical shells.Based on the influencing factors of the buckling performance of carbon fiber composite cylindrical shells,the finite element model was used to generate the neural network training set and test set.The BP neural network prediction model optimized based on the SSA combined the nonlinear mapping ability of the artificial neural network(ANN)and the global search ability of the SSA,and the predicted value was in good agreement with the target value.The maximum error from the predicted target value was 6.88%,and the average error was 2.24%.(4)The buckling characteristics of ribbed carbon fiber composite cylindrical shells under uniform external pressure were studied by experimental and numerical analysis methods,and the effects of the rib cross-section,rib geometry and rib distribution on the buckling load and buckling mode were determined.A method for analysing the buckling mode of ribbed carbon fiber composite cylindrical shells based on the Hashin damage criterion was proposed,and this method was in good agreement with the experimental results.The ribbing method and buckling analysis method of carbon fiber composite cylindrical shells were established,and the research results provided a relevant basis for the practical application of subsequent ribbed composites in engineering.