Fatigue Performance Analysis Of Composite Shell Under Internal Waves

Composite Shell of Cylinder and cone is a kind of common typical structure of marineengineering, because of the complexity and particularity of the marine environment, The oceaninternal wave which is a kind of dynamic load is very common, but now research on fatigueproperties at the cylinder-cone shell under the action of ocean internal waves is currently blank, sothis paper is aimed to study this problem, the specific research process is as follows:First the paper uses the wave force formula derived by other scholars using the boundaryelement method (in two layer fluid mode) to calculate average force of ocean internal waves on thesubmerged body when the submarine in the pycnocline, I find that the additional pressure is verybig by calculating the internal waves force.Due to the different shell has the edge effect in the connection, Second after using the forcemethod to analyze mechanical property of cylinder and cone shell under uniform external pressure,I derive the formula that can be used to calculate the composite shell of cylinder and cone’s radialjoints stress and circumferential stress in the connection. through theoretical analysis and formuladerivation, I known that composite shell of cylinder and cone is like a beam-columns as the edgeeffect in the connection under the outside pressure, it performs that the outside surface is beenpulled, and the inner surface is been pressed. I also find that the ratio of cylinder radius and shellthickness has the effect to the shell tress values in the connection.In order to verify the formula’s accuracy, I give the composite shell geometric size and unitload, then calculate the composite shell of cylinder and cone’s radial joints stress andcircumferential stress in the connection (the cone angle is from5degree to30degree), finally usethe finite element software ANSYS to inspect the function, after comparing the results obtainedfrom the ANSYS and theoretical derivation, I find that there are not much difference between thetwo sets of data,so it improves that the formula can be used to calculate composite shell of cylinderand cone’s radial joints stress and circumferential stress in the connection,and also can be used forthe practical engineering.Finally, I use the exact formula to calculate radial joints stress of the outer shell under internalwaves, Then through the Paris’s fatigue crack extension formula and Newman-Raju formula usedto calculate the Beam-columns’s stress intensity factor, I use MATLAB software to program in order to calculate the remaining life of weld. giving the weld initial imperfection, I study thecomposite Shell of tube and cone’s fatigue properties under the internal waves, including theremaining life of weld and the propagation of crack depth and crack width; and also study theeffect of different cone of half-angle, r/t, thickness under the same stress amplitude, shell materialsand weld defects to the residual life of weld.Through the above theoretical analysis I find that the r/t、shell material、 crack morphologyand other factors have the important influence to the crack growth rate and residue life. Therefore,the study has important guiding significance in the marine environment that how to improve thefatigue strength of composite shell of cylinder and cone in the future.