Analysis On Stress And Stability Of PMMA Pressure Shell

The fully permeable submersible is subjected to many of severe environmental loads such as high hydrostatic pressure,impact,alternating stress and vibration in the diving phase.Those loads factor may affect the structural stability and safety.However,the pressure hull of the fully permeable submersible is made of PMMA.The material has viscoelastic properties,and the mechanical behavior of the structure changes with time.It is very important to accurately analyze this characteristic for the structural design.In this paper,the research idea of PMMA pressure hull is first local and then global analysis,focusing on the viscoelastic singular stress field at the contact interface ends between PMMA and metal firstly.Secondly,the viscoelastic analysis of axisymmetric bending of PMMA hulls with different structures is carried out.Finally,the stability of nearly spherical and spherical pressure hulls is compared,and the nearly spherical is verified by finite element analysis.The shell has good stability.The main work is as follows:The solution of stress field at the interface end in the Laplace transform domain is obtained based on the correspondence principle,and the convolution integral expressions of the singular stress filed in the time domain is developed.On this basis,simplified formulas of the viscoelastic singular stress field are developed.The results of inversion show that kernel function can be approximated by analytical expressions obtained by the quasi-elastic method with a good accuracy.When the solution of viscoelastic stress is approximated by formulas similar to the quasi-elastic solution,the error limit can be estimated.The theoretical conclusions obtained in the front of the paper are validated by the simulation results.The axisymmetric bending problem and boundary effect of PMMA shells are analyzed.The theoretical formulas of bending moment and shear force of cylindrical shells are deduced,and the rationality of finite element calculation results is verified.The viscoelastic analysis of axisymmetric bending of cylindrical,spherical and new eggshells is carried out by finite element method.A nearly spherical shell structure is proposed,based on Brand's egg-shaped function.The bending moment,shearing force and deflection increased with time.The boundary effect at the end of the shell is better than that of spherical and cylindrical shells.A nearly spherical shell structure is proposed.The nearly spherical structure is improved on the basis of Brand's egg-shaped function.The inclination angle of the endof new the nearly spherical shell is large and the boundary effect can be reduced.The nearly spherical structure is superior to the spherical shell in space utilization.Stress analysis of spherical and nearly spherical pressure hulls is carried out by finite element method.Furthermore,linear buckling and nonlinear buckling analysis of nearly spherical and spherical shell structures are carried out.It was found that the sensitivity of the nearly spherical was lower than that of the spherical shell,and the stability of the nearly spherical was similar.