Research On The Stability Of PMMA Pressure Spherical Shell Based On Creep Characteristics

The gradual depletion of land resources has prompted countries to pay more attention to the development and utilization of the ocean.As a sharp tool for ocean exploration,manned submersible has been paid more and more attention.Because of its excellent weather resistance,low density,high light transmittance and other advantages,acrylic material is especially suitable for making fully transparent manned cabin.PMMA is a kind of viscoelastic material.When it is subjected to external pressure for a long time,the pressure resistant structure of acrylic will undergo creep deformation,resulting in the reduction of bearing capacity.Therefore,in order to make rational use of acrylic materials and ensure the safety and reliability of acrylic pressure spherical shell under external pressure,it is necessary to study and master the creep failure of acrylic pressure spherical shell.In this paper,the creep mechanical properties of PMMA and the stability of PMMA pressure spherical shell are studied by means of finite element numerical simulation and experiments.Firstly,the short-term creep experiment of PMMA under constant temperature and variable stress was carried out,and the long-term creep mechanical behavior of PMMA was characterized by time stress equivalence principle,and the WLF equation for solving the stress displacement factor was obtained by fitting.The creep curve of PMMA was fitted by linear and nonlinear Burgers model,and the UMAT subroutine with creep model was compiled and verified Preface.Secondly,the instantaneous buckling instability of PMMA pressure shell is studied.According to the mechanical theory of pressure spherical shell,the failure mode of PMMA pressure spherical shell is determined as buckling instability;the influence of shell opening on buckling critical load is analyzed;the influence of shell thickness radius ratio and initial defect amplitude on the instantaneous buckling instability critical load of PMMA pressure spherical shell is studied.Finally,the creep buckling of PMMA pressure spherical shell is studied.Using the UMAT subroutine,the creep buckling finite element calculation of PMMA pressure spherical shell is carried out.The influence of load level and shell thickness radius ratio on the creep buckling critical time of PMMA pressure spherical shell is studied,and the function relationship of the creep buckling critical time of PMMA pressure spherical shell with external load and shell thickness radius ratio is obtained.Finally,the initial defects are analyzed The influence of the size on the critical buckling time of creep buckling.