Study On Method Of Evaluating The Creep Fatigue Damage And Life For Submersible Pressure Shell

The deep submersible pressure-bearing shell is subjected to super high hydrostatic pressure during operation and large stress amplitude alternating load during the floating and dive process.The creep and fatigue behavior will damage the shell structure.Creep and fatigue behavior can produce coupling effect that may significantly reduce the service life of the pressure shell structure.At present,on the one hand,it still lacks of an effective method to evaluate the creep fatigue coupling damage and life of the submersible pressure shell in academic and engineering.Inaddition,researchers usually use the mechanism of tensile failure to evaluate the deep submersible,which may cause a large part of the pressure shell stands superr high compressive stress when operating under water.However,researchers usually is based on the mechanism of tensile failure to evaluate deep submersibles.This may probably cause a large error.Therefore,in order to evaluate the creep fatigue life of the submersible pressure shell accurately,it is necessary to establish a creep fatigue damage and life evaluation method for the structure under both compressive stress and tensile stress.Based on the continuous damage mechanics on the ABAQUS platform,this paper proposes creep,fatigue,and creep fatigue coupling damage and life evaluation method that can evaluate the structure under complex stress states,and realizes using the corresponding elastic damage constitutive equation and damage evolution equation to accumulate damage according to the unit's own stress state.Firstly,based on the damage constitutive equation of Lemaitre,an elastic damage constitutive equation is proposed,which can be conveniently applied to the finite element numerical calculation.The constitutive equation can adjust finite element's stiffness matrix based on the element stress state and damage state.Secondly,based on the existing creep damage evolution equation and fatigue damage evolution equation in tension,the creep damage evolution equation and fatigue damage evolution equation in compression are preliminarily proposed.Finally,the creep and fatigue coupling damage evolution equations in compression and tension are integrated,and it is used to accumulate damage using the corresponding damage evolution equation according to the stress state.The two types of damage are carried out by the current mainstream creep fatigue coupled damage evolution equation.Then,the nonlinear accumulation of creep fatigue coupling damage of structural units is proposed.Based on the damage evolution method,the numerical simulation in tension and compression states are carried out on the structures of compressive creep,compressive fatigue and compressive coupling of creep and fatigue.The result shows that it would exit some errors when using the tensile failure mechanism to evaluate the structures in compression.