Study On Fatigue Life Of Rubber-steel Composite Structure With Flexible Riser Joints Considering Viscoelasticity

Since the early 1930 s,after the success of high temperature vulcanization of metal and rubber,rubber-steel composite structure has been more and more widely used in civil engineering,industrial equipment and other fields.A large number of studies have shown that the comprehensive properties of rubber-steel composite structures are not similar to the simple superposition of the properties of various independent materials,but a highly nonlinear relationship.When all single materials play a synergistic role,a good composite structure will produce a coupling effect similar to one plus one greater than two.In deep-water oil and gas development,the steel catenary riser(SCR)at the top of the flexible joint of the main bearing components elastomer is a kind of rubber-steel composite structure,it not only can join the riser and the upper floating body,can also provide certain buffer for the relative rotation between the two,to improve the connection strength,reduce the connection location of the fatigue damage.In this thesis,a numerical analysis model of viscous heat generation of rubber is established,and the fatigue life of rubber-steel composite structure with flexible joints of SCR riser is studied.The main contents include:(1)Determination of hyperelastic-viscoelastic constitutive model of carbon black filled rubber.Hyperelastic and viscoelastic constitutive model parameters were fitted by referring to mechanical test data and DMA test data of carbon black filled rubber.The stress and strain differences of the hyperelastic constitutive model and the hyperelastic-viscoelastic composite constitutive model at different temperatures were compared and analyzed,and the appropriate constitutive model was selected for study.(2)Analysis model of viscous heat generation and fatigue life of rubber.Taking the energy of rubber viscosity heat generation as the internal heat source,a numerical analysis model of rubber viscosity heat generation temperature was established considering the heat conduction inside and outside the rubber.Considering the thermal strain caused by temperature rise,the influence of viscosity heat generation on rubber fatigue life was studied based on the strain-life curve of rubber.(3)Fatigue life prediction of rubber-steel composite structure with flexible joint at SCR.The dynamic response analysis model of SCR riser was established by Orcaflex,the load at the top flexible joint was extracted,the elastomer finite element model of rubber-steel composite structure was established,the fatigue life of elastomer under cyclic load was analyzed,and the effect of considering viscous heat on the fatigue life of elastomer in flexible joint of SCR riser was compared and analyzed.