A Study On Mechanical Behavior Of Interlayer Interface For Composite Pipe With Thin-alled Lining

A repair of thin-wall lining is a kind of pipeline regeneration technology which is proposed with the trenchless repair method of buried pipeline.The technology can be used to repair and strengthen the internal corrosion defect pipe.Lots of research and application were focus on the construction technology,the buckling of loose liner and the failure of lining material at present.The mechanical properties of the interface between the thin-walled lining and the base pipe steel directly affect the mechanical property of the composite pipe.Besides that,Under the action of dynamic load,the vibration will cause the overall buckling of the composite pipe or the delaminating of the thin-wall lining,which will lead to the failure of the composite pipeline.A mechanical model of the composite pipe with thin-wall lining was established,and the thin-walled stainless steel and thin-walled FRP were used as the inner layers to study the interface mechanical properties and dynamic characteristics under dynamic load.Based on the tensile and shear tests of single-sided bonding specimens of X52 tube steel with corrosion defects and normal tensile tests of T-shaped plate bonded specimens,a bilinear constitutive relationship model of interlaminar interface of composite pipes was established by using the difference method.The material properties and apparent characteristics of these pipe steels were obtained by tensile test and testing of different corrosion degrees.Based on the bilinear constitutive relation model and test results,a bilinear cohesive force finite element analysis model was established.Compared with the experimental results,it was concluded that the bilinear interfacial cohesion model can accurately simulate the interlaminar mechanical properties of the composite pipe with thin-walled lining in the finite element model analysis.Based on the established finite element analysis model,the radial stress,circumferential stress and equivalent stress at the corrosion pit of the original base pipe steel were analyzed.Different depth ratio and different repair methods were considered in the analysis.The stress redistribution and ultimate stress of the original base pipe steel before and after repair were obtained.Based on "Kirchoff-love" shell theory and "Donnell" cylindrical shell theory,the dynamic buckling governing equation of thin-walled lining composite pipe was established,and the buckling critical load of the shell was obtained by using “Hamilton”variation.Combined with the "bilinear" cohesive force model of interlayer interface,the finite element analysis model was established.The calculation method of the minimum cohesive force between the layers as determined,and the minimum thickness of the thin-walled lining was determined.In the study of delaminating buckling of inner liner,the coupling effect between layers was considered.Based on winkle beam theory,the nonlinear motion equations of each shell were established.The "Newmark" iterative method is used to solve the equation,and the dynamic characteristics of each shell are obtained.The results show that the phenomenon of "micro vibrate" occurs in the thin-walled shell.The effects of thin-walled lining thickness,material properties,shell stiffness and interlayer adhesion on the "micro vibrate" were analyzed,and the measures to reduce or eliminate the "micro vibrate" phenomenon was put forward.The research can provide theoretical basis for Trenchless continuous lining repair technology of buried pipeline.The research methods and conclusions can be used for reference in the repair of pressure vessels such as pipelines,tanks and other structural components.