Research On Surface Crack Propagation Behavior Of Pressurized Surfacing Structure

In engineering field,surfacing welding technology is used for strengthening the surface performance of the material or repairing failure structures caused by the worse service condition.However,fracture analysis is complicated because of the discontinuity of the mechanical properties and the structural damage caused by the surfacing process.Therefore,it is necessary to study the propagation behavior of crack defects in the surface of the pressurized surfacing structure,and to realize the numerical fracture evaluation of the known crack in the surfacing layer.This work has a certain theoretical difficulty and value in engineering application.In this paper,surface crack propagation behavior of surfacing pressure structure is discussed by combining the theoretical analysis,experimental method and the numerical simulation.Firstly,The stress and strain field of the crack tip of Type I,II and III are deduced.After that fracture criterion and crack propagation rate model are introduced.What's more,the cohesive force damage criterion and its applicability in the elastic-plastic problem are expounded.In the aspect of experimental,the design and preparation method of SCT specimen for surfacing surface crack are proposed.The fatigue test scheme of SCT specimen is developed and completed.It is found that the surface crack can penetrate the surfacing interface to the metal substrate.The test data is fitted for calculating the crack propagation rate.In the numerical simulation,the extended finite element XFEM method is used to simulate the subcritical propagation of the crack in both the homogeneous and bimaterial plate.The propagation direction of the bimaterial is different from that of the homogeneous material.The trend of crack propagation is from hard material to soft material.The co-simulation process of the whole life prediction of the surfacing crack propagation is established.The hydrogenation reactor was used as the analysis example.Based on the thermo-mechanical coupling analysis,the crack initiation position and life cycles were determined by Fe-safe.The stress intensity factor was calculated by static XFEM method,and the crack growth life was calculated by the fatigue crack rate fitting formula.Finally,the cohesive zone model and the dynamic XFEM were used to analyze the crack dynamic propagation.Considering the effect of corrosion and residual stress,an improved model of corrosion fatigue coupling calculation is proposed.At the same time,the residual stress caused by welding heat is qualitatively analyzed.Based on the analysis process established in this paper,the behavior and theoretical prediction of crack initiation,subcritical and instability propagation in surfacing structures are realized.