Dynamic Response Analysis Of The Pipeline Structure With Crack Under Low-velocity Impact

The research of fracture mechanics is of great significance in practical presentation.The main reason is that many engineering accidents are caused by the gradual propagation of cracks to fracture in the service process of structures with cracks.Failure to predict and control it will cause immeasurable losses.The structure with crack is prone to crack propagation under quasi-static load,and it is more likely to break when the structure is subjected to an impact load.This article mainly focuses on the pipeline structure with a central crack,and adds a heavy object on the top of the structure and applies shock acceleration to it to obtain the response of the structure and the crack propagation time history.Based on the J-A₂ method,the dynamic fracture toughness of the material is obtained.Combined with the fracture constraint theory,the dynamic fracture toughness of I-shaped cracks of the pipeline structure is modified.Combined with the finite element results and the test results,the effectiveness of the J-A₂ method in the dynamic fracture analysis of structural cracks is verified.The specific results as follows:1.The classification and development of fracture mechanics,and explained in detail the basic theory of linear elastic fracture mechanics and the corresponding fracture criterion.The classification and development of fracture mechanics are introduced,and the basic theory of linear elastic fracture mechanics and the corresponding fracture criteria are explained in detail.The basic theory of linear elastic fracture mechanics and the three main fracture toughness criteria are explained,namely COD criterion,J integral criterion and J-A₂ method.Fracture toughness transformation method is obtained based on the J-A₂ method,makes difficult tests can be obtained through a simple standard specimen test and the corresponding fracture toughness can be obtained through the conversion formula.2.The numerical calculation method of dynamic fracture mechanics,mainly the finite element method is explained.The principles,advantages and application scope of various methods are compared and explained.Determine the mechanical performance analysis method for thin-walled round pipe structure,and determined the damage constitutive model for impact fracture of thin-walled pipe.Based on the mechanical property analysis method of thin-walled round pipe structure,the damage constitutive model of impact fracture of thin-walled round pipe is obtained.3.Numerical simulations are carried out for the slender pipes and the stubby pipes based on the finite element method.The mechanical response of two pipeline structures with different size of cracks under three types of impact is analyzed.4.Numerical simulation of pipeline structure,continuously increase the load,the ultimate load of the thin-walled pipeline structure is determined by the dichotomy.And carry out the numerical simulation of multiple impact loads for the pipeline structure,the mechanical response under the impact load of a half sine wave was carried out.5.The structural crack characteristics are analyzed,the crack mouth opening displacement（COD）time history curve and the time-history curve of crack growth（Δa）are obtained.The curves of the principal stress and the stress field at the crack tip were studied.And the crack growth rate was studied.The stress field at the crack tip was analyzed.6.Compared the transformation results with the numerical calculation results by converting the J-integral critical values for different crack sizes,after error calculation,what proved the feasibility of J-A₂ method in dynamic fracture toughness transformation,which in the conditions of the pipeline structure with crack under low-velocity impact.