Study On Determination Of Fracture Toughness Of Pipeline Steel Based On Instrumental Charpy Impact Test

In recent years,the deployment and development of the national energy strategy has put forward new requirements for energy storage and transportation capacity.By the end of the 12 th five-year period,the mileage of oil and gas transmission pipelines has nearly doubled.With the increase of pipeline transportation demand,high-strength and high-toughness steels have been widely used in pipeline transportation.When such pipelines are fractured,the crack tip region is usually in a large-range yield state.Judging the fracture toughness of pipeline steel by measuring its crack initiation toughness and crack arrest toughness,it has guiding significance for its safety performance.In this paper,the test method for fracture toughness of pipe based on the instrumental Charpy impact test is studied in detail.The fracture toughness of the pipe is studied qualitatively and quantitatively through two aspects of test test and numerical simulation,and the fracture mode and propagation law are analyzed.The fracture toughness of the two material specimens was analyzed by the results of the Charpy impact test,and the crack initiation position of the specimen was determined by the compliance change rate curve method.The dynamic J-integral is solved by substituting the eigenvalues at crack initiation into the formula under quasi-static conditions.By comparing dynamic J-integral and quasi-static J-integral curves,an equation for solving quasi-static J-integrals based on the dynamic test method of CVN specimens was established;according to the dimension of the slope of load-displacement curve of J-integral and impact test,The formula for solving J-integrals based on load-displacement curves was established.According to the Gurson damage theory,the fracture finite element model of the CVN specimen was established,and the process of crack initiation and crack propagation was analyzed.Through the experimental verification,the simulation results were of a higher degree of consistency;the dynamic fracture process of the CVN specimen was obtained through finite element simulation.The CTOA values in the test were compared with other test pieces.It was found that the CVN specimen had a large deviation in the calculation of the geometric fracture toughness parameters,and was only better in the energy and mechanical parameter calculation.