| The pressure pipeline safety assessment technology based on the principle Fitness For Service has a wide range of applications in the world, of which fracture mechanics is the theoretical basis. This paper has used the finite element analysis method to calculate the fracture parameters of the mitred bend with longitudinal cracks. In the FEA software ANSYS we simulate the fracture behavior of the mitred bend with longitudinal cracks, and build the finite element model of the bend. Respectively, the stress intensity factor K1, limit load and J integral internal of the mitred bend with the part through-wall longitudinal cracks (φ=90°position) has been calculated under internal pressure and in-plane open bending moment.Besides, we calculate the limit load of mitred bend with the part through-wall longitudinal cracks (φ=90°position) under the internal pressure and open bending moment and their combination. The main work is as follows:(1) Building the finite element model of the structure wih cracks, and checking the validation of the modeling method. This paper introduces the simulation method of the crack in ANSYS and builds the finite element model to solve the stress intensity factor and limit load. By rationally selecting the element we establish the finite element model of straight pipe with longitudinal cracks, calculates and compares the results with theoretical solution in the EPRI handbook, which can verify the feasibility and the accuracy of the modeling method.(2) Establishing the finite element model of the mitred bend with part through-wall longitudinal cracks, and solving the stress intensity factor KI. We use ANSYS program and the language APDL to parameterize and calculate. Under pressure and bending moment we respectively discuss the influence of the geometric parameters:crack relative length, crack relative depth, relative thickness and load on the stress intensity factor KI. According to the formula provided by EPRI we transform the KI into the dimensionless parameter-shape factor F, and based on the the calculation data we fit the F under internal pressure and bending moment, and the calculation formula of F is presented.(3) Calculating the limit load of the mitred bend with longitudinal cracks in the ideal elastic-plastic state.This work can be divided into two parts:part through-wall cracks and through-wall cracks. A new finite element model for the mitred bend with through-wall cracks need to be built. We discuss the influence of the crack relative length, crack relative depth and relative thickness on the limit load of the mitred bend with longitudinal cracks. Particularly, the limit load of the mitred bend with longitudinal through-wall cracks is calculated under the combination of inner pressure and bending moment.(4) Solving the J integral of the mitred bend with part through-wall longitudinal cracks in the ideal elastic-plastic state and discussing respectively the influence of the crack relative length, crack relative depth and relative thickness on the J integral under pressure and bending moment. |
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