The influence of defects about mechanical strength of polyethylene pipes
For the PEHD buried pipe, the overall composed of total load (soil + traffic), internal pressure, own weight and linear expansion, contributes on reaching the limit state, as well as to the stress distribution, σl - longitudinal stress, σc - circumferential stress and σr - radial stress. is the basis for assessing the integrity of pressure vessels using, for example, von Mises breakdown criterion. The defects or local stresses, unavoidable in polyethylene pipes (due to manufacturing and welding technologies, laying of bedless pipes, fingerprints produced by a third party etc.) lead to the local concentration of stresses, representing the area susceptible to the initiation and propagation of cracks in within the breaking processes. By successively changing the depth, length and angle of generation of the defect, it was found that both the maximum equivalent stress and the maximum deformation have a continuous variation depending on the values of the characteristics of the defect. Analyzing the behavior of the PE-model pipe, it was observed that for identical values of the defect characteristics a = 2.7 mm, L = 10 mm, θ = 10 degree identical values of the maximum equivalent stress and the equivalent elastic deformation in the direction are obtained, longitudinal and radial, but different from those in the circumferential direction.
Steps to reproduce
The instruments used to acquire the date was Ansys Workbench 15.0. The depth, the length and the generation angle of geometrical discontinuity have been modified in percentage from 5 to 75 from its initial dimensions. During FEA process, the model of pipe with and without defect has been subjected to all the stages of the numerical analysis: the introduction of engineering data of material, the creation of the geometrical and discretization of the model, the settings and the solutions.