Failure analysis of cracked pipes repaired by composites under internal pressure

In order to accurately evaluate the effectiveness and failure pressure of cracked pipelines repaired by fiber composites under static load, a numerical model for the failure of cracked pipelines repaired by composites was established. The numerical model simulated the crack propagation of the pipeline by expanding finite element method. The cohesive element was used to simulate the debonding failure of the adhesive layer. The failure of the composite material was determined by the maximum stress failure criterion. The proposed numerical model of failure was verified by hydrostatic burst test. The experimental results were in good agreement with the numerical results. According to the results of numerical analysis, when the internal pressure increases to a certain value, the initial crack of the unrepaired pipe gradually expands along the axial and wall thickness directions, and then the inner wall unit of the pipe expands into a real crack. At the same time, the real crack runs through the entire wall thickness. The burst failure pressure decreases exponentially with the half length of the initial crack. The different repair conditions of cracked pipelines repaired by composite exhibit the same failure mode: under the monotonically increasing internal pressure of the pipeline, the internal surface of the pipeline first appears a cohesive crack, and the cracking tendency of its outer surface rises sharply, making the stress of the composite material layer rise sharply and reach the ultimate strength. And there are corresponding critical values of the composite layers for different initial crack sizes. © 2019, NUDT Press. All right reserved.