Structural Integrity Assessment of Defected Gas Pipelines Using a Simplified Ductile Damage Model

The finite element method using the damage model has been increasingly used to predict the failure of various structures. Thus, various damage models were presented, and recently, a phenomenological model called the local fracture strain model was presented, making it easy and accurate to predict the damage of the structure. This model has the advantage of defining fracture strain as a function of stress triaxiality with only a few notched tensile tests but has a limitation because it does not consider the damage evolution because of the void growth. This study presents an enhanced damage model that improves the accuracy of the failure simulation of defected structures by adding a parameter that considers stiffness degradation according to void growth to the damage model based on the fracture strain. Therefore, loading–unloading tests were conducted and the damage index of fracture was identified using a three-dimensional digital image correlation system. The failure simulation results using the proposed damage model were compared with experimental, such as notched tensile, single edge notched tension (SENT), and full-scale burst tests.