Reliability and fatigue life prediction of GFRP pipes by continuum damage mechanics-based damage elastic-plastic bridging model

Composite pipes are applied frequently in the industry since their strength and fatigue life are reasonable. Although they can tolerate internal cyclic hydrostatic pressure for a long time, this time depends on several parameters such as material, manufacturing process, and environment condition. Improved reliability and fatigue life prediction are very important in the field. In this study, the reliability and fatigue life of glass fiber reinforced polymer (GFRP) pipes exposed to internal cyclic hydrostatic pressure are investigated. The continuum damage mechanics (CDM) theory with nonlinear damage parameters are utilized based on the bridge micromechanics model for evaluating fatigue damage. Thus, based on the elastic-plastic bridging model, three damage variables have been determined to predict the damage response of the fiber, matrix, and shear at the ply scale. Nonlinear kinematic hardening is developed to express plasticity behavior in composite material. At first, this model was applied in the commercial software Abaqus finite element analysis (FEA) to assess the capability of the model in predicting the fatigue fracture time of GFRP pipes. The accuracy of results is evaluated by comparing them to experiments. The results display a good agreement between the experimental and simulated results. Then, a first-order reliability method (FORM) is applied to predict the reliability and fatigue life of GFRP pipes based on CDM. Eventually, the effects of applied pressure, the number of cycles, and fiber orientation on reliability and fatigue life are investigated.