Theoretical modeling of fatigue phenomenon in composite pipes

In this research, lifetime prediction of composite pipes subjected to internal cyclic hydrostatic pressure is considered. Progressive damage modeling technique is employed based on stiffness degradation for evaluating fatigue failure. The modeling procedure consists of three phases as stress analysis, damage evaluation and mechanical properties degradation. The applicability of the modeling in predicting fatigue lifetime of composite pipes is validated using available experimental data in literature. Due to the limited existing data on required mechanical properties of employed composite materials for investigated composite pipe, initial mechanical properties are computed and generic estimation of stiffness degradation is obtained. Then, Taguchi method is utilized to modify obtained stiffness degradation patterns in accordance with reported experimental observations. A very good agreement between theoretically predicted fatigue life time and experimental data imply on acceptable level of accuracy of fatigue modeling procedure. Finally, fatigue lifetimes of an industrial composite pipe subjected to different varying internal pressure are predicted and its long-term behavior over the span of 50 years of continuous operation is estimated as the dictated requirement by international rules and regulations.