Fatigue Life Prediction of a Hoop-Wrapped Composite CNG Cylinder Containing Surface Flaw

In recent years many experimental and numerical studies have been conducted on the fatigue behaviour of CNG storage pressure vessels. The main objective of these studies is to estimate the total fatigue life, which consists of two parts: i) Life till crack nucleation and ii) Crack growth life. Although fatigue evaluation methods for metal cylinders are widely covered in literature including the ASME Boiler and Pressure Vessel Code, comprehensive approaches for fatigue evaluation of composite-reinforced pressure vessels are very few. This paper calculates the fatigue life till crack nucleation for a steel-lined hoop wrapped composite pressure vessel containing a surface flaw (notch) using strain-life approach. Firstly, static stress analysis taking into account the non-linear material behaviour of steel liner was performed using finite element method to provide input for the fatigue analysis. Then fatigue analysis was carried out by applying a cyclic pressure inside the pre-stressed cylinder using strain-life approach, and the results obtained by the numerical simulations are discussed. The approach associated with these calculations can be used to study the effect of various material and geometry parameters on the fatigue life of the pressure vessel. Keywords— CNG, Hoop wrapped composite cylinder, Finite element method, ANSYS, Crack nucleation, Strain-life approach, Fatigue life.