Stress intensity factor of semi-elliptical surface crack in a cylinder with hoop wrapped composite layer

In this paper the fracture behavior of the compressed natural gas (CNG) cylinder with hoop wrapped composite layer is investigated for the axial crack at the inner surface. By the aid of the three-dimensional finite element method, the stress intensity factors along the crack front are obtained for different crack profiles. The effects of the cylinder geometry, hoop wrapped layer thickness and the property distributions of the composite layer on the stress intensity factor are discussed in detail. The numerical results show that the hoop wrapped composite cylinder can lower the stress intensity factor value greatly and ensure the safe use of pressure vessels containing defects in service. The composite property distribution owns a distinct effect on the crack behavior in different directions that provides a clear guide to the maintenance of CNG cylinder. Finally an approximate formula with high precision is proposed to evaluate the stress intensity factor along the axial crack front in the hoop wrapped cylinder with composite layer.