Fracture Analysis Of Composite Overwrapped Pressure Vessel With Metallic Liner Considering The Autofrettage Technology

Composite overwrapped pressure vessels (COPVs), substituting those made of monolithic metals, are widely applied in aerospace systems with the advantages of superior strength-to-weight and stiffness-to-weight ratios, lower mass and designable. Compared to the composite on failure, the plastically responding metallic liners in working pressure should be mainly considered, whose common failure mode is leaking before burst. Generally, the liners undergo cyclic plastic during loading and unloading in normal operating, which causes the cracks escaping from the non-destructive examination to grow through the liner thickness and leak the pressurizing fluid out. Therefore, the fracture analysis of the metallic liner in the composite overwrapped pressure vessel is very important.The finite element model of a COPV including a circular crack is constructed with ANSYS using the submodel technique, and then the J integrals along the crack front are calculated by the domain integral method. Since the plastic has a strong influence on the fracture behavior, it is also considered in the analysis. The simulation process is broken down into three parts. In the first part, the J integrals along the semicircular surface crack front in metallic liner of a cylindrical vessel under working pressure conditions considering the autofrettage technology and not are calculated separately. By contrast, it was discovered that the J integral increases significantly after autofrettage. At the same time, the effect of different autofrettage pressures on the crack tip strength is also discussed with three cases, and it is found that the J integral increases as the autofrettage pressure grows. In one word, the autofrettage technology improves the probability of crack’s growing. In the second part, comparison of the fracture parameters are conducted on the crack positions between the medial cylinder segment and the cylinder-to-dome transition region, and results show that the cracks in the medial position are more dangerous. Finally, in the third part, the cases of composite and liner with two different thicknesses are discussed, and results show that the thicknesses have strong constraint effect on the crack tip strength, the constraint becomes stronger as the crack size increases.This present work should be a great value to the safe use of COPVs.