Fracture analysis of materials used in high pressure hydrogen storage tanks

This work focused on determination of fracture toughness of a type III composite pressure tank. For this purpose, experimental and numerical studies were carried out on specimens taken from the type III composite pressure tank in accordance with the specified methods. The main purpose of this study was to accurately determine the fracture toughness of circular shaped materials such as pipes or pressure tanks in addition to the classical strength approach. For this aim, fixtures were manufactured for use in the universal test machine to determine hoop tensile strength and fracture toughness of the tank. Subsequently, split disk test (SDT) were carried out on specimens taken from the pressure tank. After determining the hoop strength of the tank using SDT method, its modulus of elasticity was also determined. In addition, the tank body was modeled as a flat plate with Abaqus using finite element method, and the modulus of elasticity was predicted with 98.34% accuracy with experimental results. Following the hoop tensile test, experimental studies were performed using curved compact tension (CCT) method to determine fracture toughness of the tank and their results compared by flat compact tension (CT) numerical model. The values of the experimental and numerical mode I stress intensity factor were measured that, experimental and numerical mode I stress intensity factor values were found. Consequently, the values found were close to each other with a deviation of 2.7%. Finally, experimental and numerical studies of the pipe ring notched bending (PRNB) method were carried out. Using the numerical model of this method, the fracture toughness of the pressure tank was computed. This model was also used to investigate the effect of varying the crack lengths on the storage pressure of the tank, focusing on the mode I critical stress intensity factor (KIC). As a result of the studies, it was determined that when the crack length to width ratio (a/w ) was 0.1, the storage pressure was 38 MPa, and when the a/w ratio was 0.5, the storage pressure decreased to 7 MPa. From these results it was concluded that the existing cracks in the tank body seriously affected the storage pressure depending on the crack length.