Applied Fracture Mechanics

Procedures for applying fracture mechanics to typical engineering problems are reviewed. Particular emphasis is placed on plane-strain fracture of materials used in fabrication of pressure vessels and booster cases. The major areas considered are: (1) material selection; (2) the estimation of structural life; and (3) the determination of nondestructive inspection acceptance limits. In order to treat these items properly, a brief discussion on the character of premature structural failure is presented, followed by a discussion on the selection of a fracture toughness specimen. In the area of material screening and selection, it is shown that the required design tool is related, not to toughness alone, but also to the design stress level and the size of the structure. In the estimation of structural life and determination of nondestructive inspection acceptance limits, emphasis is placed on the use of fracture specimen test results and the stress-intensity concept to predict critical flaw sizes and subcritical flaw growth. Both cyclic and sustained stress flaw growth are discussed and comparisons made between specimens and pressure vessels. The value of the proof test is discussed with regard to determining the maximum possible initial flaw sizes in a pressure vessel.