The traditional design approach of rocket motor case is generally based on thin shell theory wherein the ultimate or yield strength of the material enters the design along with the chosen safety factors. However, it is well known that the strength-based design carries with it an inherent assumption that the material is free from flaws and perfect fabrication . But in practice, the material may contain voids, cracks or some induced cracks in weldment and during weld repair process. These flaws can act on sites for crack initiation under certain conditions of operation and leads to catastrophic failure of the motor case.
Fracture analysis makes it possible to determine the critical crack size dimensions in selected motor case thickness for known fracture toughness of the material, which leads to failure. Based on analysis, the designer can specify the critical flaw sizes to take care in the raw material and inspection stage and selection of the material based on its fracture toughness value. For the present analysis, the following design inputs have been considered Figure 11. 1e1e36bf2d