Meeting Fracture-based Requirements in the Aerospace Industry

In the aerospace industry, fracture requirements are usually expressed in a document titled "Fracture Control Implementation Plan (FCIP)." The plan specifies the fracture control criteria and procedures to be implemented on a specific program. The primary objective of these controls is to preclude flaw-induced structural failures that could imperil a mission or a Space Transportation System and its crew. Meeting the criteria and procedures set in the FCIP is the responsibility of the program system safety engineer (SSE). The SSE maintains close communication with the design and analysis functions, where all structural components are evaluated for fracture criticality. All structural components are fracture critical, unless they fall into one or more of the following categories: fail-safe components, low-release mass components, contained parts, or lowrisk parts. Fracture critical components are subjected to tractability, NDE, and safelife analysis. Safelife analysis is an expensive analystical requirement, where an engineer must show that a flaw of non-detectable size, oriented in the most critical direction, will not undergo unstable crack growth during its life. This communication will discuss current analytical procedures used in safe-life analysis, their usage, effectiveness and applicability. The need for the development of new tools based on Greens functions and boundary integral methods is discussed.