MIL-STD-1530C(USAF)
5.1.3.5.1 Damage tolerance design concepts.
The aircraft structural damage tolerance design shall be categorized into either of the general design concepts which follow:
a. fail-safe concepts where the required residual strength of the remaining intact structure shall be maintained for a period of unrepaired usage through the use of multiple load paths or damage arrest features after a failure or partial failure. The period of unrepaired usage necessary to achieve fail-safety must be long enough to ensure the failure or partial failure will be detected visually and repaired prior to the failure of the remaining intact structure.
b. slow damage growth concepts where flaws, defects, or other damage are not allowed to attain the size required for unstable, rapid propagation failure. This concept must be used in single-load-path and non-fail-safe multiple load path structures. No significant growth which results from manufacturing defects or from damage due to high-energy impact shall be allowed for composite structures.
5.1.3.5.2 Special applications.
The safe-life design methodology may be used on a limited basis. It is expected that it will be used to establish replacement times for some specifically-approved structural components (e.g., landing gear components and rotorcraft dynamic components). Damage tolerance evaluations are required for all safe- life designed components and other selected structure. These evaluations shall define critical areas, fracture characteristics, stress spectra, maximum probable initial material and/or manufacturing defect sizes, and options for either eliminating defective components or otherwise mitigating threats to structural safety. Such options may include design features, manufacturing processes, or inspections.
Additionally, the damage tolerance evaluation shall establish individual aircraft tracking requirements so that the safe-life component replacement times and any scheduled safety inspections can be adjusted based on actual usage. Use of a safe-life approach for a structural component must be identified in the ASIP Master Plan.
5.1.3.6 Mass properties criteria.
Criteria shall be established to ensure the aircraft can accommodate aerodynamic, center of gravity, and inertia changes which result from fuel usage, store expenditure, asymmetric fuel and store loading, fuel migration at high angles of attack and roll rates, and aerial refueling.
5.1.4 Durability and Damage Tolerance Control Program.
A Durability and Damage Tolerance Control Program shall be established for the aircraft structure. This program shall identify and define all the tasks necessary to ensure compliance with the durability requirements as described in 5.1.3.4 and the damage tolerance requirements as described in 5.1.3.5. The disciplines of fracture mechanics, fatigue, materials and processes selection, environmental protection, corrosion prevention and control, design, manufacturing, quality control, nondestructive inspection, and probabilistic methods shall be considered when the durability and damage tolerance control processes are developed. This program shall include the requirement to perform durability and damage tolerance design concept, material, weight, performance, and cost trade studies early during the aircraft's design so as to obtain structurally-efficient and cost-effective designs.
5.1.4.1 Durability and Damage Tolerance Control Plan.
A Durability and Damage Tolerance Control Plan that is consistent with the design service life shall be prepared and executed throughout the System Development & Demonstration and the Production & Deployment phases. The plan shall establish a Durability and Damage Tolerance Control Board (DDTCB) responsible for establishment and oversight of the administration of the specific controls that will be applied in accordance with the plan. The board shall be comprised of representatives from
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