The Application of Fracture Mechanics to the Design of Damage‐Tolerant Components for the UTTAS Helicopter
Abstract:The principles of fracture mechanics have been used extensively in the design of damage‐tolerant structural components for the YUH‐61A UTTAS helicopter which is being designed, built, and tested by the Boeing Vertol Company under Army contract. The requirements for a high level of structural reliability, considering both combat and noncombat environments, led to establishment of a damage‐tolerance criterion. The design of major structural components was often controlled by this criterion which required specific residual fatigue life and static strength after sustaining initial damage of a given magnitude. Implementation of the damage‐tolerance criterion relied heavily on the technology of fracture mechanics. This technology was used in conducting material trade‐off studies, providing estimates of crack‐growth characteristics for sizing components, and establishing procedures for bench tests to check compliance of components with damage‐tolerance criteria. Two fracture‐mechanics‐ based techniques, in particular, were widely used to achieve damage tolerance. One technique used the approach of designing a component to prevent damage of a given size from growing under operational loads. This led to the concept of a fatigue‐crack‐growth threshold, which is a function of stress level and crack size. The other technique consisted of designing a component so that damage growth is limited to non‐catastrophic proportions. These techniques entered directly in the design of more than 10 critical dynamic‐system components for the YUH‐61A helicopter. It is concluded that fracture mechanics provides a valuable tool for the design of damage‐tolerant structure.
Document Type: Research Article
Affiliations: Boeing Vertol Company, Phiadelpnia, Pennsylvania
Publication date: 1975-07-01
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