Section 4.1.2. Fail-Safe Structure
The residual strength requirement of a fail-safe structure is
to assure damage tolerance following a partial failure of the structure. Damage tolerance is maintained through
detection of this failure prior to total loss of the structure and sufficient
residual strength capability for operating safely within the partial failure
prior to inspection. The fail-safe
structure is typically a built-up structure with multiple load paths or crack arrest
features in its design. In the event of
failure of a structural member, its load must be transferred to and withstood
by the remainder of the structure, which also contains crack damage, without
causing the loss of whole structure.
The residual strength of the built-up structure must be determined under
such critical circumstances so that the fail-safe design requirements are met.
The analysis of residual strength capability for built-up
structure requires the estimation of the critical stress level at which the
partial failure occurs, as well as an understanding of the capability of the
total structure to withstand this partial failure at and subsequent to the time
of failure. The required load
associated with the time subsequent to failure is based on the inspection
category and, the partially-failed structure must be able to maintain this load
until the time of inspection.