(b) Damage-tolerance evaluation. The evaluation must include a determination of the probable locations and modes of damage due to fatigue, corrosion, or accidental damage. [Repeated load and static analyses supported by test evidence and (if available) service experience must also be incorporated in the evaluation. Special consideration for widespread fatigue damage must be included where the design is such that this type of damage could occur. It must be demonstrated with su.cient full-scalefatigue testevidence that widespreadfatiguedamage will not occur within the design service goal of the airplane. The type certi.cate may be issued prior to completionoffull-scalefatiguetesting,provided theAdministratorhas approved a plan for completing the required tests, and the airworthiness limitations section of the instructions for continued airworthiness required by Sec. 25.1529 of this part speci.es that no airplane may be operated beyond a number of cycles equal to 1 the number of cycles accumulated on the fatigue test article, until such testing is completed.The extent ofdamagefor residual strength evaluation at anytime within the operational life of the airplane must be consistent with the initial detectability and subsequentgrowth under repeatedloads.The residual strength evaluation must showthatthe remaining structureis ableto withstandloads(considered as static ultimate loads) corresponding to the following conditions :
(1)
The limit symmetrical maneuvering conditions speci.ed in Sec. 25.337 at all speeds up to VC and in Sec. 25.345.]
(2)
The limit gust conditions speci.ed in Sec. 25.341 at the speci.ed speeds up to VC and in Sec. 25.345.
(3)
The limit rolling conditions speci.ed in Sec. 25.349 and the limit unsymmetri-calconditionsspeci.edinSecs.25.367 and25.427(a) through(c), atspeeds up to VC.
(4)
Thelimityawmaneuvering conditions speci.edinSec.25.351(a) atthe speci-.ed speeds up to VC.
(5)
For pressurized cabins, the following conditions :
(i)
The normal operating di.erential pressure combined with the expected external aerodynamicpressuresapplied simultaneously withthe .ightloa-ding conditions speci.edinparagraphs(b)(1) through(4) of this section, if they have a signi.cant e.ect.
(ii)
[The maximum value ofnormal operating di.erentialpressure(including the expected external aerodynamic pressures during 1g level .ight) mul-tiplied by a factor of 1.15, omitting other loads.]
(6)
For landing gear and directly-a.ected airframe structure, the limit ground loading conditions speci.ed in Secs. 25.473, 25.491, and 25.493.
If signi.cant changes in structural sti.ness of geometry, or both, follow from a structuralfailure, orpartial failure, the e.ect on damage tolerance must be further investigated.
(c)
Fatigue(safe-life) evaluation.Compliance withthedamage-tolerancerequirements ofparagraph(b) of this sectionis not requiredif the applicant establishes that their application for particular structure is impractical. This structure must be shown by analysis, supported by test evidence, to be able to withstand the repeated loads of variable magnitude expected during its service life without detectable cracks. Appropriate safe-life scatter factors must be applied.
(d)
Sonic fatigue strength. It must be shown by analysis, supported by test evidence, or by the service history of airplanes of similar structural design and sonic excitation environment, that–
(1)
Sonicfatiguecracksarenotprobableinanypart of the .ight structuresubject to sonic excitation; or
(2)
Catastrophic failure caused by sonic cracks is not probable assuming that the loadsprescribedinparagraph(b)ofthis section are appliedto all areas a.ected by those cracks.
(e)
Damage-tolerance(discrete source) evaluation.The airplane must be capable of suc-cessfully completing a .ightduring whichlikely structuraldamageoccursasaresult of–
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本文链接地址：FAA规章 美国联邦航空规章 Federal Aviation Regulations 3(68)
