The random stress processes, composite Gaussian or single Gaussian, are constructed on the basis of exceedance curves for different aircraft under various flight conditions. The fatigue crack propagations under such stress processes are estimated with the aid of fracture mechanics method. The crack propagation rate under random loading is assumed to be proportional to the expected value of a power of the range of stress intensity factor which is in turn proportional to the expected value of the same power of the rise and fall of the stress process involved. The residual strength is evaluated as a function of crack size either under the assumption of slow crack growth design or under the assumption of fail safe design. Two different models as to the basic mechanical nature of the crack are used for the analysis and their interrelation-ships are discussed. The first is the crack initiation model in which a crack of certain size is assumed to initiate at 'randomly distributed time' and then propagate in accordance with the propagation law of fracture mechanics; the other is the pre-existing crack model which assumes the initial existence of 'a crack of random size' that propagates immediately upon application of the stress process. With the aid of the random process theory, the failure rate is evaluated as the expected rate of upcrossing of the residual strength by the stress. The probability of aircraft failure is obtained from the failiure the failure rate taking into consideration the effect of inspection procedures and proof loads.

  • Supplemental Notes:
    • See also Volume 2, AD-A031 951.
  • Corporate Authors:

    Modern Analysis, Incorporated

    229 Oak Street
    Ridgewood, NJ  United States 
  • Authors:
    • Shinozuka, M
  • Publication Date: 1976-4

Media Info

  • Pagination: 140 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00146975
  • Record Type: Publication
  • Source Agency: National Technical Information Service
  • Report/Paper Numbers: AFFDL-TR-76-36-Vol1 Final Rpt.
  • Contract Numbers: F33615-75-C-3066
  • Files: TRIS
  • Created Date: Feb 16 1977 12:00AM