ANALYSIS OF THE PROBABILITY OF COLLAPSE OF A FAILSAFE AIRCRAFT STRUCTURE CONSISTING OF PARALLEL ELEMENTS.
AERONAUTICAL RESEARCH INST OF SWEDEN STOCKHOLM
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A study is made of the probability of collapse of a fail-safe structure, consisting of a number of parallel members, subjected to a random load spectrum. In the individual members a fatigue crack first initiated and failure of the members occurs due to a heavy load on the weakened members. The probability of element failure is obtained by a combination of the probabilities of crack initiation and of meeting a load exceeding the residual strength of the member. The probability of consecutive element failures is deduced from the probability of failure of the individual members. Collapse occurs when all members are broken, or, in practice, after a critical number of element failures. The probability of collapse of the assembly during the whole service life is the sum of the probabilities of all the inspection intervals. A numerical procedure for calculating the probability of collapse was developed and evaluations were made for an assembly of six identical, parallel members. Diagrams of the probability of collapse P versus the service life time T are plotted for various lengths of regular inspection intervals, assuming different values of the crack initiation and strength reduction parameters introduced. Author