Fatigue and Incremental Collapse

Abstract

Cyclic fatigue is said to cause the failure of a structural member which breaks during a load cycle that it has previously withstood. This type of failure is perhaps the most common in machine elements subjected to cyclic stresses in the elastic range. In the pressure vessel industry, a similar type of elastic strain fatigue occurs when a component suffers rapid vibration, for instance in welded brackets supporting unbalanced rotating machinery, in pipes under pulsating flow, etc. The amplitude of the oscillations, compared to the steady value of the load, is usually small and fracture occurs after a large number of cycles, say 10⁵–10⁷ cycles. Design to prevent this type of fatigue failure follows generally accepted rules and will not be discussed here in detail, but the reader is referred to standard books on the subject (Refs. 1, 2, 3).