Fatigue of bellows, a new design approach

Consideration of fatigue is generally an important aspect of the design of metallic bellows expansion joints. These components are subject to displace ment loading which frequently results in cyclic strains well beyond the pro portional limit for the material. At these high-strain levels, plastic stra in concentration occurs. Current design practice relies on use of empirical fatigue curves based on bellows testing. Prediction of fatigue behavior ba sed on the combination of analysis and polished bar fatigue data is not con sidered to be reliable. One of the reasons for the unreliability is plastic strain concentration. It is shown that the difference between bellows and polished bar fatigue behavior, as well as the difference between reinforced and unreinforced bellows, can be largely attributed to this strain concent ration. Further, it is shown that fatigue life of bellows can be better pre dicted by partitioning the bellows fatigue data based on a geometry paramet er. (C) 2001 Elsevier Science Ltd. All rights reserved.