A REVIEW OF BOUNDING TECHNIQUES IN SHAKEDOWN AND RATCHETING AT ELEVATED TEMPERATURES ; A REVIEW OF CREEP INSTABILITY IN HIGH-TEMPERATURE PIPING AND PRESSURE VESSELS; UPPER BOUNDS FOR ACCUMULATED STRA (To Purchase Call 1-800-854-7179 USA/Canada or 303-397-
The life span of stressed components operating at high temperature is limited by such factors as excessive deformation@ rupture@ fatigue and brittle fracture@ but in this report only the role of deformation is discussed. In components which creep@ the deformation is normally limited so that the average creep strain allowed is 1%@ or about ten times the maximum elastic strain@ while the maximum allowable strain is limited to 5%. Under constant loading@ the determination of the creep strains is a fairly straightforward procedure@ although for complex geometries the computing power required can be considerable. It is under conditions of cyclic loading@ however@ that the determination of the creep strains becomes more difficult@ and indeed it is because of the cyclic loading that deformation rates can sometimes accelerate very dramatically. Because of the 1% strain limitation@ ratcheting effects must be almost nonexistent@ since a 1% strain accumulation in 5000 cycles corresponds to a ratchet strain per cycle of only 2x10-4%