Fatigue cracks mechanism

To understand the multistage fatigue crack mechanisms for the different inclusion types, multiscale modeling and experiments were performed to develop the... 

Small Fatigue Cracks Mechanics, Mechanisms Applications. ISBN 008-043011-2... 

A. Fathulla, B. Weiss, R. Stickler Short fatigue cracks in technical P/M-Mo alloys. In The Behavior of Short Fatigue Cracks, Mechanical Engineering Publications, Vol.l (EGF Pub., Suffolk 1986) p.115... 

Eracture mechanics concepts can also be appHed to fatigue crack growth under a constant static load, but in this case the material behavior is nonlinear and time-dependent (29,30). Slow, stable crack growth data can be presented in terms of the crack growth rate per unit of time against the appHed R or J, if the nonlinearity is not too great. Eor extensive nonlinearity a viscoelastic analysis can become very complex (11) and a number of schemes based on the time rate of change of/have been proposed (31,32). 

Most cracking problems in cooling water systems result from one of two distinct cracking mechanisms stress-corrosion cracking (SCC) or corrosion fatigue. 

Mitigation or elimination of corrosion-fatigue cracks involves gaining control of the critical factors that govern the mechanism. 

Turbine rotating blades cannot be field-repaired if they are cracked. If one or two blades are damaged mechanically, the manufacturer may recommend field repair or replacement of the damaged blades. However, if several blades are fatigue cracked, it is recommended that the entire set be replaced, since the remaining blades have been exposed to the same operating conditions and, therefore, have little fatigue life left. 

N. Walker and C. J. Beevers, A Fatigue Crack Closure Mechanism in Titanium , Fatigue of Engineering Materials and Structures, Wo[. 1, 1979, pp. 135 148. 

C. J. Beevers, R. L. Carlson, K. Bell and E. A. Starke, A Model for Fatigue Crack Closure , Engineering Fracture Mechanics. 

Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogen-induced cracking and liquid metal embrittlement. Purely mechanical forms of cracking such as brittle failure are not considered here. 

The complexity of these chemical and mechanical interactions is such that each metal-environment system must be examined on an individual basis to determine the important processes influencing corrosion fatigue crack nucleation and growth rates. Thus, in the ensuing sections, examples are quoted to illustrate commonly occurring phenomena or establish more general principles with reasonably wide applicability for particular classes of metal/environment combinations. It should be noted, however, that when... 

---