Crack growth behavior

The utility of K or any elastic plastic fracture mechanics (EPFM) parameter to describe the mechanical driving force for crack growth is based on the ability of that parameter to characterize the stress-strain conditions at the crack tip in a maimer which accounts for a variety of crack lengths, component geometries and loading conditions. Equal values of K should correspond to equal crack tip stress-strain conditions and, consequently, to equivalent crack growth behavior. In such a case we have mechanical similitude. Mechanical similitude implies equivalent crack tip inelastic zones and equivalent elastic stress fields. Fracture mechanics is... 

The rate of crack growth is often it more useful parameter than is fatigue life Fracture mechanics techniques have been widely applied lo the crack growth behavior of high temperature alloy s. 

It is important to keep in mind that this transition time is an estimate based on a stationary crack analysis and that only when crack growth behavior is measured at times very much larger than tT can extensive creep conditions be reasonably assumed. In many cases, Eqn. (6) underestimates the transition time a better estimate may be the time when the creep strain equals the elastic strain in the far field.35,42... 

The crack growth behavior of polymers under cyclic loading has been intensively studied and the state of knowledge is also well documented by excellent, recently published review articles mong which the comprehensive book on Fatigue... 

For a large number of polymers the crack growth behavior under cyclic loading has been studied and documented in review articles 165.171,207,208)... 

In summary, short cracks form epsilon CTPZ development, whereas long cracks usually lack the required shear components to generate the shear-band pair, niis creates the anomalous short crack behavior. When epsilon CTPZs form, the shear bands stabilize the crack, thus allowing the DCG process to continue to much higher apparent AK, values, further differentiating from the non-epsilon CTPZ DCG crack growth behavior. 

Fatigue lifetime predictions in polymers therefore cannot be simply determined by a straightforward linear cumulative damage approach. This is especially true when crack growth mode transitions are observed and when strong history dependence of crack growth behavior occurs. 

Typical crack growth rate (da/dN) versus AK or K ax curves are shown in Fig. 7.8 [4] as a function of AK, or K ax, and other loading, environmental, and material variables. Ideally, it is desirable to characterize the fatigue crack growth behavior in terms of all of the pertinent loading, material, and environmental variables, namely. 

Dolley, E. J., and Wei, R. P., The Effect of Frequency of Chemically Short-Crack-Growth Behavior Its Impact on Fatigue Life, Proceedings of Third Joint FAA/DoD/NASA Conference on Aging Aircraft, Albuquerque, NM, September 20-23 (1999). 

Typical crack growth behavior of ceramics is represented schematically in Fig. 12.11 as log AA i versus og dc/dN). The resulting curve is sigmoidal and can be divided into three regions, labeled I, II, and III. Below is,... 

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