Fatigue final fracture

When fatigue failure was studied in more detail all authors agree that the critical crack initiates at the surface and rapidly propagates on a plane perpendicular to the stress direction until final fracture occurs. Frommeyer and Seifert (1981) give further details on this critical point in fatigue life. They observed fine shear band offsets at the... 

Fig. 10.5. Examples of fatigue fracture. The smooth regions of the surfaces, containing beach marks, are caused by fatigue the rough regions are the surfaces of final fracture. These regions wiU be explained in the following sections...

Chang, K.H. and Siddique, Z., "Re-Engineering and Fast Manufacturing for Impact-Induced Fatigue and Fracture Problems in Aging Aircrafts," Final Report, AFOSR Grant F49620-02-1-0336, January 31, 2006. 

Thus the FCGR becomes infinite as K ax approaches the toughness of the material Kc, which actually means final fracture, Stage III of fatigue. Note that in the Foreman Eq. (10.13) A and m are material characteristic whose value is different from C and n of the Paris law (10.10). Weertman [11] proposed an alternative equation for Regions II and III... 

First, the pressure vessel must be safe from plastic collapse that is, the stresses must everywhere be below general yield. Second, it must not fail by fast fracture if the largest cracks it could contain have length 2a (Fig. 16.4), then the stress intensity K CTV must everywhere be less than K. Finally, it must not fail by fatigue the slow growth of a crack to the critical size at which it runs. 

Fracture mechanics can be applied to this problem, much as it is to fatigue. We use only the final result, as follows. If the standard test which was used to measure (Tts takes a time f(test), then the stress which the sample will support safely for a time t is... 

The aim of this review is to concentrate mainly on these fundamental aspects of the fracture behavior of glassy thermoplastics. In the first Section, following an outline of the relevant fracture mechanics theory, the optical interference method is described and the nature of the results obtainable from it is discussed. The next Section then considers the behavior of cracks and crazes in specimens subjected to quasistatic loading, whilst the final Section examines the role of crazing associated with fatigue crack growth. 

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