Sharp crack tip

Electrode potential and pH at an active crack tip may be significantly different from those on boldly exposed surfaces of a material. Low-pH conditions can lead to local dissolution of metal and crack-tip blunting, which reduces stress concentration effects. In contrast, low-pH conditions favor hydrogen generation and, consequently increased risk of HEC. Reduction in local ductility associated with HEC is more likely to produce sharp crack tips, which, in turn, can exacerbate stress concentration effects for any synergistic SCC or CF. (Phull)5... 

Fig. 10. The lateral view of the crack tips shown in Fig. 9. Left craze bundle below the critical temperature. Right sharp crack tip above the critical temperature. From Ref. courtesy of Chapman and Hall, Ltd.

The elliptical hole prepares our intuition for the more extreme case that is presented by the atomically sharp crack. For the sharp crack tip, the dominant stresses near the crack tip may be shown to have a singular character with the particular form (see Rice (1968) for example). The realization that the crack tip fields within the context of linear elasticity have such a simple singular form has... 

We begin by examining the types of mixed atomistic/continuum strategies discussed earlier (see section 12.3.4) with special emphasis on how these methods have addressed the factors that determine whether an atomically sharp crack tip will cleave or emit dislocations. As shown in fig. 12.34, the lattice Green function... 

Before discussing the fracture resistances of a selection of polymers we note broadly that most, if not all, unoriented polymers are intrinsically brittle solids, in terms of the criterion of Kelly et al. (1967) whereby a defining condition is considered at an atomically sharp crack tip under mode I loading as in Fig. 12.2. As discussed in Section 12.2.2, all stresses are concentrated at the tip of such cracks as... 

Fig. 8.17 Schematic representation of a crack propagated in a a dense ceramic material and b a porous ceramic material, showing a sharp crack-tip in the dense material and a blunt crack-tip in the porous material [15]. With kind permission of Elsevier...

This review deals mainly with metals. The literature on their SCC is immense, and there are many useful texts and conference proceedings [1-12]. A brief history was published by Newman and Procter [13] and should be consulted for further historical details, especially the metal-environment combinations known to exhibit SCC. Plasticity plays a key role in SCC of metals, in contrast to inorganic glasses and ceramics, which are brittle solids and crack via reaction of the corrodent with highly stressed bonds at an atomically sharp crack tip [14]. Metal-induced fracture [15], formerly called hquid-metal embrittlement, remains a tantalizing phenomenon and... 

FIGURE 30.2 The LEFM stress intensity factor, K, describes the singular region of stress near a sharp crack tip. So long as a non-linear or inelastic zone of behavior (such as plastic deformation) is small compared to the singularity-dominated zone, K is an apt metric of crack tip effects. 

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