Creeping zone

Analogous to the arguments of small-scale yielding in linear elastic fracture mechanics, small-scale creep conditions (i.e., the situation where the size of the creep zone ahead of the fatigue crack tip is small compared to the characteristic dimensions of the test specimen, including the size of the crack and that of the uncracked liagment) can be assumed to exist when... 

High crack tip stresses cause fast crack tip creep in the creep zone surrounding the crack tip. As r- 0, ec ee, i.e., the creep strain rates are much greater than the elastic strain rates, but this intense creep is constrained by the surrounding elastic material which causes crack tip stress relaxation. This field is of the HRR type, where as r— 0 (referred to as the RR-field for Riedel and Rice3,34... 

One interpretation of C, is that it reflects the history of crack tip deformation through the rate of growth of the creep zone. From the Riedel-Rice SSC analysis of stationary cracks... 

Crack growth models in monolithic solids have been well document-ed. 1-3,36-45 These have been derived from the crack tip fields by the application of suitable fracture criteria within a creep process zone in advance of the crack tip. Generally, it is assumed that secondary failure in the crack tip process zone is initiated by a creep plastic deformation mechanism and that advance of the primary crack is controlled by such secondary fracture initiation inside the creep plastic zone. An example of such a fracture mechanism is the well-known creep-induced grain boundary void initiation, growth and coalescence inside the creep zone observed both in metals1-3 and ceramics.4-10 Such creep plastic-zone-induced failure can be described by a criterion involving both a critical plastic strain as well as a critical microstructure-dependent distance. The criterion states that advance of the primary creep crack can occur when a critical strain, ec, is exceeded over a critical distance, lc in front of the crack tip. In other words... 

The second case in this category of creep crack growth with a cohesive zone associated with viscous interfaces is the work of Nair and Gwo.32,53 Nair and Gwo32 considered intermittent crack growth whereas continuous crack growth was considered in the latter study. The principal assumption in these studies was that the stress field in the creep zone follows the ffR-field or RR-field (see Section 10.2) with applied K replaced by Keff. This is only a first approximation, because, as mentioned earlier, these crack tip fields were originally derived for traction-free crack surfaces. 

Because of the presence of a creep zone at the tip of a growing creep crack, the crack tip fields can be expressed in terms of stress-strain rate fields as a function of the distance from the crack tip within the creep zone. These... 

Geologic features map It is a compilation of features shown on the other interpretive maps. The map shows geologic features on the seafloor and to depths of 300-600 m that are of potential significance to a site. All features are described quantitatively to facilitate use by engineers. Examples are faults, slides, slumps, creep zones, steep slopes, irregular seafloor topography, unusual soil and rock conditions, and buried stream channels. 

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