Stable crack development

However, when stable-unstable fracture occurs (between Transitions 0 and I), evidence of secondary crack nucleation has been obtained by SEM on postmortem fracture surfaces. These cracks lead to parabolic markings ahead of the main blunt crack propagating in the plastic zone. Figure 8a shows an example of such secondary cracks developed at the boundary between the stable growth region and the unstable fracture surface in a 2 L45 specimen tested at 0.1 m/s. 

A critical research gap in corrosion science is the absence of the corrosion equivalent for the stress intensity factor (K) that has been the mainstay of structural mechanics for the past several decades. The stress intensity factor was developed to predict the behavior of pre-existing flaws in structural materials and the eventual life of a component under conditions in which the flaw develops into stable cracks. The power of K is in the concept of similitude well-defined cracks and crack tips that are different in size or shape but possess the same K (as determined by geometry, loading, and the theories of linear-elastic fracture mechanics) will experience the same mechanical driving force for crack growth. Thus, similitude allows small, well-defined samples to be tested in the laboratory to determine the conditions of crack growth and fracture and the results to be quantitatively extended to more complicated real-world structures containing cracks. Virtually... 

Work by Schapery, Saxena, Wilhams, and others details the analysis of cracks in creeping, strain rate dependent materials, and provides a predictive basis for the apparently brittle nature of FCP in UHMWPE [43-48]. Particularly usefid are the models developed by Schapery and Wilhams, which directly link the intrinsic, constitutive viscoelastic relaxation behavior of the material to the advance of a stable crack tip [46,48]. The power of these models is the predictive nature of the mechanics in relating ECP dynamics to the material s viscoelastic behavior that is eashy measured in a simple one-dimensional creep test The elementary consequences of the models result in the static mode fatigue crack propagation behavior that is observed in UHMWPE, and thus potentially provide a first-principles explanation of the fatigue and fracture behavior by the material. 

It is possible to expect that the endurance at the fixed loading allows to exclude the component AEl, because the development of prevailing defect is continuing, and numerous initiation of stable micro-cracks outside the zone are excepted. 

Fluid cat cracking required identifying stable operating regimes for beds of fine catalyst at high gas flow rates. Highly efficient cyclone and electrostatic systems had to be developed for catalyst recovery. Finally, the principles of pressure... 

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