Mechanism of cracking

The chemical species that can lead to EIC in each alloy system are fairly well known although the exact mechanisms of crack initiation and propagation are not thoroughly understood. The species that promote EIC in one alloy system do not necessarily promote EIC in others. A discussion of EIC and the chemical species that promote it can be found in the Hterature (34). 

This mechanism of crack inhibition is almost unique among ceramic systems, which do not undergo the plastic deformation under stress which is found in metallic systems (Figure 7.3). 

Figure 8 shows the SEM images with a low level of strain (50%). It is clear that even with a low-strain level defects are initiated in the sulfur cured system with the formation of large cracks at the boundary layer between the two phases. However, in the peroxide cured system the mechanism of crack initiation is very different. In the latter case the NR-LDPE interface is not the site for crack initiation. In this case, stress due to externally applied strains is distributed throughout the matrix by formation of fine crazes. Furthermore, such crazes are developed in the continuous rubber matrix in a direction... 

Wilde, B. E., Mechanism of Cracking of High-strength Martensitic Stainless Steel in NaCl Solutions , Corrosion, 27, 326 (1971)... 

There has been some controversy as to whether s.c.c. occurs by active path corrosion or by hydrogen embrittlement. Lack of space does not permit a full treatment of this subject here. References 14 and 15 are recent reviews on the s.c.c. of high strength steels and deal with the mechanism of cracking (see also Section 8.4). It is appropriate to discuss briefly some of the latest work which appears to provide pertinent information on the cracking mechanism. It should be noted, however, that cracking in all alloy systems may not be by the same mechanism, and that evidence from one alloy system need not constitute valid support for the same cracking mechanism in another. 

Fig. 8.2 Strain-generated active path mechanisms, (a) Often referred to as the film rupture model and (b) the slip step dissolution model. In both cases growth is by dissolution film rupture is the rate controlling step, not the mechanism of crack growth...

Mechanism The mechanism of cracking has not been established. Even the corrosion reaction that is responsible for the initial attack has not been determined. Early work led to the suggestion that chlorine gas was generated and could cause fracture by a cyclic process requiring the formation and decomposition of TiCl2 ... 

Duquette, D. J., Mechanisms of crack initiation and propagation in corrosion fatigue , Proc. Int. Conf. on Mechanisms of Environmental Cracking in Materials, University of Surrey, 4-7 April 1977, The Metals Society, pp. 305-21 (1977)... 

With reference to the mechanism of cracking dodecane assess the relative environmental merits of the thermal and catalytic cracking processes to give gasoline grade products. 

The mechanism of cracking on zeolites proceeds differently than on a metal surface. What are the differences and why do they arise ... 

The demethanizer, deethanizer, and debutanizer are fractionating columns that separate the lighter and heavier compounds from each other. Traces of triple bonds are removed by catalytic hydrogenation with a palladium catalyst in both the C2 and C3 stream. Cumulated double bonds are also hydrogenated in the C3 fraction. These are more reactive in hydrogenation than ethylene or propylene. The C2 and C3 splitters (Fig. 8.4) are distillation columns that can be as high as 200 ft. The mechanism of cracking was previously discussed in Chapter 7, Section 6. 

Most of the recent advances in the understanding of the fracture behaviour of epoxy polymers has been through the application of fracture mechanics 2) and the present Chapter is therefore concerned with the study of the mechanisms and mechanics of crack growth in crosslinked epoxies using fracture mechanics. 

Brittle Surface Degradation and Mechanism of Crack Nucleation under Indentation... 

It is appropriate to discuss this pattern of kinetic behavior, and the interpretation offered here, with reference to problems that arise in the elucidation of the mechanisms of cracking reactions of hydrocarbons on nickel. The hydrogenolysis of ethane has been the subject of many studies and it is believed by (inter alia) Sinfelt (74), Tetenyi (87, 123), Shopov (124), and their co-workers that the rate-limiting step is carbon-carbon bond rupture. In... 

Other pure mechanisms of cracking are thermal cracking and hydrogenolysis over metals. Very detailed investigations on platinum catalyzed hydrogenolysis of various alkanes, e. g., the isomeric hexanes, have been published recently (6-8). 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

Beachmarks appear as in the case of metals. Detailed mechanism of crack growth differs from metals and fatigue failure in polymers is not characterized by an endurance limit... 

J. Landes and J. Begley, A Fracture Mechanics Approach to Creep Crack Growth, in Mechanics of Crack Growth, ASTM Technical Publication 590, The American Society for Testing and Materials, Philadelphia, PA, 1976, pp. 128-148. 

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