Critical structural defect

As is seen, the interdependence of two values is rather weak. The modification action ( disturbance ) of the graphite surface (increasing A) leads to facilitating fracture of an interfacial layers, and, as a consequence, to increasing the size of critical structural defect, a fit [46, 47]. Figure 12.10 shows that the correlation of a jt to (A) meets the above concept. 

Figure 12.10 Dependence of the critical structural defect length (a t) and adhesion parameter (A) for 1 PHE-Gr-I (1) and 2 PHE-Gr-II...

Let us now consider the reasons for a weak dependence of the impact toughness A p on A (see Figure 12.9 and Equation (12.16) The length of the critical structural defect according to the modified Brown equation [50] is ... 

The length of critical structural defect can be determined with the aid of the following Eq. (17.6) ... 

In Figure 17.3, the dependence of the length of critical structural defect on interaction parameter for blends PET/PBT is adduced. The linear growth at increasing is observed, that can be described analytically follows ... 

Since in the experiment the constant value of was used then according to Equation 6.25 the value of is only the function of the plasticity of epoxy polymers, characterised by the value, and their degree of defectness, characterised by parameter Since in the experiment the samples without a notch were used then parameter characterises the critical structural defect (CSD) [66, 67]. Electron microphotographs (enlargement 300x) of the fracture surfaces, an example of which is adduced in Figure 6.21, were used for estimation of the value of... 

Figure 6.22 The dependences of the critical structural defect size on the amount of curing agent, characterised by parameter for epoxy polymers SCE-IMTHPhA (1) and SCE-DADPS (2) [52]...

Figure 6.27 The hypothetical scheme of critical structural defect formation in...

In addition to these technical problems, the complexity inherent to physical properties of gels is, as exemplified above, that they depend very sensitively on the preparation condition. This is because, in a formal language, a gel is a frozen system and we need two sets of statistical information, the preparative ensemble and the final ensemble , to understand its equilibrium properties [29]. Hence, a gel is by nature more complex than the usual equilibrium systems. We should clarify the dependence of the properties of gels on preparation conditions, and also on structural defects of the network before going into precise investigations such as critical phenomena associated with the phase transition. 

As described in Section 2, the coercivity of hard magnetic materials is generally determined by undesired structural defects. As the size of hard particles is progressively reduced, the coercive field tends to increase. This is explained by considering that the impact of a given defect extends to the volume of the concerned particle. It is reduced as the particle size is reduced. However, below a certain critical size, a reduction in coercivity is observed. The process used to reduce particle size inevitably introduces additional defects, which become dominant. 

Critical to both gas separation and membrane reactor applications, fluid leakage and any potential re-mixing of the separated species have to be avoided. The problems could arise if pin-holes or structural defects exist or if the ends of the membrane elements or the connections between the membrane elements and assembly housings or pipings are not properly sealed. 

In the case that the components are incompatible, the material strength is impaired due to imicro-inhomogeneity. Mechanical loads applied to such material will be distributed unevenly within the volume and can be higher on some portions than on other. This leads to violation of the material continuity in most loaded sites. Structural defects formed as a result quickly propagate through the whole material leading to its failure. As can be seen, mechanical compatibility of components is critical for plastic materials. 

Optimal value of the roughness was obtained here at K = 2.0. Friability and increase the structures defects was at K = 2.0 can be connected with intensive reorientation in stmcture of polymer [24]. The critical value K, at what there will be an intensive reorientation, in various films should depend on initial stmcture and anisotropy of a film [20],... 

Therefore it is necessary to take into account not only stmcture, volume, properties of additives PhOC, but also as far as the put cut ( 5 mm) is close or far from structural defect PE. By influence on ab, the critical border between PhOC in sense of their influence on defectiveness of a matrix passes between phosphinic an acid and her salts. The integrated estimation of influence PhOC on mechanical properties of polyethylene at impact results in the same conclusions, as earlier, in case of consideration the block-copolyesters and a polycarbonate. 

In conclusion, the present discussion of proposed film breakdown and pit initiation mechanisms suggests that several phenomena are responsible for the loss of passivity and the onset of pitting when a metal is polarized to a high potential in presence of aggressive anions. Structural defects in the passive film reflecting those of the metal, anion adsorption on the film and the metal surfaces and the effect of anions on the kinetics of the electrochemical reactions governing oxide formation and metal dissolution are most critical. Practical consequences of these phenomena for pitting corrosion will be discussed in Section 7.3. 

Pits that reach a critical depth can act as crack initiation sites if they lead to a higher local stress intensity. The crack initiation time in this case corresponds to the incubation time of pits of a critical size. Alternatively, precipitation reactions at the grain boundaries can render an alloy sensitive to intergranular corrosion. The preferentially corroded grain boundary then serves as initiation site of a crack. Inclusions, preexisting microcracks, or other structural defects are also likely crack initiation sites. The crack initiation time, in this case, is defined as the time required for a crack to reach a detectable size. Crack initiation may also be the result of hydrogen formed by a corrosion reaction that may cause embrittlement of the metal or of successive ruptures of a passive film or tarnish layer, but these mechanisms are more important for the propagation than the initiation of cracks. Because of the multitude of possible crack initiation mechanisms, and because of the statistical nature of the phenomenon, it is not possible to predict the crack initiation time from first principles. 

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