Fracture mechanism maps

Fig. 2.14 Fracture mechanism map for uniaxially fiber-reinforced ceramic composites under tensile loading.72...

G. D. Quinn and W. R. Braue, Fracture Mechanism Maps for Advanced Structural Ceramics, Part 2, Sintered Silicon Nitride, /. Mater. Sci., 25, 4377-4392 (1990). 

The experimental results described above can be explained within the basic fracture mechanism map after detailed consideration of the processes necessary to generate a craze at the interface. The criterion lfb > ocmze is a necessary condition for the formation of stable craze fibrils. However, it is not sufficient for the formation of a craze at an interface. Craze initiation is believed to occur by a meniscus instability process that happens within a yield zone (an active zone) at a... 

With this in mind, it is useful to represent the expected fracture mechanisms at the interface with maps. For individual connectors, the fracture mechanisms map can be presented as a function of 2/2 and N/Ne. This normalization then takes into account two important material parameters of the bulk polymers which will influence the fracture mechanisms map the crazing stress acmze (contained in 2 ) and the entanglement density (contained in Ne). 

Fig. 53. Fracture mechanisms map for interfaces between glassy polymers reinforced with connecting chains. Failure mechanisms are represented as a function of normalized degree of polymerization N/Ne and normalized areal density of connectors 1/1 ...

A similar fracture mechanisms map can also be drawn for interfaces effectively broadened by a buffer layer. In this case we assume that the buffer layer is laterally homogeneous. As shown in Fig. 54, several different fracture mecha-... 

We have shown that the fracture toughness of interfaces between polymers is dependent on the molecular structure at the interface as well as on the bulk properties of the polymers on either side of the interface. This relationship is now relatively well established for glassy polymers and the main results are summarized in Figs. 53 and 54, as well as in Sects 3.2-3.5. However, these results should be used with caution when the polymers on either side of the interface are rubbery or semicrystalline. The stress-transfer mechanisms, and in particular the role of the entanglements, will be very different from those observed for the glassy polymers and only preliminary data are currently available on those systems. In principle, fracture mechanisms maps analogous to those depicted in Figs. 53 and 54 could be drawn for these systems but the relevant parameters are not yet as clearly identified. 

Figure 20.10. Fracture mechanism map , reprinted with permission from Sha et al [91], Copyright (1996) American Chemical Society. See the text for the notation. The predominant mechanism of failure also depends strongly on N, since the line showing OpUi)0Ut as a function of X will move above the line showing oscissj0I1 if N is increased sufficiently.

Figure 12.15 Fracture mechanism map for Si iN4 using data given in Worked Example 12.4.

Figure 12.18 Fracture mechanism map for Si3N4, for which the properties are listed in Prob. 12.11.

Even though the experimental results are still limited, it appears that the predicted occurrence conditions provide the general trend compatible with the experimental results. Thus, it may be possible to examine the fracture process to be expected for hydraulic stimulation in supercritical rock masses on the basis of the fracture mechanism map given in Fig. 4. The ratio of the minimum horizontal tectonic stress to the vertical tectonic stress usually falls in the range of 0.5-1.0 for brittle rock masses (Brace Kohlstedt, 1980.). The actual difference of the tectonic stresses may be significantly smaller in supercritical rock masses due to the high temperature creep deformation (Fournier, 1999 Muraoka et al., 20()0). If we limit... 

Source Krishnamohanrao etal., Fracture Mechanism Maps for Titanium and Its Alloys, Acta Metall., Vol 34,1986, p 1783-1806... 

QUI 90] QUINN G.D., Fracture mechanism maps for advanced structural ceramics, part 1 Methodology and hot-pressed silicon nitride results , J. Mat. Sci., vol. 25, p. 4361-4376, 1990. 

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