Deformation lamellae

In specimens deformed to several percent strain (or more) at low to intermediate temperatures and stresses, where neither work-hardening nor recovery processes predominate, dislocations tend to tangle into localized walls (Kirby and McCormick 1979 McCormick 1977 McLaren et al. 1970 Morrison-Smith et al. 1976). These walls behave as optical phase objects and give rise to the deformation lamellae that are commonly observed in deformed crystals by optical microscopy (see Section 1.3 and McLaren et al. 1970). Similar walls of tangled dislocations develop in metals in the power-law-breakdown creep regime where both recovery-controlled and glide-controlled deformation mechanisms are operative (see, e.g., Drury and Humphreys 1986). 

Field and optical microscope studies showed that the fault plane is defined by a 2-3 cm wide cataclastic zone that is bounded laterally by a 1-3 m envelope of plastic and cataclastic deformation. Outside this envelope, the quartz microstructures displayed no evidence of significant deformation. Quartz in the fault envelope contains well-developed deformation bands, deformation lamellae, and intragranular healed fractures, which are visible at all scales of observation. 

Inhomogeneous recovery can produce the variations of dislocation density and fluid inclusion content of individual lamellae and may ultimately produce the extreme concentrations of fluid inclusions found to define some natural deformation lamellae (Christie and Ardell 1974). 

The deformation lamellae can be used to provide an estimate of the stress during the formation of the deformed envelope of the fault. In metals and halides, deformation lamellae form only in the exponential creep regime, which occurs above a critical stress level (Tsenn and Carter 1987). Experimental data on quartz suggest that lamellae form only at high stress, but no particular association with exponential creep can be discerned in the available data. The normalized transition stress in different... 

Koch, P. S., Christie, J. M. (1981). Spacing of deformation lamellae as a pa-leopiezometer. EOS Transactions of the American Geophysical Union, 62, 1030. 

McLaren, A. C., Turner, R. G., Boland, J. N., Hobbs, B. E. (1970). Dislocation structure of the deformation lamellae in synthetic quartz a study by electron and optical microscopy. Contrib. Mineral. Petrol., 29, 104-15. 

White, S. H. (1973). Deformation lamellae in naturally deformed quartz. Nature Physical Sciences, 245, 26-8. 

FIGURE 3.18 The drawing process, (a) Twisted crystal lamellae that make up the spheru-htic structure are pulled into (h) tilted pre-deformed lamellae during the pre-necking period. 

Fig. 4. Model of local plastic deformation of lamellae beneath the stress field of the indenter. The mosaic block structure introduces a weakness element allowing faster slip at block boundaries leading to fracture (right)...

For density values g > 0.92 g/cm3 the deformation modes of the crystals predominate. The hard elements are the lamellae. The mechanical properties are primarily determined by the large anisotropy of molecular forces. The mosaic structure of blocks introduces a specific weakness element which permits chain slip to proceed faster at the block boundaries than inside the blocks. The weakest element of the solid is the surface layer between adjacent lamellae, containing chain folds, free chain ends, tie molecules, etc. 

In comparing the correlation sought between MH and E one should emphasize the following while the plastic deformation of lamellae at larger strains when measuring MH depends primarily on crystal thickness and perfection in case of the elastic modulus the major role is played by the amorphous layer reinforced by tie molecules, which is elastically deformed at small strains. Figure 17 illustrates de... 

Desired organoleptic properties, particularly textural ones, are a direct consequence of these microstructural changes. A chip must be firm and snap easily when deformed, emitting a crunchy sound (Krokida et al., 2001a), whereas in thick products the better the contrast between a rich and soft inner structure and a crispy outside, the better the product (Moreira, 2006). Firmness is often related to starch swelling and gelatinization, as well as to the stability of pectic substances of the cell wall and middle lamellae. 

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