viewbarcode.com

Fracture in .NET Generation barcode 3 of 9 in .NET Fracture




How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
Fracture using barcode creation for none control to generate, create none image in none applications. Overview of GS1 General Specification Figure 4.21. Variat none for none ion in stress intensity factor with crevasse depth for an air- lled crevasse formed by a tensile stress of 0.

2 MPa. (Modi ed from Kenneally, 2003.).

with crevasses, and as most crevasses reach depths of at least 10 20 m, this condition is satis ed. Let us consider the case of a single crevasse in a glacier of in nite horizontal extent subjected to a tensile stress, . Two stresses are involved: the tensile stress that tends to open the crack and the weight of the overlying ice that tends to squeeze it closed.

We need a stress intensity factor for both. For the case of a crack of depth d in a medium of thickness H d subjected to a tensile stress, , K It = 1.12 d (Kanninen and Popelar, 1985, p.

31). The subscript t signi es tension. The hydrostatic stress from the weight of the ice is i gz, where i is the density of ice, g is the acceleration of gravity, and z is the depth below the surface.

The negative sign indicates that the stress is compressive. For a crack of depth d with a load varying from 0 at the surface to i gd at the crack tip, K Io = 0.683 i gd d (Kenneally, 2003).

Here, the subscript o is used for overburden. Vaughan (1993) found that tensile stresses between 0.09 and 0.

32 MPa were necessary to open crevasses. (These are considerably lower than the stresses bounding the fracture eld in Figure 4.16, probably because glacier ice has more and deeper surface aws that can develop into crevasses.

) For purposes of illustration, let us assume = 0.2 MPa. KITotal = KIt + KIo then varies with crevasse depth as shown in Figure 4.

21. From Figure 4.21, we see that once a crack 0.

16 m long is formed, KITotal exceeds KIc and the crack will propagate unstably to a depth. Flow and fracture of a crystalline material of 35 m. The depth , of course, depends on , but this is a realistic depth for crevasses. Of considerable interest in view of the recent collapse of the Larsen B Ice Shelf mentioned in 3, is the effect of water on crevasse depth.

By analogy with the KIo above, the stress intensity factor for stresses induced by water pressure in a crevasse that is lled with water is K Iw = 0.683 w gd d, where w is the density of water. KIw is positive because the water pressure tends to open the crevasse.

Because w > i , KITotal , which now includes KIw , increases continuously with depth. Thus, once it exceeds KIc , it never drops below KIc again, and the crevasse will penetrate to the bed. Three additional factors that in uence crevasse depth are: (1) the presence of low-density rn at the surface, (2) the water level in the crevasse if it is not lled, and (3) the effect of other crevasses.

In all three cases, the consequences of taking these factors into consideration are fairly obvious. Low-density rn reduces KIo so crevasses penetrate deeper; if there is not enough water in the crevasse, KIw will not exceed KIo and the crevasse may not penetrate to the bed; and if there is a eld of crevasses, the tensile stress will be relieved by adjacent crevasses and no one crevasse will penetrate as deeply as would a single crevasse. Stress intensity factors can be obtained for these three situations (Van der Veen, 1998), but the algebra, while straightforward, becomes considerably more complicated and is beyond the scope of this book.

. Summary. In this chapter we rst reviewed the crystal structure of ice, and noted that there are imperfections in this structure, called dislocations, that allow ice (and other crystalline materials) to deform under stresses that are low compared with the strength of individual molecular bonds. Processes that may limit the rate of deformation are those which (1) inhibit motion of a dislocation in a single crystallographic plane (drag), (2) prevent dislocations from climbing from one crystallographic plane to another to get around tangles, (3) impede motion on certain crystallographic planes, and (4) inhibit adjustments of boundaries between crystals. Experimental data do not, at present, provide a basis for choosing between these possible rate-limiting processes.

However, the drag mechanism does provide a theoretical basis for the commonly observed value of the exponent, n, in the ow law (see Equation 4.4). Perhaps equally important, however, are the mechanisms that allow adjustment of grain boundaries.

Because some crystals in a polycrystalline aggregate are not oriented for easy glide, stress concentrations develop. These result in. Summary. recrystallization b y three distinct processes: grain growth, polygonization, and nucleation of new grains. Recrystallization leads to preferred orientations of c-axes, and hence to more rapid deformation. The principal processes involved in the development of these fabrics appear to be nucleation of new grains and rotation of grains as slip occurs on their basal planes.

To place the creep processes in ice in a more general framework, we introduced a deformation mechanism map in which we displayed the range of temperatures and stresses under which different deformation processes occur. Within the temperature and stress ranges normally found in glaciers, power-law creep is likely to be the dominant process although diffusional creep may occur in some low stress situations. Next, we introduced Glen s ow law, and related the exponent, n, in the ow law to the creep mechanisms discussed earlier.

Then we considered how temperature, pressure, texture, fabric, and water content affect the viscosity parameter, B. Temperature and pressure effects may be incorporated into the ow law by rigorous, physically based modi cations, whereas ad hoc procedures based on empirical evidence are used to incorporate the other effects. Finally, we introduced principles of linear elastic fracture mechanics and demonstrated that these principles can be used to estimate crevasse depths.

.
Copyright © viewbarcode.com . All rights reserved.