Internal fractures

On one hand, inherent flaws or perturbations in a fracturing body, which are the sites of internal fracture nucleation, have been recognized as important in determining characteristic fracture spacing and, consequently, the nominal fragment size in a fracture event. Theoretical work based on a physical description of these material imperfections has been actively pursued (Curran et al., 1977 Grady and Kipp, 1980). 

The importance of inherent flaws as sites of weakness for the nucleation of internal fracture seems almost intuitive. There is no need to dwell on theories of the strength of solids to recognize that material tensile strengths are orders of magnitude below theoretical limits. The Griffith theory of fracture in brittle material (Griflfith, 1920) is now a well-accepted part of linear-elastic fracture mechanics, and these concepts are readily extended to other material response laws. 

In many materials, the inherent flaws are easily recognized. Brittle polycrystalline materials, for example, contain microcracks, voids, and other imperfections that can be identified in micrographs, and are expected to provide sites for internal fracture activation. Artificial flaws introduced into a hollow metal shell by uniform scoring can be expected, under rapid expansion, to fracture the shell along the paths of scoring. 

We conclude that high internal stresses are generated by simple shear of a long incompressible rectangular rubber block, if the end surfaces are stress-free. These internal stresses are due to restraints at the bonded plates. One consequence is that a high hydrostatic tension may be set up in the interior of the sheared block. For example, at an imposed shear strain of 3, the negative pressure in the interior is predicted to be about three times the shear modulus p. This is sufficiently high to cause internal fracture in a soft rubbery solid [5]. 

Features Very thin bark, greyish-brown outside with corky growths (lenticels), slight longitudinal crackings, laminate, light brown internally. Fracture forms flat splinters. 

Features Stem two to three feet high, contains milky juice. Root, wrinkled longitudinally, light brown outer surface, whitish internally fracture tough, irregular. Rootstock knotty, faintly ringed. Acrid taste. 

Early reports of the biomedical use of poly(lactic acid) date back to the 1960s [3, 175]. Since then, PLA has gained widespread application in the medical field, for use in sutures [8], drug delivery devices [15, 17, 24, 59-90], prosthetics, scaffolds, vascular grafts, and bone screws, pins and plates for temporary internal fracture fixation [10-13]. Good mechanical properties and the fact that it de-... 

Spiral mills create a high velocity helix of gas that rotates around the center of the jet mill. Solids are introduced via a venturi feed injector (Fig. 8.2) and become entrained in the turbulent helical flow. The resulting high energy collisions between particles as well as with the particles and the mill internals fracture particles to micron and submicron size. 

In the case of good adhesion between fiber and matrix, brittle fracture of the fibers is observed. A further disadvantageous behavior was found in composites used in ultracentrifuges running at high temperature (60). Internal fracturing destroyed the integrity of the matrix, and loss of matrix as carbon dust was observed. These observations led to systematic studies of carbon/carbon composites with hybrid matrices (34). 

Reflected light Light which is reflected at the surface of a specimen, or from an internal fracture (e.g. sun spangles in amber). 

It can be anticipated that XMCT wfll see widespread use in probing the internal structure of solid pharmaceuticals. Recent examples in tablets have included studies of compaction process conditions (157), the mapping of tablet density and porosity (146,158), changes in structure on hydration (159) (Fig. 6), and the detection of internal fractures (160). XMCT also has the potential to provide a powerful tool for process optimization and root cause analysis in formulation development. 

The law has been found that in cylinders of metal, the circumferential strain on the different pai-ts varies inversely as the squares of the distances of the parts from the axis. According to this ratio a two-inch gun with two inches of metal, will be internally fractured l>efore the exterior receives one-twelfth part of the strain causing the fracture. Of course increasing the thickness still more would add very little to its strength. 

Infection of bone, known as osteomyelitis, remains one of the most serious clinical complications associated with open reduction and internal fracture fixation. Gonventional intravenous therapy with systemic antibiotics is the major modality of treatment employed by clinicians, but such therapy has inherent drawbacks. Long-term intravenous therapy often requires the use of indwelling intravenous lines which have the potential for serious morbidity including line infections and deep venous thromboses. In addition, dosing of the antibiotics may be as often as several times per day, which can lead to a decrease in patient compliance as well as increased risk of infection. Additionally, many systemic antibiotics have relatively narrow therapeutic windows, and their potential for toxicity requires close clinical monitoring. But even when drug toxicity and line-related complications are avoided, treatment of such infections has a less-than-impressive success record. - ... 

With external fracture fixation, the bone fragments are held in aUgnment by pins placed through the skin onto the skeleton, structurally supported by external bars. With internal fracture fixation, the bone fragments are held by wires, screws, plates, and/or intramedullary devices. Figure 45.1a,b show radiographs of externally and internally fixed fractures. 

Note that the initial radius of the spherical cavity does not appear in Eq. (1.27). Thus, cavities of all sizes are predicted to inflate equally. However, we have neglected surface energy contributions that will tend to stabilize small cavities. When they are taken into account, it appears that only cavities having radii greater than about 100 nm will expand dramatically at the low pressures predicted by Eq. (1.27). Internal fractures suggest that vulcanized rubber must contain many precursor cavities of this effective size or larger. 

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