Bowed Fractures

When relatively minor forces are applied, children s hones are more able to hend than those of an adult. With excess force the deformity may persist (see section 8.5.1). This is called plastic deformation. The forearm and fihula are particularly prone to plastic deformation, these injuries are often referred to as bowed fractures, they maybe associated with a fracture in the adjacent bone (Fig. 8.8)... 

Fig. 8.8. Bowed fracture of the ulna with oblique fracture in the adjacent radius...

Low energy bending injuries may produce plastic deformation (bowed fractures) or, if a cortical break is produced, it may not propagate fully across the bone. The cortex and periosteum on the compression side may be intact or undisplaced, resulting in a greenstick fracture. 

The other alternative is to attempt to increase K -. Pure ceramics have a fracture toughness between 0.2 and 2 MPa m. A dispersion of particles of a second phase can increase this a little the advancing crack is pinned by the particles and bows between them, much as a dislocation is pinned by strong second phase particles (Chapter 10). 

Ionic conductors, used in electrochemical cells and batteries (Chapter 6), have high point defect populations. Slabs of solid ceramic electrolytes in fuel cells, for instance, often operate under conditions in which one side of the electrolyte is held in oxidizing conditions and the other side in reducing conditions. A signihcant change in the point defect population over the ceramic can be anticipated in these conditions, which may cause the electrolyte to bow or fracture. 

A seven-month-old child "fell over" while crawling, and now presents with a swollen leg. At age one month, the infant has multiple fractures in various states of healing (right clavicle, right humerus, right radius). At age seven months, the infant has a fracture of a bowed femur, secondary to minor trauma (see x-ray below). The bones are thin, have few trabecula, and thin cortices. A careful family history ruled out nonaccidental trauma (child abuse) as a cause of the bone fractures. The child is most likely to have a defect in ... 

Her x-ray series revealed generalized under-mineralization throughout the bony structures. Her ribs were thin, and the spine showed the presence of multiple compression fractures at the thoracolumbar level. There was marked bowing of all extremities with evidence of old fractures in femurs, humerus, and left ulna. A bone mineral density study of the lumbar vertebral bodies (L1-L4) performed at 5 years of age revealed a value of 6.57 standard deviations below the mean for children of the same age. 

Clinical manifestations of rickets and osteomalacia are a consequence of the defect in mineralization. Rachitic manifestations include bowing of the extremities, short stature, costochondral-junction swelling, indentation of the lower ribs, and flattening of the skuU. In adults, bone pain is the most common symptom, and stress fractures and frank skeletal fractures may occur. X-rays show classic findings in rickets, such as cupping and fraying of the epiphyseal and... 

Some preliminary work has been completed to explain the origin of the permeability of the sandstone units. In the Bow Island Formation, an attempt was made to correlate conductivity values from drill-stem tests with the estimated true formation resistivity determined from electric logs. The lack of correlation, however, suggests that fracture permeability may be prevalent. 

The stress-strain curves of Zr02-Ni system in three-point bending test are presented in Figure 2. It can be found that the Zr02-Ni system shows quite different deformation and fracture behavior with the change of constitution. The nickel-rich material displays typically elasto-plastic deformation behavior, which is controlled by the continuous matrix nickel phase and similar to metallic material. During bending test, the specimen can be bowed to V shape... 

Fracture mechanisms in most inorganic particle filled composites can be described by the crack-front bowing theory 1,18,19), Originally proposed by Lange in 1970 (75), it describes the relationship between a mobile crack front... 

This mechanism has been analyzed theoretically and various calculations have shown that crack bowing should lead to an increase in fracture toughness. For... 

Figure 8.51 Interaction of a crack front with an inclusion in glass showing crack bowing. The marks on the fracture surface were produced by ultrasonic fractography (frequency 1 MHz) and reflect successive crack front positions at 1 (is intervals.

Why does crack bowing increase fracture toughness ... 

This is a descriptive term and should be reserved for those fractures which penetrate one cortex and then spreads up or down the medulla but does not cross the contralateral cortex. This fracture may be associated with some bowing of the limb. This term should not be used synonymously with torus fractures. 

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