Local Flow Stress Research Articles

A quantitative study of the localization of atherosclerotic lesions in the rabbit aorta

A quantitative study of the size and location of early sudanophilic lesions has been carried out on the aortae of five rabbits. The atherosclerotic lesions were induced by feeding an average of 114 (± 3.7) egg yolks over an average period of 83 (± 1.7) days. The aortic lesions were visualized by gross staining with Sudan III and measured by the polar coordinate method. The lesions were almost entirely around orifices; their size was directly proportional to the area of the associated ostium ( P < 0.005). The sudanophilic deposits were located downstream from the ostia in areas believed to experience high shear stresses. The area of the intercostal ostia increased as one proceeded down the thoracic aorta ( P < 0.005). A deviation from the distal distribution pattern was observed where local flow and shear stresses were disturbed. The coronary lesions completely surrounded the ostia, the coeliac lesions had significant proximal components and the left renal and inferior mesenteric lesions were skewed to the right. The study suggests that hemodynamic forces and particularly high shear stress is of considerable importance in both the initiation and localization of early atherosclerotic lesions.

Some consequences of surface and size effects in plastically deformed copper single crystals

AbstractThe dislocation behaviour in deformed copper single crystals was previously shown to correspond to a lower local flow stress in the surface region than in the interior and the primary glide plane was found to undergo a characteristic bending in the surface region, reflecting a local excess density of unpaired edge dislocations. The detailed features of this “profile” are explained by a dislocation model which takes into account both surface and inner dislocation sources. It is shown that, as a result of the surface effects, dislocation glide paths in stage II as determined from slip lines are about 2.5 times larger than those in the interior. The rate of work‐hardening in stage II above a certain stress level, however, is found to be fairly constant over the cross‐section inspite of surface effects. It is concluded from Seeger's stage II work‐hardening theory that the number of dislocations per group should therefore decrease in the same way as the glide paths from the surface towards the interior. This prediction is in line with available experimental data. The shape of the macroscopic stress‐strain curve is explained by the local microscopic behaviour. Our results are consistent with Fourie's concept of preferential core‐hardening. The possibility of preferential near‐surface‐hardening is indicated.