Stress field visualization

Optically measured shear stress as a function of time for various distances from the outer, rotating wall of a Couette cell. The solution was a 0.5 wt % mixture of polystyrene (molecular weight 2x 10 ) in tricresyl phosphate. The other wall of the Couette cell was impulsively started to a speed of Scm/s. The ratio y/Z measures the distance tom the outer cylinder, normalized by the gq separation. From Fuller (1990). 

0 to 5 cin/s at r = 0. The di ferent curves illustrate the propagation of the shear wave duough the liquid, as the effect is fiist parent near the moving surface. The wave speeds deduced from these measurements were in good agreement with theoretical analysis (Joseph et al., 1986). 

---

Fig. 1. Stress field visualization through birefringence (From Ref. 2).

One application of birefringence related to polymer rheology is stress field visualization. It relies on flow-induced birefringence techniques to examine the spatial and temporal evolutions of stress in a polymer melt (see Fig. 9) (55). In this... 

This is therefore a type of slip which occurs under high stress and which has been identified as macroscopic slip. Visualization of the velocity field shows that it occurs very close to the wall (less than 10 pm) in the case of the flows with heterogeneous shear rates and stress fields considered here. 

The increasing strain near the hole was illustrated in the photos placed in order. The cracks grew through each hole visually. For low concentration of capsules, cracks led to rupture. For high concentration, big crack arose from capsules. It meant that local concentration of stress depended on overlapping of stress fields near capsules too. Theoretically, such interaction appeared when distance between capsules was less than 5 capsule diameters -Figure 29. 

The fitting/predictive capabilities of three models (extended Pom-Pom, PTT-XPP and modified Leonov model) are tested for both, steady as well as transient shear and uniaxial extensional flows of mLLDPE and HDPE. The applicability of these constitutive equations has been investigated from the coextiusion flow modeling point of view. Finally, the FEM and modified Leonov model has been employed for the stress analysis in the coextrusion flow domain and predicted stress fields have been compared with the stress measurements fl om the flow coextrusion visualization cell. 

The mechanisms of flashbacks are probably mixed. Some cases may be similar to post-traumatic stress disorder induced by a bad trip (Paton et al., 1973). Abraham (1983) suggested that some of the visual phenomena, such as trailing and after-images, were due to failure of inhibition in visual pathways, possibly mediated in the lateral geniculate nucleus which (in the macaque monkey) contains on-off colour neurons with receptor fields similar to those described in flashbacks. The neurochemical causes of such flashbacks, which can be very disturbing, remains elusive and attempts at treatment are usually ineffective. 

At the same time, to our surprise, P8 M appears visually transparent and nonbirefringent, both in bulk samples and in thin films. This is illustrated by Figure 5.3, where the spot of chiral polymer can hardly be recognized between two glasses in contrast to its racemic isomer, P8 M. We should stress here that it is impossible to induce any birefringence in P8 M using shear flow, electric field up to 15 V/pm, or magnetic field up to 2.5 T. 

There was abnormal color perception in 32% of 32 patients taking vigabatrin monotherapy in four cases there was an abnormality in the blue-yellow axis (64). In the same patients there was a positive correlation between visual contrast sensitivity and the size of the visual field macular photo-stress and glare tests were equal in both groups and did not differ from normal values there was no effect on glare sensitivity (65). 

---