Longitudinal stretch

Flow is generally classified as shear flow and extensional flow [2]. Simple shear flow is further divided into two categories Steady and unsteady shear flow. Extensional flow also could be steady and unsteady however, it is very difficult to measure steady extensional flow. Unsteady flow conditions are quite often measured. Extensional flow differs from both steady and unsteady simple shear flows in that it is a shear free flow. In extensional flow, the volume of a fluid element must remain constant. Extensional flow can be visualized as occurring when a material is longitudinally stretched as, for example, in fibre spinning. When extension occurs in a single direction, the related flow is termed uniaxial extensional flow. Extension of polymers or fibers can occur in two directions simultaneously, and hence the flow is referred as biaxial extensional or planar extensional flow. 

Formation of the Tyrrhenian Sea, and the associated counter-clockwise rotation of the Italian peninsula, resulted in longitudinal stretching of the Apennine chain and produced several arc sectors separated by important transverse tectonic lines. The main tectonic lineaments crossing the Apennine chain include the Ancona-Anzio line, the Ortona-Roccamonfma line,... 

A newer development is the manufacture of bi-axially oriented bottles, in particular for PETP. The pre-form is injection- moulded and rapidly cooled in the mould it remains amorphous (PETP crystallises very slowly) by heating above its Tg (65°) it passes into the rubbery state, and can then be blown-up and, simultaneously, longitudinally stretched. The biaxial orientation thus obtained, accelerates the crystallisation, and, at the same time, results in a very fine crystalline texture, so that a thin-walled, strong, transparent and heat-resistant bottle is obtained. 

With orientation, the thickness is reduced and the surface area enlarged. If film is longitudinally stretched, its thickness and width are reduced in the same ratio. If lateral/transverse contraction is prevented, stretching reduces the thickness only. Orientation temperature is normally 60 to... 

It should be pointed out that the analysis of the complete problem requires us to take into account the longitudinal stretching of the sample when it is transversely loaded by an alternating force. In this case, even in the absence of an external longitudinal stress, a temperature jump gives rise to a force along the rigidly clamped bar. This force is a consequence of the... 

Mechanical factors such as shear stress, longitudinal stretch and wall tension in vascular SM tissue [29,39,263,316-318], and wall stretching in non-... 

With polymers such as polyvinylidene chloride copolymers and polypropylene the bubble method is carried out in a different way. First a tube is extruded and quenched as rapidly as possible to keep the crystallinity as low as possible. As shown in Fig. 10 the collapsed tube passes through a pair of nip rolls (a) and is then heated to the desired temperature and blown up to a 4-5 times larger diameter before it reaches the next set of nip rolls (b) rotating at a higher speed to provide a longitudinal stretch ratio 1 3-1 4. 

As noted earlier in sections 2 and 3, LCPs are different from typical random coil polymers, in that the orientation that is produced in the die does not relax quickly. For this reason, the transverse stretch from internal air pressure and the longitudinal stretch from the take-up speed enhance the orientation from the die, and do so within a relatively short distance from the die lips. Typical blown film conditions would be 2 to 1 blow-up ratio, with the bubble reaching full diameter within a height equal to one to two times the die diameter. Typical LCP film thickness is 12 to 75 micrometers (0.0005 to 0.003 in.). 

Schaufele and Shimanouchi have considered the longitudinal stretching motion of an elastic rod of length L, elastic modulus E and density p and have shown that the frequency of its according motion can be written as... 

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