Lateral expansion

Flow behaviour of polymer melts is still difficult to predict in detail. Here, we only mention two aspects. The viscosity of a polymer melt decreases with increasing shear rate. This phenomenon is called shear thinning [48]. Another particularity of the flow of non-Newtonian liquids is the appearance of stress nonnal to the shear direction [48]. This type of stress is responsible for the expansion of a polymer melt at the exit of a tube that it was forced tlirough. Shear thinning and nonnal stress are both due to the change of the chain confonnation under large shear. On the one hand, the compressed coil cross section leads to a smaller viscosity. On the other hand, when the stress is released, as for example at the exit of a tube, the coils fold back to their isotropic confonnation and, thus, give rise to the lateral expansion of the melt. 

Elastomeric materials, which provide relatively low practical static deflections and have relatively high natural frequencies, are used only to isolate higher frequencies. The volume compressibiUty of elastomeric materials is relatively low, therefore the shape of the elastomeric isolator must be taken into account, and space must be provided for lateral expansion. Because of their inherent resistance to chemical and environmental deterioration, neoprene and other synthetic materials often can be used in severe environments where natural materials would deteriorate. 

Results of uniaxial strain static and gas gun compression tests on syntactic foam have been conducted. The foam was buoyant and composed of hollow glass microspheres (average diameter 100 microns) embedded in an epoxy plastic. Static testing consists of compressing a 0.25 cm x 2.5 cm dia. wafer between carefully aligned 2.5 cm dia. steel pistons. Lateral expansion of the wafer is... 

The phase transition of bilayer lipids is related to the highly ordered arrangement of the lipids inside the vesicle. In the ordered gel state below a characteristic temperature, the lipid hydrocarbon chains are in an all-trans configuration. When the temperature is increased, an endothermic phase transition occurs, during which there is a trans-gauche rotational isomerization along the chains which results in a lateral expansion and decrease in thickness of the bilayer. This so-called gel to liquid-crystalline transition has been demonstrated in many different lipid systems and the relationship of the transition to molecular structure and environmental conditions has been studied extensively. 

Theoretical considerations of charges of limited diameter have taken one of two forms. The former assumes that the effects are best described as a result of the curvature of the wave front in the explosive (this can be demonstrated experimentally), or of reduction of the driving pressure by lateral expansion. Solutions of this type have been given by Eyring and co-workers and by Jones. Alternatively, the variation in velocity of... 

GENERAL NOTE These temperature reduction criteria do not apply when Table GR-2.1.3(e) specifies lateral expansion for minimum required values. 

Lateral Expansion Requirements. Other carbon and low alloy steels having specified minimum tensile strengths equal to or greater than 656 MPa (95 ksi), all bolting materials, and all high alloy steels (P-Nos. 6, 7, and 8) shall have a lateral expansion opposite the notch of not less than 0.38 mm (0.015 in.) for all specimen sizes. The lateral expansion is the increase in width of the broken impact specimen over that of the unbroken specimen measured on the compression side, parallel to the line constituting the bottom of the V-notch (see ASTM A 370). 

When a closed cell foam is uniaxially compressed, it can be assumed that the compressive stress is a sum of the stresses taken by the polymer structure and that taken by the cell gas. For a foam with zero lateral expansion when uniaxially compressed, and isothermal gas compression, the latter contribution (Tg is given by (295) ... 

Gas compression in closed-cell polymer foams was analysed, and the effect on the uniaxial compression stress-strain curve predicted. Results were compared with experimental data for a foams with a range of cell sizes, and the heat transfer conditions inferred from the best fit with the simulations. The lateral expansion of the foam must be considered in the simulation, so in subsidiary experiments Poisson s ratio was measured at high compressive strains. 13 refs. 

The strong influence exerted by many of these factors, particularly degree of confinement and charge diameter, shows that the energy release which is initiated in the detonation front does not occur instantaneously. Hence, any theory must take account of the lateral expansion [See Detonation (and Explosion), Lateral Expansion in, etc]... 

Constant Lateral Expansion , Ibid, pp 107-16 83) S.K. Aslanov, DopodiviAkad-... 

Thus, as noted in Ref 12a, p 4, the chemical reaction in normal detonation includes a fast first stage and a slow second stage. The low-order detonation is supported by only the first the second is too slow for completion in the available time or is quenched as a result of lateral expansion or other loss mechanism... 

Detonation (and Explosion), Lateral Dispersion in. See "Detonation (and Explosion), Lateral Expansion (Dispersion), etc... 

As the wave evolves from that point, the losses connected with rearward expansion decrease. If a charge of a small diam is considered, then lateral expansion depends on the path over which the wave has traveled. The increase in cross section of a cylinder, i.e., expansion in the lateral direction, leads to a reduction in pressure and to a decrease in the deton velocity in comparison with detonation propagating in a constant cross-section cylinder. The decrease in deton vel causes, in turn, the diminution of shock amplitude wave and impairs the conditions under which the reaction can proceed. The loss caused by lateral expansion is known as lateral loss. Propagation of detonation is possible only if this loss is not smaller than a certain limit, which is characteristic for each expl... 

In the case of a condensed HE, the lateral expansion proceeds with a velocity of the same order as the velocity in forward direction (Ref 6, p 215-16)... 

Accdg to experiments conducted in Russia by Yu.B. Khariton and others, the lateral expansion is the main cause of detonation dying out (Quoted from Ref 6, p 216)... 

Eyring also stated (Ref 3> p 98, as quoted in Ref 4, p 201) that release of energy by lateral expansion of the products permits stabilization of one of the sub-ideal states in the shock front. Of the hydro-dynamic equations only that of continuity, expressing the constancy of mass velocity, is perturbed by the expansion... 

Cook (Ref 5, p 123) discussed "lateral loss in conjunction with non-ideal detonation and he also stated that H. Jones (who developed the Nozzle Theory) considered that, to a good approximation, the hydro-dynamic equations expressing conservation of momentum and energy thru the detonation wave are unchanged by the effect of "lateral expansion ... 

Dunkle (Ref 10) stated "As noted on Cook s page 123, there is an important relationship between lateral expansion and the departure of a detonation from the ideal, but we could not find this info on p 123 of Ref 3 (See also Refs 2, 7, 8 9)... 

Jones, PrRoySoc 204A, 10-11(1950) (Effect of lateral expansion on detonation velocity) 4) Dunkle s Syllabus (1957-1958), 201 205 5) Cook (1958), p 123... 

The rarefaction wave may affect the observed detonation velocity if rarefaction wave follows so closely on the detonation front that the region of reaction is overlapped by the rarefaction. The phenomenon of rarefaction may account for the lower velocity which is observed in narrow tubes, in which the radial (lateral) expansion also produces a rarefaction wave... 

Detonation, Sideways Expansion in. See Detonation, Lateral Expansion (Dispersion) and Lateral Loss in . Called by G.B. Kistiakowsky "radial expansion ... 

The strong influence exerted by many. of these factors, especially degree of confinement and charge diameter, shows that the energy release which is initiated in the deton front does not occur instantaneously. Hence, any theory (such as "curved-front or "nozzle ) must take into consideration the lateral expansion (See Ref 61, pp 188-201). This expansion (if at all appreciable during time t, where reaction zone thickness is a-Dt) will modify the deton process because a) part of the energy released is used in the expansion (See Ref 61, p 201), hence does not contribute to propaga tion of rhe wave front, and b) peak temp and pressure are lower than when lateral expansion... 

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