Volume strain

The variations of volume strain with axial true strain are displayed in Fig. 19.16 for the different materials. It is evident from this graph that nonisochoric effects are very 

The elastic portion of the curves was investigated from the recorded data in order to determine precisely the initial volume strain variations. Since we showed that lims oidev/dEs) = (1 — 2vei), the initial Poisson s ratio Vei could be determined with a precision of a few percent. The values thus obtained are displayed in Table 19.2. It is seen, by comparison with neat PP, that the elastic Poisson s ratio of the blends increases slightly with the alloying content. This is probably due (i) to the contribution of PA6 that exhibits a Poisson s ratio significantly higher than that of PP and (ii) to the contribution of the elastomer (POE) for which Vei is near to 0.5 like most rubber-like materials. 

After the yield point is passed, most curves in Fig. 19.16 show a nearly immediate increase of the volume strain. Conversely, to neat PP that exhibits continuous increase in volume strain (although this evolution tends to saturate), all the blends, at the exception of BD13, show a marked decrease in the volume strain after a rounded maximum at a given strain threshold. Conversely, the volume strain of neat PA6 shows a monotonous and relatively small increase up to Sy 0.2 for 3 = 1.0, while it reaches Sy 0.5 for PP. 

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We imagine a finite-duration shock pulse arriving at some point in the material. The strain as a function of time is shown as the upper diagram in Fig. 7.11 for elastic-perfectly-plastic response (solid line) and quasi-elastic response generally observed (dash-dot line). The maximum volume strain = 1 - PoIp is designated... 

When we translate these observations into Lagrangian wave speed, the data would look like that shown in the lower diagram of Fig. 7.11. The points e and q represent volume strains at whieh elastie-perfeetly-plastie release (e) and quasi-elastie release (q) would undergo transition to large-seale, reverse plastie flow (reverse yield point). The question is the following What is responsible for quasi-elastie release from the shoeked state, and what do release-wave data tell us about the mieromeehanieal response in the shoeked state ... 

The values of Ljb, and appear reasonable, but the large value of B q is unexpected. Pure aluminum has a drag coefficient of 10 Pa s [46] under ambient conditions, and therefore we conclude that shock compression to a volume strain of 0.17 (T = 590 K, = 20.7 GPa) results in an increase of two orders of magnitude. 

This phenomenon is still under investigation as is the substantial departure of calculated from that measured at volume strains below 0.15 as shown in Fig. 7.13. Details of these calculations are presented in the work of Johnson et al. [47]. The important consideration is that the unloading wave also contains micromechanical information if we only can be clever enough to apply proper interpretation to macroscale measurements. 

In section 3.6.3 we mentioned that in growth on a curved face the strain surface free energy os takes the role the lateral surface free energy tr played in the flat surface case, namely that of a barrier to the formation of the first stem. This analogy cannot be made since, in contrast to surface free energy is associated with the deposition of any stem. Therefore and because of its physical origin (the volume strain) it is closely linked with the free energy of fusion. This is... 

A dimensionless quantity for the change in volume, V, per unit volume. A synonymous term is bulk strain. An example of volume strain can be seen in bodies experiencing hydrostatic pressure. Volume strain is usually symbolized by 9 thus, 9 = AVIVq. 

VOLUME STRAIN BUNDLING PROTEIN BUNNETT-OLSEN EQUATIONS COX-YEATS EQUATION ACIDITY FUNCTION BURST KINETICS Buthionine sulfoximine,... 

GIBBS FREE ENERGY OF ACTIVATION ENTHALPY OF ACTIVATION ENTROPY OF ACTIVATION VOLUME OF DISTRIBUTION COMPARTMENTAL ANALYSIS VOLUME STRAIN V SYSTEMS... 

The kinetics and mechanisms of tensile deformation in ASA and ABS polymers were studied using high accuracy creep tests. Crazing was detected by volume strain measurements. 

The first quantitative study of deformation mechanisms in ABS polymers was made by Bucknall and Drinkwater, who used accurate exten-someters to make simultaneous measurements of longitudinal and lateral strains during tensile creep tests (4). Volume strains calculated from these data were used to determine the extent of craze formation, and lateral strains were used to follow shear processes. Thus the tensile deformation was analyzed in terms of the two mechanisms, and the kinetics of each mechanism were studied separately. Bucknall and Drinkwater showed that both crazing and shear processes contribute significantly to the creep of Cycolac T—an ABS emulsion polymer—at room temperature and at relatively low stresses and strain rates. 

Longitudinal strain es was measured in the central 20 mm of the specimen, and lateral strain e1 was measured simultaneously at the center of the gage portion is usually negative in a tensile test. The lateral strain e2 was not measured. In the calculations all specimens, including those cut from a drawn sheet, were assumed to be transversely isotropic— i.e., ei = e2. On the basis of this assumption the volume strain AV/V was calculated from the expression ... 

Earlier work (4,6) demonstrated that a high gradient in the volume strain-longitudinal strain curve is associated with a large drop in the modulus of the material. This is to be expected, as the crazes have much lower moduli than the material from which they were formed (7). As a result of the creep tests described above, the 100 sec tensile modulus of Luran S 757R at a strain of 0.5% fell from 1.99 to 1.30 GN/m2, and the modulus of Luran S 776S at a similar strain fell from 1.65 to 0.98 GN/m2. 

The effect of stress upon the kinetics of crazing can be represented by two rate quantities obtainable from the creep data. The linear portion at the end of the volume strain-time curve defines a maximum rate of... 

Figure 7. Volume strain vs. longitudinal strain curves for three specimens of ABS 1 at 10,000 in./min. Theoretical cavitation and shear curves are also included.

Volume Strain Vs. Longitudinal Strain. Volume strains (AV/V0) were calculated from longitudinal strain ci and lateral strain c2 by use of the following expression ... 

The (1 -f- c2)2 term arises from the assumption that specimens deform isotropically in width and thickness. Volume strain vs. longitudinal strain curves are shown for three specimens of ABS 1 in Figure 7. For comparison, theoretical curves for total cavitation, i.e., c2 = 0, and pure shear, i.e., AV = 0, are also shown. Volume strain vs. longitudinal strain curves, together with nominal stress vs. nominal strain curves, for ABS 1, ABS 2, and ABS 3 are shown in Figure 8. Because of the size of the strains involved, it is not possible to approximate Equation 3 with an expression which contains only first-order powers of strain when calculating volume strains. 

Ratio of the incremental volume strain and the incremental elongation-... 

Ague J. J. (1991) Evidence for major mass transfer and volume strain during regional metamorphism of pehtes. Geology 19, 855-858. 

Glass transition temperature Activation volume Volume strain... 

Volume strain at zero time under load Specimen width... 

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