Poisson’s ratio measurement

Foamed blends of ethylene-styrene interpolymer and LDPE were subjected to a range of mechanical tests, including compressive impact testing, Instron compression and Poisson s ratio measurements, compressive creep measurements and compression set and recovery measurements. The data obtained were compared with those for EVA and the suitability of these foamed blends as replacements for EVA in the manufacture of soccer shin guards and midsoles for sports shoes was evaluated. 20 refs. 

Extensional measurements involve a simple loading process, but with compression and torsion measurements simplifying assumptions and/or corrections need to be applied to experimental data. In compression it is necessary to assume plane strain," and Poisson s ratio measurements may be performed either at constant strain or constant stress. For a non-linear viscoelastic polymer these two methods are not equivalent. 

Fig. 1.35 Poisson s ratio measured by the (filled circle) LUFP (laser ultrasonics coupled with a Fabry-Perot interferometer) method and (plus sign) laser ultrasonic pulse technique using SiC as a standard [9]. With kind permission of Wiley and Sons...

Solutions Using Broadband Bulk, Shear and Poisson s Ratio Measured Functions... 

Thus Young s modulus measures the slope of the stress-strain curve and is analogous to the stiffness of a spring, while Poisson s ratio measures lateral eontraction. 

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

Engineering constants (sometimes known as technical constants) are generalized Young s moduli, Poisson s ratios, and shear moduli as well as some other behavioral constants that will be discussed in Section 2.6. These constants are measured in simple tests such as uniaxial tension or pure shear tests. Thus, these constants with their obvious physical interpretation have more direct meaning than the components... 

Thus, three reciprocal relations must be satisfied for an orthotropic material. Moreover, only 2, V13, and V23 need be further considered because V21, V31, and V32 can be expressed in terms of the first-mentioned group of Poisson s ratios and the Young s moduli. The latter group of Poisson s ratios should not be forgotten, however, because for some tests they are what is actually measured. 

The preceding restrictions on engineering constants for orthotropic materials are used to examine experimental data to see if they are physically consistent within the framework of the mathematical elasticity model. For boron-epoxy composite materials, Dickerson and DiMartino [2-3] measured Poisson s ratios as high as 1.97 for the negative of the strain in the 2-direction over the strain in the 1-direction due to loading in the 1-direction (v 2)- The reported values of the Young s moduli for the two directions are E = 11.86 x 10 psi (81.77 GPa) and E2 = 1.33x10 psi (9.17 GPa). Thus,... 

Tsai conducted experiments to measure the various moduli of glass-fiber-epoxy-resin composite materials [3-1]. The glass fibers and epoxy resin had a Young s modulus and Poisson s ratio of 10.6 x 10 psi (73 GPa) and. 22 and. 5 x 10 psi (3.5 GPa) and. 35, respectively. 

Equation (20) yields the elastic modulus, Ec, of the composite in terms of the moduli and Poisson s ratios of the phases. If the Ec-modulus and vc-value are accurately measured and the Ef- and Em-moduli and the Poisson rations vf and vm are known, the average modulus of the mesophase, Ef, may be determined. Poisson s ratio of the mesophase may be found from the simple relation ... 

The unit of viscosity of fluids in CGS units. It is measured in dynes/cm2 per unit velocity gradient. Poisson s Ratio... 

So for an incompressible material v = 0.5 and Equation 2.4 is recovered. The value of Poisson s ratio for rubber is usually close to 0.5 but for many other solids the value is lower and we find 0.25 < v < 0.33. We may also describe a Bulk rigidity modulus, K, such as we would measure when we compress a material with hydrostatic pressure, in terms of Young s modulus ... 

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. 

Silvery-white, soft maUeable metal exists in two aUotropic forms an alpha hexagonal from and a beta form that has body-centered cubic crystal structure the alpha allotrope converts to beta modification at 868°C paramagnetic density 7.004 g/cm compressibility 3.0x10 cm /kg melts at 1024°C vaporizes at 3027°C vapor pressure 400 torr at 2870°C electrical resistivity 65x10 ohm-cm (as measured on polycrystalline wire at 25°C) Young s modulus 3.79xl0 ii dynes/cm2 Poisson s ratio 0.306 thermal neutron cross section 46 barns. 

Silvery-gray metal hexagonal crystal structure malleable, ductile, and soft enough to be cut with a knife density 8.223 g/cm melts at 1,359°C vaporizes at 3,221°C resistivity llhxlCH ohm-cm at 25°C Young s modulus 5.75xl0n dynes/cm2 (from velocity of sound measurements) shear modulus 2.28 dynes/cm2 Poisson s ratio 0.261 thermal neutron absorption cross section, 46 barns insoluble in water soluble in acids. 

The analysis has shown that PAI may only be negative, and PAB ( both positive and negative. Therefore, the thermal effect accompanying a reversible stretching of the model depends on the ratio between p and PA,n and may be a function of strain even at small strains. Besides, Poisson s ratio for such a heterogeneous model may exeed 0.5, Direct measurements of Poisson s ratio for a number of various oriented crystalline polymers are consistent with this suggestion (see Table 5). 

Methods have not been standardised for measuring Poisson s ratio for rubber but the most obvious approach is to use a second "extensometer" to measure the change in the width of the test piece during a normal tensile test. 

Alternative procedures are to use a dilatometer to measure volume change or to calculate Poisson s ratio from measurement of two moduli. Laufer et al5 concluded that for soft rubbers the dilatometer is the best approach and describe a suitable apparatus. Kugler et al6 have given a review of attempts at measurement and describe an optical system which they employed on a series of filled rubbers. It would seem reasonable that modem instrumentation, such as a video extensometer, could be used but this does not appear to have been reported. 

Compressive measurements provide a means to determine specimen stiffness, Young s modulus of elasticity, strength at failure, stress at yield, and strain at yield. These measurements can be performed on samples such as soy milk gels (Kampf and Nussi-novitch, 1997) and apples (Lurie and Nussi-novitch, 1996). In the case of convex bodies, where Poisson s ratio is known, the Hertz model should be applied to the data in order to determine Young s modulus of elasticity (Mohsenin, 1970). It should also be noted that for biological materials, Young s modulus or the apparent elastic modulus is dependent on the rate at which a specimen is deformed. 

Here we have conducted experiments to develop an understanding of how the commercial size interacts with the matrix in the glass fiber-matrix interphase. Careful characterization of the mechanical response of the fiber-matrix interphase (interfacial shear strength and failure mode) with measurements of the relevant materials properties (tensile modulus, tensile strength, Poisson s ratio, and toughness) of size/matrix compositions typical of expected interphases has been used to develop a materials perspective of the fiber-sizing-matrix interphase which can be used to explain composite mechanical behavior and which can aid in the formulation of new sizing systems. 

Whalley (1980) presented a theoretical argument to suggest that both the thermal expansivity and Poisson s ratio should be similar to that of ice. With the above two estimates, Whalley calculated the compressional velocity of sound in hydrates with a value of 3.8 km/s, a value later confirmed by Whiffen et al. (1982) via Brillouin spectroscopy. Kiefte et al. (1985) performed similar measurements on simple hydrates to obtain values for methane, propane, and hydrogen sulfide of 3.3, 3.7, and 3.35 km/s, respectively, in substantial agreement with calculations by Pearson et al. (1984). 

For Agar gel, experimental study of these coefficients were performed [7], The coefficient E was determined by compressive tests. Ultrasonic measurements of the Poisson s ratio v showed that it is almost equal to 0.5. Compressibility K (fig. 3) is deduced from K = Ej(3(1 — 2//)). 

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