Strain-dependent measurements

Figure 8. Mooney-Rivlin plots for strain dependent measurements at 298 K. Key A, PDMS-BI , PDMS-B2 X, PDMS-B3 O, PDMS-B5 , PDMS-B6 , PDMS-B7 V, PDMS-B8 A, PDMS-B9 PDMS-B10.

Mooney-Rivlin constants obtained from strain dependent measurements at 298 K... 

Concluding, we can state that the absolute values of the small-strain moduli, which are greater for networks having comblike crosslinks, than for those with tetrafunctional junctions, are understandable, if we assume that the fluctuations of junctions are restricted by the very short chains. The strain dependent measurements do not agree quantitatively with the recent theory, although the trends are in accordance. An exact correspondence... 

For materials exhibiting the wurtzite crystal structure, Aa and Ago are usually deduced from the differences of the A-, B-, and C-exdton transition energies (for strained samples, we use the notation Ti, T2, and T3 in order of increasing energy), while the deformation potentials are determined from strain-dependent measurements. For GaN, a large number of values for Act, Ago, and D5, are reported in the hterature, which are derived from both first-principle calculations and experimental data [5-10]. The literature values for the other deformation potentials a as well as Di to D4 vary much less. 

As long as the moduli are constants, it makes no difference in either a tensile or shear experiment which variable, stress or strain, is independent and which is dependent that is, we could apply a constant force and measure the strain or induce a constant strain and measure the force responsible. The modulus is the ratio of the stress to the strain. If the ratio were calculated as the ratio of the strain to the stress, the reciprocal of the modulus would result. The latter is called the compliance and is given the symbols D and J for tensile and shear conditions, respectively. When they are independent of time, the moduli and compliances for a particular deformation are simply reciprocals. 

In this section we consider a different experimental situation the case of creep. In a creep experiment a is maintained at a constant value and the time dependence of the strain is measured. Thus it is the exact inverse of the relaxation... 

Fig. 16 a. Stress dependence of the molar fraction of the P form (x ) and b) bulk stress-strain curve measured for uniaxially oriented polybutyleneterephtalate [83]... 

In comparing the correlation sought between MH and E one should emphasize the following while the plastic deformation of lamellae at larger strains when measuring MH depends primarily on crystal thickness and perfection in case of the elastic modulus the major role is played by the amorphous layer reinforced by tie molecules, which is elastically deformed at small strains. Figure 17 illustrates de... 

Figure 18 shows the percent crystallinity obtained by birefringence measurements for NR at various elongations as a function of temperature. The relative shapes of the curves in this Figure show the pronounced temperature and strain dependence on the strain induced crystallization of NR. Of particular importance is the relatively high amounts of crystallinity that develop at room temperature. 

Equilibrium stress-strain dependences were determined in extension using a stress relaxation arrangement described earlier (21). Dry non-extracted samples were measured at 150 C in nitrogen atmosphere and extracted samples swollen in dimethylformamide were measured at 25 C. The equilibrium value of stress 6 e was reached within 2-4 min except of a few dry samples with the lowest tig, for which the equilibrium stress was determined using an extrapolation procedure described earlier (21). 

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

New biomarkers will be useful in hepatotoxicity risk assessment if the data quality and validity can be established. The FDA defines a valid biomarker as one that can be measured in an analytical test system with well-established performance characteristics and has an established scientific framework or body of evidence that elucidates the significance of the test results [160]. Although there is no formerly agreed upon path, biomarker validation should include appropriate end-points for study (i.e., toxicology, histopathology, bioanalytical chemistry, etc.) and dose- and time-dependent measurements. An assessment of species, sex and strain susceptibility is also important to evaluate across species differences. More specific considerations for validation of gene and protein expression technologies are reviewed by Corvi et al. and Rifai et al. [144, 147]. 

The strain dependence of the elastic storage modulus of clay-filled NBR has been measured and the results compared with those of unfilled vulcanizates. The corresponding data are shown in Fig. 19. From this figure it is revealed that there is no Payne effect, because the G values do not decrease with the increase in strain... 

Fig. 18 Strain dependence of G of CR vulcanizates filled with different kinds of nanofillers. The measurements were done by a moving die rheometer (Scarabaeus SIS V50) applying sinusoidal strain at constant frequency of 0.1 Hz at 60°C...

If we measure the frequency dependence of k and k" over a wide frequency range, we can obtain values erf dzJdS, SAz/dS and i.e., the strain dependence of characteristic parameters of relaxation. 

Our main result is that the nanotube can be manipulated by the gate voltage, which determines its deformation and stress, and modifies the eigen-modes. Though the eigenmodes of nanotube ropes have been measured in Ref. [12] four years ago, the strain dependence of the eigenmodes was only recently reported in Ref. [15]. ft demonstrates this effect for singly-clamped multi-wall carbon nanotubes. We expect that our predictions will soon be tested in experiments on doubly-clamped SWNTs. 

The present work summarizes opportunities of using high-resolution synchrotron and standard xrd techniques for structural characterization as well as for investigations of structure-property-relationships. xrd will be used to determine quantitatively the phase content of morphotropic pzt. Temperature dependent measurements provide information about the phase transformation of morphotropic donor doped pzt ceramics and high-resolution synchrotron X-ray diffraction gives information about the extrinsic and intrinsic contributions to the electric field induced strain, xrd results are finally compared with electrical measurements to analyze the interactions among microstructure, phase content and properties. 

Fig. 7. Rate dependence of time-to-fracture values, tf, based on crack tip strain gage measurements for all materials investigated.

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