Tension-mode experiments

DMTA measurements were carried out on film samples with a Q800 apparatus (TA Instruments) operating in tension mode. Experiments were performed at a 1 Hz frequency and a heating rate of 3°C mim from -120 to 100°C. 

In tension-mode experiments, essentially zero force should be applied to the sample (such as films or fibers) to measure the tensile properties. However, a small initial force (<2mN) may be applied to the film or fiber sample to keep the sample straight. Care should be taken not to apply more than the necessary initial force, because this can cause creep and sometimes unnecessary orientation. Too high a load may also reduce the level of shrinkage during heating. 

Fatigue Testing. Fatigue testing was conducted using an MTS closed-loop electrohydraulic test machine that was operated in load control, tension-tension mode. Loads in this experiment ranged from a minimum of 10% of the maximum load to maximum loads of 200-700 psi. 

Fig. 43 Effect of dynamic strain amplitude on storage modulus (a). Stress-strain behavior of CR/ EPDM blend in the absence and presence of nanoclay (b). For this experiment, tension mode was selected for the variation of the dynamic strain from 0.01 to 40% at 10 Hz frequency...

Equations 1.2 to 1.4 represent material functions under large deformations (e.g., continuous shear of a fluid). One may recall a simple experiment in an introductory physics course where a stress (a) is applied to a rod of length Z, in a tension mode and that results in a small deformation AL. The linear relationship between stress (ct) and strain (j/) (also relative deformation, y = AL/L) is used to define the Young s modulus of elasticity E (Pa) ... 

Mechanical Properties. Dynamic mechanical properties were determined both in torsion and tension. For torsional modulus measurements, a rectangular sample with dimensions of 45 by 12.5 mm was cut from the extruded sheet. Then the sample was mounted on the Rheometrics Mechanical Spectrometer (RMS 800) using the solid fixtures. The frequency of oscillation was 10 rad/sec and the strain was 0.1% for most samples. The auto tension mode was used to keep a small amount of tension on the sample during heating. In the temperature sweep experiments the temperature was raised at a rate of 5°C to 8°C per minute until the modulus of a given sample dropped remarkably. The elastic component of the torsional modulus, G, of the samples was measured as a function of temperature. For the dynamic tensile modulus measurements a Rheometrics Solid Analyzer (RSA II) was used. The frequency used was 10 Hz and the strain was 0.5 % for all tests. 

Now we discuss briefly the results obtained from the relaxation of the bending mode. As a comparison with the bulk value for the surface indicates (Table I), there is a discrepancy between this surface tension and the surface tension obtained from the bending mode experiments. It should be realized, however, that the film tension value is obtained from experiments on a time scale totally different from the time scale encountered in obtaining the bulk value. This implies the possibility of processes that influence both values in a completely different way, like adsorption and desorption phenomena of surface active materials at the interface. 

The experiments on the polycarbonate film were performed in the tension mode of TMAl only. The stage and pro of TMAl were replaced with their tensile counterparts and temperature was recalibrated using indium wire (0.5 mm >99.99% pme from Alfa-Aesar) mounted in the tensile clamps. The ends of the wire were wrapped in aluminiun foil to protect the clamps. 

We shall follow the same approach as the last section, starting with an examination of the predicted behavior of a Voigt model in a creep experiment. We should not be surprised to discover that the model oversimplifies the behavior of actual polymeric materials. We shall continue to use a shear experiment as the basis for discussion, although a creep experiment could be carried out in either a tension or shear mode. Again we begin by assuming that the Hookean spring in the model is characterized by a modulus G, and the Newtonian dash-pot by a viscosity 77. ... 

Although the creep behavior of a material could be measured in any mode, such experiments are most often run in tension or flexure. In the first, a test specimen is subjected to a constant tensile load and its elongation is measured as a function of time. After a sufficiently long period of time, the specimen will fracture that is a phenomenon called tensile creep failure. In general, the higher the applied tensile stress, the shorter the time and the greater the total strain to specimen failure. Furthermore, as the stress level decreases, the fracture mode changes from ductile to brittle. With flexural, a test specimen... 

It follows from Eqs. (73) and (74) that the only stabilizing force for a-modes at long X is the membrane tension, and critical voltage vanishes as cr 0. In experiments with black lipid membranes the surface tension a arises from the contact of the bilayer with the bulk phase contained in the surrounding rim and is typically < 0.002 N/m. Then choosing... 

It is well known that the equation of state of Eq. (28) based on the Gaussian statistics is only partially successful in representing experimental relationships tension-extension and fails to fit the experiments over a wide range of strain modes 29-33 34). The deviations from the Gaussian network behaviour may have various sources discussed by Dusek and Prins34). Therefore, phenomenological equations of state are often used. The most often used phenomenological equation of state for rubber elasticity is the Mooney-Rivlin equation 29 ,3-34>... 

It is important to note that the lamellar phase is thus stabilized by the balance of a negative interfacial tension (of the free oil/water interface covered by an amphiphilic monolayer), which tends to increase the internal area, and a repulsive interaction between interfaces. The result, Eq. (48), indicates that the scattering intensity in a lamellar phase, with wave vector q parallel to the membranes, should have a peak at nonzero q for d > d due to the negative coefficient of the q term in the spectrum of Eq. (40). just as in the microemulsion phase. This effect should be very small for strongly swollen lamellar phases (in coexistence with excess oil and excess water), as both very small [96]. Very similar behavior has been observed in smectic liquid crystals (Helfrich-Hurault effect) [122]. Experimentally, the lamellar phase under an external tension can be studied with the surface-force apparatus [123,124] simultaneous scattering experiments have to be performed to detect the undulation modes. 

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