Stretching device

Another type of experiment involves a fluid filament being drawn upward against gravity from a reservoir of the fluid (101,213,214), a phenomenon often called the tubeless siphon. The maximum height of the siphon is a measure of the spinnabiUty and extensional viscosity of the fluid. Mote quantitative measures of stress, strain, and strain rate can be determined from the pressure difference and filament diameter. A more recent filament stretching device ia which the specimen is held between two disks that move apart allows measurements ia low viscosity Hquids (215). AH of these methods are limited to spinnable fluids under small total strains and strain rates. High strain rates tend to break the column or filament. 

Figure 4. Experimental setup for stress-relaxation and cross-linking at constant simple extension. Key A, electron accelerator B, beam aperture C, force transducer D, thermostated box E, sample F, stretching device G, connecting rods.

Each film was cut into a 5-cm width strip and stretched by 10% at 230°C to 280°C using an automatic biaxial stretching device. 

The filament stretching device could play a new role in rheometry by providing a new direction for studying substances that exhibit severe slip effects during conventional rotational rheometry. 

Figure 12.8. Stretching device for electrical measurements under uniaxial extension.

Cold stretched films were made by deforming compression molded 40/60 PET/POB films In a T. M. Long biaxial stretching device. Specimens were originally 60 mm x 60 mm. Following a five minute preheat, the films were unlaxlally stretched 2 x 1 at 750%/mln. with... 

A piston driven stretching device has been developed by Koch et al. Stretching occurred in a fraction of a second. The sample can be heated by a stream of hot air. For stretching velocities up to 0.75 mm s , a stretching device has been developed by Holland Moritz and Stach which can also be used for real time fourier transformed infrared (FTIR) experiments. Both the force and elongation are transferred to a PDF 11/24 computer by a CAMAC based voltage/frequency converter (Fig. 31). 

H measurements of PBT under strains of up to 20% relative deformation (e) were performed using a stretching device. The strain s is defined ass = ( — o) /f o where q and are the starting and stretched lengths of the sample, respectively. The indentation anisotropy AH = 1 — (d /dj ) was also derived (see eq. (2.6)). In order to evaluate the contribution of each polymorphic phase to the total H it is necessary to know their mass fractions at the different deformation stages as required by the additivity law (eq. (4.3)). For this purpose the data of Tashiro et al. (1980) obtained by the infrared study of the a-fi transition have been used. The same authors have shown that just in the transition deformation interval (e = 4-16%) the relationship between s and the amount of the phase is linear. 

The same PEE material was used for this study as in the previous sections. Using a stretching device it was possible to perform measurements up to 70% overall relative deformation s at which point the sample broke. Again the deformation was increased in steps of 5%. The main difference was that in previous studies (Sections 6.2.1-6.2.3) the deformation was increased continuously without relaxation, whereas in this case the sample was unloaded and allowed to relax after each H measurement under stress before the next H measurement without stress (a = 0) was performed. The sample was then stretched to the next deformation and H was measured again. It should be noted that beyond some overall deformation (typically s > 20%) the unstressed sample shows some residual (plastic) deformation amounting about 50% of the strain s under stress. The same deformation cycle has been used for SAXS measurements aimed at the morphological characterization of these PEE samples. 

Tirtaatmadja V, Sridhar T (1993) A filament stretching device for measurement of extensional viscosity. J Rheol 37 1081-1102... 

A stretching device described elsewhere [67] was made by us which extended the PU samples uniformly from both ends while it was centered in the IR beam. The samples were placed at an intermediate focus in the infrared source beam at an angle of 45° to the sUts. Wire grid polarizers were placed in the sample and reference beams at a setting of 45. The entire stretching device rotated around the centre of the IR polarized beam (and the sample) to allow absorption experiments while stretching the sample both parallel and transverse to the plane of the polarized... 

The elastic recovery was determined from cyclic deformation experiments, where the samples were stretched three times to kcyc = 8 (where Xcyc = kyc/h and /eye = the length of the sample stretched to X = 8), and the stress was released to be zero. Subsequently, the samples were removed from the stretching device and stored without strain for 24 hours to allow them to recover before measuring the final sample length used in Equation 9.4. 

Although the time structure of the primary positron beams may be of advantage to some experiments (see e g. Howell et al. [3.18]), the saturation and pile-up effects inherently connected with high-intensity bunched beams often cause problems in other experiments. Therefore, a number of present electro-producing positron facilities have been equipped with storage and pulse-stretching devices (see, e.g., Ebel et al. [3.17], Akahane and Chiba [3.19], Ito et al. [3.20], and Hulett et al. [3.21]). 

Rotational viscometers are also sometimes adapted to act as stretching devices, with the rotor of the apparatus serving as a roll onto which one end of the specimen that is being stretched is wound. The other end of the sample is attached to a slotted vertical spindle, and the force exerted by the polymer on this spindle is measured. The winder is usually raised during the course of the experiment to ensure that the filament does not wrap on itself. This technique has been used by Macosko and Lomtson, ) Everage and Ballman,(39) and Connelly et among others. 

PIG. 6-2. Apparatus of Kramer for measuring stress relaxation in simple extension. The stretching device can be operated at a controlled rate of extension prior to the relaxation at constant extension. 

The sample environment is generally an easily accessible region where a variety of equipment can be mounted in the beam, e.g. heating jackets, flow cells, magnets, stretching devices and automatic sample chargers. Each instrument has its own particular features, and details are obtainable from the parent institutions. Additional details are provided here of the LOQ diffractometer at ISIS. 

Like cartilage, tendon and ligaments sustain quite large in vivo stress, strain and torsion, possess lower cell densities than many other tissues, and are practically avascular, and aneural. Bioreactors for such tissue have employed stretching devices that apply physiologic strain, as well as provide traction and torsion (Table 22.1). 

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