Strain-controlled programming

In a strain-controlled programming protocol Rf is given by the ratio of the strain in the stress-free state after the withdrawal of the tensile stress in the A(th cycle (N) and the maximum strain m (7). In the case of a stress-controlled programming protocol, Rf is given by the ratio of the tensile strain after unloading, (N), to the maximum strain at (7 = (7m after cooling to Tjow, (N) (8). 

Corrosion detection plays an important role in any corrosion control program. Most of the methods employ nondestructive test methods and include hydrogen evaluation, radiography, dynamic pressure, corrosion probes, strain gauges and eddy current measurements. Of these, the methods employed in cooling tower practice are hydrogen evaluation and corrosion probes. 

Fig. 1 Torsion vs. axial analyzers The PerkinElmer Diamond DMA (A) is an axial analyzer while the ATS Rheo (B) is a torsional instrument. Both are controlled stress but can act as strain controlled because of the feedback programmed in. Photos taken by the author of Equipment at the University of North Texas (C) shows the TBA. (Courtesy of Dr. John Enns of Polymer Network Characterizations, Inc.) (View this art in color at www.dekker.com.)...

Figure 3.17 Strain versus time representation of the stress-controlled programming performed at 263 kPa followed by free recovery. The creep effect in the foam during step 1 is shown in the subplot. Source [41] Reproduced with permission from Elsevier...

A strain-controlled or fully confined recovery test was conducted. It started immediately after completion of the programming with the same loading device and environmental chamber. The chamber was heated at a ramp rate of 0.6°C/min. The heating was continued until the temperature starting the programming (71 °C or 79 °C) was reached. After that, the temperature was maintained constant for several hours and the stress was continuously recorded. This process was stopped when further stress recovery was negligible. 

In order to conduct 2-D programming, a special truss fixture was fabricated and cruciform specimens were used [57]. It has been realized that this may not be realistic for large panels or structures. Together with the requirement for high temperature, and loading rate and pre-strain control, it turns out to be a challenging task. Therefore, an alternative programming approach is... 

Different test procedures have been described in the literature for quantification of an SME. One of the most powerful and widely used test procedures are cyclic, thermomechanical tensile tests. Quantification of the SME by cyclic, thermomechanical tensile tests follows tailored test procedures. These test procedures consist of a programming module, where the temporary shape is created, and a recovery module, where the permanent shape is recovered. The programming module can be performed under stress-controlled or strain-controlled conditions the recovery module can be carried out under stress-free conditions or under constant strain [4, 13]. The combination of certain programming and recovery modules results in different cycle types, which are presented in Table 2. Several thermomechanical... 

The shape recovery ratio Rr quantifies how well the permanent shape has been memorized, i.e., is a measure of how far a strain, that was applied in the course of the programming, is recovered as a result of the SME [4]. The shape recovery ratio Rr for the strain-controlled protocol is... 

Figure 12 Torsion versus axial analyzers The PerkinElmer DMA 7e (a) is am axial analyzer, while the Rheometric Sciences SR-5 (b) is a torsional instrument. Both are controlled stress but can act as strain controlled because of the feedback loop programmed in.

Specific Commercial Rotational Viscometers. Information on selected commercial rotational viscometers can be found ia Table 7. The ATS RheoSystems Stresstech rheometer is an iastmment that combines controlled stress as well as controlled strain (shear rate) and oscillatory measurements. It has a torque range of 10 to 50 mN-m, an angular velocity range of 0 to 300 rad/s, and a frequency range of seven decades. Operation and temperature programming (—30 to 150°C higher temperatures optional) are computer controlled. 

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