Sweep tests

The sweeping test, following X, Y and Z axes, on the aluminum plate containing four standard defects and the processing software comparing between the impedance variation of the sane reference and the sample to be controlled allow the reconstitution of an image of the piece. 

Strain Sweep Test Protocols for Nonlinear Viscoelasticity Investigations.826... 

It is clear that this data treatment is strictly valid providing the tested material exhibits linear viscoelastic behavior, i.e., that the measured torque remains always proportional to the applied strain. In other words, when the applied strain is sinusoidal, so must remain the measured torque. The RPA built-in data treatment does not check this y(o )/S (o)) proportionality but a strain sweep test is the usual manner to verify the strain amplitude range for constant complex torque reading at fixed frequency (and constant temperature). 

At sufficiently low strain, most polymer materials exhibit a linear viscoelastic response and, once the appropriate strain amplitude has been determined through a preliminary strain sweep test, valid frequency sweep tests can be performed. Filled mbber compounds however hardly exhibit a linear viscoelastic response when submitted to harmonic strains and the current practice consists in testing such materials at the lowest permitted strain for satisfactory reproducibility an approach that obviously provides apparent material properties, at best. From a fundamental point of view, for instance in terms of material sciences, such measurements have a limited meaning because theoretical relationships that relate material structure to properties have so far been established only in the linear viscoelastic domain. Nevertheless, experience proves that apparent test results can be well reproducible and related to a number of other viscoelastic effects, including certain processing phenomena. 

Strain Sweep Test Protocols eor Nonlinear Viscoelasticity Investigations... 

According to strain sweep test protocols described above, RPA-FT experiments and data treatment yield essentially two types of information, which reflects how the main torque component, i.e., r(l[Pg.829]

Conversion efficiencies of the dynamometer-aged catalysts were measured in a standard A/F sweep test on an engine dynamometer [6]. The sweep experiments were carried out at 450 and 85,000 h space velocity (volumetric basis standard conditions). The sweep ranged from 0.5 A/F lean of stoichiometry to 0.5 A/F rich of stoichiometry with imposed A/F perturbations of+.0.5 A/F at 1 Hz. After sweep evaluation, small samples of catalyst were renrroved from the front region of the brick for chemisorption and flow reactor experiments. 

A threshold level of oxygen storage (via bulk PdO) is required to reach Ngh CO/NOx conversion levels in dynamometer sweep tests Pd loading, rather than dispersion or surface area, is the most impoirtant factor affecting oxygen uptakes. 

Figure H3.1.3 For oscillatory (sweep) testing, four control parameters can be varied amplitude, frequency, time, and temperature.

The sample is loaded onto the instrument and the time reference is noted by starting a timer or resetting a timer in the software. A dynamic test for viscoelastic structure is then used to monitor changes in the sample that could result from mechanical relaxation, drying, or thixotropy. A time sweep test is usually performed at a constant temperature. The test is also run at a constant frequency that is comparable to real-time observation (typically 1 Hz) or at a constant angular frequency (10 rad/sec or 1.6 Hz). 

In the frequency sweep test, the idea is to obtain LVE data from the test material over the widest possible (or realistic) range of frequencies. The lower limit of testing is never difficult for a rheometer to achieve physically, but it may be impractical to explore. Typically, the time required to obtain data at frequencies of <0.01 rad/sec or 0.006 Hz is impractical for a laboratory schedule. (At 0.006 Hz, each data point would take 167 sec for a single iteration most rheometers perform at least two or three iterations.) Furthermore, samples may change or degrade in nonsterile conditions over extremely long tests (i.e., hours). If it is desirable to obtain... 

Fora farther discussion of a frequency sweep test, see UNITH3.1. The range of frequencies used here and in step 5 will depend on both the sample and the rheometer type. 

Figure H3.2.6 Three types of materials that are Theologically distinguishable based on a frequency sweep test. O, storage modulus G, loss modulus.

Because the duration for one measurement is very short (e.g., with a 1-Hz input, a cycle is completed in 1 sec), a dynamic test is suitable for gaining information in a short time frame or for monitoring time-dependent changes in gel network properties. When monitoring the gelation process at a fixed frequency, it usually takes a few hours for G to become approximately constant. The constancy can be judged by a constant value of G at a fixed frequency during a subsequent frequency or strain sweep test, which usually takes several minutes. 

FIGURE 2.12 Rheometric frequency sweep test of slurries conducted at 5-30 °C. G, G", and complex = rj + if]" reduce as temperature increases. 

Frequency sweep studies in which G and G" are determined as a function of frequency (o)) at a fixed temperature. When properly conducted, frequency sweep tests provide data over a wide range of frequencies. However, if fundamental parameters are required, each test must be restricted to linear viscoelastic behavior. Figure 3-31... 

Rheology Rheological measurements were performed at 25°C with an ARES 2 KFRT controlled strain rheometer (Rheometric Scientific). For the measurements parallel plates of 50 mm diameter were used. The gels were loaded between the plates (2-mm gap) and allowed to rest for 3 min. A strain sweep (0.1 to 100%) was performed at 1 Hz frequency to determine the range of viscoelasticity for each sample and a 2% strain was selected for all samples. A frequency sweep test (0.1 to 16 Hz) was then performed. Samples of 30 and 50% s/w concentration could not be analyzed because of the difficulty in obtaining samples of proper and constant geometry. 

An example of an indirect method is the use of a steady-shear-rate sweep test, which examines the steady-shear viscosity rf) and shear stress a as functions of shear rate (/). The results, once obtained, may be plotted in terms of steady-shear viscosity (tj) versus shear stress (shear stress is indicative of a yield stress, and the asymptotic stress is defined as the yield stress (measurable yield stress. This is shown diagrammatically in Figure 4.3. 

The work of several authors (Peters et al, 1993, Halley et al, 1994) has demonstrated the use of non-isothermal dynamic sweep tests to examine the combined effects of shear rate and curing on the chemoviscosity of a highly filled epoxy resin simultaneously. These tests use a selected temperature ramp with repeated dynamic rate sweeps to investigate the effects on the chemoviscosity. The advantage of these tests is that the effects of shear rate and cure are not separated, which is similar to processing conditions. 

Examples of time sweep test results at 2 Hz for an antibacterial hand soap are shown in Figure 4.11 and Figure 4.12. Figure 4.11 summarizes the complex modulus components, G andG", and the complex viscosity, n, while Figure4.12 shows the experimental variables of phase angle and amplitude obtained at 23 to 24°C. 

Figure 1 Static engine sweep test results for catalyst types I and II. (100 g Pd/ft ...

---