Dynamic hysteresis measurement

To obtain the dynamic hysteresis loop of a ferroelectric capacitor the polarization is measured versus the applied voltage. Since the hysteresis is neither a linear nor a time invariant property, the hysteresis loop is dependent on the sample history and on the measurement method. To have a standardized and comparable hysteresis loop, certain parameters are commonly fixed. One is the absolute position of the loop on the polarization axis, since the initial (virgin) state of the polarization is unknown in almost all cases, the hysteresis loop is balanced to a reference value. Most commonly the positive and negative saturation polarization are set to 

The third loop establishes the sample into the positive remanent polarization state without sampling data. The fourth loop now starts in the positive relaxed remanent polarization state (Prrei+), turns into the negative saturation (Pmax-), then crosses the polarization axis at zero volts excitation signal in the negative remanent polarization state (Pr ). Afterwards the sample is driven into the positive saturation (Pmax+) and ends up in the positive remanent polarization state (Pr+) when the voltage is zero again. Subsequently, the hysteresis loop is balanced respectively to the values P(+Vmax) and P(-Vmax). From the data of the second loop the parameters Vc-, Pr, Prrei- are determined and from the data of the fourth loop the parameters Vc+, Pr+, Prrei+ The closed hysteresis loop (continuous loop) can be calculated from the second half of the second loop and the second half of the fourth loop. 

It is of particular importance to emphasize that the shape of the hysteresis curve changes with frequency, amplitude, shape, and relaxation time between prepolarization and recording pulses of the excitation signal. Therefore the extracted characteristic values differ for two 

Furthermore, the history of a hysteresis loop plays an important role in the determination of lifetime and reliability of ferroelectric capacitors, especially for applications in ferroelectric memories. Three main effects are characterized in particular as changes in the hysteresis loop under various conditions, which are described later in this chapter as fatigue, retention, and imprint with the corresponding ways to measure these effects. 

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The creep deformation behavior of TPU under static load can be determined by dynamic hysteresis measurements in reduced testing times without the risk of changing morphoiogy. 

In addition to the properties noted above, the formulation parameter in iPP-E-plastomer blends have a profound influence on the dynamic loading (e.g., vibration) performance. The load limits of the blend for applications in which dynamic stresses are predominant were studied by using the hysteresis measurement method. However, their technical application requires knowledge of critical load values. 

In Figure 3.12 a static hysteresis loop is shown in correlation to a dynamic hysteresis loop. Two clippings of the excitation signal of the static hysteresis loop are shown. Each of them is used to measure one data point of the curve. To record 20 points for one loop, 20 of these excitation signals have to be applied to the sample, each one stopping at a different voltage. 

In general, dynamic hysteresis is smaller with smaller cross-sectional area because the effect of buoyancy is less. Thus, the dynamic hysteresis is not a measure of surface characteristics. Intrinsic hysteresis is a measure of the surface dynamic stability of the surface. 

The dependence of the concentration of ionized groups (and consequently the water uptake) on the duration tgx of th immersion in the solution leads to an additional dynamical hysteresis in the sensor output characteristic which can be minimized by setting constant tgx for all pH measurements. 

R Renz, V Altstadt and G W Ehrenstein, Hysteresis measurement for characterising the dynamic fatigue of R-SMC , J Reinforced Plastics Compos 1988 7 413. 

Hysteresis A type of path-dependent error caused by the time lag of sensor properties (see Fig. le) response to the dynamics of measured ... 

Contact angle hysteresis measured experimentally may be due to heterogeneities in the composition of the solid surface, surface irregularities, or dynamic effects due to adsorption or desorption phenomena, molecular reorientations, or similar. 

In dynamic mechanical measurements, the closed curve representing successive stress-strain cycles during cyclic deformation is called the hysteresis loop. The area of the resulting elliptical loop is equal to the heat generated in the system. 

The normal test for dynamic evaluation of materials or components is the Wohler fatigue test, to characterize fatigue behaviour. Hysteresis measurements are carried out on flax and glass mat-reinforced polypropylene, with a needle-punched flax mat using green and retted fibres to make plates with a quasi-isotropic composite structure, and with treatment by a coupling agent. 

SELECTING MATERIALS UNDER DYNAMIC LOADING Hysteresis Measurement Gives Dynamic Characteristics... 

If the dynamic behavior of a material or a component must be guaranteed, the material and its processing conditions are normally subject to continuous checking to ensure that the properties do not vary. The better way, of monitoring the dynamic properties directly, is confronted with the current high cost of testing. The hysteresis measurement procedure offers the possibility of obtaining the maximum of information on the dynamic behavior of a material or a component in a very short time. 

Furthermore, the hysteresis-measurement procedure is very effective when values of dynamic characteristics and efficiencies are required as indices of quality for example, in the choice of suitable foam materials for sport shoes, the pattern of modulus change under dynamic load, or the damping index, can be used. 

In order to avoid critical stresses that may lead to first structural damage, it is useful to determine the dynamic load limits of the material. For this purpose the hysteresis measurement method [793], [794] can be applied. Figure 5.229. The stress ratio should not result in a maximum stress higher than the dynamic load limit. 

Note Optimization = 3 factor, 2,2 and 2-level full factmial design—8 compounds and experiments. Responses (properties) to be measured Dynamic hysteresis heat resistance, 1008 hat 120°C resistance to application fluids, 70 h at 120 C extrusion processing. 

Both tear resistance and hysteresis increase on incorporation of silica, but the effect is less pronounced as compared to the stress-strain properties. Tension set of the ZnO-neutralized m-EPDM system is low (around 20%) and incorporation of filler causes only a marginal increase in set due to chain slippage over the filler surface, as previously discussed. Measurement of physical properties reveal that there occurs an interaction between the filler surface and the polymer. Results of dynamic mechanical studies, subsequently discussed, support the conclusions derived from other physical properties. 

Cyclic polarisation This type of measurement is similar to potentio-dynamic anodic polarisation with the difference that, following an anodic polarisation plot, the test specimen is subjected to a cathodic stimulus, i.e. a reverse scan. Any hysteresis, i.e. deviation from the anodic plot, can... 

In particular it can be shown that the dynamic flocculation model of stress softening and hysteresis fulfils a plausibility criterion, important, e.g., for finite element (FE) apphcations. Accordingly, any deformation mode can be predicted based solely on uniaxial stress-strain measurements, which can be carried out relatively easily. From the simulations of stress-strain cycles at medium and large strain it can be concluded that the model of cluster breakdown and reaggregation for prestrained samples represents a fundamental micromechanical basis for the description of nonlinear viscoelasticity of filler-reinforced rubbers. Thereby, the mechanisms of energy storage and dissipation are traced back to the elastic response of tender but fragile filler clusters [24]. 

Fig. 9.13 Time evolution of the NFS intensity for various temperatures around the HS-LS transition of [Fe(tpa)(NCS)2]. The measurements were performed at 1D18, ESRF in hybrid-bunch mode. The left-hand side shows measurements in the transition region performed with decreasing temperature and the right-hand side with increasing temperature. (The spectral patterns at comparable temperatures do not match due to hysteresis in the spin-transition behavior). The points give the measured data and the curves are results from calculations performed with CONUSS [9, 10]. The dashed line drawn in the 133 K spectmm represents dynamical beating. (Taken from [41])...

An apparatus for measuring the dynamic modulus and hysteresis of elastomers. The stress-strain oscillogram is shown on a ground-glass screen by means of an optical system. Now superseded by modem computer controlled servo hydraulic and dynamic mechanical thermal analysis machines. Roll Bending... 

An instrument designed to follow hysteresis losses in polymers by measuring the resistance to the rolling of small balls over the surface of the test piece it can investigate transitions in polymers to as low a temperature as -120 °C. Superseded by modem dynamic mechanical thermal analysis equipment. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

After several cycles of the compression and expansion, the dynamic jc-A curve becomes a single closed loop, somewhat distorted from a genuine ellipsoid. In order to analyze the forms of the hysteresis loop under stationary conditions, we have measured the time trace of the dynamic surface pressure after five cycles of the compression and expansion, and then Fourier-transformed it to the frequency domain. The Fourier-transformation was adapted to evaluate the nonlinear viscoelasticity in a quantitative manner. The detailed theoretical consideration for the use of the Fourier transformation to evaluate the nonlinearity, are contained in the published articles [8,43]. 

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