Hysteresis-effect

An example will be given to show how dynamic loading can lead to product failure by hysteresis heating. When this condition exists the failure will be catastrophic rather than 

The designer can use several approaches to prevent hysteresis failure. The first is material selection. The stiffer the material is, the smaller the strain is for a given stress level and the lower the hysteresis loss per cycle. Some materials are additionally fairly linear in stress-strain characteristics and have smaller hysteresis loops. These would be preferred in dynamic loading applications. 

Another approach is to improve the heat transfer conditions from the product. This can be accomplished in several ways. One way is to operate in a coolant medium that would also act as the lubricant for the system. The heat transfer to a liquid is usually much better than to air, and the liquid can be cooled by passing it through a heat exchanger device. A second approach is to improve the heat transfer to air. This can be done by increasing the surface area of the product by means of fins or other surface projections. The larger area will increase the heat flow 

Basically, anything that can be done to reduce the temperature of the product by removal of heat generated by the cyclical stress will improve the possibilities of surviving the cyclical stress. If the heat transfer capability is limited, then the only alternative is to use stiff materials and low stress levels on the product compared with the strength capability of the material. The heavier products that result will be relatively inefficient in the use of material. In some cases when the load applied is an inertial load (such as an impeller on a pump) it may be that only a trade-off of weight for low stress level can cause failure. 

This energy is converted from mechanical to frictional energy (heat). It can represent the difference in a measurement signal for a given process property value when approached first from a zero load and then from a full scale as shown in Figs. 3.4 and 3.5. They provide examples of recovery to near zero strain. It shows that material can withstand stress beyond its proportional limit for a short time, resulting in different degrees of the hysteresis effect. 

The hysteresis heating failure occius more commonly in plastic members subject to dynamic loads. An example is a plastic gear. With the gear teeth under load once per revolution, it is subjected to a bending load that transmits the power fi om one gear to another. Another example is a link that is used to move a paper sheet in a copier or in an accounting machine 

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The situation is complicated, however, because some of the drag on a skidding tire is due to the elastic hysteresis effect discussed in Section XII-2E. That is, asperities in the road surface produce a traveling depression in the tire with energy loss due to imperfect elasticity of the tire material. In fact, tires made of high-elastic hysteresis material will tend to show superior skid resistance and coefficient of friction. 

Ferroelectric crystals exhibit spontaneous electric polarization and hysteresis effects in the relation between polarization and electric field, as shown in Figure 1. This behavior is usually observed in a limited temperature range, ie, usually below a transition temperature (10). 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

In Part III heterogeneous equilibria involving clathrates are discussed from the experimental point of view. In particular a method is presented for the reversible investigation of the equilibrium between clathrate and gas, circumventing the hysteresis effects. The phase diagrams of a number of binary and ternary systems are considered in some detail, since controversial statements have appeared in the literature on this subject. 

When studying heterogeneous equilibria involving clathrates, one is faced with peculiar difficulties owing to the hysteresis effects mentioned in the introduction the solute in a clathrate crystal of hydroquinone, for instance, will not come to thermodynamic equilibrium with the vapor in which it is placed. Consequently it is impossible, or at least very difficult, to measure the equilibrium vapor pressure of the solute in a clathrate by placing some crystals in a tensometer (cf. the experiments of Wynne-Jones and Anderson,58 and those of Leech and Richards reported by Powell33). 

Hysteresis effect The hysteresis effect is a retardation of the strain when a material is subjected to a force or load. Figure 2-12 are examples of different hysteresis recovery rates. 

Dielectric loss The dielectric loss factor represents energy that is lost to the insulator as a result of its being subjected to alternating current (AC) fields. The effect is caused by the rotation of dipoles in the plastic structure and by the displacement effects in the plastic chain caused by the electrical fields. The frictional effects cause energy absorption and the effect is analogous to the mechanical hysteresis effects except that the motion of the material is field induced instead of mechanically induced. 

The isotherms represented in Fig. 1 give a general idea of the equilibria in the Pd-H system under different p-T conditions. Most experimental evidence shows, however, that the equilibrium pressure over a + /3 coexisting phases depends on the direction of the phase transformation process p a-p > pp-a (T, H/Pd constant). This hysteresis effect at 100°... 

Electrostrictive Stress 0.2—2 MPa Small strains, but large forces, easy Elimination of hysteresis effects... 

Here the phenomenon of capillary pore condensation comes into play. The adsorption on an infinitely extended, microporous material is described by the Type I isotherm of Fig. 5.20. Here the plateau measures the internal volume of the micropores. For mesoporous materials, one will first observe the filling of a monolayer at relatively low pressures, as in a Type II isotherm, followed by build up of multilayers until capillary condensation sets in and puts a limit to the amount of gas that can be accommodated in the material. Removal of the gas from the pores will show a hysteresis effect the gas leaves the pores at lower equilibrium pressures than at which it entered, because capillary forces have to be overcome. This Type IV isotherm. 

Table 2. Hysteresis effects associated with abrupt spin-state transitions...

As far as the solid complexes are concerned, the qbove conclusions are generally valid for gradual spin-state transitions, whereas additional features such as hysteresis effects are observed for transitions which show abrupt changes of physical properties. In fact, abrupt transitions seem to be formed if the volume change A V associated with the spin-state conversion of the molecules cannot be conveniently accommodated by the lattice. 

Because these analysers do not employ magnets, peak switching for selected ion monitoring can be done more quickly without hysteresis effects, which makes this system ideal for depth profiling, where it is necessary constantly to switch among masses. These instruments do have the disadvantage of loss of transmission and mass... 

For partition studies, only SUV [385,386] or LUV [149] should be used MLVs have many layers of trapped solution, which usually cause hysteresis effects [162],... 

Figure 4.22 Hysteresis effect of wall temperature at various qualities during blowdown and core cooling.

Braver, H., and F. Mayinger, 1992, Onset of Nucleate Boiling and Hysteresis Effects under Convective and Pool Boiling, Engineering Foundation Conf. on Pool and External Flow Boiling, Santa Barbara, CA, pp. 1 14. (4)... 

Type IV behavior is similar to Type II behavior except that a limited pore volume is indicated by the horizontal approach to the right-hand ordinate axis. This type of curve is relatively common for porous structures of many kinds. Hysteresis effects associated with... 

The desorption isotherm approach is the second generally accepted method for determining the distribution of pore sizes. In principle either a desorption or adsorption isotherm would suffice but, in practice, the desorption isotherm is much more widely used when hysteresis effects are observed. The basis of this approach is the fact that capillary condensation occurs in narrow pores at pressures less than the saturation vapor pressure of the adsorbate. The smaller the radius of the capillary, the greater is the lowering of the vapor pressure. Hence, in very small pores, vapor will condense to liquid at pressures considerably below the normal vapor pressure. Mathematical details of the analysis have been presented by Cranston and Inkley (16) and need not concern us here. 

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