Completely reversed stress

High endurance under completely reversed stress... 

High endurance under completely reversed stress Very resistant against abrasion Low thermal expansion coelEcient (9-30 x 10 °C)... 

Very high strength and rigidity, almost constant up to 140 °C Processable up to 250 °C, in the short nm up to 300 °C Very low creep tendency High endurance under completely reversed stress High abrasion resistance up to 250 °C, favottrable sliding behaviour Low thermal expansion coefficient Low absorption of water... 

In general, during the initial stages of deformation, a material is deformed elastically. That is to say, any change in shape caused by the applied stress is completely reversible, and the specimen will return to its original shape upon release of the applied stress. During elastic deformation, the stress-strain relationship for a specimen is described by Hooke s law ... 

Hysteresis is observed not only in the sorption isotherms but also in calorimetric measurements of heat of wetting at different moisture contents, and it is thus a combined entropy and enthalpy phenomenon. A reliable explanation for this effect is not currently available, but there is speculation that it is due to the stresses which are induced as the cellulose swells. Since the swelling of cellulose is not completely reversible, mechanical recovery is incomplete and hysteresis will therefore be present both in the internal stress-strain curve of the sample, and also in the water adsorption isotherm. 

Elastic Any change in shape is completely reversible, and the material returns to its original shape upon release of applied stress. 

Exposure to 70 °C gives similar results for the surface treated fiber (Fig. 24). That is, a complete reversibility in noted. The finished fiber (i.e. the fiber with the interphase consisting of the amine deficient brittle interlayer) experiences a nonrecovery of interfacial shear strength after moisture exposure and dehydration. Parallel surface spectroscopic investigation of the fiber surfaces show that under these conditions the fiber surface chemistry is not permanently altered by this exposure. Model studies of epoxies with the amine deficient composition of the interphase show that, the wet Tb of this material is about 70 °C. Therefore, the interphase is at or above its wet Tg and therefore because of the compliant nature of this material, stresses cannot be transfered efficiently and the interface is permanently distorted. 

The most striking feature of the stress softening phenomenon of thermoelastoplastics is its complete reversibility under certain conditions, consisting in a reformation process in the stress-free state which involves healing of cracks and reaching the initial integrity of the hard phase 119,120,12 ). The reformation kinetics in stress-softened samples indicates that this process is controlled by diffusion. 

When we pour a solution, or stir it or shake it, we are applying a stress to the solution and are deforming it. For a Newtonian fluid, this deformation is irreversible. If we pour some olive oil from a bottle into a frying pan, the liquid flows across the bottom of the pan, assuming a new shape. On the other hand, if we stretch a rubber band and then release it, the rubber band returns to its original shape. This deformation is completely reversible, and is called elastic. These two types of deformation, reversible (elastic) and irre- /... 

Influence of Solvents. The stress-strain curves of untreated and ether-extracted corneum in water show marked differences (81). Untreated corneum, extended 5% and relaxed, shows hysteresis similar to that observed for other keratinaceous structures (Figure 35). The deformation mechanism is completely reversible, and hydrogen-bond breakdown and slow reformation may be the major factors determining the stress-strain relationships. With ether-extracted samples, complete recovery is observed from 5% extension but with little or no hysteresis. The more rapid swelling and lack of hysteresis of ether-extracted corneum in water may be related to the breakdown of hydrogen bonds normally shielded from the eflFects of water by the lipid-like materials removed by ether. 

Shrinkage is not a completely reversible process. If a concrete unit is saturated with water after having fully shrunk, it will not expand to its original volume. The rate decreases with time since older concretes are more resistant to stress and consequently undergo less shrinkage, such that the shrinkage strain becomes almost asymptotic with time. 

The above perspectives are natural consequences of both the hydrophobic and the elastic consilient mechanisms as applied to the structural data on the myosin II motor. Here we briefly explore the elastic element. An ideal elastomer exhibits exactly reversible stress-strain curves with complete recovery on relaxation of the energy of deformation. On the other hand, an elastomer that exhibits hysteresis does not recover all of the energy on relaxation that was expended on deformation. Accordingly, efficient muscle contraction should involve the deformation of near-ideal elastic segments to utilize more efficiently the energy expended in driving contraction. The mechanism of elasticity that can provide such near-ideal elasticity is the damping of internal chain dynamics on extension. 

When this process is completed, the stress becomes reversible (Figure 8.5), this in turn confirming that the insertion-deinsertion of lithium ions in activated, lithiated LiyNiOx thin film electrodes ... 

A large number of experiments on fatigue were performed with completely reversed cycles (indicated in Fig. 7.2a), where the mean stress is zero (o max = o min)- Often in components exposed to fatigue, a pattern (as shown in Fig. 7.2b) is observed, resulting from the superposition of a static preload during the reversed cycle (see 7.2a) also note that the names of the cycle-patterns shown in Fig. 7.2 may have different nomenclature in the literature. This is also often stated differently, namely that the mean stress is ffm(= Cmean). represents a steady-state stress and the alternating stress is a variable stress. This stress cycle is asymmetrical, since the sum of Cmax and Cniin 0. Clearly, machine parts in service exposed to cyclic stresses may experience particular conditions in which min 0 or (7max 5 0-... 

The stress depressions observed for hard elastic polypropylene and Gore-Tex were completely reversible... 

Liquid-induced stress depression was also observed for hard-elastic PP. llte specimen was stretched to 10% elongation under vacuum. After one hour relaxation, ethanol vapor was introduced leading to a rapid drop in equilibrium stress to a new level. The process is completely reversible, i.e. after removing the vapor, the stress returned to the original relaxed value as measured in vacuo [2]. 

---