Reversed stress

Resistance to fatigue and corrosion fatigue The resistance of titanium to fracture by fatigue, induced by imposition of rapidly reversing stresses. 

Consistent with the Newtonian flow of concentrated PAMAM solutions, it was found that all three types of dendrimers [40, 41, 50] under steady-shear conditions, and both PAMAMs [40] and PPIs [50] under creep [16,50] showed typical viscous behavior at all applied stress levels and testing temperatures. For example, as illustrated in Figure 14.9 [40], all of the first seven generations of PAMAMs showed constant viscosities over the entire ranges of shear rates investigated, and in addition to this, there was no hysteresis between the forward and the reverse stress sweeps in steady shearing, indicating the absence of thixotropy. 

Figure 5.40 Variation of stress with time that accounts for fatigue failure by (a) a reversed stress cycle and (b) a repeated stress cycle. Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 210. Copyright 2000 by John WUey Sons, Inc.

In Eq. (25) the term v (V r) represents reversible stress work, while r Vv represents irreversible or entropy-producing stress work. The following are expressions for the latter quantity in rectangular Cartesian, cylindrical polar, and spherical polar coordinates ... 

This relation, called the mechanical energy equation, describes the rate of increase of kinetic energy in a fluid element as a result of the action of external body forces, pressure, and reversible stress work. 

PP2C A large family of protein phosphatases. Reverses stress-induced, SAP kinase phosphorylation cascades... 

A vacuum (the negative difference between atmospheric and below-atmospheric pressure) can be as damaging as the high-pressure systems. Sometimes a vacuum is more damaging to the structures that may not be built to withstand reversal stresses. 

When smooth specimens of PS are cycled at 26.7 Hz in a tensile mode at a maximum stress of 17.2 MPa discontinuous crack growth bands similar to those shown in Fig. 8 are seen in the mirror region near the fracture source. These bands are also similar in morphology to those observed in testing notched PS specimens at a minimum stress that is maintained at one-tenth the maximum stress However, DCG bands were not seen when tests are carried out under a fully reversed stress of 17.2 MPa at... 

Fig. 8.18. Reversible stress diagram of boehmite membranes dried at 40°C with RH values changing cyclic between 60 and 90% RH. From Voncken et al. [26].

The complicated morphology of crystalline polymer solids and the coexistence of crystalline and amorphous phases make the stress and strain fields extremely nonhomogeneous and anisotropic. The actual local strain in the amorphous component is usually greater and that in the crystalline component is smaller than the macroscopic strain. In the composite structure, the crystal lamellae and taut tie molecules act as force transmitters, and the amorphous layers are the main contributors to the strain. Hence in a very rough approximation, the Lennard-Jones or Morse type force field between adjacent macro-molecular chain sections (6, 7) describes fairly well the initial reversible stress-strain relation of a spherulitic polymer solid almost up to the yield point, i.e. up to a true strain of about 10%. 

Record of typical non-reversing stress test on loose sand, K = 2.0, e = 0.87. (From Chaney, R.C., and Fang, H.Y., Static and dynamic properties of marine sediments. Proceedings of the Symposium on Marine Geotechnology and Nearshore/Offshore Structures, Shanghai, China, ASTM STP 923, pp. 74-111, 1986. Reprinted with permission. Copyright ASTM.)... 

PROPERTIES OF SPECIAL INTEREST Low glass transition temjjerature, mesophase behavior including reversible stress-induced mesophase formation accompanied by necking-denecking phenomena in cyclic deformation of elastomers at room temperature and above. 

Ttmes, F.G., Troncoso, O.P., Lopez, D., Grande, C., Gomez, C.M. Reversible stress softerring and stress recovery of cellulose networks. Soft Matter 5, 4185-4190 (2009)... 

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. 

Alloy Condition R Fatigue Reversed-Stress (MPa) R Rotating Bending Fatigue Strength (MPa)... 

Elasticity The reversible stress-strain behavior by which a body resists and recovers from deformation produced by a force. 

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