Fading memory materials

Experience indicates that highly filled polymers do not fall into the category of fading memory materials even at small strains below detectable dewetting [1,2] or volume dilatation. These materials suffer from the "Mullins Effect" [2-8], which is a stresssoftening that occurs with deformation, and causes a permanent hysteresis on repeat loading. 

Day W.A., The Thermodynamics of Simple Materials with Fading Memory, Springer Tracks on Natural Philosophy, 22, Berlin (1972). 

Here we confine ourselves to the short range memory expressed by the constitutive principle of differential memory constitutive equations are functions of values and time derivatives of the thermokinetic process (2.5) taken in the present instant. Such constitutive equations may be expected in the material with fading memory where the history (2.5) is developed in the Taylor series about the present instant with restriction to the slow processes (2.5) when higher time derivatives are negligible, cf. [31]. ... 

The problem is rather in the physical identification of these hidden fSj but if they are known the use of internal variables with evolution Eq. (2.72) is another way to describe materials with (long range) memory. Solutions of (2.72) is facilitated in the case of fading memory (where always // < 0 [61]), but also more intricate cases may be described as phase changes [65], plasticity and generally any hysteresis [66], cf. also Rem. 31 in Chap. 3 important are applications in chemically reacting mixtures (where [3j may be, e.g., extent of reaction ) which will be discussed here in Sect. 2.4 and in Chap. 4. 

Lubliner, J. On fading memory in materials of evolutionary type. Acta Mech. 8,75-81 (1969) BataiUe, J., Kestin, J. Irreversible processes and physical interpretation of rational thermodynamics. J. Non-Equilib. Thermodyn. 4,229-258 (1979)... 

In summary, polymeric materials exhibit rubber elasticity if they satisfy three requirements (a) the polymer must be composed of long-chain molecules, (b) the secondary bond forces between molecules must be weak, and (c) there must be some occasional interlocking of the molecules along the chain lengths to form three-dimensional networks. Should the interlocking arrangements be absent, then elastomers lack memory, or have a fading memory and are not capable of completely reversible elastic deformations. 

The evidence and references cited support considering LCP s as liquid crystals it is also necessary to consider how they are similar or different from isotropic polymers. Solutions and melts of polymers are non-linear viscoelastic [18] - the stress depends not only on the instantaneous rate of deformation, but upon the entire history of the deformation. The material has a fading memory for previous configurations, the rate of fading memory for previous configurations, the rate of fading determined by a relaxation time or, in practice, by an entire spectrum of relaxation times. 

Filled polymer systems display the ability to recoil by virtue of their viscoelastic nature. However, they do not return completely to their original state when stretched because of their fading memory. Viscoelasticity allows the material to remember where it came from, but the memory of its recent configurations is always much better than that... 

This behavior provides evidence of the fading memory property of the material. Therefore, the entire strain (and temperature) history must affect the constimtive behavior of filled rubber elastomers. While the strain-rate sensitivity and the failure time dependency are recognized and well-documented in the case of other materials such metals, the incorporation of history-dependent properties of elastomers requires further clarification. 

Fabrizio M, Giorgi C, Mono A (1995) Internal dissipation, relaxation property and free-energy in materials with fading memory. J Blast 40 107-122... 

According to Boltzmann, the stress in the material at any time t depends on its entire past strain history, although since Gr(t) is a decreasing function of time, the further back a Ay(t,) has occurred, the smaller will be its influence in the present. This leads to the anthropomorphic concept of viscoelastic materials having a fading memory (like an aging professor), with Grit) sometimes known as the memory function. (The concept, of course, is valid even in the absence of linear additivity—it is just much more difficult to quantify.) ... 

Equation (4.4) represents a viscoelastic material where all the time effects come from the history of the scalar invariants of strain and also from aging effects, which can be eliminated by removing the variable t. Depending on the form of the functionals 4 3, this particular constitutive equation can describe both permanent and fading memory viscoelasticity with strain coupling. When the history dependence is eliminated from the functionals then... 

Pipkin, A. C., and Rivlin, R. S., "Small Deformations Superposed on Large Deformations in Materials with Fading Memory," Arch, Rat. Mech. Anal., 8, 297-308 (1961). 

In Section 4.2.2 the central role of atomic diffusion in many aspects of materials science was underlined. This is equally true for polymers, but the nature of diffusion is quite different in these materials, because polymer chains get mutually entangled and one chain cannot cross another. An important aspect of viscoelastic behavior of polymer melts is memory such a material can be deformed by hundreds of per cent and still recover its original shape almost completely if the stress is removed after a short time (Ferry 1980). This underlies the use of shrink-fit cling-film in supermarkets. On the other hand, because of diffusion, if the original stress is maintained for a long time, the memory of the original shape fades. 

Dithiolene complexes, and more specifically the nickel derivatives, are involved in materials used for optical data storage, such as compact disc or laser disc read-only memory (CD- or LD-ROM), and also in copiers or photography related devices. In the latter case, it is the IR-absorbing property that is exploited. Some of these compounds can be found in reviews by Mueller-Westerhoff et al. (353, 354). Recent patents are given as examples in references (458—481). In the field of optical storage, short reviews were published in 1988 (482) and 1990 (362, 483). Here, the dithiolene complexes act as inhibitors of the laser-induced fading of the colored thin layers of the optical discs. They also act as an antioxidant and increase the photostability of the cyanine dyes that constitute the recording layer. Contrary to what was observed for the two... 

While GOLum project topics vary widely, one shared characteristic required of every project is that it must have a potentially sustainable impact beyond the team s presentation. Too often, outreach presentations become like fireworks exhibitions that are brilliant to behold but quickly fade into memory. To prevent this from happening, each team must develop ways to ensure that its project continues to be useful after its formal presentation. For example, GOLum presentations to high-school chemistry classes have provided host chemistry teachers with resource materials related to the presentations so that the teachers... 

Linear viscoelastic materials thus retain a memory of their entire mechanical history although, conveniently for the experimentalist, the memory fades with t — u, and for practical purposes the lower limit of integration in Eqs. (32) and (33) is often set to zero. Equations (32) and (33) may be used to calculate the response to an arbitrary deformation using E(t) or D(t) determined from simple static experiments (creep or relaxation). 

Viscoelasticity or Rheology The study of materials whose mechanical properties have characteristics of both solid and fluid materials. Viscoelasticity is a term often used by those whose primary interest is solid mechanics while rheology is a term often used by those whose primary interest is fluid mechanics. The term also implies that mechanical properties are a function of time due to the intrinsic nature of a material and that the material possesses a memory (fading) of past events. The latter separates such materials from those with time dependent properties due primarily to changing environments or corrosion. All polymers (fluid or solid) have time or temperature domains in which they are viscoelastic. 

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