Aging rejuvenation effects

Keywords Aging dynamics Glass transition Heterogeneous dynamics Interfacial interaction Memory and rejuvenation effects Stacked thin polymer films... 

Fukao K, Sakamoto A (2005) Aging phenomena in poty(methyl methacrylate) thin films memory and rejuvenation effects. Phys Rev E 71 041803... 

In the GRP model type 1, the corrective maintenance has a rejuvenating effect proportional to the time elapsed since the previous maintenance. The virtual age (Ar) of the equipment immediately after the r th mamtenance action (at time tr) is given by the formula 6. 

The Effect of Large Stresses on Physical Aging Rejuvenation... 

Although camosine s ability to suppress both formation and reactivity of some of the age-associated macromolecular modifications (e.g., protein-protein cross-links and protein AGEs) could contribute to its apparent antisenescent effects, these prophylactic actions cannot by themselves explain the dipeptide s apparent rejuvenating activity towards cultured human fibroblasts observed by McFarland and Holliday (1994,... 

Regarding the effect of physical ageing, the associated densification hinders the intramolecular ft-a cooperativity (as discussed in [1], Sect. 8.1.3). This makes the conformational changes more difficult and, so, require a larger stress. The resulting increase of ay corresponds to the situation encountered at a temperature shifted downward by 20 °C. The physical ageing densification does not influence the plastic flow stress. The reason is that the plastic flow happens in a material that has been strained, and it is known that strain induces a disappearance of the physical ageing effects, this is called rejuvenation . 

The aging rate, Aay/At, is reduced if the crosslink density increases (Cook et al., 1999). This effect could be erased by rejuvenating the sample by heating above Tg or applying large deformations above ey (Oyanguren et al., 1994). 

Struik showed furthermore that for amorphous and semi-crystalline polymers the ageing effect after complicated thermal histories is strikingly similar. In both cases high stresses can erase previous ageing and "rejuvenate" the material. 

The effect of imperfect maintenance interventions is often modeled by resorting to the concept of effective age it is assumed that the expression of the failure rale as a function of time is not altered by a maintenance action, but that the latter leads to a rejuvenation of the equipment embodied by an effective (or virtual) age, usually smaller than the calendar time elapsed since it was first operated. The issue is then to write the relation between the effective age after maintenance and its value before the intervention. 

Effective age models implicitly assume that maintenance actions do not affect the failuie rate expression proper, but lead to a shift in time. There exists thus for the component under study an intrinsic failure density, which corresponds to a situation in which no maintenance action is ever performed on the component. When the effect of maintenance is accounted for, the calendar age is replaced, as mentioned before, by the effective age, i.e. an equivalent operating time of the component time giving allowance to the level of rejuvenation obtained via maintenance. The actual failuie density of the component is hence modified according to the changes in the effective age value. 

This situation can be modeled in different fashions. A first option consists in defining a maximum calendar time tum, after which the inescapabUity of aging is observable in the following ways even if the effective age of the component still Ues below the elasticity limit, the rejuvenation obtained by a maintenance action does no longer allow to reach the target state above the elasticity setpoint, the maintenance efficiency is further reduced. 

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