Accelerated-aging tests

The accelerated aging test should take into account the associated materials as well as the atmosphere that will be encountered in actual use, since they are also controlling factors. It is helpful to include materials of known performance against which to rate the new material, since this allows a check of controlling factors and further validates the extrapolation. Thus, existing data from long term tests may be of considerable value. 

Report 84 Rheology and its Role in Plastics Processing, P. Prentice, The Nottingham Trent University. Report 110 Long-Term and Accelerated Ageing Tests on Rubbers, R.P. Brown, M.J. Forrest and G. Soulagnet, Rapra Technology Ltd. 

The most common test used to study the oxidation resistance of mbber compounds involves the accelerated aging of tensile dumbbell samples in an oxygen-containing atmosphere. Brown et al. [22] recently reviewed long-term and accelerated aging test procedures. The ASTM practices (D 454 (09.01) D 865 (09.01) D 2000 (09.01, 09.02) D3137 (09.01) D 572 (09.01) D 3676 (09.02) D 380 (09.02)) for these tests clearly state that they are accelerated tests and should be used for relative comparisons of various compounds and that the tests may not correlate to actual long-term... 

Thomas, R. E. Gaines, B. G. "Methodology for Designing Accelerated Aging Tests for Predicting Life of Photovoltaic Arrays" Department of Energy/National Bureau of Standards Workshop on Stability of Thin Film Solar Cells and Materials, Washington, D.C., May 1-3, 1978. 

These findings clearly illustrate how the results of so-called "accelerated-aging" tests can be affected by the high temperatures in ordinary xenon- and carbon-arc equipment and can, therefore, lead to erroneous conclusions regarding the photochemical behavior of materials at near-normal temperatures (23). 

M. Regert, S. Colinart, L. Degrand, O. Decavallas, Chemical alteration and use of beeswax through time accelerated ageing tests and analysis of archaeological samples from various environmental contexts, Archaeometry, 43, 549 569 (2001). 

Figure 7.2 Summary of the main chemical transformations undergone by beeswax during accelerated ageing tests. Reprinted from Archaeometry, 2001, 43, 549 569, Regert, Col inart, Degrand and Decavallas, with permission from Wiley Blackwell...

An electrically heated oven supplied with circulating kit, originally used in accelerated ageing tests. 

The life time of a catalyst is an important criterion for its commercial application. The reforming reactions in most of the cases have been studied only for hours of time on-stream, but not for days or weeks. Superior catalysts need to be evaluated by operating continuously for thousands of hours. Simple accelerated aging test that allows assessment of catalyst life in hours or days rather than the usual priod of months will be helpful. 

ISO 2440 1997 Flexible and rigid cellular polymeric materials - Accelerated ageing tests ISO 6914 2004 Rubber, vulcanized - Determination of ageing characteristics by measurement of stress at a given elongation... 

In an automobile s catalytic converter, CO and hydrocarbons present in the exhaust gases are oxidized. Unfortunately the effectiveness of these units decreases with use. The phenomenon was studied by Summers and Hegedus in /. Catalysis, 51, 185 (1978) by means of an accelerated aging test on a palladium impregnated porous pellet packed bed converter. From the reported data on hydrocarbon conversion shown below, develop an expression to represent the deactivation rate of this catalyst. 

A prediction of useful life for solid propellant rockets is quite important, from the standpoint of operational readiness and economic considerations. The premature removal and replacement of deployed systems, based on inaccurate storage life estimates, can be costly. A specific missile system and propellant combination could become obsolete while long term storage data are being compiled. Accelerated aging tests are normally used to give qualitative indications of storability, but the deficiencies of these tests are obvious and are discussed later. 

Aging becomes a difficult problem to study in practice, because it proceeds too slow in use conditions (typical lifetime of years). It is then necessary to make accelerated aging tests to build kinetic models that describe the time changes of the material s behaviour, and to use these models to predict the durability from a conventional lifetime criterion. Indeed, the pertinence of the choice of accelerated aging conditions, the mathematical form of kinetic model, and lifetime criterion has to be proved. Empirical models are highly questionable in this domain because they have to be used in extrapolations for which they are not appropriate. 

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