Accelerated aging

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Accelerated aging is used to obtain information on the design, durability and qualification of materials or (preferably electrical) devices that are made up of aging materials. For this purpose, tests (function tests, property tests ...) are carried out on the respective (electrotechnical) device after it has reached the end of its service life or service life. With the help of the corresponding test results can then specify lifetimes or use lives of the respective device (see also highly accelerated life test , highly accelerated life cycle test or rapid aging test ). Since the service life is sometimes many years, you cannot wait that long and have to apply the effects of aging over the entire service life or accelerate them. Different equations are used for this, depending on the type of aging or the influence of aging.

Accelerated thermal aging

Accelerated thermal aging is usually calculated according to the very common, relatively simple but still mostly relatively realistic Arrhenius equation :

${\displaystyle t_{E}=t_{Q}\cdot e^{{\frac {E_{A}}{R}}\cdot \left({\frac {1}{T_{E}}}-{\frac {1}{T_{Q}}}\right)}}$

With:

${\displaystyle E_{A}}$= Activation energy (of the aging reaction); is (primarily) a material constant or a constant for the pairing of substances that react with one another

${\displaystyle R}$= Gas constant

${\displaystyle t_{E}}$ = qualified service life at absolute operating temperature ${\displaystyle T_{E}}$

${\displaystyle t_{Q}}$ = Test or qualification duration at absolute test or qualification temperature ${\displaystyle T_{Q}}$

If the accelerated thermal aging is to be calculated for an (electrotechnical) device that contains several different polymers, the thermally conductive material must be determined beforehand. This thermally ages the fastest (in the specified temperature window to ) and thus dominates the aging behavior of the entire device. In the case of the cyclic aging of lithium-ion batteries , accelerated aging with a reduction in temperature is also typical below a limit temperature. This leads to an "apparently negative value" and is typical of a change in the aging mechanism . ${\displaystyle T_{E}}$ ${\displaystyle T_{Q}}$ ${\displaystyle E_{a}}$

Accelerated radiological aging

The accelerated radiological aging (usually with gamma radiation ) is - if one wants to take into account the so-called dose rate effect - usually calculated according to the Wilski equation :

${\displaystyle t_{E}=t_{Q}\cdot \left({\frac {DL_{E}}{DL_{Q}}}\right)^{psi-1}}$

With:

${\displaystyle psi}$= Dose rate effect exponent (of the aging reaction); is (primarily) a material constant or a constant for the pairing of substances that react with one another

${\displaystyle t_{E}}$ = qualified service life at the dose rate used ${\displaystyle DL_{E}}$

${\displaystyle t_{Q}}$ = Test or qualification duration for test or qualification dose rate ${\displaystyle DL_{Q}}$

If the accelerated radiological aging is to be calculated for an (electrotechnical) device that contains several different polymers, the radiologically leading material must be determined beforehand. This ages radiologically the fastest (in the specified dose rate window to ) and thus dominates the aging behavior of the entire device. ${\displaystyle DL_{E}}$ ${\displaystyle DL_{Q}}$

Individual evidence

1. ↑ Thomas Waldmann, Marcel Wilka, Michael Kasper, Meike Fleischhammer, Margret Wohlfahrt-Mehrens: Temperature dependent aging mechanisms in Lithium-ion batteries - A Post-Mortem study. In: Journal of Power Sources . 262, 2014, pp. 129–135, doi : 10.1016 / j.jpowsour.2014.03.112 .