Accelerated aging protocols

Although cyclic environmental chamber test procedures may suffice for failure processes Involving, for example, mechanical stress, kinetic controlled processes dependent upon time and temperature such as oxidation and diffusion do not lend themselves to adequate Identification and analysis based solely on number of cycles. Thus Sandia National Laboratories developed an accelerated aging protocol for environmental testing which (1) identifies material incompatibilities and subsequent failure modes in Phase I and (2) proceeds with kinetic analysis of the Arrhenius type of failure mode processes which allow extrapolation necessary for lifetime prediction of components in Phase II. Thus two phases are necessary in a complete analysis to accurately predict system lifetimes. The accelerated aging protocol requires the Identification of the stresses that are most likely to damage the performance of the component under test. However, data is frequently not available on the performance of a system under a particular stress. When this is the case, it becomes necessary to make predictions of those stresses most likely to cause degradation and then test to see if the stresses selected are dominant. 

The net result of publishing expiration dates is that there must be some documented evidence that supports the product expiration claims, thus the need to perform shelf life studies. However, real-time shelf life studies are not an alternative in a fast-changing industry that can see two to three generations of products developed over the time it would take to document a 2-year shelf life claim. So, the need for accelerated aging protocols as an alternative in developing a product and introducing... 

Notice that these principles do not explicitly define the test parameters. However, the guidance documents developed by CDHR do provide accelerated aging protocols for specific devices within their jurisdiction based on the Q,q theory for chemical reactions. So, the theory postulated by Von t Hof using the Qio value (which states that a rise in temperature of 10°C will double the rate of chemical reaction) is the most convenient method of estimating the approximate ambient storage time equivalent at a selected accelerated aging temperature, despite flie Imown limitations and concerns for use on complex and dissimilar material structures. 

Figure 8.11 Scheme of the accelerated aging protocol (a) and magnification of the fifth galvanostatic cycle (b). The fifth discharge cycle of each series is considered to estimate the capacitance and ESR values. 

Reich concludes, however, that the concept can be useful (as a rationale) for the accelerated aging of packages. Hemmerich concurs that this type of conservative relationship is appropriate for a wide range of medical polymers that have been previously characterized. Nevertheless, the simplified protocol for accelerated shelf-life testing is not a replacement for more complex and advanced accelerated aging (techniques). ... 

Hemmerich, K., General Aging Theory and Simplified Protocol for Accelerated Aging of Medical Devices, Medical Plastics and Biomaterials, July/August 1998, pp. 16-23. 

Hemmerich, K. J. (1998) Accelerated aging. General aging theory and simplified protocol for accelerated aging of medical devices. Medical Plastics and Biomaterials, 16-23. 

Numerous protocols have been proposed for accelerated aging of UHMWPE [95]. Yet, the current standard protocols [ASTM F2003 -02(2008)] for accelerated aging of UHMWPE in air are based on two distinct techniques Method A aging in a air furnace at 80°C at 1 atm during 23 days [96] Method B 60° and 70°C under a pressure of 5 atm of pure oxygen during 14 days [97]. 

Opacifiers, disinfectants and artificial aging were found as the factors affecting dimensional stability and detail reproduction of PDMS material [53, 68]. Accelerated aging was the most affective test protocol on the dimensional changes in PDMS elastomer [68]. 

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