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Accelerated tests for environmental simulation - Benefits and risks
Beschleunigte Alterungstests bei der Umweltsimulation - Vorteile und Risiken
One of the most important goals of environmental qualification is the prediction of a product's long-time behavior or service life using tests of short duration. Different strategies are available for conducting accelerated aging investigations, depending on whether the primary aging process is dependent on periodic or continuous loads. Using cause and effect relationships, it is possible to substitute higher intensity loads in order to bring about the same effects which would occur over long time periods under milder loading conditions. Cause and effect relationships are only linear for simple cases; more often than not the relationships are nonlinear e.g. exponential or discontinuous with threshold points at which the behavior changes. While it is often done in practice, it is actually futile to attempt to conduct accelerated aging by increasing the intensity of the loads, if the relationship between the load intensity and the resulting processes is unknown. Especiallydifficult are those cases which are nonlinear, because often in these cases exceeding the threshold loading values can dramatically alter the behavior of the test material. There are general rules which limit the use of accelerated aging for those cases where the loading conditions change with time. A further possibility for reducing test time is to refine the methods for determining the effects of the applied loads on the test piece. The principle of test-tailoring allows one to establish whether tests should be conducted simultaneously or sequentially. The life cycle of the test piece will generally determine the order and priority of the various tests. If doubt remains as to the proper sequence, then the expected failure mechanisms can be considered in order to determine the appropriate test procedure.