in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time.
This is particularly useful in several cases: For instance, a reliability test on circuits that must last years at use conditions (high longevity) would need to yield results in a much shorter time.
If the test wanted to estimate how frequently the circuits needed to be replaced, then the category of low failure would also be applicable.
Furthermore, if the circuits wore out from gradual use rather than extreme use (such as a large sudden shock), the wear out category would be involved.
A model is an equation that accurately relates a test object's performance to the levels of stress on it.
This is usually referred to as a life distribution, the probability density function of which represents the proportion of products failing at a given time.
Tests at various stress levels would yield different values for the mean and standard deviation of the distribution.
These are widely modeled under the assumption that survival life of a product depends only on the current level of stress and how many test subjects have failed so far.