Five of the most important functions in reliability and life testing are the following: (1) The failure probability density function. (2) The reliability function. (3) The conditional reliability function. (4) The failure rate function. (5) The mean life function. Given these five functions, most reliability and life testing problems may be solved.
The failure probability density function enables the determination of the number of failures occurring over a period of time referred to the original, total population. The reliability function enables the determination of the probability of success of any unit in undertaking a mission of a prescribed duration or operating for the desired function period. The conditional reliability function enables the determination of the probability of success of any unit in undertaking a new mission given the unit already survived the previous mission. The failure rate function enables the determination of the number of failures occurring per unit time referred to the size of the population existing at the beginning of the period for which the failure rate is to be calculated. The mean life provides the average time of operation to a failure.
The work of a reliability and life test engineer starts with observations of times to failure, cycles to failure, revolutions to failure, actuations to failure, miles to failure, number of failed operations, and the like, for parts, components, equipment, products, or systems (all of which will be referred to as unit in this book),...
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