TABLE OF CONTENTS The expected number of spare parts needed for a particular product, for a prescribed period of time can be determined from the expected number of failures [1, Vol. 1, p. 193], or from
where
| N F( T 2 ? T 1) | = | estimate of the expected number of failures for a life period ( T 2 ? T 1), per part, |
| ?( T) | = | failure rate function for a life period ( T 2 ? T 1) for that part, |
and
| ( T 2 ? T 1) = | part life period for which the spare parts provisioning is to be determined. |
Equation (14.1) applies to any type of reliability bathtub curve (RBTC), with or without preventive and/or corrective maintenance, provided the RBTC is representative of the situation for which the number of spare parts is determined, the appropriate ?( T) is used, and the total number of identical parts in use remains essentially constant. Then, the total number of expected spare parts is given by
where
| N FT( T 2 ? T 1) = | total number of expected spare parts in life period ( T 2 ? T 1), |
and
| N T = | total number of identical parts in use during life period ( T 2 ? T 1). |
If N T varies with T, then
where
| N T( T) = | functional relationship for... |
