It is defined as the probability that a given system will perform it’s function adequately for it’s specified period of lifetime under specified operating conditions.
Common measures are :
1. Failure rate.
2. Mean time between failures(MTBF)
3. Survival percentage.
Rate which components of population fail.
Ns(t)- No. of components that survived during time ’t’
Nf(t) – No. of failures that occurred during the same time.
Mean time between Failures(MTBF):
The reciprocal of the failure rate(1/λ).
λ —-Failure rate.
Failure rate = (No.of failure )/(Time period during all components were exposed to failure)
Failure Mode and Effect Analysis(FMEA)
1. To recommend design changes.
2. To identify design weakness.
3. To help in choosing alternatives.
Ist Stage – System boundaries and the scope of the analysis is decided.
IInd Stage – Data Collection
Ex: Specification,Operating Procedure,Working Conditions.
IIIrd Stage- Preparing the component or parts list.
IVth Stage – Failure frequency and the functions of the part identified,causes of failures,Failure detection.