Feb 03

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.

01-reliability-analysis-life time analysis-life time warranty

Common measures are :

1. Failure rate.

2. Mean time between failures(MTBF)

3. Survival percentage.

Failure Rate:

01-the bathtub curve-failure rate vs time - Reliability test-failure analysis-calculate life time of a product

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.

01-web- failure analysis-unexpected failure-operational fracture-failure rate

01-preheater-tube-failure-failure rate-circumferential cracking-probability of failure

Mean time between Failures(MTBF):

01-mtbf-mean time between failures-measurement of reliability-repairable items

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)

Reliability Analysis:

Failure Mode and Effect Analysis(FMEA)

01-FMEA-failure mode and effect analysis-effective analysis-risk priority number-severity number-probability number-reliability analysis

Purpose :

1. To recommend design changes.

2. To identify design weakness.

3. To help in choosing alternatives.

01-space-shuttle-failure mode-effects-criticality analysis-fmea-reliability test

Four Stages:

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.

01-Bathtub-life span of product-annual failure-mtbf prediction-mathematical model of reliability-improving quality

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