Reliability

Reliability : 

1 Reliability

Reliability : 

2 Reliability Generally defined as the ability of a product to perform as expected over time Formally defined as the probability that a product, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions

Maintainability : 

Maintainability The probability that a system or product can be retained in, or one that has failed can be restored to, operating condition in a specified amount of time.

Types of Failures : 

Types of Failures Functional failure – failure that occurs at the start of product life due to manufacturing or material detects Reliability failure – failure after some period of use

Types of Reliability : 

Types of Reliability Inherent reliability – predicted by product design Achieved reliability – observed during use

Reliability Measurement : 

Reliability Measurement Failure rate (l) – number of failures per unit time Alternative measures Mean time to failure Mean time between failures

Cumulative Failure Rate Curve : 

Cumulative Failure Rate Curve

Failure Rate Curve : 

Failure Rate Curve “Infant mortality period”

Average Failure Rate : 

Average Failure Rate

Reliability Function : 

Reliability Function Probability density function of failures f(t) = le-lt for t > 0 Probability of failure from (0, T) F(t) = 1 – e-lT Reliability function R(T) = 1 – F(T) = e-lT

Series Systems : 

11 Series Systems RS = R1 R2 ... Rn

Parallel Systems : 

12 Parallel Systems RS = 1 - (1 - R1) (1 - R2)... (1 - Rn)

Series-Parallel Systems : 

Series-Parallel Systems Convert to equivalent series system A B C C D RA RB RC RD RC A B C’ D RA RB RD RC’ = 1 – (1-RC)(1-RC)

Reliability Engineering : 

14 Reliability Engineering Standardization Redundancy Physics of failure Reliability testing Burn-in Failure mode and effects analysis Fault tree analysis

Reliability Management : 

Reliability Management Define customer performance requirements Determine important economic factors and relationship with reliability requirements Define the environment and conditions of product use Select components, designs, and vendors that meet reliability and cost criteria Determine reliability requirements for machines and equipment Analyze field reliability for improvement

Configuration Management : 

Configuration Management Establish approved baseline configurations (designs) Maintain control over all changes in the baseline programs (change control) Provide traceability of baselines and changes (configuration accounting)

Maintainability : 

19 Maintainability Maintainability is the totality of design factors that allows maintenance to be accomplished easily Preventive maintenance reduces the risk of failure Corrective maintenance is the response to failures

Design Issues : 

Design Issues Access of parts for repair Modular construction and standardization Diagnostic repair procedures and expert systems

Availability : 

Availability Operational availability Inherent availability MTBM = mean time between maintenance MTD = mean down time MTBF = mean time between failures MTTR = mean time to repair