Design-for-reliability combines the application of the advancing body of knowledge for mission reliability with the current body of knowledge for material and part design analysis. Reliability analysis at the material or part design level provides methods that must be employed by engineers performing design analysis, design art and part selection (bill of materials) in a specific discipline [mechanical, structural, aerospace, electrical or chemical. Key concepts are: Interference theory to characterize reliability math models, design of experiments, reliability failure analysis and reliability math modeling and simulation.
Reliability-centered maintenance, RCM, includes the application of the advancing body of knowledge for mission reliability, maintainability and availability to achieve life-cycle sustainability by making the transition from restoring system functionality through unscheduled repair maintenance (corrective maintenance) to preserving system functionality through scheduled maintenance (preventive maintenance). The implementation of RCM is achieved by following one of three paths: condition-based maintenance, CBM, time-directed maintenance, TDM, and stress-directed maintenance, SDM. Determination of the appropriate path is achieved by reliability failure analysis. Key concepts include: understanding the economic and safety benefits of RCM, the three paths of RCM and the method to determine the applicable path, and understanding the how the organization’s risk of failure enables determination of an cost optimum policy for part replacement.
Reliability Engineering and Analysis
Reliability engineering and analysis includes the application of the advancing body of knowledge for mission reliability, maintainability and availability to achieve design requirements and life-cycle sustainability. Reliability analysis at the material or part design level provides methods that must be employed by engineers performing design analysis, design art and part selection (bill of materials) in a specific discipline [mechanical, structural, aerospace, electrical or chemical]. Reliability at the system design level provides methods to allocate requirements down to the assembly design configuration and subsequently achieve integration of design and reliability parameters into an assembly design configuration continuing up the system.
Probabilistic Risk Assessment (PRA)
PRA is similar to a FMECA, but it differs in that it takes a top down approach to modeling system downing events and a not a bottom up (part level). PRA identifies critical parts (CIL) that cause system downing events, to include the consequence analysis. PRA provides insight on the strengths and weaknesses of the design and operation of the system. RFAL is involved in several projects that a PRA is required.
FMECA (Failure Modes Effects and Criticality Analysis)
FMECA is a part level (Bottom Up) approach to model failures. It determines the failure mechanisms, modes, and effects. FMECA includes the criticality analysis. This is used to show the significance of the failure modes occurring. A FMECA is essential in implementing both design for reliability and implementing a RCM (Reliability Centered Maintenance) solution. RFAL is involved in several projects that are centered on a FMECA.
Reliability Centered Maintenance (RCM)
“A Process used to determine the maintenance requirements of any physical asset in its operating context” 1
There are two different classifications of maintenance: Proactive Maintenance and Reactive Maintenance. Reactive maintenance only restores system functionality, leads to unscheduled downtime, and can be very expensive. RCM is a proactive maintenance seeks to preserve system functionality and prevent any unscheduled downtime by understanding the consumed useful life.
Categories of Failure:
Catastrophic Failure: Death/injury to people or destruction of the system
Operational Failure: Immediate mission abort and maintenance is required
Degraded Mode: Ability to complete mission, then maintenance action is required
Run-to-Failure: The cost of a RCM solution is greater than the cost of a failure
RFAL developed an RCM guideline to illustrate the process that is used to determine the maintenance solution that should be implemented. RFAL is also working on several projects implementing maintenance solutions for systems.
Condition Based Maintenance (CBM)
CBM makes use of condition indicators to monitor the consumed useful life of the part to allow for the allocation of resources to prevent unscheduled downtime while trying to minimize costs.
Time-Directed Maintenance (TDM)
TDM applies the failure risk threshold to determine scheduled maintenance intervals based upon the hazard function. This maintenance solution should only be used for parts/systems that have one failure mode and whose stress loads are predictable.
Stress Directed Maintenance (SDM)
SDM research is being performed at the Reliability and Failure Analysis Lab to model the stress loads upon the part to fit the hazard function. Maintenance actions are based upon the stress loads on the part. The scheduled maintenance interval is reached when the stress profile approaches the risk based allowable stress limit.
 John Moubray, Reliability-centered Maintenance