Design_for_Reliability,_Serviceability

Design_for_Reliability,_Serviceability - Design for...

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Unformatted text preview: Design for Reliability, Serviceability, Quality RAMS: Reliability, availability, maintainability, and safetyintegrity. Reliability Engineering "Reliability is a measure of a the capability of a part or a system to operate without failure in the service environment." (Dieter.) Reliability engineering is based on the idea that for every component, there is a statistical probability of failure that must be controlled to an extent that depends on the consequence of failure. Deterministic vs. Probabilistic - loads are known - dimensions are as specified - material properties re known and constant - external loads are stochastic - dimensions vary within tolerances - material properties vary, both initially and overtime 1 Justification for Reliability Engineering - optimum burning time or breaking in period - optimum warranty period and estimated costs warranty - optimum preventive replacement - spare parts - reduction - trade off study - reduction warranty costs - increase profit or same profit more safety early life useful life warranty life BURN-IN SHIP burn in period 2 optimum total cost preshipment cost postshipment cost Simple example of mathematics of reliability engineering Bolts have a distribution of strengths Simple Approach Reliability Engineering Tolerance for risk is different for bolts used in swingsets or airplane propellors. Numerical approach to reliability 3 Design for Maximizing Reliability: Principles Overdesign: Derating: Simplicity: Redundancy: Durability: Damage Tolerance: Failsafe: Inspectability/Maintainability: Specificity: safety factor safety factor for non structured eg - motor few moving parts parallel systems or components choose durable materials resistant to corrosion, wear, fatigue allow for partial damage without failure failure is not catastrophic regular maintenance be specific in design - materials tolerance etc. Based on Dieter, pg. 547 Quality Engineering Quality engineering ensures that designs are implemented as intended: parts meet specs. etc. Quality Control (QC) is the monitoring of process to produce a predictable and consistent output. Variability in the manufacturing and performance of a product is the enemy of quality. Modern concepts of quality control are based on statistical methods. Design for Inspectability Maintainability - design systems with inspection and dealing with mainanance in mind prolong lifetime minimize chance of in-service failure 4 Design for Inspectability Maintainability: Principles - components that are suspectable to wear, fatigue etc - regular inspection - should be easy to inspect and replace - design sacrificial parts that are easy to replace - specify regular maintenance so in-service failure Ex. Water Pumps for the third world Throughout Africa, access to potable water is a significant problem Standard Piston Pumps can be made inexpensively from PVC tubing. When they break, however, very difficult to maintain. The Challenge: Design a pump that can be maintained using only local materials available in rural Africa. Note that it is not necessary that the pump be built using only local materials. 5 ...
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