System Engineering Exam 3 Flashcards
Reliability
the probaility of a system to perform the intended functions under given condition for a given period of time
Failure
the termination of ability of an item to perform a required function
3 reasons why engineering items fail
- the item may be overstreesed in some way
- the design might be essentially incapable, the more complex the design is. the more difficult to overcome the problem.
- failures can be caused by errors such as incorrect specification, design, fault assembly or test.
3 function of reliability engineering
- ensure that designs meets product reliability requirements
- identify design discrepancies and resolve
- predict system reliability and availability
Why reliability is needed
- safety
- customer requirements
- competition
difference between reliability and quality
- reliability looks at the behavior of failure rate over a long period of time while quality control looks at the percent of defective at certain point of time
- they both use different statistical tool to evalute
- reliability deals with all periods of existence of a product, with prime emphasis on design , while quality control deals on the manufacturing stage
bathtub curve
this curve describe a particular form of failure rate function. three different types are: early failure, random failure and wear out failure
Different types of probability distribution and their uses
exponential: use for electronic parts with constant failure rates
Weibull: versality to any application
Lognormal: products for wear out
normal: consumerable items where failure rates are always increasing, like electric filament devices.
What is Beta, Eta, Gamma in Weibull distribution
beta: shape
Eta: scale
Gamma: location
Fault Tree Analysis (FTA)
FTA is a way to visually show how different problems or failures can lead to a bigger, unwanted event (called the top event).
Maintainability
Maintainability means how easy it is to keep something working properly or fix it when it breaks.
It depends on:
Doing maintenance at the right times,
Having skilled people,
Using the right tools and instructions.
Better maintainability means repairs can be done faster and more easily.
what does maintenance include
All actions necessary to fix a servicible condition. it includes servicing, repair, modification, overhaul, inspection, condition determination, corrosion control
Define Uptime and Downtime
Define MTTR, MTTF,
MTTR: is a measure of maintainability. it measures the average time to repair a failed component.
MTTF: it represents the length of time that an item is expected to last in operation until it fails.
