Design for Reliability and Safety Flashcards
What is single point failure
a single failure that leads to catastrophic failure
What is common mode failure
single effect that causes several sub-systems to fail
What is cascade failure
one failure that leads to another
What is a fault intolerant system
single failure causes system to fail (chain)
What is a fail safe
fail in a non-catastrophic way
What is a safe life
period of safe operation
Failure rate (lambda)
number of fails per time period
Mean time between failures (MTBF)
1/lambda
What 3 trends to failure distributions follow
exponential, normal, Weibull
Equation for component reliability
R(t) = exp(-lambda*t)
What are non-redundant components
a product which consists of a number of components that must all work for the product to function
What is ‘One-in-two’ element redundancy
Fault tolerant system as system can still function if one of two components fail (computers on an aircraft)
What effect does maximising m and n for a given m/n ratio have
The more components there are the less chance it will fail (3/6 is better than 1/2)
Name 3 ways a fail safe can fail a system safely
Overheating causing a fuse to trip
Ductile failure saving loss of structural support
Twin circuits in tandem
What does FMECA stand for
Failure mode effects and criticality analysis
What is the RPN and how is it calculated
Risk priority number - Multiplying Occurence, Severity and Detectability together (all out of 10)
What is fault tree analysis (FTA)
It models how a failure or disaster can occur based on a series of events using AND or OR boxes
What does a failure mode efffects analysis (FMEA) graph look like?
headings are:
Function; Failure mode; Effects; Causes; current controls; Occurence (O); Severity (S); Detectability (D); RPN (OSD)
