Systems Thinking
Reliability & Failure Modes
13 minStudent plan
Working out what will break before it does, and designing so that when it does, it breaks safely.
After this lesson you can
- Recognise the three phases of the bathtub curve
- Run a simple FMEA on your own design
- Design something that fails safely
Failure has a shape
Plot failure rate against age for a population of parts and you get a bathtub. Early failures come from manufacturing defects and fall away quickly. Then a long flat period of low random failure. Then wear-out, rising steeply at the end of life.
Burn-in exists to push products past the first region before shipping. Scheduled replacement exists to retire them before the third.
Mean time between failures describes only the flat middle, and it is routinely misread. An MTBF of 100,000 hours does not mean a unit lasts eleven years; it means that during the flat period, a large population fails at that average rate. Wear-out is a separate mechanism the figure says nothing about.
In the full lesson
- Failure has a shape
- FMEA
- Failing safely
This lesson comes with the Student plan. The first module of Engineering Foundations is free.