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C H A P T E R 8
Reliability to Trust
8.1 RELIABILITY
Reliability is one of the most important components of quality, i.e., value. Until very recently,
reliability was evaluated by statistics. But, it was a completely data-driven statistics. Figure 8.1
shows a bathtub curve, which constitutes the basics of reliability engineering. e bathtub curve
shows the change of failure rate over time. e failure rate is defined by:
Failure rate D e number of failed products/e number of remaining products.
ese numbers are counted over the fixed time interval.
Decreasing
Failure
Rate
Increasing
Failure
Rate
Constant
Failure
Rate
Observed Failure
Rate
Constant (Random)
Fai
lures
We
ar Out
Fai
lures
Ea
rly
“
Infant Mortality”
Failure
Failure Rate
Time
Figure 8.1: Bathtub curve.
When products were produced in mass, this approach worked very well and customers
did not care too much about their own product. If their products failed, then they asked for a
new one and they were happy.
8.2 TRUST
However, situations are quickly changing these days. Diversification and personalization
progress rapidly, so products are becoming diversified and personalized. It therefore becomes
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