Why Things Fail: From Tires to Helicopter Blades, Everything Breaks Eventually | Wired Design
►http://www.wired.com/design/2012/10/ff-why-products-fail/all
The Failure Curve
Product failure happens in what’s called a Weibull distribution and often looks roughly like a bell curve. Ensuring reliability requires knowing where this curve begins and where it peaks. The chart below shows the logarithmic failure curve of steel bars placed in a fatigue machine. Most fail after 1 million cycles, but if you were to test only a few bars, those failures might occur after 10 million cycles. This might cause you to think the steel is much stronger than it actually is.