Once parts or components of mechanical products in one of the following three states, it can be defined as the failure: they are completely unable to work; because of serious injury and unable to use reliably and safely, they need to repairing or replacing; they can still work, but they cannot achieve the desired function with satisfying.

When the failure occurs, we need to analyze the failure. The main purpose and effect of failure analysis are:

(1) Accumulating experience, learning from experience

(2) Ensuring the root causes of failure

(3) Preventing failure accidents from happening again

(4) Promoting maintenance and replacement of facilitate equipment

(5) Reducing the cost of production and usage

(6) Evaluating responsibility of failure accidents