Question

Production lots and vendor sources for parts that comprise a design are subject to change. Variability in parts characteristics is likely to occur during the field lifecycle of a product. How does this affect design decisions that impact reliability?

Answer 1

Variability in parts characteristics in real life is one of the factors that need to be taken into account while design a reliable product. It is very important for reliability engineers to assess and design for uncertainty of performance in areas like spacecrafts, aircrafts, etc. where a minor glitch in the design of parts could have irreparable consequences.

There should always be a consideration for safety factor in the design of critical system parts, which takes into account the different stress scenarios the parts may be go through in live conditions. This distribution of variability in stress is sometimes modeled in terms of a mean and std deviation .

The failures of the components might also manifest early as design defects, during stability phase because of unusual stress scenarios, or when the part has aged due to wear and tear, which accelerates the failure rate. These phases have different failure rates and need to be addressed at the time of design of the parts by modeling the 3 phases of the failure curve accordingly. These are important to ensure the overall system has a high reliability during field lifecycle.