Quanterion publishes an electronic version of “Reliability Ques” periodically as a means of keeping its customers and other interested parties up-to-date on effective tools, techniques, and approaches to improving the reliability, maintainability, and quality of products and systems.
Calculating an Average Infant Mortality Factor Over a Given Service Life Using the 217Plus™ Methodology
Infant mortality is a term that is often used to describe early-life failures – that is, failures that occur due to premature excitation of failure mechanisms. Such failures are typically due to inferior material (e.g., parts used in the manufacturing process that are out of tolerance), poor workmanship due to inadequate skills being used in… Read More
In simplest terms, an item fails when a stress to which it is subjected exceeds the corresponding strength. In this sense, strength can be viewed as “resistance to failure”. Good design practice is such that the strength is always greater than the expected stress. The safety factor “η” can be defined in terms of strength… Read More
The practice of limiting electrical, thermal and mechanical stresses on parts to levels below their specified ratings is called derating. MIL-STD-721C offers the following definitions of derating:
Using an item in such a way that applied stresses are below rated values
The lowering of the rating of an item in one stress field to allow an increase… Read More
Reliability growth is the intentional positive improvement that is made in the reliability of a product or system as defects are detected, analyzed for root cause, and removed. The process of defect removal can be ad hoc, as they are discovered during design and development, a function of an informal test-analyze-and-fix process (TAAF), or it… Read More
Product reliability is an important discriminator in today’s global marketplace but does your organization know how it’s doing compared to competitors in terms of designing and building reliability into its products? Could/should you be doing more “upfront” reliability activities to improve customer satisfaction, to reduce warranty costs, and to reduce in-plant rework costs? Do you… Read More
The general form of this type of reliability block diagram has two series circuits in a parallel arrangement combined through a center or “keystone” unit. You are often given the reliability of each block and asked to calculate the reliability of the circuit.
For example let’s say we are given the following five block arrangement pictured… Read More