Previously, I discussed failure mechanisms and root causes and classified failure into three types based on when failures occur: early life, random, and wear-out.  Here I will focus on the first two: early life and random failures.

EARLY LIFE FAILURES

Early life failures are generally due to latent defects within a product or damage that occurs to a product. A few examples include faulty components, faulty assembly, transportation damage, or installation damage. The rate of early life  failures tends to decrease over time. This may be because only a subset of products has the faulty batch of components, for example.

The ability to create a product often relies on the supply chain being able to provide consistent materials and components. If the material property that is important to the functioning of a product varies unacceptably, the product is more likely to fail. If the manufacturing process varies unacceptably and produces inferior product, those too are more likely to fail. For manufacturers, understanding the elements most at risk to moisture, electrostatic discharge, or corrosion and related causes of premature product failure will assist them in creating reliable products without latent defects.

The wrong material or poor assembly of a product tends to lead to early life failures. When the supply chain and manufacturing processes are working properly the unwanted variations will be identified and eliminated before a product goes to market. Those defects that make it to market may have no effect on product life or may shorten product life. Predicting the impact will require an understanding of the nature of the variation and how that will interact with use conditions.

Because the nature of the failure mechanism may be unknown, failure may be difficult to predict and further study may be required when the consequence of failure is high and the possibility of unwanted variation is high. One technique is to create products with a range of material or manufacturing variation and then evaluate the impact on product life. This may lead to an improved product or understanding of the need to carefully control the incoming material and assembly processes. Normally, we do not attempt to predict how long products with unknown supply chain or manufacturing errors may last. The proper focus most of the time is on supply chain and manufacturing consistency and control.

RANDOM FAILURES

Generally, random failures are events that afflict a product or component from an outside agent or event. These tend to occur in unpredictable fashion and with random frequency. The source of a random failure can be from, e.g., a lightning strike, severe overloading, the product being dropped or undergoing an impact, or accidental operation.

The probability of these failures can be monitored, estimated, and predicted. Although most failure mechanisms have either an increasing or decreasing failure rate, some have a very small change over a period of time of interest and thus are effectively constant. Thus, the failure rate can still be essentially constant, meaning that during each hour (unit of time) there is the same chance of failure as any other hour.

Random failures are unavoidable but with care can be minimized.

Bio:

Fred Schenkelberg is an experienced reliability engineering and management consultant with his firm FMS Reliability. His passion is working with teams to create cost-effective reliability programs that solve problems, create durable and reliable products, increase customer satisfaction, and reduce warranty costs. If you enjoyed this articles consider subscribing to the ongoing series Musings on Reliability and Maintenance Topics.