| Process Improvement Glossary |
| criticality – Criticality is a combination of severity and likelihood. |
| failure mode ratio – The fraction of the part failure rate attributable to the particular failure mode under consideration. Often identified by the symbol α. |
| infant mortality period – Is characterized by an initially high failure rate which decreases rapidly. Failures are due primarily to poor manufacturing techniques and quality control. Infant mortality failures can be reduced by a process FMEA. |
| part failure rate – The probability that the part will fail during a specified time interval. Often identified by the symbol λp. |
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reliability – Reliability is the probability that a product will perform its designated function without failure under given conditions in a given period of time. For example, the powertrain of an automobile may be engineered to the following specifications:
Performance: 0-60 mph in 10 seconds Durability: 100,000 miles Reliability: 89% The reliability rating above means that 89 out of 100 powertrains manufactured will meet the performance and durability specifications without failure. |
| useful life period – Is characterized by a nearly level failure rate. Failures are random and are due primarily to inadequate design. Useful life failures can be reduced by a design FMEA. |
| wearout period – Are characterized by an increasing failure rate. Failures are due to natural aging, sometimes poor maintenance. Some wearout failures can be delayed by a service FMEA. |