Articles tagged Physics of Failure (PoF)

Physics-of-Failure warns us to keep the sum of all static and cyclic loads on a part’s microstructure below its fatigue stress limit.

The image below shows two example metal fatigue limit failure curves. These curves were determined based on controlled laboratory experiments. These experiments use a machine with a fixed load to test the selected piece’s microstructure stress levels. Curve A shows that at a high stress level, close to the Ultimate Tensile Strength of steel, the test piece failed after 10,000 cycles. As the fatigue stress level is reduced, the test piece lasts longer. When the imposed stress is limited to around 50% of the UTS, the cycles to failure had no measurable limit. On the other hand, Curve B shows that at all levels of fatigue stress the component would eventually fail. However, the same outcome can be seen, that as stress reduces the service lifetime before failure increases.

 What Every Manager Needs to Know About Business Risk from Equipment Reliability 

 Figure 1 shows how equipment risks start and transfer through a business. Tens of thousands of business risks, even hundreds of thousands in big operations, come from your plant and machinery. 

When engineers design a machinery part, they begin by defining the operating load range it will experience during its service life. This range will include the loads when the machine part is not working through to the maximum stress that it will operate under. Examples of high stress situations include operating overload events, or when starting up under a large load. How great the imposed stress reaches and how often those events occur changes a part’s reliability.