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.
By using this information, we can easily identify how to increase the reliability of machines. The graph uses a logarithmic scale on the X-axis (cycles to failure). As such, a 10% decrease in stress in a part increases its reliability and lifecycle by a factor of 10. This is a massive increase in service lifetime reliability for small reductions in the amount of cyclic stress.
When machines do not last for long service lifetimes, it is almost certainly because one or more of the working parts are suffering high microstructure cyclic stress. They are being pushed to failure due to microstructure fatigue. As a result, they fail well before their intended service lifetime. If Precision Operating Standards are used, then equipment will last much longer without failure.
The establishment and use of both precision operation and precision maintenance standards are vital requirements in companies using Plant Wellness Way EAM methodology. Preventing failure by reducing component material-of-construction stresses to the least possible will, as the fatigue limit curves tell us, naturally produce a massive rise in their reliability.
Contact us if you want to get all the benefits and profits that outstanding reliability brings to PWWEAM users.
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