MTBF in the Age of Physics of Failure
MTBF is the inverse of a failure rate, it is not reliability. Physics of failure (PoF) is a fundamental understanding and modeling of failure mechanisms. It’s the chemistry or physical activity that leads a functional product to fail. PoF is also not reliability.
Both MTBF and PoF have the capability to estimate or describe the time to failure behavior for a product. MTBF requires the knowledge of the underlying distribution of the data. PoF requires the use stresses and duration to allow a calculation of the expected probability of success over time.
MTBF start with a point estimate. PoF starts with the relationship of stress on the deterioration or damage to the material. One starts with time to failure data and consolidates into a single value, the other starts with determining the failure mechanism model.
Does MTBF has a Role Anymore?
Given the ability to model at the failure mechanism level even for a complex system, is there a need to summarize the time to failure information into a single value?
MTBF was convenient when we had limited computing power and little understanding of failure mechanisms. Today, we can use the time to failure distributions directly. We can accommodate different stresses, different use pattern and thousands of potential failure mechanisms on a laptop computer.
MTBF has no purpose anymore. MTBF describes something we have and should have little interest in knowing.
Sure, PoF modeling takes time and resources to create. Sure, we may need complex mathematical models to adequately describe a failure mechanism. And, we may need to use simulation tools to estimate time to failure across a range of use and environmental conditions. Yet, it provide an estimate of reliability that is not possible using MTBF at any point in the process. PoF provides a means to support design and production decisions, to accommodate the changing nature of failure rates given specific experiences.
When will PoF become dominant?
When will we stop using MTBF? I think the answer to both is about the same time. It is going to happen when we, reliability minded professionals, decide to use the best available methods to create information that support the many decisions we have to make. PoF will become dominant soon. It provides superior information and superior decision, thus superior products. The market will eventually decide, and everyone will have to follow. Or, we can decide now to provide our customers reliable products.
We can help PoF become dominant by not waiting for it to become dominant.