Accelerated Testing Assumptions
Chris and Fred discuss accelerated testing. Accelerated testing is great for getting lots of information in a short period of time. You can compress a lot of ‘real-time’ life into a really small amount of testing. But how do you do it right? You need to understand the underlying physics of failure to work out how the compression of time works.
Join Chris and Fred as they discuss accelerated testing. Fred once had a client, who was in the process of doing accelerated testing, tell him that they were going to assume that the thing they were studying had this thing called ‘activation energy.’ This relates to a model that helps us understand the rate at which a chemical reaction occurs. The higher the activation energy, the slower the chemical reaction occurs. Temperature (thermal energy) often drives chemical reactions because there is more energy to meet the ‘activation energy’ requirement for the reaction to occur. So all we need to do is turn up the temperature to make things happen faster?
But … Fred’s client simply assumed that the activation energy for the particular chemical reaction was 0.7 (the units are omitted for the gist of this podcast). This is not the way to do this …
- Reach out to an expert. If you need to make an assumption about how your thing degrades, ask an expert. There are plenty out there. We don’t always have time to run tests to get this information ourselves. So get it from someone else! If you can’t find an expert, go to the library.
- What is your model? You have to have a model for accelerated testing. This model allows you to create what we call acceleration factors (AFs). If you have an AF of 10, that means every 1 hour of testing (perhaps at higher temperatures) equates to 10 hours of ‘real-life’ use. To be able to quantify your reliability estimates, these AFs need to be accurate. How accurate is your AF if you assume that the activation energy is 0.7 without any further thought?
- Accelerated testing factors are RARELY independent. Fred’s client not only wanted to increase temperature – they also wanted to increase the load (pressure). The huge problem with this is that these factors are rarely independent. That means that if we increase the load we are also likely to change the way temperature increases the rate of chemical reaction. And all sorts of other things can happen as well. Sometimes increasing pressure changes the ‘state’ of the thing you are studying. The molecular structure changes, meaning that other accelerated testing models become irrelevant. It is very challenging to have more than one factor applied to accelerated testing.
- Are you trying measure or improve reliability? Accelerated testing can be hard. But if you are only interested in improving reliability, then you can move into the domain of highly accelerated life testing (HALT). This is where stresses are increased in a scientific way, but not in a way where we try to extrapolate reliability in ‘real-life’ conditions. HALT focuses on finding the weak points only.
So what are you trying to achieve?
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