Star engineers excel at failure investigation. Full stop.
We’ve been working on some really interesting failure investigations at Fractyl recently, and I always like to take a step back to learn from my team. Here are a few observations that might help you up your failure investigation game.
Write the equations first. Writing the equations helps understand the relative importance of each of the factors that can cause a problem. A talented engineer on my team wrote the equation for a flow restriction issue, and was able to rule out certain root causes that mathematically could not have caused a restriction issue of the size we observed. Writing the equations identifies potential root causes more reliably than brainstorming. For a bond failure, writing the equations forces you to identify the relevant force vectors, the materials being bonded, the adhesive properties, and the environment (temperature, humidity).
Inspect closely. It’s amazing what you can learn from close analysis of a failure. Veryst has some really nice inspection examples on their website, here and here. At Candela, high magnification images of a fractured fiber told us that a failure was mechanical, not optical. At Fractyl we rented a high speed, high resolution camera to look closely at a bond failure as it occurred, enabling us to differentiate between peel and shear failure modes.
Be pragmatic about root cause identification in view of the potential solution space. Time and resources are limited. At Fractyl we experienced repeated failures due to a damaged plastic tube in our product, and we identified several potential root causes of the damage, including tube dimensions, tube material, and assembly processes. At the same time, a proposed design solution involved removing the tube altogether. Rather than expend significant effort understanding the root cause of the component damage, we invested our effort in developing the new design that did not include the component. It’s important to note that we did identify the root cause of the product failure as a component failure, but we did not need to explore the next branches of the tree to understand why the component failed. Diagramming potential root causes in a fishbone is a great technique, that enables you to identify sub-branches that may not need to be explored.