I'm skeptical of this claim. Can you expand on your answer that there are materials that can be cycled infinitely in the plastic regime, or point to some sources that explain further?
I did a PhD in a materials science lab, and my understanding is that at least for metals, you still eventually run into fatigue & failure, even if you stay within the elastic regime (which nominally appears reversible). I'm not sure why plastic deformation would be any better, given that you'll have atom positions shifting and (if crystalline) dislocations propagating. I'm not a fatigue expert by any means, so I'd love to learn more.
On the Wikipedia page for fatigue limit[1], I see a link to a reference that says there are no metallic materials that can be infinitely cycled[2]. Is the bonding somehow different in this 3D printed material that causes fatigue to work differently?
One of the graduate students I worked with studied the TI micro-mirrors used in DLP projectors. They were designed in the first round of micromachined devices so by EEs rather than MEs, and as a result they used aluminim.
So the question to answer is, "how does a multi-million pixel display unit array of doubly supported tortional Al hinges going through >1% strain survive for 1000s of hours (much longer than the bulbs) oscillating at 100s of kHz". That's ~10^12 cycles each with ppm defect rates!
Since you know that this far exceeds any reasonable fatigue strain and the defect density /dislocation propagation should be huge! The key is that the aluminum is <1um thick a few um wide and <100um long. The majority if the strain is concentrated at the supported ends, but it's so thin that the whole high strain region is single crystal!
TI didn't originally know why it worked... just that it did.
I won't say mechanical gates are a great idea... and at 1MHz they might start failing after a few continuous months. The truly unfortunate part is that the manufacturing processes aren't really designed to control for the grain structure... they're designed for etch repeatability and conduction stability so yield could fall apart while tour processes seem nominal.
I don't pretend to understand this, but they could be saying that it's not infinite, just very, very large. According to the S/N curve on Wikipedia, it looks like staying in the plastic region for steel means you effectively get enough cycles that the part will "effectively" be immortal (just maybe not going to last until the death of our sun at MHz cycles).
An analogy might be with transistors - if you run them at high temps, you might get ten years out of them. If you're running them at room temps, you might not be able to see signs of anything other than sporadic failure even over long periods of time.
In the industry flexures are considered to have 'infinite' life if they are correctly designed and if you stay well within the working parameters. If you stay within about 2/3rds of the elastic range it lasts forever. Dan Gelbart: https://youtu.be/PaypcVFPs48?t=660
Sorry I meant elastic range. These are only a few hundred atoms across in the flexure areas so if you stay well within the range, it does last 'forever' (years)
I did a PhD in a materials science lab, and my understanding is that at least for metals, you still eventually run into fatigue & failure, even if you stay within the elastic regime (which nominally appears reversible). I'm not sure why plastic deformation would be any better, given that you'll have atom positions shifting and (if crystalline) dislocations propagating. I'm not a fatigue expert by any means, so I'd love to learn more.
On the Wikipedia page for fatigue limit[1], I see a link to a reference that says there are no metallic materials that can be infinitely cycled[2]. Is the bonding somehow different in this 3D printed material that causes fatigue to work differently?
[1] https://en.wikipedia.org/wiki/Fatigue_limit
[2] https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1460-2695....