It has mild strength downsides, but very severe fatigue and damage tolerance downsides. Knowing this, it makes sense that 3d printing tech would make headway in space industry but not (yet) in aviation
3D printed metal is now as strong as machined metal, assuming an identical alloy. The process has been pretty well perfected.
The strength loss comes from the fact that not all alloys are 3d-printing friendly, so you often have to compromise and you end up with a less than ideal alloy for your application.
Sure, but I mean what's the technical reason a material isn't it 3D printing friendly? Are we talking grain structure here? Is it something that can be at least partly mitigated by some post-printing heat treatments, like tempering?
crack growth in metals is driven by microscopic flaws that cause high-intensity but very localized stress concentrations. Over time even low stress levels cause these flaws to grow to the point where they start causing strength problems. Even in traditional aluminum machined parts, increased surface roughness can have a large impact on fatigue life.
3D printed parts are chock-full of these microscopic flaws, porosity, and have horrible surface roughness (most parts you see in production are post-machined to improve the finish). Additionally, the repeated heating-cooling of the layers as they are deposited builds up residual stress in the part. All just due to the nature of how they are manufactured.
Is there a known source of internal flaws/porosity in an otherwise solid part? Presumably laser melting produces a puddle which shouldn't allow for internal pores, as long as it isn't printed too fast (or solidifies too fast, which is why I think most chambers are internally heated to near melting temp).
Re: surface roughness, I can understand that the powder grain size creates a sort of minimal structure size, and can in principle be the start of a crack if a surface grain gets knocked loose. Is that the sort of thing you mean? I can see that for any internal or external surfaces, and a rocket engine combustion is certainly applying a lot of heat and pressure on surface grains. Can this be alleviated by smaller grain sizes, or is there some limit there?
Re: repeated heating/cooling and internal stresses, this strikes me as just requiring standard post-printing stages like tempering to alleviate internal stresses.
I can't speak to the proximal cause of the roughness and porosity, but if you've ever held a raw printed aluminum part in your hand it is immediately apparent.
That said there are processes to deal with porosity like Hot Isostatic Pressure (HIP) treatment that basically crushes all the voids with immense pressure. This does come at the cost of dimensional accuracy though (HIP will compress the part somewhat).
Similarly, annealing a 3D-print to relieve residual stress does work, but it also will cause warping as those stresses are relieved. Again, sacrificing dimensional accuracy. Frontier AM companies have ways to compensate for all of these effects but it's a trial and error process for each part essentially.
At this point you're now stacking multiple processes on each other just to try to get to near-billet properties. Calibration Trials > Print > HIP > Anneal > Machine. The cost adds up quickly. It can be justified especially in non-fatigue-critical applications but it's no free lunch
you may have the causality reversed. perhaps treasury yields are rising because bond investors would rather fund data center build out than buy 10yr notes
It's not like he was going to be a Congressional staffer nor working at a newspaper. But if he was on-call for a lot of his career that'd be kind of amusing
I use bitwarden, but it not being able to share a single secret is becoming an issue.
In my search for alternatived I stumbled across https://passbolt.com/ AGPLv3 and does support sharing single secrets, but no free hosted version. Free if you self host of course.
It guess it's a vaultwarden without "the man in Nebraska" problem.
On iPhone, Firefox Mobile can work as a password manager.
I'd like something that is easier to self-host, and isn't tied to Firefox.
But my botched migration to Bitwarden has left me looking for something that works better; in the meantime, I'm staying with Firefox + Firefox Sync. I use another browser on iPhone, since Firefox Mobile has memory problems with many tabs. (The problem was there for years, got fixed, and reoccurred.)
just turned 32 and I feel this as well. I feel into a deep depression shortly after graduating for this exact reason; mourning the loss of that regular contact with similar-age, similar-interest people as they all moved across the country to start their careers. Similar thing happened a few years later when I was internally transferred to another group at work with no people my age. It's never been the same since.
I've always scoffed at paying for those "activity groups" (what kind of loser would pay for friends?), but recently I've started reconsidering.
The standard advice is always to buy a transmitter and get started with the simulator. Then buy / build your custom racing drone that suits your flying style and area. Anything from 20 gram whoops that fly indoors to 5" racing quads that need a lot of open space.
But with dji neo 2 / avata you get a fairly beginner friendly set up. Once you're used to it, you can upgrade to a good racing drone by building one yourself.
There's a thriving community of aerospace startups in the US right now that are eager to snatch these NASA folks up. It won't be the right move for all of them, and it's unfortunate to get displaced from a comfortable, prestigious job like that, but I strongly believe a lot of these people will go on to do great things in industry, and potentially have a far greater impact on aerospace than they ever could at NASA.
Not saying I agree with the cuts, just pointing out there may be a silver lining.
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