Blame It On The Sockets: Forensic Analysis Of The Arecibo Collapse

Nearly three years after the rapid unplanned disassembly of the Arecibo radio telescope, we finally have a culprit in the collapse: bad sockets.

In case you somehow missed it, back in 2020 we started getting ominous reports that the cables supporting the 900-ton instrument platform above the 300-meter primary reflector of what was at the time the world’s largest radio telescope were slowly coming undone. From the first sign of problems in August, when the first broken cable smashed a hole in the reflector, to the failure of a second cable in November, it surely seemed like Arecibo’s days were numbered, and that it would fall victim to all the other bad luck we seemed to be rapidly accruing in that fateful year. The inevitable finally happened on December 1, when over-stressed cables on support tower four finally gave way, sending the platform on a graceful swing into the side of the natural depression that cradled the reflector, damaging the telescope beyond all hope of repair.

The long run-up to the telescope’s final act had a silver lining in that it provided engineers and scientists with a chance to carefully observe the failure in real-time. So there was no real mystery as to what happened, at least from a big-picture perspective. But one always wants to know the fine-scale details of such failures, a task which fell to forensic investigation firm Thornton Tomasetti. They enlisted the help of the Columbia University Strength of Materials lab, which sent pieces of the failed cable to the Oak Ridge National Laboratory’s High Flux Isotope reactor for neutron imaging, which is like an X-ray study but uses streams of neutrons that interact with the material’s nuclei rather than their electrons.

The full report (PDF) reveals five proximate causes for the collapse, chief of which is “[T]he manual and inconsistent splay of the wires during cable socketing,” which we take to mean that the individual strands of the cables were not spread out correctly before the molten zinc “spelter socket” was molded around them. The resulting shear stress caused the zinc to slowly flow around the cable strands, letting them slip out of the surrounding steel socket and — well, you can watch the rest below for yourself.

As is usually the case with such failures, there are multiple causes, all of which are covered in the 300+ page report. But being able to pin the bulk of the failure on a single, easily understood — and easily addressed — defect is comforting, in a way. It’s cold comfort to astronomers and Arecibo staff, perhaps, but at least it’s a lesson that might prevent future failures of cable-supported structures.

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Better Car Hinges By 3D Printing

We often use 3D printing to replicate items we might otherwise make with traditional machining methods. Fraunhofer’s new door hinge for a sports car takes a different tack: it tries to be better than the equivalent machined part. The company claims that the new part is half the cost and weighs 35% less than the normal hinge.

Using tools in their 3D Spark software, the team analyzed different factors that led to manufacturing cost. Some of these were specific to the part while others were specific to the process. For example, orienting the part to minimize support and maximize the quantity that fit on the build surface.

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Finite Element Analysis Vs Real World

In advanced engineering circles, the finite element method — or, more commonly, finite element analysis — is a real staple. With the advent of more powerful home computers, though, even your home projects can benefit. The technique itself is very general, but you usually see it used for structural analysis. However, you might wonder how well it corresponds to reality. That is if analysis shows a segment of your part is weak (or strong) does that hold true when you actually build the part? [Fiveohno] wondered the same thing and decided to do some testing, which you can see in the video below.

Of course, like any simulation, the accuracy will only be as good as your data input and model. But if you work carefully, it should match up pretty well to the real world, so it is interesting to see the results of a real-world test. In fact, a video from Solidworks that shows a similar part points out — inadvertently — what not to do. For example, the force used in that analysis was too low and at a point where the part was at relatively low stress instead of at the maximum stress.

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Remoticon Video: The Mechanics Of Finite Element Analysis

Hardware hacking can be extremely multidisciplinary. If you only know bits and bytes, but not solder and electrons, you’re limited in what you can build. The same is true for mechanical design, where the forces of stress and strain suddenly apply to your project and the pile of code and PCBs comes crashing to the ground.

In the first half of his workshop, Naman Pushp walks you through some of the important first concepts in mechanical engineering — how to think about the forces in the world that act on physical objects. And he brings along a great range of home-built Jugaad props that include a gravity-defying tensegrity string sculpture and some fancy origami that help hammer the topics home.

In the second half of the workshop, Naman takes these concepts into computer simulation, and gives us good insight into the way that finite-element analysis simulation packages model these same forces on tiny chunks of your project’s geometry to see if it’ll hold up under real world load. The software he uses isn’t free by any definition — it’s not even cheap unless you have a student license — but it’s nonetheless illuminating to watch him work through the flow of roughly designing an object, putting simulated stresses and strains on it, and interpreting the results. If you’ve never used FEA tools before, or are looking for a compressed introduction to first-semester mechanical engineering, this talk might be right up your alley. Continue reading “Remoticon Video: The Mechanics Of Finite Element Analysis”

Hackaday Podcast 005: Undead Lightbulbs, Home Chemistry, And The Strength Of 3D Printing

Catch up on interesting hacks from the past week with Hackaday Editors Mike Szczys and Elliot Williams. This week we discuss the story behind falling lifetime ratings for LED bulbs, look at finite element analysis to strengthen 3D printed parts, admire the beauty of blacksmithing, and marvel at open source Lidar development. We delve into great reader suggestions for Blue Pill projects sparked by last week’s podcast, discuss some history of the V2 rocket, and cover Chromecast control hardware, glowing home chemistry, K40 laser cutter add-ons, and more.

Links for all discussed on the show are found below. As always, join in the comments below as we’ll be watching those as we work on next week’s episode!

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

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Finite Element Analysis Results In Smart Infill

If you would like to make a 3D print stronger, just add more material. Increase the density of the infill, or add more perimeters. The problem you’ll encounter though is that you don’t need to add more plastic everywhere, only in the weak areas of the part that will be subjected to the most stress. Studying where parts will be the weakest is the domain of finite element analysis, and yes, you can do it in Fusion 360. With the right techniques, you can make a stronger part on your 3D printer, and [Stefan] is here to show you how to do it.

The inspiration for this build comes from [Adrian Bowyer]’s blog, where he talks about adding ‘fibers’ to the interior of 3D printed objects to increase strength. These ‘fibers’ aren’t really fibers at all, but long, thin, cylindrical voids. The theory of this is that the slicer will interpret this as a hole and place perimeters around these voids, effectively increasing the density of the infill in a local area in the print. Combine this with finite element analysis, and you get a part that is stronger where it needs to be, and doesn’t waste plastic.

However, there is an easier way. Fusion 360 and ANSYS Finite Element Simulation are both free-ish tools that allow for some amount of finite element analysis on an imported 3D object. This can be used to find the weakest part of any 3D print, and it can this can be exported as a 3D mesh. Slic3r has a modifier mesh function, and combining this finite element analysis mesh (printed at 100% infill) with the original part (printed at 10% or so infill) results in something that’s strong where it needs to be, doesn’t waste plastic, and is much easier to set up than [Adrian Bowyer]’s ‘fiber’ technique.

After printing a few 3D printed hooks with varying degrees and techniques of infill, [Stefan] found the baseline of 2 perimeters failed in a test hook at about 50kg load. The Smart Infill hook failed at about 100kg. Not bad, and the fancy-pants hook only weighs about 30% more.

You can check out a video of the entire toolchain and testing below. Thanks [Keith] for sending this one in.

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