Amidst all the (well-deserved) hype around graphene, it’s important to remember that its properties are not unique to carbon. More atoms can be coaxed into stable 2-dimensional configuration, with molybdenene previously theoretically possible. This is now demonstrated by Tumesh Kumar Sahu and colleagues in a recent Nature Nanotechnology article, through the manufacturing of a 2D molybdenum-based material which they showed to be indeed molybdenene. Essentially, this is a 2D lattice of molybdenum atoms, a configuration in which it qualifies as Dirac matter, just like graphene. For those of us unfamiliar with Dirac materials, this gentle introduction by Jérôme Cayssol in Comptes Rendus Physique might be of use.
In order to create molybdenene, the researchers started with molybdenum disulfide (MoS2), which using a microwave-assisted field underwent electrochemical transformation into whiskers that when examined turned out to consist out of monolayers of Mo. The sulfur atoms were separated using a graphene sheet. As is typical, molybdenene sheets were exfoliated using Scotch tape, in a process reminiscent of the early days of graphene research.
Much like graphene and other Dirac materials, molybdenene has many potential uses as a catalyst, as cantilever in scanning electron microscope (SEM) tips, and more. If the past decades of research into graphene has demonstrated anything, it is that what once seemed more of a novelty, suddenly turned out to have endless potential in fields nobody had considered previously. One of these being as coatings for hard disk platters, for example, which has become feasible due to increasingly more efficient ways to produce graphene in large quantities.
Material testing is important in big industry, where manufacturers must be able to trust the properties of the raw materials they’re using. The rest of us generally take a supplier’s word for it that they’re giving us what we’ve paid for. However, you could always take on material testing yourself with the Universal Tensile Testing Machine from [Xieshi Zhang].
Unlike a six-figure industrial machine, this build is much more affordable, costing on the order of $300 to build. It uses an Arduino to read a tensile strain gauge, and is capable of applying up to a kilonewton of force. To achieve this, it uses a NEMA 17 stepper motor driving a lead screw to apply tensile strain or compression to the specimen under test. The test fixture is assembled from 3D-printed components, and built on top of a piece of aluminium extrusion.
Fundamentally, it’s a smaller version of a machine most engineering undergraduates will see in a materials lab experiment. It could be highly useful for anyone wanting to experiment with 3D printed structures; it would be more than capable of testing various filaments and infill types for their tensile and compression performance. Video after the break.
Since desktop 3D printers have become more common, we’ve seen dramatic shifts in all kinds of areas such as rapid prototyping, antique restoration, mass production of consumer goods, or even household repairs that might not have been possible otherwise. There are a lot of unique manufacturing methods that can be explored in depth with a 3D printer as well, and [Slant 3D] demonstrates how one such method known as the living hinge can be created with this revolutionary new tool.
Living hinges, unlike a metal hinge you might pick up at a hardware store, are integrated into the design of the part and made of the same material. Typically found in plastic containers, they allow for flexibility while keeping parts count and cost low. The major downside is that they create stresses in the materials when used, so their lifespan is finite. But there are a number of ways to extend their life, albeit with a few trade-offs.
The first note is to make sure that you’re using the right kind of plastic, but after that’s taken care of [Slant 3D] builds a few flexible parts starting with longer circular-shaped living hinge which allows greater range of motion and distributes the forces across a wider area, at a cost of greater used space and increased complexity. A few other types of living hinges are shown to use less space in some areas, but make the hinges only suitable for use in other narrower applications.
One of the more interesting living hinges he demonstrates is one that’s more commonly seen in woodworking, known there as a kerf bend. By removing strips of material from a sheet, the entire sheet can be rotated around the cuts. In woodworking this is often done by subtracting material with a CNC machine or a laser cutter, but in 3D printing the voids can simply be designed into the part.
For a large part of human history, people made things from what they could find. Some stones make arrowheads. Others make sparks. Trees can turn into lumber. But the real power is when you can take those same materials and make them into something with very different properties. For example, plant fibers turning into cloth, or rocks giving up the metals inside. One of the oldest engineered materials is glass. You’d think as old as glass is (dating back at least 4,500 years), we’d understand all there is to know about it by now. According to an interesting post by [Jon Cartwright] writing in Physics World, we don’t. Not by a long shot.
There are a lot of ways that stresses can show up, at least when discussing materials science. Cracks in concrete are a common enough example, but any catastrophic failure in a material is often attributable to some stress that couldn’t be withstood. If you’re interested in viewing those stresses before they result in damage to the underlying material, take a look at this DIY polariscope which can view internal stresses in glass and other clear objects.
The polariscope takes its name from the fact that it uses polarized light to view the internal structure of a transparent object such as glass. When the polarized light passes through glass in a certain way, the stresses show up as lighter areas thanks to the stressed glass bending the light back into view. This one is constructed with a polarizing filter placed in front of an LCD screen set to display a completely white image. When glass is placed between the screen and the filter no light is seen through the polariscope unless there are stresses in the glass. Even placing a force on an otherwise un-stressed glass tube can show this effect, and [Advanced Tinkering], this project’s creator, has several other creations which show this effect in striking detail.
The effect can also be observed as colored areas in other plastic materials as well. It’s an interesting tool which can help anyone who frequently works with glass, but it’s also interesting on its own to see clues left behind from the manufacturing process of various household items. We’ve seen some other investigative methods for determining how other household items are mass produced as well, like this project which breaks down the injection molding process.
Come on now, admit it. You’ve done it. We’ve done it. You know — you were really sure that sheet of plastic stock you found lying around the hackerspace was acrylic right? You dialled in the settings, loaded the design, set the focus and pushed the little green ‘start’ button. Lots of black smoke, fire, and general badness ensued as you lunged for the red ‘stop’ button, before lifting the lid to work out how you’re going to clean this one up.
The technique makes use of so-called ‘speckle imaging’ where a material illuminated by a laser will produce a unique pattern of reflected spots, or speckles into a camera. By training a deep neural model with a large set of samples, it was found possible to detect up to 30 types of material with 98% accuracy.
The pre-baked model runs on a Raspberry PI zero with an off-the-shelf camera all powered from a power bank. This allows the whole assembly to simply drop onto an existing laser cutter head, with no wiring needed.
Even if you’re a seasoned laser cutter user, with a well-controlled stock pile, the peace-of-mind this could give would definitely be worth the effort. A more detailed description and more videos may be found by reading the full paper. Here’s hoping they release the system as open source, one day in the not-to-distant future. If not, then, you know what to do :)
[Zachary]’s foray into the strange world of microlattices began when he happened upon a 2011 paper on the subject in Science. By using a special photocurable resin, the researchers were able to use light shining through a mask with fine holes to create a plastic lattice, which was then plated with nickel using the electroless process, similar to the first half of the electroless nickel immersion gold (ENIG) process used for PCBs. After removing the resin with a concentrated base solution, the resulting microlattice is strong, stiff, and incredibly light.
Lacking access to the advanced materials and methods originally used, [Zachary] did the best he could with what he had. An SLA printer with off-the-shelf resin was used to print the skeleton using the same algorithms used in the original paper. Those actually turned out pretty decent, but rather than electroless plating, he had to go with standard electroplating after a coat of graphite paint. The plated skeletons looked great — until he tried to dissolve the resin. When chemical approaches failed, into the oven went the plated prints. Sadly, it turns out that the polymers in the resin expand when heated, which blew the plating apart. A skeleton in PLA printed on an FDM printer fared little better; when heated to drive out the plastic, it became clear that the tortuous interior of the lattice didn’t plate very well.
From aerogels to graphene, we love these DIY explorations of new and exotic materials, so hats off to [Zachary] for giving it a try in the first place.