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Scientists 3D print gunpowder substitute, achieve 420m/s bullet velocity - 3D Printing Industry:
Researchers from the Xi'an Modern Chemistry Research Institute in China have 3D printed a functional gun propellant using SLA technology. The gunpowder-esque substance is a carefully constructed blend of photopolymer resin, RDX (a high explosive), and other reactive additives. Initial gun testing of the 3D printed propellant has garnered some promising results, as the scientists managed to achieve a more-than-lethal muzzle velocity of 420m/s. This, of course, depends on your definition of 'promising'.
[...] Currently, the main ways to improve the ballistic efficiency and damage potential of propellants are to increase the burning surface or the burning rate. This is commonly done by foaming the propellants, coating them, or packing them in their casings in selective layers. According to the researchers, simply filling the cylindrical casing with a granular propellant works but is quite limited in its energy release efficiency. So, the team looked to 3D printing to see if it could pack a greater punch.
[...] Once the UV safety of the newly formulated explosive was confirmed, the team 3D printed a set of thin disks, each about 40mm in diameter. These disks could be stacked on top of each other to form a longer cylinder, resembling the body of a bullet casing. Each layer featured a honeycomb-like structure with holes and was about 5mm thick.
Then came time for the grand finale – the gun test. The cylindrical stack was loaded into a 30mm barrel with a 200g mass acting as the bullet, although at 200g it's probably closer to a mini cannonball. The team set up a high speed camera and an internal pressure gauge in the barrel before pulling the trigger. Once the smoke cleared, the researchers calculated a rather high pressure exponent value of 1.46 and a muzzle velocity of 420m/s, with plans to increase the chamber pressure in future tests.
Journal Reference:
Weitao Yang, Rui Hu, Lin Zheng, Guanghu Yan, Wenrong Yan. Fabrication and investigation of 3D-printed gun propellants [open], Materials & Design (DOI: 10.1016/j.matdes.2020.108761)
(Score: 3, Insightful) by Immerman on Monday July 20 2020, @06:24PM (3 children)
I've got to say, that's the dfirst time I've heard metric called "arbitrary"
I mean sure, to a certain extent *every* unit of measure is arbitrary, but metric is at least consistent, both with different unit sizes (how many inches in a mile again? how about cubic inches per gallon, or gallons per cubic foot?), and with the relationships between units. The sizes are even largely based very closely on traditional European units:
1 decimeter = 1 hand
4L = 1 gal
1bar = 1 atmosphere (okay, so bar isn't technically an SI unit, but 100kPa is a lot cleaner conversion than 14.7..psi)
gravity ~=10m/s^2 instead of ~32ft/s^2
And of course Fahrenheit is *completely* arbitrary, with zero about 270 degrees too hot to be useful for anything other than measuring relative temperature differences.
Conversions aren't perfect of course, but they're also completely irrelevant unless you're trying to use both systems simultaneously
And of course imperial unit sizes are terrible - there's almost nothing that you'd weigh in pounds where you don't also want the remainder in ounces, or in feet where you don't also want inches. And of course inches are too big to be useful for almost anything, you always need fractions as well. Cooking is probably the one place where SI is (possibly) more convenient since it has such a plentitude of unit sizes in the range you use for cooking. Of course as soon as you try scaling the recipe you'd better be good with fractions and/or remember a host of conversion factors.
(Score: 0) by Anonymous Coward on Monday July 20 2020, @11:59PM (2 children)
I'm not surprised, most people have been brainwashed into thinking that the measures were defined in a sensible way. The moment we leave the Earth for a permanent colony on another planet, the metric measures are going to look far worse than the Imperial measures. Even now, the official Kilogram is a known problem as it's been observed to change mass by slight, but significant, amounts. And you have issues calibrating thermometers when you're not at sealevel.
Imperial measures are definitely not perfect, but basing most measures on estimates of human measures means that it's going to remain at least moderately useful on whatever planet we wind up living on. Plus, we have a number of useful estimating devices on us at all times.
(Score: 2) by ChrisMaple on Tuesday July 21 2020, @05:20AM
As of May 20, 2019, the kilogram is no longer defined by any physical object.
(Score: 2) by Immerman on Tuesday July 21 2020, @02:06PM
Imperial units will be completely arbitrary everywhere in the universe, while metric will just lose a few convenient local constant approximations like gravity.
You do realize the official pound, etc. suffer from the exact same drift issues as the kilogram used to (before they redefined the kilogram in terms of invariant physical constants.). *Any* physical reference unit will suffer from the exact same problem. And of course these days virtually all the imperial units are officially defined in terms of their metric alternatives anyway - their traditional definitions were useless for any purpose requiring high accuracy.
Meanwhile, all the closely related units in imperial are completely arbitrary - measures of length, area, and volume have large arbitrary constants connecting them, as do measures of the same quantity at different scales (e.g. inches, feet, yards, and miles) Quick, how many teaspoons in a cubic mile? I can tell you easily that there's 10^15 ml in a cubic km, and thus that a cubic km of water weighs roughly 10^12 kg.
There is something to be said for the high divisibility of base 12 - but it's used only sporadically in Imperial, and introduces lots of inconveniences when mixed with base-10 numbers.
The biggest objective complaint against metric I've heard is actually just a complaint about the rulers - they can be hard to read, and the lack of fractional subdivisions makes finding midpoints more difficult (important for building things) - but of course you can buy fractional metric rulers if you're one of the few people that has a frequent use for them.