A team of researchers at the Institute of Synthetic Polymer Materials of the Russian Academy of Sciences, MIPT and elsewhere has determined how the regularity of polypropylene molecules and thermal treatment affect the mechanical properties of the end product. Their new insights make it possible to synthesize a material with predetermined properties such as elasticity or hardness. The paper detailing the study was published in Polymer.
In terms of production volume, polypropylene it is second only to polyethylene. By tweaking its molecular structure, polypropylene can be used to manufacture materials with a wide range of features, from elastic bands to high-impact plastic. However, the relationship between the polymer’s chemical structure and its mechanical properties is not fully understood.
What makes the properties of polymer materials so variable is their makeup. A polymer molecule is a long chain of repeating units of unequal length. If these molecules are jumbled up more or less at random in a material, it is said to be amorphous. Such polymers are soft. In other materials, the polymer chains form interconnections called crosslinks. This gives rise to regions of highly regular atomic structure (fig. 1), similar to that of crystals, hence the name crystallites. They hold the whole molecular network together, and the more crystallites there are in a material, the harder it is. To form crosslinks, molecular chains need to possess a certain structural regularity called isotacticity.
For decades, materials scientists have taken inspiration from the natural world. They’ll identify a biological material that has some desirable trait — such as the toughness of bones or conch shells — and reverse-engineer it. Then, once they’ve determined the material’s “microstructure,” they’ll try to approximate it in human-made materials.
Researchers at MIT’s Computer Science and Artificial Intelligence Laboratory have developed a new system that puts the design of microstructures on a much more secure empirical footing. With their system, designers numerically specify the properties they want their materials to have, and the system generates a microstructure that matches the specification.
The researchers have reported their results in Science Advances. In their paper, they describe using the system to produce microstructures with optimal trade-offs between three different mechanical properties. But according to associate professor of electrical engineering and computer science Wojciech Matusik, whose group developed the new system, the researchers’ approach could be adapted to any combination of properties.
“We did it for relatively simple mechanical properties, but you can apply it to more complex mechanical properties, or you could apply it to combinations of thermal, mechanical, optical, and electromagnetic properties,” Matusik says. “Basically, this is a completely automated process for discovering optimal structure families for metamaterials.”
What kills me tho, is that that in MCU canon, explicitly stated, is the fact that Vibranium absorbs and diffuses all vibration. So it could never, ever bounce, rebound, or make that sound that it makes.
You’re absolutely right. In Captain America: The First Avenger, Howard Stark explains that vibranium is “completely vibration absorbent.” Basically, when thrown, Steve’s shield ought to impact with its target completely silently and immediately fall to the ground without bouncing or rebounding at all.
However, the directors say in the audio commentary for the Winter Soldier that
… the shield can do what we want. So sometimes it absorbs impact, and in this case [the bridge scene] it sends the bullets back at the [shooters] …
So no, the shield can’t ricochet, but simultaneously it can because Rule of Cool.
This question really has been asked a lot
Why does Captain America’s shied bounce? If the defining feature of the vibranium-laced shield is that it absorbs large amounts of kinetic energy, why does it not simply drop when it hits a wall or other objects. Shouldn’t the kinetic energy just get absorbed?
My favorite answer so far is that we need to factor in the law of conservation of energy. Energy cannot be created or destroyed. When an object with mass is in motion, it gains kinetic energy (½ mv^2). When said object (with kinetic energy) stops moving, that is because it is acted upon by some outside force. The energy then transforms into sounds, or heat, or into permanently deforming the material.
We never really hear a significant sound when Cap’s perfectly shaped shield hits something, nor do we see it get significantly heated up, and of course it doesn’t permanently deformed because the shield is indestructible. So after it absorbs a kinetic energy, where does it go?
The only plausible explanation is that the shield absorbs kinetic energy and that energy is then returned to the shield. That would explain why the shield bounces. If the vibranium-steel-(mystery element) alloy was a perfect mixture of real world properties like elasticity and strength, it could regain most of the kinetic energy given to it by Captain america to bounce off a wall, to ricochet bullets, and to be otherwise a very good shield.
In objects like a super ball, it bounces because the material that makes it up deforms. When it does, the kinetic energy of the ball’s motion is transformed into elastic potential energy. The atoms and molecules bend to accommodate the impact force, but when that force is removed, the atoms and molecules snap back into their original positions, returning this elastic potential energy to the ball as kinetic energy that makes the ball bounces.
Materials that are potentially good bouncers are usually elastic. Elasticity is the ability of a body to resist a distorting influence or deforming force and to return to its original size and shape when that influence or force is removed. Metals are incredibly elastic, even more so than rubber. When you graph out how much force per area it takes to deform a metal of some amounts, you get a curve like this
where f=stress (force/area) and ε=strain (change in length/original length).
In the elastic zone, any amount of energy input to the object could be potentially returned as kinetic energy as long as it doesn’t get pass the failure point where it deforms too much.
The problem is, for most metals you can blow right pass the elastic zone and into the failure point where the metal deforms too much and is not ‘bouncy’ anymore. This happens at impact velocity of only 0.1 m/s, while Captain America whips his shield way faster than that.
So, metals are incredibly elastic under the right condition, but not necessarily shield-throwing condition. This is where vibranium comes in. There is actually a measure of how good a material is at absorbing and returning kinetic energy called Coefficient of Restitution, or COR. The closer the COR of a material is to 1, the better it is at staying at the critical elastic range. If Captain America’s shield is going to absorb and return energy effectively, the vibranium that makes it up needs to have a pretty high COR.
Vibranium absorbs kinetic energy, meaning it should be elastic, and the shield is indestructible, meaning the mixture has a high yield strength. So if the shield was made to bounce these properties in the right way, it should have an amazing coefficient of restitution at velocities that no other metals could take impacts at.
If Howard Stark built the shield the way it looks like with vibranium-laced rings running around it, it would allow some deformation along the long axis. Captain America could throw the shield, it would impact the surface, deform slightly, and then snap back into position to regain more energy at the velocity that no other metal could, and it would have more energy going into the next impact, and it would be a lot of energy because it would be thrown by the Captain America, and that is why the shield bounces!
Sea sponges known as Venus’ flower baskets remain fixed to the sea floor with nothing more than an array of thin, hair-like anchors made essentially of glass. It’s an important job, and new research suggests that it’s the internal architecture of those anchors, known as basalia spicules, that helps them to do it.
The spicules, each about half the diameter of a human hair, are made of a central silica (glass) core clad within 25 thin silica cylinders. Viewed in cross-section, the arrangement looks like the rings in a tree trunk. The new study by researchers in Brown University’s School of Engineering shows that compared to spicules taken from a different sponge species that lacks the tree-ring architecture, the basalia spicules are able to bend up to 2.4 times further before breaking.
“We compared two natural materials with very similar chemical compositions, one of which has this intricate architecture while the other doesn’t,” said Michael Monn a Brown University graduate student and first author of the research. “While the mechanical properties of the spicules have been measured in the past, this is the first study that isolates the effect of the architecture on the spicules’ properties and quantifies how the architecture enhances the spicules’ ability to bend more before breaking.”
