#materials engineering

[bisexual-engineer-girl]

What do you call a group of fish people who are all married and clean up plastic in the ocean?

Polymermaids!

[mindblowingscience]

Scientists finally succeed in growing dolomite in the lab by dissolving structural defects during growth

For 200 years, scientists have failed to grow a common mineral in the laboratory under the conditions believed to have formed it naturally.

For 200 years, scientists have failed to grow a common mineral in the laboratory under the conditions believed to have formed it naturally. Now, a team of researchers from the University of Michigan and Hokkaido University in Sapporo, Japan have finally succeeded, thanks to a new theory developed from atomic simulations. Their success resolves a long-standing geology mystery called the "Dolomite Problem." Dolomite—a key mineral in the Dolomite mountains in Italy, Niagara Falls, the White Cliffs of Dover and Utah's Hoodoos—is very abundant in rocks older than 100 million years, but nearly absent in younger formations. "If we understand how dolomite grows in nature, we might learn new strategies to promote the crystal growth of modern technological materials," said Wenhao Sun, the Dow Early Career Professor of Materials Science and Engineering at U-M and the corresponding author of the paper published today in Science. The secret to finally growing dolomite in the lab was removing defects in the mineral structure as it grows. When minerals form in water, atoms usually deposit neatly onto an edge of the growing crystal surface. However, the growth edge of dolomite consists of alternating rows of calcium and magnesium.

Continue Reading.

[saeran-exe]

20/08/24

I forgot to post this yesterday 'cause I got home so late from uni 😭

Yesterday was a pretty tiring, but worth it, day of studying since I missed an entire week of class and had to study all of the content from last week's welding technology class + study from a texbook on science and engineering of materials.

Content studied yesterday:

> Stress-Strain of metals under tension, compression, sheer and torsion tests ;

> Stress-Strain graph (elastic and plastic strain, recognition of ductile and brittle materials, points of elastic limit, yielding, ultimate strength and rupture) ;

> General types of welding ;

> Concepts of welding technology .

My welding technology class went great and I was relieved when I found myself following the explanations with ease and being able to participate because of successful studying and absorption of the last class' content through photos of the board that my classmate sent me. I was really scared I would fall behind but I feel pretty confident and intrigued by the subject and engineering in general... I think I'm finally falling in love with it!

[penultimatestalematewithdeath]

Just found out the OceanGate sub hull was made with Carbon Fiber???? Can fail under compression with one poorly manufactured air bubble carbon fiber??? Subjective to failure inducing embrittlement at low temperatures carbon fiber???? That carbon fiber????

I am in absolute horrified Awe. Like. I don’t know much about submarines, but I know rockets and we use carbon fiber for hobby rockets and. You can’t?? Make a pressurized vessel out of carbon fiber?? And expect it to survive cyclical loads?? Especially one experiencing temperatures as low as the waters by the Titanic!! Like the polymer matrix would DEFFO experience embrittlement and at MINIMUM crack but more likely would fail catastrophically!! Your threasbold for acceptable cracking would be MINISCULE at that pressure; you couldn’t afford brittle cracking almost at all!!

This article goes into some detail about the safety concerns with the material used and how they were literally brought up and ignored! like. This is the literal scenario they train us for ethics wise in college! Legit the definition! Of when you should put human life before the company!!

A whistleblower raised safety concerns about OceanGate’s submersible in 2018. Then he was fired.

The director of marine operations at OceanGate was fired after raising concerns about its first-of-a-kind carbon fiber hull.

Idk it’s just. There’s so much wrong with the situation, but like. To not perform nondestructive testing on the hull?? To ignore visible defects on a supplied material??

So many red flags, so many things that should Never have happened.

[nanotechnologyworld]

Metastable states of floating crystals

Magnetocapillary interactions between particles allow self-assembly of floating crystals along liquid interfaces. For a fixed number of particles, different states with different symmetric characteristics, called metastable states, coexist. Various pioneering works have observed the existence of metastable states in floating crystals. As different states coexist, it is difficult to control the formation of specific structures. However, controlling the formation of metastable states is a key ingredient to functionalize such assemblies, paving the way for self-assembling microrobots for example. The way to control the state of a floating crystal has never been studied before.

https://www.nanotechnologyworld.org/post/metastable-states-of-floating-crystals

[pyrot3ch-nick]

Quotes from my material science professor from lecture.

Carbon "pack bonds" with nearly EVERYTHING

Metallic bonds are "not like other bonds"

Working with gold is like working with a golden retriever

If gold is a dog, silver is a cat.

[vitomurgida]

3D METAL PRINTING

There are different types of Metal Additive Manufacturing technologies, here are the most important.

Directed Energy Deposition (DED):

It is composed by a head from where a laser, or a electron or a plasma ray exits. On the head, a pressurized system is installed, from where metal powder is ejected in a way that hits the ray and melting occurs. Both the head and component can move. It is possible to use, instead of powder, a filament, cheaper but that gives lower quality.

Turn up the volume!

https://www.youtube.com/watch?v=oL7bMhPTtDI

Powder Bed Fusion:

A powder bed is deposited and material is melted only where necessary. Once the material is melted, another layer of powder is deposited, and so on.

Depending on the energy source, we speak of:

1. Selective Laser Melting (SLM):

The source is a laser and the working chamber is filled with inert gas, to avoid combustion or explosions. The head moves, the component is fixed. Selective Laser Sintering (SLS) is similar, but the material is not really melted, is sinterized (lower temperatures).

Maximum obtainable dimensions are (600x400x500) mm^3.

https://www.youtube.com/watch?v=te9OaSZ0kf8

2. Electron Beam Melting (EBM):

The source is an electron gun. It is composed by a cathode made of tungsten that is heated until it reaches temperature higher than 2000 °C, (melting point of tungsten is about 3400 °C, this is why tungsten is used) emitting electrons than are accelerated through the application of a voltage (V or Volt) between the same cathode and an anode collocated below.

In this way, an electron beam is emitted, that is focused through a repulsive disk (a magnet) and reaches the material, melting it.

The electron beam can be oriented through a magnetic field, removing any moving part and so, any friction. This makes this technology faster but also more expensive (not less than 1 million euros).

The chamber has to be taken under vacuum and at a temperature of 1000 °C. Working at these temperature reduces thermal stresses.

Maximum obtainable dimensions are (350x350x380) mm^3.

https://www.youtube.com/watch?v=CUeDevI6kyE

The main parameters that infleunce the quality of a component obtained with Additive Manufacturing are:

Energy density: we have to set the right     power of the source, the right speed, the right distance, avoiding     material vaporization or chemical composition changes (too much energy) or     lack of fusion (too low energy). The quality of the component is     measured comparing the final mass with the expected from theory one: in     fact, generally speaking, components obtained with AM have a lower density     than ones obtained through CNC technologies, because of the higher air     inclusions. This results in lower mechanical porperties;

Powder: chemical composition,     dimensions (we can reach nanometers), morphology, physical properties,     storaging, reutilizability and dangerousness. Aluminum powder cost is 30     €/Kg, Steel 70 €/kg, Titanium 150 €/Kg, NiTiNOL 700 €/Kg (approximate     values);

Deposition strategy: it influences material     orientation, resulting in a material anisotropy (different mechanical     properties in different directions). In conclusion, it influences the mechanical     properties of the component;

Rugosity; we obtain higher rugosity than in traditional technologies (CNC). Surface post processing is necessary.

Metal Additive Manufacturing is a competitive technology, considering time and costs, only for low numbers of components, with very complex geometries that are not obtainable with other technologies.

For big lots and simpler geometry, CNC technologies are still the best choice.

Regards!