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Let's call this fictional metal, "Lightium" or Lg. Properties of its best alloy in comparison to Titanium-G5 alloy include:

  1. It has twice the Specific Strength than Ti
  2. It has one-tenth density of Ti
  3. 900 C melting point vs 1400 C of Ti
  4. Less Corrosion resistance than Ti, roughly that of Al.

So, if you were to make (1m x 1m)sheets of both metal with equal 'strength'
The Lg Sheet will weigh half of Ti, but will be 5x thicker as well. So it's a trade-off between Weight vs Volume.

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How useful this material would be compared to Al and Ti, if aiming for equivalent durability/strength in following scenarios:

  1. Airplane Construction
  2. Warship Construction
  3. Bullet Resistant Armor, especially since density is so low
  4. Tanks/ Armored Vehicle

Is having half the weight worth it occupying five times the volume? Since it could drastically alter form factor and aerodynamic of the machines.

Or would be there any scenario, where having same strength and weight in larger volume be more preferable?

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  • $\begingroup$ There are loads of questions here, can you focus it down to just the one? $\endgroup$ Jun 4, 2022 at 7:57
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    $\begingroup$ Such a material exists, and it is widely used: balsa wood has about twice the specific strength of titanium alloys (about 520 kN·m/kg vs. about 260 kN·m/kg) and is about 30 times lighter (relative density 0.14 vs. 4.8). (And the questions about aircraft show a fundamental misunderstanding of how aircraft are built. The structural strength of an aircraft is provided by an inner skeleton; the skin which provides a nice aerodynamic shape has very little strength. In fact, in olden days the outer skin was quite often made of paper.) $\endgroup$
    – AlexP
    Jun 4, 2022 at 8:58
  • $\begingroup$ @AlexP I really must insist you use this information and go on to answer the bullet pointed questions about applications. I think airplane construction has potential. $\endgroup$
    – Willk
    Jun 4, 2022 at 16:28
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    $\begingroup$ @Willk: Unfortunately, I cannot answer the question. Mostly because the specific strength is a quantity most useful for characterizing ropes or cordage -- it measures the strength of a material in tension. In most mechanical structures, we are much more interested in the strength of materials in compression. For example, concrete has a piss poor specific strength of about 5 kN·m/kg; but this doesn't prevent its use a structural material, because it has a decently large compressive strength of about 20 MPa. (That's why we need to reinforce concrete whenever it has to be used in tension.) $\endgroup$
    – AlexP
    Jun 4, 2022 at 16:51
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    $\begingroup$ The suspension bridge engineers are going to be breaking your door down, but you aren't specifying anything in your parameters that will interest any of the people you're talking about. $\endgroup$ Jun 6, 2022 at 0:20

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(Expect the question will be focussed more.. For now some notes on aircraft, this is a worked out comment on AlexP's remark)

Passenger jets and freight jets

This Lg material would be ideal to produce large aircraft. Currently, large aircraft structural integrity rely on

  1. precision of hull shape. Compare eggs.

  2. reinforced skeleton which resides inside the hull skin.

The reinforcing skeleton is quite thick and heavy, about six inches in case of passenger jets - which adds a lot of weight, costing energy. Below A320 as an example..

enter image description here

The passenger cabin inside could be made of Lg as well: seats, doors, bins.. The Lg material could also be used for all mechanics outside (aeleron, elevator) and for parts of the jet engine and jet engine support structure and wings.

Electric engines

Currently, passengers and their luggage represent only 25% of the weight, 40% is fuel. The Lg material would be nice for electric engines as well, reducing their weight considerably. When Lg would become available, future passenger aircraft may return to propellor flight, be powered by solar energy. This eliminates the weight of fuel.. and most of the cost of flight..

For hypersonic or space flight, melting point is a bit low

Although Boeing would welcome Lg for large traffic and freight aircraft. I think it would be less suitable for space flight. Its melting temperature will not allow for hypersonic flight, or a safe return into the atmosphere. A heat shield will still be needed. To be usable for these purposes, Lg has to allow coatings. Also to prevent corrosion..

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  • $\begingroup$ I don't know what you mean by "hull thickness", but I am quite sure that the skin of an A320 is a one millimeter thin sheet of metal. $\endgroup$
    – AlexP
    Jun 4, 2022 at 16:33
  • $\begingroup$ Ah, and I have no idea what makes you think that a material would be useful for making electric motors when you know nothing of its electrical and magnetic properties. What part of an electric motor could be replaced with this material? The windings of the coils? The magnetic cores? Why? $\endgroup$
    – AlexP
    Jun 4, 2022 at 16:43
  • $\begingroup$ @AlexP my answer is about passenger jets, WALL thickness. An outer "SKIN" (plate?) thickness of 6 inches would never lift off. The 6 inches includes the strengthening construct on the inside. As for electricity and conductivity of Lg, it would be nice if the motor coils can be replaced by Lg as well, but if not, there would still be weight profit: take into account not all parts of an electric engine need to conduct electricity.. Engines have housing.. a body, an axis.. and an electric propeller engine may need gears as well. $\endgroup$
    – Goodies
    Jun 4, 2022 at 17:36
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    $\begingroup$ Ah, you mean the ribs. Yes, the ribs may well be 150 mm thick. (But I don't see how you translate specific strength to compressive strength and stiffness, which are what counts for the ribs.) The specific strength of a material tells you nothing at all about its usability as the material for an axis designed to transmit torque. (The specific strength tells you whether the material is good for making a rope, or a cable.) (And anyway, the heavy components of an electric motor are the windings and the magnetic cores. The axle is a very minor contributor.) $\endgroup$
    – AlexP
    Jun 4, 2022 at 17:53
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    $\begingroup$ I did put in a comment under the question, explaining that specific strength is a measure of the strength of a material in tension. I even gave the example of concrete, a material with very low specific strength which is nevertheless quite useful to built strong structures because of its decently large compressive strength. I even gave the example of a real-world "lightium", namely balsa wood. We don't build aircraft out of balsa. (We do build aircraft models. I did build such extremely light aircraft when I was in high-school.) $\endgroup$
    – AlexP
    Jun 4, 2022 at 18:00
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Look at auto manufacturing. It should be very easy to see how the balance of weight vs strength comes into play. Aluminum takes up a good bit more space, but the overall weight saving from steel is enough to make it worth it.

The Lotus cars (that are ending production this year or last) are a great example of using Aluminum.

I will agree that the larger the craft, the more reasonable the trade-off is.

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