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What are common practices used in making a material light weight and giving it more strength. By practice I mean:

  1. Making holes in the material to reduce weight

  2. Reduce thickness to the bare minimum to keep it light

  3. Create air pockets to occupy a larger volume with the same mass.

Which one is the best practice for giving light weight and exceptional strength

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  • $\begingroup$ How does 1 compare to 3? What about geodetic construction? $\endgroup$ – Solar Mike Oct 5 '20 at 4:43
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    $\begingroup$ I believe that this question scope is too broad. Also, IMHO it is probably confusing the term material with the turn structure which I believe is more appropriate. $\endgroup$ – NMech Oct 5 '20 at 7:00
  • $\begingroup$ Would the answer to this not depend on the material and the kind of strength desired? E.g. are we talking tensile strength? Steel? Aluminium? It's a lot to cover inn the generic case, it wouldn't be possible to select just one $\endgroup$ – Tom J Nowell Oct 5 '20 at 11:20
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First of all, a point regarding the difference in the material, material system and structure, because IMHO they are being used interchangeably in this Question, giving rise to confusion.

With the term:

  • material: I usually refer to specific element or alloy with specific density properties and more or less determined strength (there are ways to increase strength, chemical and mechaninal

  • material system: I usually refer to composite materials. Materials that have two (or more) distinctive phases at different ratios.

  • structure: an engineering construction with load bearing characteristics that can be made from one or more materials or material systems in different geometric configurations.

I believe this post is implicitly referring to the later (structure), however since material is used I will start with the material. One thing to point out that based on my interpretation of the term, one cannot change the density (therefore the weight) only the strength properties. That improves the strength to weight ratio.

However, even then there are so many things to do in so many different levels.

Material

Chemical or thermal process

To adjust the strength properties you can use :

  • CVD or PVD in different ways and combinations to change the outer layers of the material and improve the strength (and chemical resistance of a material).

  • Heat treatment processes to change the phase of the material

  • Case hardening (in all its variations)

  • differential hardening

  • ...

mechanical processes

you can use

  • work hardening
  • shot peening to introduce compressive stresses that in turn increase tensile properties.
  • ...

Material system

When you are getting into material system, then you can affect the density by changing the ratio of the materials in the system.

Also the strength properties can be tailored by a few things:

  • the type of reinforcement material (particle, short randomly oriented fiber, long fibers)
  • the combination of reinforcement material and matrix material (and more precisely the way they interact and how well do they adhere).

Structure

When it comes to structures, then the options truly increase exponentially. Because you can combine the materials/material systems with different geometries.

I will give only one example I found impressive when I stumbled upon it in a science journal a few weeks ago, about a structure which mimics the structure of Euplectella aspergillum. Apparently their structure offers significantly higher buckling resistance to weight ratio compared to a solid structure.

enter image description here

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The aviation industry and designing the structure of planes and parts of them like wings, aerofoils, fuselage, landing gear, empennage, flaps, engine pylons are some examples of designing for strength and resilience while using the least safe amount of material.

For wings and flaps, they use lightweight strong alloys of titanium as the mainframe all with perforations to save weight and allow the passage of electrical and hydraulic controls with strong carbon fiber cladding as a replacement for aluminum cladding.

For landing gear, they use a computer-assisted design of links and shafts and undercarriages that are a pleasure to observe for a keen eye. Every rib and stiffener is exactly in the optimal place connected just perfectly to its partner.

Sometimes there is an air show near Los Angeles where I live and they let you get into the airplanes like the big bird C5 M Galaxi and go into the engine nacelle or into the huge compartment of the landing gear. One can see how the system has been designed from earthly heavy parts to lighter but huge wings and rudder and ailerons, etc. From heavy to light.

There is research on infusing the materials with foam-like embedded air pockets like the birds' bones, but it is not yet reached a practical stage.

When it comes to investigating how to make lighter structures one should always keep an eye on thermal properties and fatigue stress.

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There is a relatively new process coming into vogue in industrial design: Topological Optimization. Essentially, one designs a part, specifying both architecture and material composition, then simulates the part within its intended use environment, applying expected mechanical stresses from outside the part. During the simulation one measures patterns of stress throughout the part. When one finds regions within the part where stress is minimal or even absent, one can then remove those regions from the part, leaving holes (i.e altering the topology, hence the technique name) without compromising the required structural properties of the part. By the end of the simulation one arrives at a version of the part which uses significantly less material to do the required job.

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