Metal foam

[JoeRoccoCassara]

Yes, but are we talking about tensile strength by weight or by volume? Is the tensile strength of 10" of metal foam better than 1" of solid metal or worse? If you have a 24" wide, 144" long piece of metal foam 10" thick what is it's strength in comparison to a piece of solid metal 1" thick 24" wide and 144" long?

 

Ah, it's ten times lighter, but their's ten times more of it so it's stronger!!!!

[DFINITLYDISTRUBD]

Yes, but are we talking about tensile strength by weight or by volume? Is the tensile strength of 10" of metal foam better than 1" of solid metal or worse?

Life experience (playing with styrene) would lead me to believe worse for tensile strength BUT as a core compressive strength and rigidity should be significantly better. Sadly porous metals almost* always end up weaker (porosity's a welders worst nightmare as the weld has to be ground out and rewelded as the joint will fracture at affected area and the fracture will spread rather rapidly from there)

 

Almost* qualifier applied as I cannot say with absolute certainty that there are no situations where metal may benefit from porosity (though as someone whose livelyhood is focused entirely on turning steel, stainless, copper and aluminum into machinery I gotta say it's highly unlikely except as a core used in a similar manner to styrene)

[Moontanman]

Life experience (playing with styrene) would lead me to believe worse for tensile strength BUT as a core compressive strength and rigidity should be significantly better. Sadly porous metals almost* always end up weaker (porosity's a welders worst nightmare as the weld has to be ground out and rewelded as the joint will fracture at affected area and the fracture will spread rather rapidly from there)

 

Almost* qualifier applied as I cannot say with absolute certainty that there are no situations where metal may benefit from porosity (though as someone whose livelyhood is focused entirely on turning steel, stainless, copper and aluminum into machinery I gotta say it's highly unlikely except as a core used in a similar manner to styrene)

 

I was thinking more along the lines of closed cell foam, I think the idea of foam is best shown against it's base material. The plastic Styrofoam is made if has little or no strength when it's not foamed by weight. a piece of non foamed plastic of the same width and length is much less strong than a piece of foam with the same width and length and amount of material. As for welding, I have never welded but the idea of a cast foam space craft would seem to negate a large amount of welding.

[DFINITLYDISTRUBD]

Well Moontanman (why does your name always cause a mental pic of Dracula in trunks and shades:hihi:) the bad news is that there could be no welds even with closed cells as cells would rupture and create porosity...The worse is that encapsulated (like the bubbles in styrofoam) porosity actually causes metal failure faster (a problem I haden't given proper thought before I posted my ideas for metal foam made by injecting gas) Basically the metal contracts more than the gas and the pressure causes fatigue and then in short order failure...Upon further thought on the matter and further study of my "welders bible" solid inclusions (materials trapped in the metal also weaken the structure of it.)

It's still an interesting Idea though.

 

That said hollow metal spheres could be pressed like styrene in a form and fused with resistance, ultrasonic, or microwave welding instead of steam which is used to bond styrene spheres into structural foam. Which would be super strong and light...And could easily be done here on the ground. But again welding formed components together would be difficult to impossible.

[CraigD]

We discussed this some in this nanotech thread in the watercooler.

One of the strongest materials commonly available today in strength to weight is Styrofoam.

My experience with expanded polystyrene foam – nearly all of it with model airplane wings, boat hulls, and sail/surfboards – is that while EPS is an excellent shaping and stiffening material, by itself it’s rather fragile. Though I’ve never actually tried finding or getting my own strength ratings of it, I’ve easily be snapped big (eg: 3” x 6” x 24”) blocks of it with just a little muscle force. Though some cheap model airplanes (usually “sailplane” style hand-launched gliders) are made of uncovered XPS (true Styrofoam), strong wings are always EPS covered with fiberglass and resin or similar coatings, as are all but the cheapest boats and boards. (I once had an small uncovered XPS lateen-rigged sailboat, which I had to fiberglass to prevent it from breaking up. :(

 

Note that EPS – expanded polystyrene foam – and XPS – extruded polystyrene foam, of which Styrofoam is a brand name - are significantly different materials. EPS is truly foamed – gas is injected into it – while XPS is a sort of amalgamate of blobs of foam. XPS is weaker than EPS.

 

The primary value of Styrofoam is as insulation.

Just a tiny amount of plastic when foamed will make a large volume of very strong Styrofoam.

Typical plastic foams are between 20% and 3% as dense as the solid plastic they’re made of. As noted above, I don’t know much about exact strength measurements of plastic foam. However, I suspect that, like metal foams, the relationship between strength and density in plastic foams is worse than linear – that is, 20% density XPS is less than 20% as strong as solid polystyrene, 10% density foam less than half as strong as 20%, etc.

 

In short, polystyrene foam isn’t very strong, and it takes more than a tiny amount of solid polystyrene it to make a large volume of foam.

Metal foam could only be made in zero gee in anything other than tiny quantities.

You can purchase foams of many metals in large quantities from many vendors, such as this one.

How many applications could be revolutionized by metal foam? …

I think metal foam is underutilized, largely because it’s only been available in quantity at reasonable prices for a couple of decades. However, I think it’s a slight exaggeration to describe its potential applications as revolutionary. However, “revolutionary is as revolutionary does”, and someone using the stuff to make something revolutionary is all it would take to prove my thinking wrong.

 

Polystyrene and other plastic foam, on the other hand, I would unhesitating call revolutionary, if only for its influence on surfboard making. Before it appeared, wood boards were heavy, and more significantly, took a long time to shape (or so I’ve heard – I’ve never shaped one out of anything but foam). The smaller, more buoyant fiberglass over foam (a decent board also has a wood or fiberglass stringer running its length, to lessen the chance of snapping in half) dramatically changed the style and popularity of surfing. One can make a pretty good argument that without it, sailboards would have never evolved into being. In principle, you could build one with a hollow wood core, but in practice it would be a lot of work, and result in a boat too expensive to be very popular.

 

Metal foam differs from plastic foam in a several interesting, significant ways.

• Where EPS is one of the easiest materials to work (you can cut it fast with a hot wire, and it sands quickly and easily), metal foam is so hard to work that its sellers recommend they make your pieces from spec. Cutting it makes a jagged surface, which sanding doesn’t make much better – you’re supposed to use a water jet to cut it, and melting to smooth it. It has cool art uses (the piece of aluminum foam I got to play with years ago was bought by a sculptor who wound up not using it, but leaving it lying around the school studio as a plaything), but is pretty technical stuff to build with.
• While most plastic foams spring at least somewhat back to shape when compressed, most metal foams compress smoothly, and stay compressed. According to the manufacturer’s site I read above, you can actually take metal foam of one density, and get a higher density foam by uniformly compressing it

It’s worth noting that materials such as metal honeycomb have many of the characteristics of metal foams, are in many ways superior, and have long been used in aerospace applications. Some foam manufacturers also make 2 and 3-d honeycomb, and refer to it as a kind of “regular celled” foam.

 

Foam made neither of plastic nor of metal, but of glass (glass foam is commonly called ceramic), has played a major role in spaceflight. Famously, the Space Shuttle thermal protection system uses pure silica glass ceramic tiles. Space shuttle tiles float high in water (specific gravity from 0.144 to 0.352), and a fragile enough to crush with your bare hands. People have been arguing for more than 30 years about whether their use was a good or bad idea. :)

[Moontanman]

We discussed this some in this nanotech thread in the watercooler.My experience with expanded polystyrene foam – nearly all of it with model airplane wings, boat hulls, and sail/surfboards – is that while EPS is an excellent shaping and stiffening material, by itself it’s rather fragile. Though I’ve never actually tried finding or getting my own strength ratings of it, I’ve easily be snapped big (eg: 3” x 6” x 24”) blocks of it with just a little muscle force. Though some cheap model airplanes (usually “sailplane” style hand-launched gliders) are made of uncovered XPS (true Styrofoam), strong wings are always EPS covered with fiberglass and resin or similar coatings, as are all but the cheapest boats and boards. (I once had an small uncovered XPS lateen-rigged sailboat, which I had to fiberglass to prevent it from breaking up. :hihi:

 

Note that EPS – expanded polystyrene foam – and XPS – extruded polystyrene foam, of which Styrofoam is a brand name - are significantly different materials. EPS is truly foamed – gas is injected into it – while XPS is a sort of amalgamate of blobs of foam. XPS is weaker than EPS.

 

The primary value of Styrofoam is as insulation.Typical plastic foams are between 20% and 3% as dense as the solid plastic they’re made of. As noted above, I don’t know much about exact strength measurements of plastic foam. However, I suspect that, like metal foams, the relationship between strength and density in plastic foams is worse than linear – that is, 20% density XPS is less than 20% as strong as solid polystyrene, 10% density foam less than half as strong as 20%, etc.

 

In short, polystyrene foam isn’t very strong, and it takes more than a tiny amount of solid polystyrene it to make a large volume of foam.You can purchase foams of many metals in large quantities from many vendors, such as this one.I think metal foam is underutilized, largely because it’s only been available in quantity at reasonable prices for a couple of decades. However, I think it’s a slight exaggeration to describe its potential applications as revolutionary. However, “revolutionary is as revolutionary does”, and someone using the stuff to make something revolutionary is all it would take to prove my thinking wrong.

 

Polystyrene and other plastic foam, on the other hand, I would unhesitating call revolutionary, if only for its influence on surfboard making. Before it appeared, wood boards were heavy, and more significantly, took a long time to shape (or so I’ve heard – I’ve never shaped one out of anything but foam). The smaller, more buoyant fiberglass over foam (a decent board also has a wood or fiberglass stringer running its length, to lessen the chance of snapping in half) dramatically changed the style and popularity of surfing. One can make a pretty good argument that without it, sailboards would have never evolved into being. In principle, you could build one with a hollow wood core, but in practice it would be a lot of work, and result in a boat too expensive to be very popular.

 

Metal foam differs from plastic foam in a several interesting, significant ways.

• Where EPS is one of the easiest materials to work (you can cut it fast with a hot wire, and it sands quickly and easily), metal foam is so hard to work that its sellers recommend they make your pieces from spec. Cutting it makes a jagged surface, which sanding doesn’t make much better – you’re supposed to use a water jet to cut it, and melting to smooth it. It has cool art uses (the piece of aluminum foam I got to play with years ago was bought by a sculptor who wound up not using it, but leaving it lying around the school studio as a plaything), but is pretty technical stuff to build with.
• While most plastic foams spring at least somewhat back to shape when compressed, most metal foams compress smoothly, and stay compressed. According to the manufacturer’s site I read above, you can actually take metal foam of one density, and get a higher density foam by uniformly compressing it

It’s worth noting that materials such as metal honeycomb have many of the characteristics of metal foams, are in many ways superior, and have long been used in aerospace applications. Some foam manufacturers also make 2 and 3-d honeycomb, and refer to it as a kind of “regular celled” foam.

 

Foam made neither of plastic nor of metal, but of glass (glass foam is commonly called ceramic), has played a major role in spaceflight. Famously, the Space Shuttle thermal protection system uses pure silica glass ceramic tiles. Space shuttle tiles float high in water (specific gravity from 0.144 to 0.352), and a fragile enough to crush with your bare hands. People have been arguing for more than 30 years about whether their use was a good or bad idea.

 

I'm not sure we are on the same page, how would a piece of plastic foam, say 24" wide and 96" long and 6" thick compare to the same mass of plastic 24" wide and 96" long in strength? that mass of solid plastic that wide and long could hardly hold up under it's own weight. foaming it makes it much stronger than solid mass of plastic that wide and long but only 1/4" thick or what ever the thickness of the solid plastic of that mass would be. would it not be the same principle that a flat strip of metal is no where near as strong as a piece of pipe rolled from that same strip of metal?

[DFINITLYDISTRUBD]

how would a piece of plastic foam, say 24" wide and 96" long and 6" thick compare to the same mass of plastic 24" wide and 96" long in strength?

that mass of solid plastic that wide and long could hardly hold up under it's own weight. foaming it makes it much stronger than solid mass of plastic that wide and long but only 1/4" thick or what ever the thickness of the solid plastic of that mass would be.

I think you're confusing the rigidity caused by the thickness of the material with strength...The other piece may be flimsy but I dare you to try to break it or pull it apart. I have to agree with CraigD the fluffier the foam the weaker the material.

While you are gaining rigidity (to a point) you are reducing the thickness of the walls of each bubble which means less there is less plastic thickness to pull against more air at any given point.

[modest]

I'm not sure we are on the same page, how would a piece of plastic foam, say 24" wide and 96" long and 6" thick compare to the same mass of plastic 24" wide and 96" long in strength? that mass of solid plastic that wide and long could hardly hold up under it's own weight. foaming it makes it much stronger than solid mass of plastic that wide and long but only 1/4" thick or what ever the thickness of the solid plastic of that mass would be.

 

This is called flexural strength. Values for non-foamed polystyrene and a description of flexural strength in plastics are given,

 

Flexural Strength Testing of Plastics

 

Stats for Styrofoam are the last listed group here:

 

Products

 

Density of foam is .03 g/cm^3. Unfoamed is 1.008 g/cm^3. Styrofoam is therefore 3% as dense as solid polystyrene.

 

Strength of foam is 55 psi. Unfoamed is 1900 psi. Styrofoam is therefore 0.54% as strong as solid polystyrene. To be as strong by weight as its counterpart, it would need to be at least 3%. I’m afraid Styrofoam is weaker by both volume and mass.

 

To convince yourself of this you could try to break something like a CD case in your hand. A piece of 1/4 inch Styrofoam should weigh about the same and should be a bit easier to break.

 

~modest

[DFINITLYDISTRUBD]

Just saw a company that makes metal foam on TV the other night...Ain't technological progress cool!

A link to a company that makes pretty groovy stuff from it

 

http://www.integran.com/pages/energy_noise_absorbing_metal_foams.html?gclid=CPbhqbqNlrQCFYKK4Aod_AgAIg

[Mountain]

I think one of the problems in the thought process here is that metal is strong and yes it is, but what makes it strong no longer applies when you foam it. The crystalline structures aligned within the metal is what gives it strength and hardness, by foaming you remove this structure and therefore the strength to weight ratio that you are familiar with.

 

I have myself had much the same thought process as you on the uses of light weight foamed materials for use in engineering. I realized very quickly that metal was not a good candidate, or at least on it's own anyway. The idea of foaming metal is somewhat tricky as well. I finally wound up in the region of creating foamed ceramic by adding ironically enough styrofoam to it in the form of very small pellets. When heated the foam pellets become gas leaving a foamed ceramic. Then use your metal to melt into your ceramic in layers. A similar process is used to create ceramet, a ceramic aluminum armor plating.

 

Have you done any research on aerofoam? An intensely fascinating subject of study, for me at any rate.

Edited September 8, 2013 by Mountain

[CraigD]

Have you done any research on aerofoam? An intensely fascinating subject of study, for me at any rate.

I read about aerogel years ago, and bought a little sample of silicon aerogel as a tourist souvenir a few years ago. Though amazingly strong for its density (which is only a little greater than air), letting people handle it at parties over the next few months crushed and broke it into pieces. It’s translucent, and feels like fine-grained Styrofoam (polystyrene).

 

Like Styrofoam, silicon aerogel is a good insulator. I see from its Wikipedia article that it can be made much more transparent than my little sample, and has been used experimentally in windows and skylights.

 

Many spaceflight enthusiasts who hadn’t heard of it before got acquainted with its use a sample-collecting material after the big (for science) news crash of the Genesis solar wind sample return spacecraft in 2004.

[cujet]

I had some foamed aluminum pliers many years ago. They were nearly useless, but they were light. A better design would have used a tubular aluminum set of handles at roughly the same weight, but significantly stronger.

 

Besides the fact that the pliers bent readily on typical loads, they yielded suddenly (broke in half) with only modest pressure. Ever since then, I've avoided foamed aluminum, trending towards carbon and Kevlar composites and/or conventionally manufactured metals.

[Moontanman]

I read about aerogel years ago, and bought a little sample of silicon aerogel as a tourist souvenir a few years ago. Though amazingly strong for its density (which is only a little greater than air), letting people handle it at parties over the next few months crushed and broke it into pieces. It’s translucent, and feels like fine-grained Styrofoam (polystyrene).

 

Like Styrofoam, silicon aerogel is a good insulator. I see from its Wikipedia article that it can be made much more transparent than my little sample, and has been used experimentally in windows and skylights.

 

Many spaceflight enthusiasts who hadn’t heard of it before got acquainted with its use a sample-collecting material after the big (for science) news crash of the Genesis solar wind sample return spacecraft in 2004.

 

Sounds like it would be great to insulate a greenhouse with...

[DFINITLYDISTRUBD]

Sounds like it would be great to insulate a greenhouse with...

Indeed it (other than expense) would make a right fine insulator for greenhouses....especially if the plants are sensitive to direct sun. Being translucent instead of outright transparent would definitely help prevent sunburned plants....these days everything seems to be sensitive or more likely I suspect, the sunlight reaching the surface of the earth these days is stronger than it used to be. In all of my years here in wine country I've never seen so many scorched vines as in the past five. What's wrong with the following picture?