Transparent Aluminum or Glass?

[Shikarnov]

My wife and I were watching Generations yesterday evening, when I noticed something I hadn't before -- during the saucer crash sequence, there are scenes which show the outer windows shattering into crew quarters... And then, later, the bridge dome appears to be broken in a very glass-like manner.

I'd always thought (maybe assumed?) that the Enterprise's windows were all made from transparent aluminum. Should I just consider my earlier assumption to be wrong, revise my understanding of transparent aluminum to include properties which allow it to shatter, or just chalk it up to yet-another-screwup from B&B?

TIA,

Z

 

[Gagarin]

That scene, the crash, only revised my opinion of the TNG creative team.

 

[sojourner]

Bad scene is bad.

 

[Timo]

To be sure, if something is transparent, it's likely to crack, aluminum or not. Those things go hand in hand: transparency is due to the substance having a rigid arrangement of atoms, with covalent bonds between them, and without the characteristically metallic "sea" of electrons wallowing between positive nuclei. That "electron sea" is what makes metals strong and flexible and unlikely to crack - but it's also something that necessarily turns the substance opaque.

It would appear that at least one window on the E-D was more likely to crack than the ship's opaque wall sections were. Whether that should count as a "weakness" is a question of taste: the only time we see such shattering is when the saucer section is written off anyway, and quite possibly several other (opaque) parts of the hull failed earlier, more easily and more catastrophically.

Timo Saloniemi

 

[Shazam!]

Data says that the windows are transparent aluminum in the series.

 

[USS Jack Riley]

To build on Timo's statement, I actually brought this question up years ago (while TNG was still on the air). To give you a better frame work as to the time period involved, I asked the question on a Trek board on Prodigy (RIP)!!! Essentially I asked the same question - does transparent aluminum bend (like a metal) or shatter (like glass). At the time, we had not seen any evidence one way or the other (that I can recall).

The answer (as best as I can remember from that time) was that the transparency was due to the crystalline structure of the transparent material. This made it prone to cracking and, given the right amount of force, shattering. Similar to plexiglass being plastic, but still shattering if someone applies enough force to it (e.g., plexiglass in flight helmets can crack if it strikes the canopy with enough force).

Just my $0.02 based on foggy recollections of a simlar discussion way back when.

 

[Londo]

That skylight at the very top of the ship, whatever its construction, would seem likely to be the last window in the whole saucer to break given the way the landing happened.
I guess a bird dropped on it!

 

[Tom]

Just an FYI this topic is covered in RLM's reveiw of generations:

http://www.youtube.com/user/redlettermedia?blend=1&ob=4#p/u/49/azSh47-oRPI

At the 5:25 mark

I love this guys review of the TNG Movies.

 

[SpyOne]

...or just chalk it up to yet-another-screwup from B&B?

That.
IMO.

 

[bryce]

I guess it's also possible that whatever nanotech self-repair abilities that the transparent aluminum (assume that is indeed what Trek starship windows are made out of) had in nuTrek (the front 'windscreen" cracks in Star Trek started to heal up after the ship was out of danger) were knocked offline when the ship crashed.

Perhaps the self-repair abilities require an external input of power/energy -- or perhaps they don't, but they just can't keep up in the strain of an event like the crash in Generations or the gravitational(?) stresses on the ship in Star Trek...???

I'm gonna assume that it takes a HELL OF A LOT MORE stress to crack transparent aluminum than it does to crack glass...

 

[Tiberius]

So the metal has cracked? SO what. Metal does that. behold:

http://squarezero.org/blogpix/2007/crackXL.jpg

http://www.hotrodders.com/gallery/data/500/medium/cylinder_crack.jpg

http://www.kellyroofing.com/images/rep.maintenance/metal/torn_cracked_broken.jpg

The difference between bending or cracking is down to the force that is applied. If the force is a big sudden force, the metal will crack. If it is applied slower, the metal will bend.

it's kinda like clay. If you push the clay slowly, it will bend. If you hit it hard, it will snap off.

 

[Timo]

...Of course, clay may well be aluminum. Aluminum oxide, that is.

Indeed, most things containing aluminum are very brittle. It's only the unnaturally pure metallic aluminum (with its corrosion-resistant oxide surface) that we industrially produce that gives us the idea that stuff with aluminum in it might be somewhat like iron or steel in its properties. But as said, that sort of pure aluminum is likely to be opaque to visible light under all conditions. To make it transparent means turning it into something more like glass or clay. In ST4, we explicitly see that transparent aluminum is some sort of a molecule that contains a lot more than just aluminum. It may be a polymer, with just one unit shown, or then some sort of a fluid that just flows very slowly. It's a bit unlikely to be a crystal with its unit cells shaped like that, although I guess that's not completely impossible. Based on that ST4 image, what it can never be like is the sort of pure aluminum we see in sheets and spars and profiles in today's world...

Timo Saloniemi

 

[publiusr]

When I think of transparent Aluminum, I don't think of the real materials with the grainy look to them, but real aluminum metal doped with some kind of science-fictiony trans-periodic element or something.

 

[Rack of T'Pol]

Four things...

1) Remember in the movie, First Contact, when Pichard shows Lilly earth from Enterprise? He commented that there is nothing between the ship and space other than the force field, which comprised the window...So, no need for "Transparent" anything.

2) "Transparent Aluminum" is one of the reasons I don't care for the movie The Voyage Home. They didn't have to have clear walls for the whales...Standard bulkheads would have done just fine...They needed the transparency because it was a movie, and needed to show the whales inside the ship.

3) When you make anything "Transparent", it has to be thicker than say, just sheet metal, because it's inherently not as "Impact Resistant". But then again, you can't see through sheet metal...So, we're back to something strong, yet see-through...

4) I used to be what was called a "Lexan Product Manager" for a national chain (About 350 locations) of "Plastic, Rod, Sheet and Tube" distributors. "Lexan" as many of you may know, is General Electric's version of "Polycarbonate" sheet. You can literally hit an 1/8 inch thick sheet of polycarbonate with a sledgehammer, and not do any damage. Polycarbonate is 25 times stronger than acrylic, or using the brand name, Plexiglass. This is because polycarbonate is much softer than acrylic...Which, makes it more forgiving to brunt-trauma (But also created the problem with cleaning the polycarbonate...As many of you already know, but never really thought about it, you can clean glass with a paper-towel all day long and never scuff it up...But if you clean acrylic with paper towel over and over, you will eventually create "Mars" in the acrylic, resulting in a cloudy appearance...And with polycarbonate, you can create these mars with far fewer cleanings, because it is so soft...As a matter of fact, the instructions call for using "Soapy water and a new, cloth towel, to lightly clean polycarbonate (Thus resulting in longer life for the window.) Also, G.E. manufactures a product called "Mar-Guard"...Polycarbonate, as strong as standard polycarbonate, but with a coating that is very hard (And clear, of course), which makes for a better choice in a high-cleaning window area...But at a stiff price too...If memory serves, about 3-4 times the cost of standard polycarbonate, 6-8 times the price of standard acrylic and 10-15 times the cost of standard class. But, for instance, in a prison setting, the extra cost pays for itself with less break-outs, or much less important, less vandalism by the inmates.

Now...There are many different applications for polycarbonate, where the end-user is happy to give-up cleaning ability for safety...For instance, we had a large customer who made tool cleansing units. If they used glass, or even acrylic, shards would spin-off of the tools and bust the glass or acrylic very quickly over it's use-life. So, we got them to use Lexan (Polycarbonate) and in this case, Mar-Guard. And, to take the example to an extreme, they "Cold-Formed" the Mar-Guard (Take a sheet of 3/8 thick and put it in a press, and "Cold-Form" bends instead of trying to glue edges together in the cleansing equipment...Something that was not encouraged by G.E. as many of you may guess, because the hard coating of the "Mar-Guard" would crack over time. (More on that in a moment) but, this was worth the risk/changing of the clear guards in the field, as was proven over years and years of using the polycarbonate with the hard, Mar-Guard finish and the customer finding that it was still cost-effective...Less changes in the field...Simple as that.

Now, all of the above polycarbonate examples I've listed concerns simple, different thicknesses of polycarbonate sheet...From films (Which you still could not tear with your bear hands) down to 10 mils, all the way up to sheet that is 1/2 inch thick. Differing thicknesses needed for differing applications. When I said above, that you could not break 1/8 inch thick polycarbonate with a sledge-hammer, I meant it...But, if you use a pick, you can eventually create a "Tear" in the polycarbonate sheet and eventually break through that sheet of polycarbonate (Or, use a pair of scissors to start a cut in film, and then easily tear that film the rest of the way). This is because polycarbonate is "Notch Sensitive"...Meaning: Once a notch is created in any thickness of polycarbonate, a breach, or hole, will appear, in that specific spot, after constant bashing with a heavy pick...Or, like I already said, start a cut in polycarbonate film with scissors and then easily tear it the rest of the way...So...

G.E. came up with the idea of laminating sheets of polycarbonate together to create strength...Both against physical abuse and in the use for bullet-resistant windows. Because, it's relatively easy to create one notch in a polycarbonate sheet, but if you had 3 sheets, lamninated together, to equate a 3/8 inch sheet, it was untold times more strong than one sheet of 3/8 inch thick polycarbonate...So much so, that...

I've got one of my old business cards, which were made from 10 mil Lexan film...Which made for easy presentations of the strength of polycarbonate...Just hand your business card to a customer and ask him or her to try to tear it, bare handed...As I am sure you've guessed, they could not tear it...Thus, a handy way to teach a customer about Lexan...But, I would then teach the customer about Lexan being "Notch Sensitive" by cutting my business card just a bit, and then letting the customer tear the business card in half, at that "Notch Point" very easily (And please note...This job was a good 15 years ago, and my info may be a bit dated)...This business card of mine is encased in a 1 1/4 thick sheet of laminated polycarbonate...5 layers thick...The inside and outside of the laminated sheet being 1/8 inch thick, with a "Mar-Guard" coating...Then two sheets of 3/8 inch thick, and one sheet of 1/4 inch thick...Making the total thickness of 1 1/4 inch. They did this, again, because polycarbonate is "Notch Sensitive"...Meaning, if a bullet hit a sheet of 1 1/4 inch thick standard polycarbonate, once that bullet got through the surface, it then traveled quite easily through the entire 1 1/4 inch thick sheet...But by laminating it, the bullet now has to break through 5 layers...So...Again, this piece of 1 1/4 inch thick polycarbonate, with my business card in the middle, was shot with a 44 magnum pistol from 15 feet. The bullet, literally looking like a marshmallow inside Jello. Yes, it went through the first 1/8 inch thick piece of polycarbonate, but stopped in the middle...Literally, leaving the other side absolutely flat, because the layers of polycarbonate stopped the bullet. A pretty cool example of the strength of Lexan, I am sure you'll agree?

We used to go to prisons and put on displays. We'd have the officers shoot our differing thickness of laminated Lexan, just to prove to them how tough it was by stopping their bullets cold...We would also line-up the inmates, with a pick, and tell them to "Have at it, passing off the pick to the next inmate when you get tired of swinging it", and offering a carton of cigarettes to the first inmate to bust through the sheet...For these applications, we'd use a 3 laminate, 3/8 inch thick sheet, to lower the cost because it would be inside a prison where guns are not allowed, but inmates abuse the windows, as they abuse everything (And differing thicknesses, laminated or not, had different "Safety Ratings" based on the minimum amount of time, as guaranteed by General Electric, it would take to bust through the window with any tools short of power saws and whatnot). The same prison would use 1 1/4 inch thick Lexan, called "Lexguard" for windows in guard towers where gun-fire might come into play...

The same 1 1/4 inch thick, 5-laminate Lexan is also used by lots of convenience stores, because if it can stop a 44 Magnum round, a 44 Magnum being the most powerful of all handguns, it will stop shots from any hand gun...Where the bullets could fly straight through thick glass or acrylic or even thick polycarbonate, when it's not laminated. (The same thing can be achieved by laminating anything to create differing thicknesses, with differing totals of sheets that make up the substrate...In other words, "Notch Sensitive" is universal in all products.)

So...After this long-winded post on what I am sure is WAY more information than you ever needed about, from weakest to strongest, glass, acrylic, polycarbonate and sheet metal...I'll just say "Transparent Aluminum" is a bit of an oxymoron. All it needed to be was, like I already stated, preferably a standard bulk-head, and if they just HAD to have something see-through, just laminate it X amount of times to get Y amount of strength..."Six inch thick transparent aluminum", as I think I remember the thickness being in the movie, could be reduced to say, 2 inches thick if you laminate it ("Transparent Aluminum", or polycarbonate)...Down to say, a 3/8 inch thick, non-transparent, bulkhead...Made out of something a LOT more strong than sheet metal in Trekdom, of course.

 

[Albertese]

...

I'll just say "Transparent Aluminum" is a bit of an oxymoron. All it needed to be was, like I already stated, preferably a standard bulk-head, and if they just HAD to have something see-through, just laminate it X amount of times to get Y amount of strength..."Six inch thick transparent aluminum", as I think I remember the thickness being in the movie, could be reduced to say, 2 inches thick if you laminate it ("Transparent Aluminum", or polycarbonate)...Down to say, a 3/8 inch thick, non-transparent, bulkhead...Made out of something a LOT more strong than sheet metal in Trekdom, of course.

As I recall in the movie, they used the 6" Plexiglass in the BoP, not transparent aluminum. The formula for the TA was given to to the plant manager for his own development in payment. Recall that it would "take years to ... something, something... the dynamics of this matrix .. something..."

Also, the TA was advertised by Scotty to be able to do the same job as the 6" plexi at only 1" thickness.

But you're right. There's no need for it to have been a clear material except that it was a movie.

--Alex

 

[Timo]

1) Remember in the movie, First Contact, when Pichard shows Lilly earth from Enterprise? He commented that there is nothing between the ship and space other than the force field, which comprised the window...So, no need for "Transparent" anything.

Of course, that opening was

1) never stated to be a window
2) equipped with its own control console
3) in a room apparently only accessible through Jeffries tubes

so odds are that it wasn't a window, but rather some sort of a utility orifice that wasn't meant to be opened for sightseeing, but could be used for that if the user needed to convince a pretty primitive of the fact that she wasn't in Montana any more.

2) "Transparent Aluminum" is one of the reasons I don't care for the movie The Voyage Home. They didn't have to have clear walls for the whales...Standard bulkheads would have done just fine...They needed the transparency because it was a movie, and needed to show the whales inside the ship.

But they didn't use transparent aluminum for creating the walls. As stated above, they used transparent aluminum for paying for the walls.

The walls could have been solid steel or whatever - but plexiglass was probably the best choice, as it was strong enough, and cheap enough, yet also light enough, and the transparency was a nice bonus for monitoring the status of the cetacean passengers.

That is, there'd probably have been polymer constructs that offer better strength/cost or strength/weight ratio, but obtaining those might be much more difficult than obtaining simple plexiglass... And the industrialist most likely to accept transparent aluminum as payment would be one already in the business for transparent materials!

3) When you make anything "Transparent", it has to be thicker than say, just sheet metal, because it's inherently not as "Impact Resistant".

That's a bit too categorical IMHO. You can compensate for the lack of metal flexibility by having appropriately greater overall strength, and obtain better impact resistance that way. A sheet of diamond could well be much thinner than the equivalent sheet of non-transparent carbon, or of non-transparent carbon-based material. That is, if we're talking about monocrystalline diamond more than half a centimeter thick - at that point, immense rigidity would probably start to offer better protection than great flexibility.

The thing is, you can't turn a metal-like substance transparent without making it very much un-metal-like, which makes the above sort of comparisons rather meaningless. There's no way to turn steel transparent to visible light, for example, even though one can construct transparent materials that contain iron and carbon and chromium and nickel just like stainless steel does.

Timo Saloniemi

 

[Rack of T'Pol]

...

I'll just say "Transparent Aluminum" is a bit of an oxymoron. All it needed to be was, like I already stated, preferably a standard bulk-head, and if they just HAD to have something see-through, just laminate it X amount of times to get Y amount of strength..."Six inch thick transparent aluminum", as I think I remember the thickness being in the movie, could be reduced to say, 2 inches thick if you laminate it ("Transparent Aluminum", or polycarbonate)...Down to say, a 3/8 inch thick, non-transparent, bulkhead...Made out of something a LOT more strong than sheet metal in Trekdom, of course.

As I recall in the movie, they used the 6" Plexiglass in the BoP, not transparent aluminum. The formula for the TA was given to to the plant manager for his own development in payment. Recall that it would "take years to ... something, something... the dynamics of this matrix .. something..."

Also, the TA was advertised by Scotty to be able to do the same job as the 6" plexi at only 1" thickness.

But you're right. There's no need for it to have been a clear material except that it was a movie.

--Alex

Errr...Yeah, I meant 6 inch thick acrylic...Not transparent aluminum.

 

[AstroSmurf]

I thought of something while reading through the thread. What if the windows were shattering because of torsional stress and not a direct impact? We are talking about a very large constructed mass skipping across a planet's surface here. From the matte painting showing the aftermath of the D's massive belly-flop, it looks like she plowed through several miles of forest before friction stopped her forward momentum.

It is really just simple physics so let me break this down for you: This is not a solid mass. We are talking about a beam and truss construction here. (Don't get me wrong. That is still A LOT of mass even with her honeycombed construction.) As the saucer plows along the ground, her ventral surface would be pushed backwards while her inertia would still be pushing the rest of her forward. The stress on the inner support system would be enormous. (And without the structural integrity field keeping her together we would be looking at a debris field instead of a simple slide out.) It would no doubt warp her space frame and buckle the outer hull plating. So instead of a transparent aluminum window housed in a nice plum window frame, we have brittle transparent aluminum being squeezed and twisted by the outer hull. To relieve the pressure, either the frame is going to give or the window is. My bet is on the window.

 

[Rack of T'Pol]

I thought of something while reading through the thread. What if the windows were shattering because of torsional stress and not a direct impact? We are talking about a very large constructed mass skipping across a planet's surface here. From the matte painting showing the aftermath of the D's massive belly-flop, it looks like she plowed through several miles of forest before friction stopped her forward momentum.

It is really just simple physics so let me break this down for you: This is not a solid mass. We are talking about a beam and truss construction here. (Don't get me wrong. That is still A LOT of mass even with her honeycombed construction.) As the saucer plows along the ground, her ventral surface would be pushed backwards while her inertia would still be pushing the rest of her forward. The stress on the inner support system would be enormous. (And without the structural integrity field keeping her together we would be looking at a debris field instead of a simple slide out.) It would no doubt warp her space frame and buckle the outer hull plating. So instead of a transparent aluminum window housed in a nice plum window frame, we have brittle transparent aluminum being squeezed and twisted by the outer hull. To relieve the pressure, either the frame is going to give or the window is. My bet is on the window.

Again...Going back to the book I wrote about (From strongest to weakest) some form of super sheet metal (Transparent or not), sheet metal, polycarbonate (Lexan) (You can shoot it with a 44 magnum and all it does is absorb the bullet (Because it IS soft and forgiving), acrylic (Plexiglass) (A 44 magnum shot would probably sail right through a six inch thickness piece (Because it is harder than polycarbonate, and therefore has no give), and glass (Which as we all know, is not very tough...It shatters very easily)...

And then the fake "Transparent Aluminum"...And none of us know how that would react to the abuses I've listed for Lexan.

So, I've got to believe, that by the time Trek is taking place, we will have invented a soft (Bends but does not break, takes bullet shots, but just absorbs them...And maybe the same thing with fazer shots) type of clear plastic...

Think Kevlar (Or bullet-proof vests). The Kevlar is very thin but still stops various weapon rounds. This is because we're not trying to make it clear. (When you want to make anything clear, its inherent strength is compromised, and you need more of that material to make it as strong as an opaque material.) For example, to do the job of 1/4 inch thick Kevlar, you would need 1 1/4 inch laminated Lexan...Thus, weight becoming a huge problem.

My guess is the windows on star ships are a combination of glass (On both surfaces, so it's easily cleaned without creating a "Cloudy surface" after rubbing it over and over, with polycarbonate in the middle (Laminated, so it can stop any bullet fired by any gun, but also fazer shots, just like the hull can take.

My guess as pertaining to the original poster's question...

Mistake by production. If in fact some of the windows broke while crash landing, they only included that because they were clueless about the benefits of laminating any given substrate (Glass, polycarbonate, acrylic, etc...). Frankly, there is no reason to believe that the windows were weaker than the hull.

 

[JarodRussell]

Transparent Aluminum exists today: Aluminium oxynitride. It's harder than glass. But that also means that it breaks instead of being deformed.