^ If memory serves it is a ceramic so I would think it would shatter under stress rather than bend. (Where on earth is Timo when you need him.) And Rack of T'Pol, we are not really talking about a car window here (which is basically what you keep describing). This is about transparent aluminum and why did it shatter in the crash. We also need to remember that the E-D's windows would not normally be subjected to that much stress. Basically it would need to be able to hold pressure and keep a stray micrometeorites from penetrating if one slipped passed the deflector or shields. The amount of stress put on them in a crash like that would be way beyond their most stressful day in interstellar space.
Yeah, the stuff definitely is a ceramic (read: it consists of molecules made of metals that have been oxidized into being chemically rather inert, with those molecules arranged in a rigid crystal lattice through medium-strength EM interaction - an ionic crystal). It's very brittle, but like most ceramics, it takes compression stresses well - so it is a good choice for the outer layer of armored glass. In order not to shatter, it needs to be backed up by a flexible polymer inner layer, though. And Wikipedia informs us that it's also backed up by a layer of ordinary amorphic glass in the armor application. AlON is apparently more crystalline than yer average quartz (that is, the crystalline order stretches across greater areas - but neither material consists of a single giant crystal, at least not with current manufacturing techniques), which helps against shattering. Both AlON and quartz are superior in this respect to ordinary glass, which isn't crystalline at all (glass may actually consist of the same molecules as quartz, yet any internal order only stretches across a couple of molecules). Due to lacking that crystal order, ordinary glass is less brittle, but also less capable of resisting compression. Still, all these materials become armored glass the same way: by being the compression-absorbing layer, backed up by a flexible layer. AlON can do its job with a single pair of layers, while ordinary glass and its polymer backing need to be stacked dozens of pairs high in order to stop bullets. That means more weight and poorer transparency... A diamond would be even better, because it is organized in a rigid lattice - but not in a lattice of molecules. Instead, all the atoms there latch individually on to their neighbors with very strong EM forces, so the entire diamond is actually a single molecule of carbon (in the ideal case). Something like that would be very difficult to achieve with a substance that contained appreciable amounts of aluminum or any other metal: the metal would want to chemically react with specific types of fellow substances, and the atoms would no longer individually latch on to their companions, but would want to do that ionic-crystal thing with the weaker forces. And if the stuff were mostly aluminum, it would want to be a metal, and metals have the defining quality of not letting visual range EM radiation through - the way the metal atoms hold on to each other, through sharing their electrons in a great group orgy, dictates that the EM radiation is always absorbed. Yeah, AlON is a substance that could perhaps be called "transparent aluminum". But it's better called "transparent alumina" or "transparent alumina&aluminum nitride" because the aluminum there exists in those chemical forms, bonded to other atom types. Depends on who's speaking and listening, though. The company marketing the stuff (or the Star Trek entity manufacturing those starship windows) is definitely not obligated to speak the exact jargon of 20th-21st century chemists! Indeed, there may be no such reason even in face of the ST:GEN evidence. The window broke, yes - but it appears that the hull broke as well! At least we see lots of broken wall when Picard rummages through his possessions. STXI is more explicit about this sort of thing: we see the bridge ceiling, wall and window/monitor surfaces all break in equal cracks when the ship fights the black hole. Timo Saloniemi
But I go back to what I know...Polycarbonate (Strong), Laminated Polycarbonate (Very strong), and some kind of space-age, clear material...Yes, possibly laminated transparent aluminum (Strongest). So I've got to believe that in TNG's time, the windows would be as strong as the hull. And certainly not prone to "Shattering". Blowing completely out of their frames...possibly? Because that would be the weakest area (Where the windows are glazed into the hull), but not shattering in the same way we think of glass.
Why? Because window technology has improved? But the technology of opaque materials would have improved as well, perhaps keeping those ahead in the durability game. And I think shattering is a viable failure mode for a dome like the one atop the E-D bridge, even if said dome is made of thick steel. There'd be compression stresses from multiple directions against the dome, best relieved if a crack started to develop at the top/middle and then spread outwards. Timo Saloniemi
Because if those windows were not just as strong as the opaque bits of the hull, they should have opaque covers that could be moved into place in the event of combat/space anomaly that is distorting the hull/other source of potential hull breach. They are just a huge weak point otherwise.
^ Would the window being a "huge weak point" be a problem with a ship capable of sealing any breach in the hull with a force field? Any sign of a sudden pressure change and the safety systems would kick in to compensate. And even if something were to happen to the safety system, it would take hours for the air to vent into space through a crack. Anyone trapped in a breached area would have plenty of time to escape before they suffocated. And I think we are also over-thinking the necessary strength of the outer hull. NASA sends astronauts into space all the time with nothing more than a few inches between them and the vacuum of space. On the Enterprise warp stresses are countered by the inertial dampeners and the structural integrity field helps unify the vessel when in flight. Excess radiation, debris and energy anomalies are blocked out by the navigational deflector and the shields. The structural stability of a window would be no more of a threat on a starship than one would be on an airplane or a ocean vessel. And again, I would like to point out that a saucer crash would produce stresses on the hull that it would never encounter in space. And if you were to hit the surface of a planet with that much tonnage and speed behind you I doubt any of you would finish with all your windows intact either.
The softer something is, the more impact-resistant it is, due to its flexibility. It's also easier to scratch. Take watch lenses. The venerable, shatterproof Casio G-Shock - plastic lens. Can take a mallet to it, no problem. However, the lens is recessed below a protective ring around the edge, to prevent you from lightly brushing the face up against a brick wall or something and scratching it to bits. On the other end of the spectrum, we have sapphire watch faces. A rockwell hardness just below that of diamond. Almost completely scratchproof... but a solid blow will turn it into tiny fragments. The compromise - watch faces using normal 'mineral crystal', which is the watch industry's fancy name for... glass. Heat-treating it can make it harder and more scratch resistant, leading to industry terms for such manipulated material, such as Seiko's 'hardlex'. Anyway, softer is more forgiving to breakage but easy to mar, and harder is scratch-resistant but more brittle. In any case... it really doesn't matter what the material was in Generations. They have structural integrity fields for that sort of thing. The question we should focus on is this: why have a friggin' skylight on the bridge in the first place? How come we never saw Picard look up at the starry sky through the little window over his chair at any point in the series prior?
Indeed, while the skylight could be nice and practical for many reasons, we also have "Justice" where LaForge needs to get a clear view of the outside - and leaves the bridge to reach a porthole! Granted that the target dead ahead wasn't visible through the skylight, which points up, but surely Picard could have tilted the ship a little? Or would the god have interpreted that little bow as a hostile move? Also, there are instances where the ship bathes in bright exterior light, yet none seems to come from directly above. In vacuum conditions, that's probably to be expected, if the light source isn't positioned in the exact direction of the skylight. But one would expect interactive light whenever the ship is in a brightly glowing nebula. So, perhaps there is no skylight there. Perhaps there's just solid, opaque hull. Which happens to consist of a transparent core with opaque surface finish, and the crash shattered both the inner and outer surfaces, exposing the equally shattered core... Timo Saloniemi
Well, no, that was most of the time TV budget restrictions. In Generations the sets were much better lit, matching the VFX exterior shots.