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All that is needed is to make the tempered simular to a windshield glass which has a tough plastic with in the layers to keep the glass intact if it cracks and fractures.
Light pipes come in several flavors from a reflective tube with the hard lens on the outer with the diffuser on the opposite end.
The other use a ridgid plastic to make the path more of a means to isolate the chance for a void in the system to cause air leaks.
With the last being smaller lenses with flexible fiber optics to bring light into more places.
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I think I posted this link in another thread: Scientific American: How is tempered glass made?
Tempered glass is about four times stronger than "ordinary," or annealed, glass. And unlike annealed glass, which can shatter into jagged shards when broken, tempered glass fractures into small, relatively harmless pieces. As a result, tempered glass is used in those environments where human safety is an issue. Applications include side and rear windows in vehicles, entrance doors, shower and tub enclosures, racquetball courts, patio furniture, microwave ovens and skylights.
To prepare glass for the tempering process, it must first be cut to the desired size. (Strength reductions or product failure can occur if any fabrication operations, such as etching or edging, take place after heat treatment.) The glass is then examined for imperfections that could cause breakage at any step during tempering. An abrasivesuch as sandpapertakes sharp edges off the glass, which is subsequently washed.
Next, the glass begins a heat treatment process in which it travels through a tempering oven, either in a batch or continuous feed. The oven heats the glass to a temperature of more than 600 degrees Celsius. (The industry standard is 620 degrees Celsius.) The glass then undergoes a high-pressure cooling procedure called "quenching." During this process, which lasts just seconds, high-pressure air blasts the surface of the glass from an array of nozzles in varying positions. Quenching cools the outer surfaces of the glass much more quickly than the center. As the center of the glass cools, it tries to pull back from the outer surfaces. As a result, the center remains in tension, and the outer surfaces go into compression, which gives tempered glass its strength.
Glass in tension breaks about five times more easily than it does in compression. Annealed glass will break at 6,000 pounds per square inch (psi). Tempered glass, according to federal specifications, must have a surface compression of 10,000 psi or more; it generally breaks at approximately 24,000 psi.
Another approach to making tempered glass is chemical tempering, in which various chemicals exchange ions on the surface of the glass in order to create compression. But because this method costs far more than using tempering ovens and quenching, it is not widely used.
The last sentence mentions chemical tempering. That's used for glass of smartphones. The glass is very thin, as thin as a sheet of plastic. Normal glass would break as soon as you touch it. Glass must be tempered to not break when it's that thin. But plastic will scratch, so not useful for a touch screen. Flip phones had plastic screens, which they could get away with because you never touched the display. But with smartphones, you touch it constantly. With plastic, as soon as you run your fingernail across it, you scratch it. Sure, you could use polycarbonate which is harder so scratch resistant. But tempered glass is so hard that fingernails or precious metal jewellery won't scratch it. But steel can still scratch it, and some platinum alloys, so please don't test that.
Plastic is not necessary for tempered glass. Glass doors of retail stores such as those in a mall are tempered glass. Those glass doors don't have plastic. Although tempered glass is strong and hard, enough force will still break it. When tempered glass breaks, the tension that makes it tempered will cause it to shatter. You don't want a car windshield to spray glass over the driver and passenger(s), so plastic is there to hold the pieces. Again, that plastic is only in car windshields. Other uses for tempered glass don't have that plastic.
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The glass Spacenut mentioned is more properly termed "safety glass". There are two panes of ordinary glass, bonded together by a thin layer of plastic sheet between. When broken, most (not all) the fragments adhere to the plastic, which limits greatly how rapidly and far the shards can spread. If you look at a pane of auto glass (windshield or side windows, makes no difference), you will see the name "safety glass" somewhere, in any installation from the factory. Because it really works to save lives, it is a legal requirement to use it for all transparencies in production cars and trucks.
The "tempered glass" that Robert describes was also known as "frangible glass" in the defense industry about 4 decades ago. We used it for the inlet port cover of the ASALM-PTV ramjet, which featured an integral booster. Tempered/frangible glass typically shatters into chunks of dimension comparable to the part thickness, when you damage it in some way. An explosive charge did that in ASALM-PTV, to open-up the inlet after the booster burn.
Whether thermally or chemically tempered, the "trick" is to have surface in compression with interior in tension, as Robert describes. That is what makes it stronger, and also what makes it vulnerable to certain kinds of damage, such as the machining or scratching that Robert describes. We simply overstressed it in ASALM-PTV with the shock wave of the explosive charge at boost burnout, triggered by the suddenly-decreasing booster pressure. Because the entire part shatters into chunks, the inlet is fully opened in an instant, and flowing full air an instant after that.
The port cover in ASALM-PTV was an inch thick, and domed a bit inward into the combustor for arch strength. It had to hold 3000 psi worth of hydroburst pressure, and had a thin fiber-reinforced rubber membrane on it for heat protection against the hot booster gases for the 3 seconds of booster burn. The ramjet nozzle was big enough to have passed the intact port cover, but never had to. Every one we ever tested shattered into 1-inch chunks virtually instantaneously. After hundreds of ground tests, it worked perfectly in 7 flight tests.
By the way, that final sentence in the previous paragraph is EXACTLY why a successful feasibility demonstration does NOT mean you have a technology that is ready-to-apply! You simply have to do the necessary verification testing and design development/refinement. That takes time and money. Ground tests are cheaper than flight tests. You can do more of them, enough to have some real confidence that you got your design right.
GW
Last edited by GW Johnson (2021-07-10 12:01:53)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Evan Plant-Weir
https://www.youtube.com/watch?v=qCbI7-qer3k
Scientists figure out how to produce metallic iron on Mars
https://www.mining.com/scientists-figur … n-on-mars/
PAINFUL TRUTH: Wonder of Mars still remains
https://www.aldergrovestar.com/columns/ … l-remains/
Colonization may not be imminent, but travel to Mars is
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