I was recently watching a guy blowing glass in his home based glass studio and every time he ‘blew’ an object there was a trailer piece that would be left between the object and the pipe. He would snip it off and throw it on the floor. I picked one of these leftovers up and it was about half a millimeter thick piece of string about 6 inches long. And son-of-a-gun the damn thing could bend. It was cooled and still bendy.
The guy said you can bend it all around but do not touch the ends to one another it will shatter. So being the big kid that I am I of course bent it until the ends touched. And poof, it burst into a cloud of glass powder. idiot I know.
So my question is this: How the hell was that glass able to bend? And why?
As a kid I used to do lab work in my basement, including glass blowing. I have R. L. Strong’s book on Experimental Technique, and it’s got whole chapters on glassworking, and on making fine threads as you describe.
You have to realize that the relative bending of a piece less than 1 mm in diameter and several inches long is pretty small – I mean that the relative deflection for the thickness and overall length. In addition, since the stresses increase rap[idly with thickness, relatively thin pieces will bend through an even larger range than you would think – more in proportion to their size than a larger piece scaled down.
Of course, if you exceed the tensile strength of the glass the whole thing will shatter – as you found.
All glass is flexible to an extent but you have to stay within the elastic limits. If you make a thin strand like fiberglass a sharp bend doesn’t stretch or compress the glass much on a local level. It’s no different than any other material. A guitar string and a girder on a building as made out of the same stuff (or close enough for this discussion) . they have the same elastic qualities but the girder is more rigid by virtue of its thickness.
Hard to explain verbally but when you bend something you are stretching the part on the ouside of the bend and compressing the part on the inside. The amount of requird stretch goes up dramatically if you make the object thicker.
One added point: when you put it under tension (as in the outside of a bend) brittle fracture tends to be initiated by surface cracks and scratches. A freshly-blown piece doesn’t have such cracks, so the glass is better at resisting tension.