Does glass undergo internal damage in a similar way to wood when struck hard, even if it doesn't visibly break, and is this damage accumulated gradually over time, or does it occur as a binary response, unlike wood.
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10
No, wood and glass fail in completely different ways.
Wood is a composite structure consisting of cellulose fibers held together with lignin glue. In wood, an impact force breaks the lignin loose from the cellulose and the cellulose fibers are then free to slip past one another without taking up any tension load. the tension loads then are felt by the lignin which cannot sustain them, and the piece of wood slowly and gradually comes apart under load.
Glass is a classically brittle substance which possesses no plastic deformation mechanisms at room temperature. An impact load cannot be distributed over a larger area through plastic deformation and is instead concentrated as a near-point load which locally exceeds the tensile strength of the glass, which initiates a series of cracks which then travel through the part at about the speed of sound in the glass, which then explodes into a cloud of jagged fragments.
answered Sep 24 at 16:14
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2$\begingroup$ Can the series of cracks be invisible? If I drop a glass and it did not break is it as good as before the drop or is there is some amount of effect occurred after the drop. Is there any test that can determine if an unbroken glass is dropped or not? $\endgroup$ Sep 24 at 18:21
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12$\begingroup$ @Talespin_Kit, good glass is rendered fragile by the presence of microcracks (i.e., tiny scratches) in its surface. these happen mostly by abrasion and not by droppage. Here is a test for microcracks: take a perfectly dry glass. get you a bottle of your favorite carbonated beverage (beer works really well) and gently pour the glass full. microcracks will be revealed as teeny points on the surface of the glass from which streams of bubbles extend upwards towards the surface. photographers deliberately microscratch beer glasses before filling them, to obtain a goodly showing of those bubbles. $\endgroup$ Sep 24 at 21:09
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2$\begingroup$ and yes, the cracks are far too small to see without a microscope. $\endgroup$ Sep 24 at 21:15
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3$\begingroup$ I find your comment even more enlightening than your post, although I don't know how you might work that into the post. $\endgroup$ Sep 25 at 6:57
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1$\begingroup$ @PasserBy, I don't know either. Perhaps I could ask a question about that and answer it myself (BTW the rules here do allow you to answer your own question). $\endgroup$ Sep 25 at 7:12