Temperature update: Going to be 106oF today. I think at 7:30am when I got up today it was already in the mid 80s (although that might have been partly due to reduced airflow indoors – I had to rush outside to take a deep breath). Gosh.
Above is part of a puzzle I was working on for a while on Saturday. A more detailed and larger image will follow below. I did pretty well, but then I got distracted after a while (see below). The last puzzle pieces came from (I suspect) a single puzzle piece shattering in a secondary event. The primary event? Bit embarrassing. I was preparing dinner on Thursday night, a guest was about to arrive, and a fly entered the kitchen. I hate flies in my kitchen at the best of times, and this was just too much. I tried to open the window to encourage the beast to depart, and it refused. I tried to open the window further and exasperatedly wafted my hand in its direction to scare it off the window pane, misjudged that action and pushed my hand through the window. Felt like a real idiot, of course: An expensive mistake, an awkward thing to explain, and of course a million flies and other creatures now had unrestricted access… The good news is that I only got a slight nick from the razor sharp edges, my guest did not think I was too insane (or no more than I usually am) and dinner was tasty. So all’s well that ends well.
The next morning I woke up and immediately thought “I can’t believe I put my hand through my window”. Went downstairs to check. Yes, it was true. There was a nice shatter pattern (notice the cracks radiating outward from the reconstructed impact point – see photo and discussion below) to admire, and lots of bits of glass on the patio floor outside. I left it for a day, and on Saturday morning began to face up to the fact that I’d then have the annoying and expensive task of getting a window person to come around and redo the window. This would mean making appointments (during a busy work week), estimates, and all that aggro. I envisioned this all costing me hundreds of dollars.
First I began to gather up the broken glass and then remove the rest from the pane, shard by shard (wearing thick gardening gloves), in a fascinating exercise of deconstruction: The order one could remove the pieces very much depended on the pattern of shatter in an interesting way. the curves of the cracks overlap in a way that give a preferred direction of movement of one piece relative to another. If you don’t get one piece out first, you can’t move the other without breaking or stressing in a way that might produce shattering. This became an interesting exercise after a while, thwarted by some of the larger pieces being too well stuck into the frame edges. Then I began to experiment a bit with the window frame, wondering how hard it might be to remove, in order to get the rest of the broken parts out. I also realized that if I could do that, I could just take the entire frame to a store! Two screws that I discovered were calling out to me, and after a bit of scouting the edges of the frame, I concluded that if I undid those screws, I could in fact lift the entire thing out (after some scraping and huffing and puffing to overcome some contact seals made by weathering and slight corrosion here and there).
Then I reassembled the broken pane on a table out of curiosity:
There’s some nice observations to be made about the pattern. You can see the radial cracks of breakage from the original impact point. That point created the stress that broke the glass and then almost everything radiates outward from there, communicating outward the effects of the stress. Almost all cracks do this, which is why you see this shatter pattern so commonly. The two big non-radial cracks to the bottom left result from the stress placed on the glass at a point on the frame where it is held. They also then radiate outward from that point and hit the primary cracks, resulting in that piece falling out. There’s another one like that to the bottom right, although harder to see. Most of the smaller cracks that do not conform to the big radials are from a secondary process: Those are the bits of glass that fell to the floor outside and then broke upon impact.
Some pieces were so small (I’ve put some on the left of the pane) so as to make the perfect challenge jigsaw: there’s no pattern painted on the puzzle pieces (say that out loud fast) and either side could be the right side. Hmmm… this could be the basis for revitalization of family jigsaw night (modulo the razor sharp edges)! While the picture might be a bit boring, that’s missing the point. The design could all be about the beautiful shatter pattern. Let’s see how long I’ll have to wait to see this idea taken successfully to market – by someone else, of course.
A trip to the local hardware store with the frame resulted in a newly re-glazed frame in about two hours. $27.50 Huh. What did I do to deserve such a hassle-free and relatively low cost solution (other than having a cheap aluminium frame in the kitchen window that I never liked but now am very happy with)…?
Well, of course, about to leave on my way back to the hardware store to get the new pane, I had an idea. I might as well find out about screens for two windows (at the front) and one door (at the back). I could more freely throw them all open to get increased airflow (against the heat) without worrying about flies, moths (at night) and other critters (including confused baby lizards – really) coming into the place. I’d half had this thought a number of times in the past but then forgot about it, but the current heatwave (and my reluctance to have air conditioner working all the time – or at all if I can help it) and the window incident (and the fact that I was on the way to the hardware store) got the idea off the shelf and dusted off. So I ran around with the tape measure for a few minutes and then went to the store to inquire about screens.
It would take two days if I wanted them made to my specifications. I asked if they sold the raw materials – screens are trivial to make, (as I discovered upon taking one apart when I was very young) and I sort of fancied the idea of having a go. The guy in the store looked a bit surprised about this. They normally don’t sell the raw materials for complete frame construction (only some bits for repairing holes in existing screens), but after I selected some tools from the main part of the shop, he took me back to the workshop and I pointed out what I wanted and then they (after a bit of internal consultation) charged me a sum for the collection.
I took everything home (love those 12ft stretches of aluminium frame material -click above right for larger view) and began measuring and sawing. In several minutes, a frame takes shape, and in some more minutes, a screen can be put onto it.
Steps to the screen. Click for larger views. (My finger is on the hacksaw blade only to steady it for the photo.) The black block is a guide to make simpler the 45 degree angle I cut on the ends to the frame segments.
A few more minutes to install into place (into wooden frames) and – critter-free airflow night and day! Just in time for the 100+oF weather I’ve been mentioning.
That was too much fun, for no hassle. I find myself a tad concerned that a major piece of hassle must be waiting in store for me somewhere. Mustn’t think that way. Bad thought. Bad.
-cvj
I’m not an expert, and I’m sure that there are studies of this, but I would guess that this is really the most natural solution, since stress is very local, and communicated by local processes, so disconnected responses like concentric circles would seem to be ruled out on that basis alone. That leaves lines coming out of the impact point, and the question of why they are radial and, say, spiralling. I’d have guessed radial since that is the shortest path outward from the source, and secondly, because its the only thing consistent with the symmetry – what would determine the curve direction of the spiral? So in an infinite sheet of glass with no preferred history of defects pointing one way or another, I’d say there’d be a radial pattern because of locality and symmetry.
Maybe a true expert will stumble upon this post and say more – or point out that I missed a major issue – so check back from time to time.
Cheers,
-cvj
Hi Clifford:
Thanks for a fascinating post. I was wondering why radial lines more efficiently relieve the stress (in an infinite pane of glass with no edge effects) rather than another configuration, eg concentric circles? Pehaps it is somehow related to the amount of area encased by the break (energetically desirable) relative to the length of the break (energetically undesirable)?
Cheers,
Des
Glass-
I have a car that my colleague gave to me instead of putting in the junk yard. At times I’ve hung onto the driver’s door while driving because the broken door latch didn’t catch, the battery continues to need to be replaced because there is a leak in the electrical system somewhere, the driver’s side electrical window doesn’t work, and the seats don’t adjust any more. However I’m proud that I’ve managed to keep the car’s engine in good mechanical shape, while the car’s body disintegrates or falls off.
A couple of years ago, my interior mirror fell off, so I ran to the hardware store and bought some superglue to glue it back on. I didn’t read the package very well though, because it said clearly *Not For Use on Glass*. Yes indeed, the next day after gluing my mirror to the inside of my front windshield, some lovely new cracks formed around the point of contact of the mirror and one of those cracks reached a tentacle downwards. I asked some glass people how much time I have, and they expected that it would reach the bottom of the windshield within a few months. “But anyway, don’t worry,” they said, “automobile glass is two layers with the outer layer not affected by the inner layer, so I’ll still be protected when it rains.”
Well, I keep watching that downward crack, and last summer it seems to have stalled in the midpoint of my front windshield. It has been a fascinating study in glass mechanics.
Hi Amara,
They are not in pots. Interesting tip. I think they’d be fried by the sun if I did do that. The new screens are doing the trick, though.
Hi Elliot,
The hand is fine. Fully healed. It was just a small nick.
Best,
-cvj
Dear Clifford: A trick on the flies that some German family friends told me: If you put tomato plants near the window openings, it deters flies. I haven’t tried it myself, so I don’t know if it is a wives tale, but if you have any of your tomato plants in pots, it might be worth a try.
I’m ok with most bugs, however, fleas, mosquitoes and cockroaches are the ones that bother me. I’ve accidently broken light fixures trying to kill mosquitoes, and by cockroaches, I mean the ones that are about 5 cm and fly (I’m squeamish on those).
I have a business arrangement with the daddy long leg spiders that I will let 5 cohabitat my apartment (the others I catch and put outside), because they catch the other bugs.
I hate flies too. I usually stop whatever i am doing and kill them. They are very unclean creatures. I’d rather have a thousand cockroaches, than one fly. But I suspect others feel differently. Sorry about your hand.
Elliot
Cracks tend to occur where stresses were concentrated before cracking, but the cracks themselves are a form of stress relief. That is, when the glass cracks here, stresses are relieved near that area, so the next crack is relatively far away.
A microscopic crack in a crystal is called a dislocation. Interestingly, these tend to have properties that remind one of the Lorentz equation.