Tempered Glass

After removing the glass. So glad it's not raining.

Yesterday morning was garbage day for non-burnables, and I threw out the rolled-up remains of my minivan's rear window. For those of you whom I've neglected to tell, I had a little altercation with an orange tree the other day. The glass didn't take a direct impact, but there was some trunk-to-trunk loving and and the glass crinkled into a myriad of little bits that the car repair shop informed me I should pull down before driving away from the seen.

As I was picking up bits of glass from the entrance to somebody's orange grove, it occurred to me that the bits were not sharp — which was a damn good thing because I didn't see how I was going to pull down the crinkled window — 90% of which was still hanging precariously in place—without risking cutting myself big-time.

Anyways, I did it, as evidenced by the photo, and I am still alive to rave about the extraordinary properties of tempered glass. Tempered glass, so the Wikipedia tells me, is glass that can take a beating — whether that be in your oven or on the road or in a bar, or whatever circumstances you subject your cellphone to. It's used in lots of places, but I feel I should mention that the front windshield of a car, is, according to automobile-glass people, special: It's laminated to act like a cushion for your head.

What makes tempered glass so special — being crazy strong and heat resistant, and, in the off-case it does break, crinkling into thousands of not-sharp bits instead of giant blade-like shards — has to do, of course, with how it's made. Apparently, it starts life pretty normally, (whatever that means. Did you know they make windows by floating glass on a conveyor belt of molten tin? [1]) The cool thing about glass is, it's glass: If you heat it enough, but not so much that it melts it gets rubbery. That's what makes the subtle curves of a car's front and rear windows possible.

To make tempered glass, the glass is heated well above this transition state, and then blasted with cold air to quench it, locking the molecules on the surface in place, while the molecules in the interior try to shrink back to a comfortable shape [1]. (These days, they can do this chemically, too [2].)Therefore, the surface of the glass ends up in a state of compression, and, like the arches of a bridge, becomes much stronger. However, if it does break, you lose that compression, and the tension in the interior causes it to crack on the spot [3]. Imagine taking out a couple stone blocks from an arch bridge and the whole thing falls apart.

So finally, why isn't it sharp? I actually failed to find a solid, convincing answer, but I did find a couple leads. Let's start from the more basic question, why does glass shatter into sharp shards? (Say that five times fast!) Before you can answer that, you have to define "sharp". For something to cut your skin, it has to have a certain shape, size, and hardness. When you strike a piece of glass, it fractures into long, pointy pieces as it cracks, releasing energy under strain. According to [4], "the energy release rate increases linearly with crack length," so as a crack grows, there is more energy to drive its growth. The crack forms wedge-shaped edges that are ridiculously sharp, and the crack grows faster and faster, with a maximum speed of around 1.5 kilometers per second [5], (That's a measley 150 times slower than light speed! Right?) until it branches (or maybe stops, if the crack gets to a particularly hard region), creating shards. With tempered glass, you get lots of branchings, and, therefore, lots of fragments. But it's not just the primary cracks that radiate out from the center of impact, perpendicular cracks also form in a process called "dicing" or "cubing," supposedly an interaction of tempered glass with humidity [4]. Like the name says, you end up, not with long, jagged shards, but with lots and lots of little cuboid chunks of glass. So why aren't these sharp? I don't know! [3] finds tempered glass shards to be blunter and less penetrating in certain circumstances, but [3] was a study of beer pint glasses, which — one can conclude from the paper — are not tempered very evenly. Unfortunately, the original paper on dicing is locked in the ivory tower of $40/article. TT

So, my conclusion about why chunks of broken tempered glass are blunt, which I've been awake since 2am trying to reach, is that nobody knows (including the blokes on reddit), the folks in the materials department aren't talking (which makes sense, because most people in other fields probably wouldn't care about the details), or I'm still asking the wrong question (like, what if hard things are always sharp when they crack, and I should be asking why glass is hard. . .but there plenty of things are harder than glass but not sharp when they fracture).

I can make lots of guesses. Maybe there's so much tension stored up in tempered glass that when it cracks, all the little sharp edges just get blown off and obliterated into dust. Maybe dicing can reset the speed of a crack, slow it down and encourage right-angle fractures. I don't know, but tempered glass rocks my world.


[1] L. S. Millberg. Automobile Windshield. How Products are Made: Vol. 1.

[2] Mitch Jacoby. Chemically strengthened glass finds a new application. Chemical and Engineering News. 2018, Vol. 96(3): 16-17.


[3] Richard W. Earp. The Effect of Thermal Tempering Processes on the Sharpness and Injury Potential of Pint Glasses (Doctoral Thesis). University of Leicester: 2016.

[4] Richard C. Bradt. The Fractography and Crack Patterns of Broken Glass. J Fail. Anal. and Preven. (2011) 11: 79. https://doi.org/10.1007/s11668-011-9432-5.

[5] G. Molnar et al. Fragmentation of wedge loaded tempered structural glass. Glass Struct. Eng. (2016) 1:385–394.

Superhuman abilities vs. Quelched innate potential

During the past month, I've had the fortune of hiking with several families up to Jomon Sugi and back-- 22km and a lot of rocky staircases. You know what I've learned?
1. Moms rock and seem to have magic reserves of energy, and
2. Kids have so much wasted physical potential. I mean it; it's as if part of growing up is leaving your natural abilities behind.

Especially on a fantastic little island like Yakushima, there's a lot of talk about supernatural abilities. When the topic comes up, I often fumble trying to explain my position. While I do not believe anyone having supernatural abilities, ("Not likely" is my working definition of supernatural.) I do fully believe in our wasted, untapped potential abilities.

Take, for example, all those little elementary-aged kids that run and climb and seem to bounce up the mountain trail to Jomon Sugi. When they are told to "walk with the group" on the railroad tracks they complain that they are hungry, sleepy, and too tired to go on. But the instant the trail gets a bit more natural, there is no holding them back. Still, I know that, as they get older, they will eventually learn to favor flat, hairless terrain, and there's little chance that they will ever hike among mountains with as speed and much energy as they have now.

Take, for example, the a rock-climber from Korea I met the other day. She'd only been climbing for four years, but she had muscles like cabbages and climbed like a monkey. Everyone marvels at the agility of monkeys. Well, I think we could all be monkeys or kung fu masters or whatever. (And you know, monkeys do fall out of trees sometimes.)

I don't believe in supernatural abilities, but I do believe in news stories about the blind kid who makes clicked with his tongue to sound out his surroundings, about people who survive incredible periods of freezing temperatures, and animal "whisperers" who understand how to become excepted by wild animals. (To me, who hates even jogging, the fact that some people can run a marathon, or even hundreds of kilometers, is just as amazing.) If you are a skeptic, then read one of Richard Feynman's anecdotal books, in which he often describes the little things that impressed the hell out of his acquaintances (such as smelling books to find out which one has been touched recently). Or come to Yakushima, where the deer will except you until you make a movement that is not natural.

We spend so much of our childhoods getting stamped down into molds, it's disgusting. We turn the lights on as soon as the colors of sunset appear. We sleep and sit on furniture of perfect comfort. We install safety catches--timers, alarms, navigation systems, auto-sensors, speed-dial extra buttons--so that we don't have to pay attention to anything. Turn up the volume, spray some air freshener, label it. Who knows what potentials we squash!

Why do humans have to study to become fill-in-the-blank masters in order to be great? I think we could all be great, if we'd just give our minds and bodies a chance. And then maybe the line between human greatness worthy of respect and boasts of supernatural bull would be crystal clear.

bugyoinfog.jpg

5 Things I Believe

Without trying to explain myself too much, I'm a bit afraid this blog is going to piss off a few of my friends.

1.) Good and evil are simplified labels that do not describe the real world. These words are often used to whitewash oneself and create barriers around problems we feel presently unable to cope with.

(For example, gay people have been called evil, but homosexuality has been shown to have a physical, biological basis. When we call terrorists evil, we do not try to understand their motives. Irrational murder clearly falls in the evil category, but I believe mental illness is more likely than possession by evil spirits.)

2.) The burden that our unsustainable living habits places on other populations is involuntary holocaust.

(Please contemplate that before saying anything. If we didn't wreck the environment and force people to live in unarable shitholes so that we could have stockpiles of every convenience possible I bet everyone would be a lot happier. I bet in a couple hundred years our descendants will look back an say what ignorantly cruel people we were.)

3.) People are specialists.

(Just as our right hand gets stronger than our left, we get used to things, and we get better at what we're good at. And then
we start to believe in it. Conversely, if we don't understand something, it's a problem for somebody else.)

4.) People have evolved to thrive in or near the natural environment.

(This explains some of our instincts: Fear of the dark, thrill of hide-and-seek, fight-or-flight, interest in fire, love of blue skies. It would seem natural if we are happiest living in harmony with nature, but our ancestors never had to make that choice. So it's no wonder if we haven't evolved instincts to choose to be one with nature. We'll have to trust our minds for this one!)

5.) In order to change, we need to be humble enough to admit that our assumptions are flawed, and our parents' assumptions are also flawed.

(Can we look at our lives and say, "I am wrecking the environment and causing pain and suffering in foreign lands." Can we take the even harder step of changing our ways, or will we say, "But at least I am contributing to the well-being of my associates, and this is who I am.")

(Background is from a rocket launch earlier this month.)

Today's pointless musing: Dogma

Maybe dogma (over-)develops because of the way our minds have evolved to handle information. We arrange the facts we have with the facts we'd like to have into patterns, fill in the gaps with goop, and believe this is the truth. (Hah, I'm doing that as I write this!)

Maybe this is a survival tactic. For example, let's say there's 100 plant species I can eat, and another 100 that will kill me. A fact which I don't have, but would like to have, is that there is an easy rule for determining which is which. So I search for a rule, such as plants with red berries are bad, but plants with blue berries are good. (oh no, which was which? red=blood=death, blue=sky=good; got it!) For every instance where that rule fails, I add some goop. Say, plants with red veins and red berries are also okay. And I keep going until I've memorized all the species. The original rule may not even apply in most cases, but it has helped me memorize all the species, and until I go back and count up the instances of good vs bad red berries (something I can't do without first memorizing all the berries), I believe it.

This patch-it-up-as-you-go-method is kind of how the Standard Model of modern physics developed, and it's not hard to imagine that the personalities attributed to the Greek Gods also developed like this. I'll avoid drawing parallels to modern religions, politics, and nuclear reactors until we've assembled all our berries.

Until we--not just see, but actually--have an intuition for the entire picture, we'll just believe that red berries are bad. In the long run, such prejudiced fallicies may help us move forward. Ony at the end of the day, when such a fallicy has been uncovered, can we judge our progress. Just hope it's not too late. . .

Perhaps this applies to individuals and societies.

Sakurajima & Kagosihma

It's been a fast week:
For the first time since he got sick a couple weeks ago, my 15-year old dog was back in his normal right-across-the-front-doormat-so-no-one-can-enter/exit spot and I had to lift all my suitcases over him to get out on the way to the airport.
(Man, I can never get over the views from the airplane window. Right after the sunest, when you're flying over a blanket of clouds that are lit from below, bright orange so it looks like the world is smoldering. . .)

Tomorrow I'll finally be back in Yakushima so I can find out what's going on and start being a hiking guide!

In the meantime, I'm chilling/playind kendo in Kagoshima, a beautiful coastal city with mountains . . .

bridge

. . .and an active volcano in the harbor, called Sakurajima.

Sakurajima

Around the volcano, the air is a bit dusty with ash, but the water is a beautiful torquoise. . .


water
boats
sunset


. . .and there is a public footbath!

feet