A long time ago, when I was going to school in Pennsylvania, I had a friend named Barry Kramer. Barry’s father is a machinist, and he gave Barry a metal rod, about a foot long and an inch or so in diameter, that had been mis-machined.
Barry used this rod (which weighed a good five or ten pounds) to beat things up–road signs, walls, pavement, that sort of thing. There’s something inherently, irrationally satisfying about holding a heavy piece of steel in your hands and really whacking the holy hell out of something…but I digress.
Anyway, one afternoon, a mutual friend of ours went over to Barry’s house, picked up the heavy steel bar, and delicately tapped on the ringer for the doorbell with it.
The steel bar failed instantly–it cracked in half and fell in two pieces to the floor.
I got to thinking about Barry this evening as I was leaving the office. I have a large laptop carrying case I’ve used for years; I’ve had it for so long it’s starting to come apart, and the strap is frayed. I walked outside and was just ambling along toward the car, minding my own business and thinking about cognitive limits and modeling of human intelligence, when I heard a distinct Tink! and the strap of the laptop bag went slithering over my shoulder, sending the bag plummeting to the ground.
I caught the bag before anything bad happened, and hauled it up expecting to see that the strap had failed. But no. The metal latch at the end of the strap had failed and split, very cleanly, in two.
Metal fatigue is really interesting. Most metals do not have an infinite fatigue life. In fact, with most metals, if you take a rod of metal capable of holding, say, 100 pounds of weight, bolt it to your ceiling, and hang a 90-pound weight from it, eventually the metal will fail and the weight will fall. Titanium doesn’t behave this way, but many other metals do.
The split where the metal latch failed is surprisingly clean. The metal broke precisely in an almost perfectly straight line; the geometry of fatigue failure is not fractal, which isn’t what I would expect.
But goddammit, now I have to buy a new laptop case.
There’s something inherently, irrationally satisfying about holding a heavy piece of steel in your hands and really whacking the holy hell out of something
Have you ever taken apart an old metal shed with a crowbar? Damn, that’s a lot of fun, especially first thing in the morning.
I haven’t! It sounds like great fun, though.
There’s something inherently, irrationally satisfying about holding a heavy piece of steel in your hands and really whacking the holy hell out of something
Have you ever taken apart an old metal shed with a crowbar? Damn, that’s a lot of fun, especially first thing in the morning.
I haven’t! It sounds like great fun, though.
There’s something inherently, irrationally satisfying about holding a heavy piece of steel in your hands and really whacking the holy hell out of something
That’s why (what we call) Chainsaw Load Outs are so much fun!
Too bad about your laptop bag though
There’s something inherently, irrationally satisfying about holding a heavy piece of steel in your hands and really whacking the holy hell out of something
That’s why (what we call) Chainsaw Load Outs are so much fun!
Too bad about your laptop bag though
…wait, this isn’t going to be a metaphor about relationships and communication?
So much for predictability. 🙂
Heh. Not this time; I do think about other things occasionally! 😛
Well, sure, but they usually involve breasts.
Now hold on a minute… you WERE talking about cleavage!
…wait, this isn’t going to be a metaphor about relationships and communication?
So much for predictability. 🙂
Heh. Not this time; I do think about other things occasionally! 😛
Well, sure, but they usually involve breasts.
Now hold on a minute… you WERE talking about cleavage!
I can tell you were never forced to sit through tedious lectures on materials engineering. As you’ve discovered, the subject matter is pretty interesting, but teaching technique can make it less so.
Composites, by the way, fail in a totally different way than do metals. Metals fail all of sudden – they go from 100% strength (for a long time) to 98% (for a short time) to 0% very quickly; Composites steadily degrade – 100% for a while, then 99% for X time, then 98% for X time, then 97% for X time, etc, all the way down to 0%. So maintenance done by those used to metals always involves much freaking out “OMG, we caught it at just the right time! One more day and we’d have a disaster!” When they should have just left the damn thing along. This was apparently a big problem for aircraft maintenance when composites were first being used, since they were being replaced far more frequently than the manufacturers recommended.
Nope, I’ve never taken any materials classes. I can see where the lectures might be tedious, but the manner in which things fail is oftentimes very interesting.
I understand that the aircraft industry had problems with composite materials failing through delamination for a while.
I understand that the aircraft industry had problems with composite materials failing through delamination for a while.
Yeah, when the technology was new, there wasn’t enough accumulated knowledge and experience of how to do it properly (techniques, timing, materials, etc). It’s a hell of a lot better now.
I can tell you were never forced to sit through tedious lectures on materials engineering. As you’ve discovered, the subject matter is pretty interesting, but teaching technique can make it less so.
Composites, by the way, fail in a totally different way than do metals. Metals fail all of sudden – they go from 100% strength (for a long time) to 98% (for a short time) to 0% very quickly; Composites steadily degrade – 100% for a while, then 99% for X time, then 98% for X time, then 97% for X time, etc, all the way down to 0%. So maintenance done by those used to metals always involves much freaking out “OMG, we caught it at just the right time! One more day and we’d have a disaster!” When they should have just left the damn thing along. This was apparently a big problem for aircraft maintenance when composites were first being used, since they were being replaced far more frequently than the manufacturers recommended.
Not directly related to this post, but I’ve enjoyed peering through your posts. Thank you for sharing them. Mind if I add you to my f-list?
Not at all…welcome aboard!
Not directly related to this post, but I’ve enjoyed peering through your posts. Thank you for sharing them. Mind if I add you to my f-list?
From what little chemistry I currently remember, aren’t the atoms in metal arranged in a crystalline pattern? If they are, I think a “shearing” sort of break would result in said breaks as the first bit of fatigue would rapidly run through the “crystal”.
From what little chemistry I currently remember, aren’t the atoms in metal arranged in a crystalline pattern? If they are, I think a “shearing” sort of break would result in said breaks as the first bit of fatigue would rapidly run through the “crystal”.
Y’know, I’ve read most of xeromag and followed links to your LJ at least three times. *settles in and adds you to her f-list* So, hello there 🙂
Howdy, and welcome board!
Y’know, I’ve read most of xeromag and followed links to your LJ at least three times. *settles in and adds you to her f-list* So, hello there 🙂
please consider a Crumpler bag as a replacement – designed and (used to be) made in Australia (I think some models still are but most are now made next door in SE Asia) – very funky and they have coloured interiors so you can see all those black things that fall to the bottom of the bag. The bags all have funky names – we have a “Sheep Scarer” and a “Team Player” whilst I have some photography friends with “Six Million Dollar Homes”. They have a cool website too. Dub Dub Dub dot crumpler dot com do au
My DH adds: they are incredibly reliable even under the trying circumstances of an alpha geek with oftem more than one laptop (plus o’reilly journals).
he’s had his “team player” for about 4 years and it’s showing no signs of wear.
Those look like neat bags! I’ve already replaced mine (Selly had one she wasn’t using), but when the time comes to buy a new one, I’ll have to look at those again.
please consider a Crumpler bag as a replacement – designed and (used to be) made in Australia (I think some models still are but most are now made next door in SE Asia) – very funky and they have coloured interiors so you can see all those black things that fall to the bottom of the bag. The bags all have funky names – we have a “Sheep Scarer” and a “Team Player” whilst I have some photography friends with “Six Million Dollar Homes”. They have a cool website too. Dub Dub Dub dot crumpler dot com do au
My DH adds: they are incredibly reliable even under the trying circumstances of an alpha geek with oftem more than one laptop (plus o’reilly journals).
he’s had his “team player” for about 4 years and it’s showing no signs of wear.
Howdy, and welcome board!
Those look like neat bags! I’ve already replaced mine (Selly had one she wasn’t using), but when the time comes to buy a new one, I’ll have to look at those again.
Nope, I’ve never taken any materials classes. I can see where the lectures might be tedious, but the manner in which things fail is oftentimes very interesting.
I understand that the aircraft industry had problems with composite materials failing through delamination for a while.
Not at all…welcome aboard!
I understand that the aircraft industry had problems with composite materials failing through delamination for a while.
Yeah, when the technology was new, there wasn’t enough accumulated knowledge and experience of how to do it properly (techniques, timing, materials, etc). It’s a hell of a lot better now.