I used to think that the padlock design of using many layers of metal stacked to form the main body was a cost-cutting consideration. This was my assumption before I came across the idea that it was really a way to make the lock stronger. It might have been from a TV commercial which showed a bullet penetrating a lock in slow motion. This was many, many years ago, but I have always wondered about that. Although anectodal, my experience finds that really sturdy, heavy duty equipment usually has a nice solid frame or enclosure. I'm not counting things like cars that are designed with "crumple zones", because in such cases weight is a major factor. I'm thinking about manufacture where weight isn't an issue, like padlocks. Does anyone have knowledge of something that would support this claim?

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    $\begingroup$ I guess it's unlikely to have any irregular structure/weaknesses that go all the way through if it's made of sheets of metal on top of each other $\endgroup$ – innisfree Mar 25 '16 at 14:06
  • $\begingroup$ It appears this method (folding) was used by Japsnese sword smiths en.m.wikipedia.org/wiki/Japanese_swordsmithing#Forging $\endgroup$ – innisfree Mar 25 '16 at 14:10
  • $\begingroup$ A strong casing is considered strongly associated with a durable object, but that's only half true. Internal components that are well-connected to the shell and won't be easily unhinged by sudden movements are only improved by a strong outer shell. However, studies have shown that say, the brain on impact only have minimal improvements with a helmet. $\endgroup$ – Neil Mar 25 '16 at 14:27
  • $\begingroup$ @innisfree - Yeah, those Samurai sword-smiths were phenomenal: right on the cutting-edge of technology :+D (sorry 'bout that one, just couldn't resist!). I saw an excellent documentary on their amazing ability to produce and work with metal. They were able to make super precise woodworking tools too. As a result, their carpenters were of the highest caliber. They would build entire houses using only dovetails, tongue-and-groove, dowels etc. and not even a single nail! But the most mind blowing thing to me, was how the carpenters would spend two to three hours a day sharpening their tools! $\endgroup$ – user106404 Mar 26 '16 at 8:15

The multi-layered structure protects against impact fracture.

If you hit an object very hard, you can create a crack; stresses will concentrate at that crack, and make it easier for the crack to propagate (think of the little notch in the ketchup packet: that's where you can tear the plastic...)

Now if you have a solid body (of anything), then that crack can continue to grow. But if you laminate, then the crack will hit the end of one lamina, and stop. That means that a laminated object will be much more impact resistant: it's easy to initiate a crack on the outermost surface (for example with a carbide-tipped object), but it's much harder to do so on an inner surface (which your tool cannot reach).

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    $\begingroup$ Great answer! Concise, thorough, and well balanced in its vocabulay (ie daily use vs technical/higher learning stuff). You used just enough power to make the point; spiking the ball would be a waste of energy. But I especially appreciate how you seem to really know your audience. Since the question was from everyday-life, using everyday-life examples in your answer was right on the mark (bullseye with the ketchup packet). I smiled and thought to myself, "Why didn't I think of that?" But best of all, was how it resonated. It made me think of how rip-stop nylon resists the propigation of tears $\endgroup$ – user106404 Mar 26 '16 at 8:01

@Floris answer is great, but there is another characteristic of a laminated lock, compared to a solid lock, to consider.

A laminated lock, has as few as 4 pins (6 or 8 on larger locks) holding the laminations together. The pins are basically rivets that run from the top of the lock, through all the laminations to the bottom of the lock, at the 4 corners. On larger locks, there will be additional rivets near the edges toward the middle.

Depending on the characteristics of the impact, these rivets might be the failure point. Breaking even just 1 of the rivets leaves the laminations unsupported and subject to easier penetration. Breaking just 2 rivets (3 on larger locks) will most likely lead to a catastrophic lock failure.


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