Engineering Question

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Engineering Question

Postby Jason Bernard » Mon Sep 28, 1998 4:26 pm


One of the reasons it is possible to break
concrete and brick is that although they
are hard they are rather brittle.

I have also heard that iron is rather
brittle. Does anybody know if anybody has
tried breaking iron with any success?
Any engineering types care to explain why
this can or cannot be done as with concrete?

Other than natural stone, can anybody
recommend anything else that might be of
interest for breaking? Especially something
unusual that most people do not regularly
break. I am even open to new things that
nobody else has tried and I will try it.

Lastly, does anybody know roughly the p.s.i.
required to break a concrete block (2" thick) or any other measurement used to detail the strength of substances? Does the p.s.i. (or whatever) go up linearly as you break multiple concrete blocks or is it non-linear (my instincts tell me it is not
linear since 5 boards just seems MUCH tougher than 4, and 6 even more so)?

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Engineering Question

Postby gmattson » Mon Sep 28, 1998 8:44 pm

I've had lots of experience breaking things Jason. Never knew how it worked, but back in the early 70s, one of my students, who was involved with high speed photography, filmed my breaking 5 one inch pine boards. (no spacers) The film showed the bottom board actually breaking first, then the fourth etc.

Most demonstrations of concrete breaks have the blocks separated by a spacer of some kind. In these breaks, the top block breaks, then second, .. But you are essentially breaking one at a time. If they were placed together, without spacers, the break would be much more difficult. Of course, you have the usual demo skullduggery. . . baking the bricks, special mix in the concrete and so on. When some sensei came to town and demonstrated at my early tourneys, they sent a "recipe" for the preparation of their breaking material.

Now at the other extreme, let me tell you about some of the breaks our group did, using untreated, green lumber!!! I think I have a picture of Art Rabesa having a rather large and green 2X2 pole broken over his arm! It took five trys, but eventually broke. We weren't smart enough to treat our materials!

And of course we have Danny Pai's famous Madison Square Garden 2 ton ice break. He took a little too long with his meditation and preliminary ritual, and as he was raising his arm for the break, the ice simply collapsed on the floor. I thought the audience would break up laughing, but Danny, ever the showman. . . simply raised both arms and proclaimed "POWER OF MY CHI!" And the audience gave him a standing ovation.

[This message has been edited by gmattson (edited 09-28-98).]
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Engineering Question

Postby Jason Bernard » Mon Sep 28, 1998 8:56 pm

Osu Sensei Matteson,

I have heard of these various methods
of "improving your odds of success"
although I have yet to try any of them.
I will have to someday just to see how
much of a difference it makes.

Just this Saturday I broke 4 concrete
slabs (6"x16"x2") and well, as happy
as I am with the progress I really want
to try something different. I am going
to try break a 4"x4"x16" and see how that
goes, but I am really searching for something
new (i.e. not concrete or natural rock).

Of all things in martial arts, I think I
enjoy breaking the most. I think it is
because it allows me to use FULL power
that I cannot use against a person (for
fear of injuring them) and only risk my own
body. Plus, it is different than hitting a
heavy bag because it is very measurable (2
slabs as opposed to 3 as opposed to 4, etc) and, of course, the risk factor.

Again, any suggestions for unusual, rare or
completely new breaks would be appreciated!


P.s. - Another funny story about breaking. I
was breaking 4 1" boards last Thursday
and didn't notice that the top one had a bow
shape to it (I was in a rush). Anyway,
I hit it and the bottom three broke but
not the top. I have never see that before.
We figure the top board bent, broke the other
three boards and then snapped back. Kind
of wish we had that on tape ... it would have been neat to see in slow motion.
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Engineering Question

Postby Bill Glasheen » Mon Sep 28, 1998 9:18 pm


As is usually the case with a biomedical engineer, I know enough about what you want to know where to look (and not a lot more). What you really want is a materials scientist.

Some time back I had two physics PhD candidates as students in my UVa karate club. They did a project where they worked with a local artisan to make traditional bos out of various available types of wood. But before they touched the first piece of wood, they went to the books and did their homework. They came back with a chart that had each wood as a row variable and the physical properties of the wood as a column variable. Then they made their orders, and had several bos made of each type of wood. As I can recall, they used the following types of wood: oak, hickory, wallnut, teac, cherry, mahogony, ironwood, purpleheart, greenheart, etc.

After all the work was done, our next step was to unleash our kobudo folks on the bos. We had some prearranged kumite that we were working on. Some of it involved some rather hard-style blocks. Some of the more dramatically powerful blocks used whole-body power in both attack and defense.

The thing I remember most vividly is how wood that we normally think of as "hard" ended up being so brittle. The walnut, mahogony, teac, etc shattered with only a few blocks from our boistrous group. Some of the others lasted a bit longer.

The winners? The number one wood, in my opinion, was.....oak. Really! It had the right combination of level of hardness and flexibility. Purpleheart and greenheart were second because they maintained their surface integrity via hardness and yet did not shatter anywhere near as easily.

Bottom line...there are a host of different properties of materials to consider if you want to look for things that shatter easily. I'll talk to my buddies (one's a professor at UNC, the other works for Lucent I think) and see if I can get them to give me the list. Then maybe we can create a set of criteria that would determine if something has the smashing index you desire.

If anyone else can steer us there quicker, by all means do so.

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Engineering Question

Postby Kevin Mackie » Mon Sep 28, 1998 10:09 pm

Jason, iron IS rather brittle, but then again eveything is relative. The very basic definition of brittle is very little deflection before break. The difference between iron and cement is the amount of energy it can absorb under load. The amount of energy is derived by the area under the stress-strain curve up to the point of fracture.( you get this through lab testing) In the case of a brittle material, it is just the area of the triangle with the one side being the stress (lbs/, the other the strain (in/in). E(in*lbs)=1/2(bh). The ultimate tensile strength of iron is at least 15-20 times that of un-reinforced concrete. And I would venture a supposition that the steel can take greater strain in tension than concrete. (brittle materials will always fail in tension in bending such as a brick). Therefore, the energy required to cause fracture of a like piece of iron is at least 15 times greater than that for concrete.

Years ago, my friend and I dismantled an upright piano with a sledge hammer. The cast iron plate that holds the string pin block would just not break.

Stick to the wood.

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Engineering Question

Postby Greg » Wed Sep 30, 1998 4:24 am

Interesting tests using the kobudo, Bill. Especially since in the Japanese koryu with which I am familiar, oak (white oak in particular) is the preferred wood with which to make bokken, bo, and jo. The combination of strenth and flexibility lends itself to hard training with a minimum of splintering and breaking. This is especially important for uke, who, when the weapon breaks risks some serious injury (BTW, Bill, who did you find to do the testing???).

Jason: Although I have very little breaking experience (except for some children's birthday parties I demoed at- which causes a bit of embarassment nowadays...), if you want a serious challenge, forget the iron, use oak!

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Engineering Question

Postby david » Wed Sep 30, 1998 10:31 am

As an aside, white oak is the traditional material of choice for bokken, jo and bo because it was material native to Japan.

In the U.S., we have hickory. This wood seem to have more density and strength than oak while sharing the same flexibility. I heard though that it has more of a tendency to warp if not properly taken care.

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Engineering Question

Postby Jason Bernard » Wed Sep 30, 1998 1:29 pm


Thank you all for your input. It is truly
valued. I will take a look a getting
some oak/hickory, and I am going to see about maybe 1/8" iron (start from there and work
my way up maybe to 1" of iron someday).

Dr. Glasheen, if you hear back from your university friends, I would love to know
if they recommend anything. Something
that really shatters (i.e. into many
fragments), while still being hard would
be great (maybe a ceramic, or how about
a plastic?).

Again, my thanks to everybody. I will let
you know how the iron in particular ends

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