![[:-)]](graphics/symbols/smiley.gif)
, when fencing and the
puncture characteristics of our "armor" change.
Original posting is available.
Thomas and Dylan, thank you for a well thought out follow up. I am asking for more data and picking at some "holes" in your experiment. This is not a criticism but an attempt to make your results even more significant. Again, thank you very much for your data!
A couple of comments:
As I asked the "other two" folks doing these experiments,
we need to measure "wet" material. What I am suggesting is
a "wet" piece of leather and "wet" trigger comparisons. We
sweat, every once in a while , when fencing and the
puncture characteristics of our "armor" change.
...sample (about 8 inches square) was duct-taped onto the top of the can.
Duct Taping is not really "reliably reproducible" from one sample to the next. Areas where you might find `experimental error' include:
Suggestion: stretcher frame (round) for holding embroidery or a wooden, round frame that you can "nail/tack" the material to. There are issues with either technique. Another idea for the "wooden round" holder is to put a metal band clamp around the edge. Lastly, your could use two wooden boards with a hole drilled though both, press the material between the boards to hold it steady. If you find this does not have enough friction, add sandpaper (specify grit and manufacturer), and/or "pins" that hold the material tight (I would find a screw that was "just a bit" longer then the depth of one board).
The sample was pulled taut, but was not overly stretched. The sample would not push into the can more than 2.5 cm in any test.
Was the same can/diameter used for each test? Did it "deform" in the testing?
What do you mean that "it would not push into the can more than 2.5 cm in any test"? Does this indicate the "tautness" of the material? Good idea, [see the next comment on this...], I would recommend that you "measure" how far it would "deform" at a "constant" weight. This does effect the outcome of your experiments.
Testing Theory:
What follows is the physics details of the test. Feel free to ignore it if so inclined.
Thank you, please complete the full analysis. I know you have a better background in this than I. If you need some more "physics" help we could ask Sir Maghnos (sp?) here in BMDL (a physist, PhD I believe), Patri in Carolingia (PhD science history/physics), or Garrick in Ravenhill (PhD physics, I believe) for some assistance.
When a sample is struck, the blade imparts energy to the fabric. If the energy is more than the fabric can absorb, it tears. The equation for kinetic energy is
You need to address the "more than the fabric can absorb" issue. If the fabric can "stretch" it will "absorb" the energy but it will not protect you. Imagine this the ultimate "stretch" fabric: you stab the person, the material stretches over the tip of the weapon, the weapon AND the fabric pierce the person, upon withdrawal of the weapon, the fabric returns to its original shape with no broken fibers. The person is bleeding.
As such, "protective" qualities of the fabric must include its
ability to resist puncture and deformation. How to represent this
with mathematics is the physicist's job, or the mechanical engineer's,
not the mathematician's (I am a math guy ).
The Drop: The tip of the blade was held 30 cm above the sample, and dropped straight down through a 35 cm length of copper tube to prevent deflection (and creaming Dylan on the noggin).
Its important the the "tip" of the weapon always strike "at the same angle". Preferably, 90 degrees. Even a "slight" deviation from this will result in widely different readings. I am glad to see "the same" distance is used throughout, and that you rely on the Earth's gravity for excelleration. These constants will help a lot. Since this description is fairly "vague", could you describe the apparatus more and is there any possibility that the weapon might strike at an angle?
If you find that the weapon does have room to "maneuver" within the pipe, I suggest forming some "guides" which you could fit around the weapon. One way to do this and guarantee that the tip will stay at 90, is to make wooden plugs that are smaller than the pipe (burn them out using a similar (thicker walled) steel pipe). Then, heat the weapon and pierce each of the guides with the weapon but in an orientation that keeps the tip at 90. Of course, these guides should be as "thin" as possible to reduce or eliminate any drag. I suggest burning them out because the resulting edges are filled with carbon for lubrication. Addition of oils would likely swell the wood. Another great material to use would be teflon, but not everyone has access to teflon. NOTE: if you change the "bending" characteristics of the blade, I do not believe this "invalidates" the findings since you don't really care about the blades flexibility, but more about the fabrics reliability in turning a broken blade.
The Blades: There were four test blades: a broken foil, broken 22.5 cm from the tip, a broken epee, broken 17.5 cm from the tip, an untipped schlager with a factory tip (slightly pointed shovel-shape), and an untipped schlager, with a flattened tip. Note that during these tests, the flex of the blades did not significantly affect the outcome.
Which leads to the next point, you make an assumption that "blade" bending/flex/absorption of the resulting impact is nil. I think that is an unwise assumption without further data. You could ENSURE that there is no flex by creating a jig that clamps "near" to the tip and extends back to the pommel-threads and "weight" assembly. This "jig" would be rigid and its "flex" would be constant throughout the experiment. If I was making it, I would use "steel" threaded rod. You may have better resources than I. (undoubtably, since I don't have the free cash this month to buy such materials :-)
As to the weapons, please describe the "make" and other physical descriptions of each blade. A "Hosten-plus" epee is much different than a "Russian" epee. Also, for the "broken weapon" did the tip travel 30cm's or did it travel 30cm + the length of the break? I assumed the "first" but this should be made clear. [never assume with experimental data] The "schlager", who's? Was it the oval cross section or the German diamond? Again, please characterize the blade. Suggestion:
I would include "photo's" of the tips layed out against a graph-paper background. Ensure that each tip has a surface that is "ground" to flat or rounded profile. I am very hesitant to believe that even the manufacturer is in any way consistent with their grinding of the tips.
Again, thank you very very much for this well through out experiment.
Don Danulf Donaldson
(who has done similar but less documented work with an epee and foil in the
past. NOTE: Garick Mapmaker has a "tool" to check puncture resistance of
material which uses a constant spring. Way cool.)
