Bathroom Scale Apparatus Gets An Upgrade!

In a previous post I talked about some unholy things (and by unholy, I mean awesome) I did to a digital bathroom scale so I could make a force measurement setup. Well, I finally arrived at a setup that I was able to use, so I wanted to take some time to document the equipment. The equipment discussed here is the same equipment used to collect the force data in the thrusts and column buckling post.

Here's the DAQ system and a single load cell being tested.

Update 4 March 2014: fixed a typo in the force resolution. It should have been 6 N, not 0.6 N.

Thrusts, Columns and You!

In an earlier post, I talked about determining the effective bending stiffness for sword trainers. Towards the end of that post I mentioned that this quantity, the product of the elastic modulus and the relevant area moment of inertia (\(EI\)), is useful when looking at what occurs when a blade just begins to flex. This sort of analysis can be used to look at how the effective bending stiffness of a trainer can be translated into an equipment safety design rule.

And after the last spattering of materials science related posts, I promised some more classical mechanics. So here we go!

Let's start with a simple and common scenario: a fencer thrusts at a target with a flexible trainer. I'm willing to bet that a lot of the readers of this blog have been on both ends of this scenario.

I won't say which one I am.

From experience, you'll know that the blade begins to flex after contact. Let's look in detail at what happens in that moment.

Update, 4 March 2014: fixed a typo in the force resolution. It should have been 6 N, not 0.6 N.

Update, 14 Feb 2014: I revisited the initial image analysis and found the approximate speed at time of impact to be about 2 m/s (~6.6 ft/s or ~4.5 mph), though this suffers from the same limitations as the other conclusions from the same analysis.

Update, 9 Feb 2014: I went back and repeated the thrust force measurement with my Lichtenauer (same weapon as the test shown), and my Tinker-Hanwei Arming Sword and Longsword. The results for the Lichtenauer were consistent with those shown here. Woot for repeatability. The data from the Tinker-Hanwei swords exhibited similar characteristics as well, but at lower load ranges as expected based on the buckling load work I discuss here. Yay for predictive science! I am still working through the data, but felt this was worth an update.