Droppin' Stuff!

Now that the International Congress on Medieval Studies in Kalamazoo, MI has come and gone, I can talk about some tests I did for a good friend's paper at the conference: penetration testing on a reconstruction of the Lubbek Wappenrock. This marks the first real outing of Da Towa, and so this post will also discuss some of the changes I have made and will make in the future.

The post-drop carnage.

What's That Sound?

Since I'm chugging away on a rather detailed follow-on post to the thrust & buckling post, I figured it was time for a fun one… and this time it's one that I'd been thinking about for a while.

Ever heard that metallic ping when heating a metal pan on a stove, or letting one cool? I'm willing to bet most people have.

Ever wonder where it came from?

Effective Bending Stiffness & Buckling Load Update!

Last year, I wrote a post about the effective bending stiffness of flexible trainers and had measurements of trainers I was able to get my hands on at the time. Well, thanks to my good friends at the Chicago Swordplay Guild, CSG North, the CSG 'Southern Expeditionary Force', the Rocky Mountain Swordplay Guild, and the Susquehanna Valley Swordplay Guild, I was able to get a pile more during a recent trip to Chicago.

So let's get down to details, then into the data:

• The measurement process was the same as outlined in the previous post
• I only added arming sword and longsword measurements. Sorry rapieristi and other later-period types: I'll give you all some love once I put together a portable method to deal with all them crazy hilt fittings.
• I decided to calculate the absolute error in the effective bending stiffness, \(EI\), based on the estimated accuracy of my measurement methods. These will be included on the graphs given here. For the FIE ranges, since these were back-calculated, I've assumed the error to be zero (no measurements, no error).
• I also updated the buckling load list, and will include those as well to help put things in perspective.
• I decided to interpret the data based my own personal experience with the weapons based on the Subjective Index of Sparky Skewering Efficacy, or SISS-E, since I found some of the trends interesting.

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.

The 'Temper of Iron'

"He [Fiore Dei Liberi] also longed to learn the temper of iron, of the nature of each weapon and of its aptness for defense and offense." -- Fiore Dei Liberi, Getty MS as translated by Tom Leoni.

In an earlier post we discussed some of the basics of phase diagrams, using the iron-carbon (i.e. steel/cast iron) system as an example. While some talk of heating, heat treatment and quenching came up in the discussion, this is such an interesting and important area I wanted to give it its own space. Besides, Fiore apparently thought it was important too.

Let's first start with the use of hot working in blacksmithing: I am willing to bet that pretty much everyone reading this blog has seen a blacksmithing scene in a movie that goes something like this:

[Dramatic music plays over a dark scene, a Blacksmith, covered in soot with biceps like sacks of melons, forearms like hams, and a beard ZZ Top would be proud of stands before a glowing forge.]
[Blacksmith pumps bellows as flames jump out of the forge]
[Blacksmith grabs glowing hunk of metal from the forge, and begins hammering it madly]
[Blacksmith looks at the piece, and dips it into a vat of water. The water sizzles as steam dramatically rises from the water]
[Blacksmith then plunges the dark metal back into the forge and repeats the process]
[Fade to black, Fade music]

Let's start with why the above process is ridiculous (and not surprisingly, is not done by blacksmiths)

Concept Clarification 3: 'Instantaneous'

I wanted to do something short and fun, and this lets me bring up one of my favorite units of measure... So here we go:

In previous posts, and in many posts that will follow, I'll say things like 'if we assume we did this instantaneously' or 'If we can do this very rapidly' or 'the change happens nearly instantaneously'. On the outside, this seems pretty simple: I'm talking about something happening in a short period of time.

But how short is short? Like so many things I've mentioned: it depends on who you ask.

Alloys, Microstructures and Phase Diagrams

With some of the basics of material crystal structure out of the way, we can move on to a more detailed discussion of alloys and microstructures. Here, I'll focus on the binary iron-carbon system, the most basic components of all steel alloys and cast iron. The solid solution formed is probably the most widely studied system in materials science and one of the most common engineering materials out there. It also makes for an interesting comparison to the common body of knowledge that trades like blacksmithing developed long before the formal background work was done.

It Glows!... Wait. Why is it glowing!?

Everyone probably knows the phrase 'white hot', many people know that steel glows different colors as you heat it up, and a fair few know that some metals don't really glow much even when you melt them, like lead or aluminum. Also, that molten rock (i.e. magma. You know you said that in Dr. Evil's voice) can appear pretty much the same color as hot steel.

Wazupwitdat?

Let's find out.

Effective Bending Stiffness of Flexible Sword Trainers

Right before WMAW 2013, I got to thinking about certain aspects of equipment safety as discussed a bit in an earlier post. Part of this was about starting an on-going investigation into the behavior of flexible sword trainers from an engineering mechanics standpoint. The hope is that it may inform safety requirements for groups and competitions as well as equipment design, and if nothing else be a bit of science-y fun.

This post will focus on the first part of that investigation: the determination of an effective bending stiffness for flexible sword trainers. I'll present data based on weapons I was able to measure myself, and provide the methodology so others may do the same. I'll take any and all data reported to me, cross-verify it where possible and make it freely available here.

Back in October, I made available a pdf of the procedure I'll discuss here, but this post will get into more detail and present more data so should be thought of as the 'real deal'.

Edit, 10 Dec 13: I fixed a sign error in the flexure formula. Signs be crazy, bro.