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.

Introduction to Crystal Structure

I talked a lot about mechanics in my previous posts, but there is another field that is critically important to understanding material behavior. That field is called materials science, and it focuses on the study of the various properties of materials. It's a fascinating field, covering atomic-level structure and bonding to macroscopic behavior such as stress-strain relations and the origins of plasticity. In many ways, the rather general field of materials science owes its origins to the much older field of metallurgy (the study of metals specifically).

So let's talk some mat sci (or materials science, if you're not into brevity… man.), specifically: crystal structure and defects in crystalline materials. As an aside, I'm kind of an odd duck for a mechanical engineer when it comes to this stuff: nanoscale mechanics was my bread and butter for almost a decade. I find this stuff as fascinating as continuum mechanics.

Concept Clarification 2: 'Why?'

In this concept clarification post, I wanted to tackle something part pragmatic, part philosophical. Because of this, don't take this as more than my thoughts on this rather detailed topic.

That something is the question 'Why does X happen?'.