Saturday, November 30, 2013

Y U No Cite Books!?

If you've been reading along in my posts and wondered at the number of references to online sources instead of actual texts, the reason is simple:
You'll probably follow a link, but I doubt you'll buy or even borrow about a dozen different engineering textbooks. Let alone keep them handy while you're reading this blog.

For many of the topics I'm covering, the Wikipedia articles are well enough written and good enough for the purposes of providing a place to go get a bit more detail. If you want more than that, go read some books.

Here are some of the texts I regularly consult while working on posts, because they are on my shelf (caveat: some of these are not the clearest or best laid out):
  • Belytschko, T. et al. Nonlinear Finite Elements for Continua and Structures. 2003. John Wiley & Sons.
  • Callister, W.D. Materials Science and Engineering: An Introduction, 5th ed. 2000. John Wiley & Sons.
  • Chadwick, P. Continuum Mechanics: Concise Theory and Problems. 1999. Dover.
  • Kreyszig, E. Advanced Engineering Mathematics,  8th ed. 1999. John Wiley & Sons.
  • Hibbeler, R.C. Mechanics of Materials, 4th ed. 2000. Prentice Hall.
  • Incropera, F.P. & Dewit, D.P. Fundamentals of Heat and Mass Transfer, 5th ed. 2001. John Wiley & Sons.  
  • Malvern, L.E.. Introduction to the Mechanics of a Continuous Medium, 1969. Prentice-Hall
  • Powers, D.L. Boundary Value Problems. 1999. Elsevier.
  • Pettifor, D. Bonding and Structure of Molecules and Solids. 2002. Oxford University Press.
  • Reddy, J.N. An Introduction to the Finite Element Method. 2nd ed. 1994. McGraw-Hill.
  • Shigley, J.E. & Mischke, C.R. Mechanical Engineering Design, 6th ed. 2001. McGraw-Hill.
  • Sims, L. The Backyard Blacksmith. 2009. Crestline Books.
As an aside, The Boundary Value Problems text by Powers is one of the few times I was very happy to have a book written by the professor teaching the class. If you are interested in the topic, it's a great book.

I'll add others to this list as I go, but these cover the basics. I'm missing a basic physics book, a statics and a dynamics book because, unfortunately, I sold those as an undergrad. Luckily, those topics are very well covered by a number of internet sources.

Wednesday, November 27, 2013

Blogger to me: OMNOMNOMNOM, was Mechanics 101, part 5

Well, this post was going to be a really long explanation of the analysis of our deformable tight-rope support, with some derivations and discussions on some of the finer points of strengths of materials. Then Blogger ate it and saved a blank page. Rather than go through the two weeks worth of work again, I'm just going to skip it and move on to other things.

Lessons learned: don't use browser 'undo' functionality while writing blog. Also: write text of long posts elsewhere and copy it in.

So moving on...

Concept Clarification 1: Strength & Stiffness

I realized that in some of my hurry to get to the fun stuff, I may gloss over some things that are a bit confusing, or I plain forgot to include it. Or hell, I may even have just made a mistake.

These Concept Clarification posts will try to help clear some of those issues up in a short and sweet post. This one will focus on the concepts of Strength and Stiffness.

Tuesday, November 26, 2013

From bathroom scale to scientific test apparatus

It all started with thinking about how I could instrument my drop tower. More to the point: how I could instrument it without resorting to the thousand dollar setups from places like Omega Engineering. During my search, I came across the affordable button load cells sold at for robotics and hobby electronics. This one in particular caught my eye, with its 1000 kg-f (9800 N) rated limit. Certainly enough for any materials I may want to test, and even high enough to make a thrusting target for measuring thrust loads.

I kept digging, and learned that the 1000 kg-f load cell I'd found was only rated for 100-1000 kg-f, so any low end force data couldn't be measured. I also found some bathroom scales advertising that they used load cells. One advertised being able to measure a load up to 400 lbs-f (1780 N): for less than half the cost of a big button load cell. So, like any good engineer would, I bought the cheap thing and started figuring out how to make it useful.
This scale has no idea what's about to happen to it.

Monday, November 25, 2013

Why a fuller doesn't make a sword stiffer

"Fullers make swords stiffer"
You've all probably heard it at least once, and possibly even said it. If you said it with me around, I probably made sure you never said it again.

For the impatient: No, they don't. Stop saying it. But kudos for not calling it a 'blood-groove'.
For the impatient who call it a blood-grove: Just stop. Please.

For the patient, read on.
For the patient wondering about hammered fullers and other things, read on... and I'll get to that.

Let's talk about sensors, baby.

In my drop tower post, I mentioned that I plan on adding a force transducer to the penetrator so I could get more useful data. For my part, the really fun thing is that setting this kind of thing up from nothing is pretty new to me. Additionally, being able to set up sensors will really open up the opportunities I have for experiments.

So let's talk about these force transducer thingies.

Sunday, November 24, 2013

Mechanics 101, part 4

In my last installment of posts on the basics of mechanics, we discussed some basic principles of dynamics and applied them to a falling ball colliding with a table. Prior to that, we discussed statics. At the end of both posts, I talked about how the deformation of real systems becomes important in creating physically realistic models for events.

In this post, we'll cover some basics of Strength of Materials and talk a little about how we can analyze deforming systems in the context of solid mechanics.

Update 26 Nov:  I added a little bit more to the talk of the Young's Modulus, specifically about how it doesn't generally change much for a given metal alloy, except as you go to high temperatures.
Update 25 Nov: I totally forgot to mention the Poisson effect during the loading experiment. This has been rectified. Please don't hate me.

Saturday, November 23, 2013

Da Towa of Testin'!

Another post to break up the mechanics posts. This time, about some of the test equipment I've been setting up. In this post, we'll take a look at my on-going construction of a drop testing tower, mainly for testing garment samples based on the tests outlined in CEN EN13567 (The standard that FIE homologation is based on. See these posts for more details).

Da Towa pities the fool. Note the manly tool bag.

Mechanics 101, part 3

My last post on mechanics walked through a few examples of statics, with the promise of some dynamics in this post. So here we go!

Delightful Dynamics

In dynamics, we're concerned with bodies in motion. Specifically, we're interested in bodies that have a net force acting on them, since statics can also be applied to bodies at constant velocity (no net force). This can include falling objects, objects colliding, a ball being thrown, etc. Let's get into some examples to show the basic principles at work.

Friday, November 22, 2013

Standards, Part 3: What the standards are good for

The last in the series of posts from my Nov 2013 article on equipment standards. See part 1 and part 2 for the rest.

Now we turn to the big question: Are any of the aspects of the FIE homologation standard (EN13567) actually relevant to our needs in HES? This question is tricky to answer fully, and is one reason I am hoping to get folks interested in better understanding the protective needs of our community. This blog is part of that effort.

Standards, Part 2: Fe, F.I.E., fo, fum!

This is the continuation of my last post, regarding standards and homologation of safety equipment.

In the HES world, one of the more commonly quoted homologations is that granted by the Federation Internationale d’Escrime (FIE) for sport fencing equipment (masks and clothing in particular). Because of its prevalence, let’s dig into it a bit.

Standards, Part 1: Homologation and you

Just after WMAW 2013, spurred on by some of the conversations I had while there, I decided to write a little article about standards. Not standards as in how well you chose who you date or how well you teach your students: standards as in safety and equipment standards. Particularly: why they are useful, why it's important to understand them, and how we, as a community, may be able to develop our own.

The original article is available here in its glorious 11-page pdf form. But I've decided to post a brief version of it here, broken into several parts, as well:

Mechanics 101, part 2

In my last post, we covered some basic concepts and definitions in mechanics. Now, let's look at using some of these concepts in the context of statics. This is mainly to act as a primer for some of the more complex analyses which will come in later posts.

Simply Statics

 In statics, we're mainly concerned with the reactions (forces and moments) that result from applying a load (either a force or torque) to a rigid object. In this context, rigid means completely unable to deform regardless of the applied loads.

Wednesday, November 20, 2013

Mechanics 101, part 1

Let's talk about basic classical mechanics since some folks may not be familiar with the precise meaning of some terminology I'll regularly use, or need a refresher.

Mechanics, or more specifically classical mechanics, is the part of physics that deals with the motion and reaction of objects under some influence (like a force). A ball bouncing, a vase sitting on a table, and a satellite orbiting Earth are all examples of classical mechanical systems. The fields of civil, mechanical and aeronautical engineering are concerned mainly with the application of classical mechanics, applied mechanics or engineering mechanics, and this is most of what will be discussed in this blog.

Within the field of applied mechanics, there are a number of sub-fields but the following are the most relevant to this blog:

  • Statics: the field dealing with the study of bodies at rest
  • Dynamics: the field dealing with the study of bodies in motion
  • Mechanics of materials (or more generally: continuum mechanics): the field dealing with the behavior of deformable objects. When applied to solid materials, referred to as solid mechanics.

Now let's look at some important terms and concepts in classical mechanics. This is useful because some of the formal meanings of these words differ from their common usages.

UPDATE 27 Nov: I added a quick definition of displacement, strength, stiffness and hardness.

Here we go!

I went and did it. I decided that sharing stuff I was working via Facebook and mailing lists was annoying, so I started this blog.

Over the next few days, I'll post some material but for now it's mostly about getting the ball rolling.

I've decided to go with fully moderated comments mostly because I don't want this to become a spammer's paradise, I don't expect too much comment traffic so we'll see how it goes. Basically: keep it civil, keep it constructive and your posts will keep showing up. Otherwise I'll just delete them because I don't feed trolls, and the goal here is to provide something useful and a bit fun.