My Thesis
As of today (May 6th, 2009), I have about five weeks before my thesis has to be completed for my master’s degree at Georgia Tech. In addition to the necessity of hunting for a job, I’ll be putting “new blog posts” on the backburner until my thesis is officially done in early July. I might put small updates on my research here before I return to regular writing, but I’ll stay active through Twitter (my tweets are visible in the right sidebar here).
My thesis is on fatigue crack initiation in cross-ply carbon fiber laminates. The majority of the work was experimental tensile testing of that material (the image above shows one of my test specimens in the grips of an MTS brand servo-hydraulic tensile testing machine), but I’m also supplementing that experimental work with analytical and Finite Element modeling, as any good engineer must.
Behold, a crack in one of the test specimens:
The horizontal bands in the image above are the individual carbon fiber laminas: there are ten 90 degree laminas in the middle of this layup with a 0 degree lamina on the “top” and “bottom” of the layup. The thickness of that 12 ply layup is 0.093″. Below is a further magnified view of the 90 degree plies–the circles in the image are the cross-sectional tips of the carbon fibers, which are embedded in the surrounding epoxy matrix:
When I return, you can call me Master.
Valuable Mechanisms: The Design & Engineering Blog of Justin Ketterer 
Quick question: did you fabricate your test sample as part of this research or is it ‘off the shelf’ as it were? (Is there even such a thing as off-the-shelf carbon fiber laminate material?)
Hey Earl,
The specimens I’m using were made and sent to us by the project sponsor, Boeing. They were cut from a plate of “cross-play layup” (i.e., 0 degree and 90 degree fiber orientation) material using a diamond saw. The plate was made out of unidirectional prepreg tapes of Hexcel IM-7 fibers with Cytec’s 977-3 epoxy as a matrix, which has to be cured in an autoclave. We have a few autoclaves here on campus at Georgia Tech (which unfortunately I haven’t had the privelege of using–but I’ve got a few more months here!), but Boeing wanted to manufacture the specimens in-house, to “aerospace grade” specifications.
For cruder, autoclave-free laminate fabrication, I’d recommend checking out my post on racecar fender fabrication. It’s a pretty extensive write-up, and describes the mold-making and vacuum bagging process. If you get room temperature curing epoxy, then even fancy vacuum bagging systems and heating rooms aren’t necessary to make the composites.
Cured carbon fiber laminate can be bought off the shelf though. GMail’s creepy email-reading algorithm always thinks I’m interested in buying the stuff, and keeps recommending the following site to me:
http://dragonplate.com/
I haven’t checked to see if McMaster-Carr sells cured C.F. laminate, but I’ve stopped suspecting that they wouldn’t carry anything humans would ever need, hahahaha.
(p.s.: lol )
Hmmm I might have to try a few experiments of my own (think: chair.) At least now I have a go-to-guy for product testing!
Booyah!