Week 4: My Kevlar Gets Stuck

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Friday, July 5, 2013


Alec Lindman

My main accomplishments this week comprised one material project and one conceptual breakthrough: I built a fully analogous test rig for the Kevlar strands, and I figured out an elegant way to route them. Since the Kevlar strands are the most critical component of the source assembly, it’s important to verify that they behave as expected. My test system consists of adding the proper end attachments to new samples and breaking them with the force meter.

In the final assembly, the Kevlar will suspend a central rod from a frame, holding it very precisely in place while thermally insulating it. The key point in attaching them is to ensure they don’t bend where they meet the support, so knots won’t work. The solution we employ is to glue them in place with epoxy, in such a way that they run straight out from the support towards the load. The previous test I ran used knots, but with unexpected results: even when the strand failed in the middle between the end knots, it broke consistently at about 50% of the theoretical load. The knots were having some subtle but significant effect, and testing the fibers with epoxy terminations will be important to verify they can attain their design strength. On Friday afternoon, I completed the test jig and will break the samples first thing on Monday.

How the Kevlar is routed around the structure is another important factor in the mechanical and thermal performance of the source. Previously, we had considered using four threads to hold the center rod, but I simulated the deflection in that configuration and ruled it out as too flexible. Six threads will provide complete geometrical constraint, and I have figured out how to arrange this with only three separate Kevlar segments.

On Thursday afternoon, we had a delightful reception with the Development Board at ACP, and I had the opportunity to meet a number of exceptionally interesting people. Dr. Mather was in full swing answering questions about Webb, and I even had an extended conversation with the emeritus director of NIST. It’s wonderful that so many significant people in science are specifically interested in interns like us – though they all went through their own similar experiences to get where they are.

Our meeting with the SPS Executive Committee on Friday was a bit more lighthearted – we conducted many trials of an experiment involving small-scale rubber band rockets and each other. The committee members even got involved, and we concluded they are, in fact, fun. As has been our whole summer so far, definitely including the performance of the Capitol Steps on Friday night.

Alec Lindman