Thursday, 1 December 2011

RepRap Material Test Facility - Part II

Hmmmmm ...

... this may need a little more thought.

I made some sample test pieces and a test bed, and the first thing that became apparent is that the original design is all a bit unstable for the sorts of loads that are required to load the test pieces to destruction - basically, the whole assembly will probably topple over long before you can get the full load applied, if you use my original part designs.

So I modified the designs to make it all a bit more stable, by adding some broader  feet to the test bed, and making the supports on the test pieces a bit wider. I also added the option of a removable Load Platen, to allow the test load to be applied more easily to the load pad on the top flange of the test piece, if desired:

and here are the parts I made:

and here's the complete assembly (using the lighter, weaker I-Beam test piece, rather than the solid rectangular beam) sitting on my kitchen scale (so I can do some quick load testing):

and here it is with my thumb applying a 5 kg load:

You can see that the test piece is bending, but it has only deflected about 3 mm with 5 kg load, and it is nowhere near structural failure. At a guess, it is going to be able to sustain more than 10 kg of point load.

So, what's the problem? Well, 10 kg is going to be quite a pile of weights, and I am not sure how to apply that much weight to such a small load pad in a stable fashion , and still have room to get my digital calipers in to accurately measure the deflection for the various load increments. I'm going to have to work out a simpler loading mechanism which can apply 10 or 20 kg of load, while still being able to measure both applied load and the resulting deflections.

Does anyone have any suggestions?