This week we finished cutting and polishing our samples.  We measured the dimensions of our samples and found their mass and density.

We then completed a quasi-static tension test.  We clamped the top and bottom of our rectangular sample and the machine moved the top clamp upward slowly until the sample broke.  We set the strain rate to be constant at 0.001 per second for each sample.  As tension was applied, we collected data of the extension length and load applied.  We viewed the results as a graph in real time.

After collecting the data, we calculated the stress and strain for each sample.  We are making graphs of stress vs. strain and determining Young's modulus and the ultimate stress, which is the stress at which the sample cracks.  All of our samples were brittle.  That is, they broke without deforming.  After completing the analysis of all of the samples, we will check the consistency of our results.

Looking back on the process of making and testing our samples, we encountered a number of issues that will potentially result in inaccuracy.  Our 5% hemp sample had a lot of holes in it, which weakened it.  We think that if it were compacted more when preparing it, we would be able to eliminate that issue.  Also, we needed to run the tension test on some of the samples multiple times because the clamps didn't grip the sample hard enough so the sample slid on the grabs.  This is a problem if we applied a force beyond the elastic region because then we would have permanently deformed the material, making subsequent test results invalid.  However, since the material is brittle and maintained a linear relationship between stress and strain prior to breaking that was likely not an issue. 

We wanted to make a new sample of each concentration and test those now that we understand the process better.  We made a new 1%, 5% and 10% hemp composite.  However after we poured them into the mold, the 5% and 10% sample began to heat up and bubble. Either we used epoxy that was too warm (we had to heat it to melt it) or the hardener was old or we stirred too vigorously.  Now we have a foam.  Professor Gupta advised that we can test this material for compression and look under the microscope to see if the hemp goes through the holes or if the holes are completely filled with air alone.  That is what we will do next week.