Today marks the final day of my brief yet incomparable time at Chesterfield. I started the day continuing to use the Lulzbots with Natalia. We printed another cylinder out of PCU for dog bone testing and finally got the other printer to work properly! For that one, we used a slightly different polymer that was more rigid at room temperature. Instead of printing a cylinder that would be cut into dog bones later, we directly printed dog bones onto the second Lulzbot, even though they did not turn out great (many of the samples ended up breaking). Natalia also fixed the other material extrusion printer that can go up to 600*C at the nozzle for printing special polymers, and we started some dog bone prints on that as well.
As we waited for the prints to finish, she explained to me some of the science behind the data analysis. There are two main things of importance when analyzing the data from mechanical testing of these dog bones: the stress vs. the strain. The strain is how much distance the sample moves while the stress is the amount of force used by/exerted on the object. As depicted in the graph below, the stress is the y-axis variable and the strain is the x-axis variable. Stress is measured in Megapascals (a standardized measurement of force) and strain is measured in millimeters. The x-mark on each curve represents the stress and strain at which the material breaks. The linear representation of glass in the graph reveals its brittleness: low strain yields high stress because it will break under a lot of force without stretching much. A material like rubber, evidently, will stretch more even when experiencing less stress. The unique corner on the aluminum curve represents the yield strength: the point at which the material will no longer return to its original shape after being stretched since the strain has exceeded the material’s ability to repair. Another interesting note is that the “stiffness” of each material is represented by the slope of the curve before the yield strength.
That’s basically all we did today! It was concise but fun at the same time. What strikes me is that my experience in the past eight days has been so much more beneficial than I had anticipated. I did not expect to understand so much of the information I was given, and it inspires me that there are such dynamic lab groups working on extraordinary projects that are truly aimed towards helping humankind. I think the bigger picture is what got me; the people I met here at Chesterfield are not motivated by publishing papers or pursuing degrees. Rather, they cherish the excitement that comes from developing devices that they know will go to help those in need. I sure will remember all the phenomenal educational learning opportunities I have had, and I definitely will not forget the benevolence and dedication of all the people I have worked with throughout this journey.