Flixtix,
I'm one of the four students that worked on the project and we had about 11 weeks to complete the project.
Fracture strength is the amount of load that a sample can hold before it breaks. This is dependent on the cross sectional area. We used an ASTM standard (D638) for tensile testing, so our dogbone-shaped samples were of uniform cross-sectional area, allowing for easy comparison to other materials.

A 2^4 Full Factorial experiment takes four factors (print orientation, print speed, anneal temperature, anneal time) at two levels (high and low) and puts them together in all possible combinations. For example, one sample was printed at the horizontal print orientation, at 45mm/sec, annealed for 70˚C for 15 minutes in an oven. After testing, we were able to investigate which factors/parameters were the most influential on the strength of the part.

Anneal temperature and time are actually post-print processing techniques more commonly used in metals processing. Once our samples were printed, we placed them in an industrial furnace at the appropriate temperature (25˚C, 70˚C, 140˚C) for the specified length of time. Our samples were printed at 190˚C at the hot end of our printer.

Thanks for your interest and let me know if you have any more questions,
Ben