This is one of Leslie Mashonga's Honor's projects at YSU Engineering. We wanted to see if we could see the increase in the ultimate yield stress of a material good only in compression (like cement, concrete, or here, plaster of paris) is we prestressed it into compression. We did this by having the material set around stretched rubber bands and then tested them by pulling them to failure.

Here is the 3d printed mold for the test specimen 'dogbones', with room for the rubber bands. From his report it looks like it worked! Well, in fact. Perhaps too well, as described in his thoughts collected at the end.

The mold is printed at 60% infill and in PLA.