I wondered how much stronger a printed I-beam would be if it were reinforced with steel bar. So, I printed three beams and broke them.
Results:
The steel reinforced beam was 50% stronger and 100% heavier. However, I believe using smaller reinforcement bars and adding more web area to the beam would drive the strength results way up and the weight way down.
This sparked my imagination a little and I really believe that using 3D concrete printers to make structural members with rebar installed layer by layer would be a very viable business. It would be much cheaper than making expensive molds while allowing for nearly limitless design possibilities.
Those diamond shaped holes are forming a shear plane down the dead center causing a split. Changing these to true circles/ellipses would help prevent this. Also, printing them face-flat should also increase the strength. Very interesting testing, thanks for posting.
I forgot I had already posted this. I just put the diamonds in the center to make it print with less warping and without supports. I didn't play with it after this test. The most obvious change is probably to use a smaller steel bar (which I meant to do to start with) as well as adding more shear area in the web. If I were to do this again I'd probably try to run some simulations in CAD to get the stresses evened out all over the beam.
I was hoping it would spur some interest and others would post some tests of improved versions and novel applications.
I would like to see you try that using carbon rods instead of steel. It would not be quite as stiff, but I think you could get better bonding between the carbon and plastic than between steel and plastic. Also the thermal coefficients would be closer.