Adhesive tape strength
The hypothesis that the duct tape will require the greatest amount of force to be pulled off the steel surface, is correct.
Duct tape was initially developed in 1942 during World War II to seal ammunition cases. It was made with rubber based adhesive for water resistance. Fabric was included in the tape to give it strength. These properties made it useful in making quick repairs of firearms, vehicles and even airplanes.
Repeat the experiment with various other brands of the same types of tape. Observe if there is any difference.
Try to repeat the science fair project using double sided tape.
The experiment can also be done to see the effect of a wet or oily surface on the adhesive strength of the different types of tape.
Different types of adhesive tape and what is it used for - http://ezinearticles.com/?Different-Types-of-Adhesive-Tape-and-What-it-is-Used-For&id=1798338
Types of adhesive tape and what is it used for - http://www.ehow.com/facts_5793389_types-adhesive-tape-_amp_-used.html