Texas A&M mechanical engineering student, John Mayo, wondered if it’s true what they say about ceramics – that they are strong in compression. Armed with his pick-up truck and four trade show coffee mugs, he set to find out. Credit: John Mayo.
John Mayo, who is finishing his second year as a mechanical engineering student at Texas A&M, is a “show me, don’t tell me” kind of guy.
This spring he’s been taking a class, Materials and Manufacturing Selection in Design, and came across this in the textbook:
“Since cracks and flaws tend to remain closed in compression, brittle materials such as concrete are often incorporated into designs so that only compressive stresses act on the part. Often, we find that brittle materials fail at much higher compressive stresses than tensile stresses This is why it is possible to support a fire truck on four coffee cups; however, ceramics have very limited mechanical toughness. Hence, when we drop a ceramic coffee cup, it can break easily.”
Which got him thinking — was this a true statement? John says, “I am one to test the limits, and this statement certainly captured my attention.”
Because (legal) access to fire trucks is limited, he decided to test the statement using his Ford Ranger pick-up truck weighing just over 3000 pounds and four ceramic coffee mugs gleaned from trade shows.
Here is his description of the experiment (I especially like the mechanical engineering details):
I cut pieces of scrap wood to place above and below the cups, to provide a uniform surface. The wood also would insulate the ceramic from unevenness of the concrete driveway, especially if the truck shifted and put excessive pressure on only one edge of a cup. With a jack, two jack stands and wood blocks to keep the truck from rolling, I began at the front, left wheel. After ensuring that the transmission was set to ‘park’ and the parking brake engaged, I jacked up the wheel and gently lowered it back on the cup between two wood pieces. The cup did not break, so I added one under the front, passenger side next. The truck seemed stable, so I jacked the rear end under the differential, lifting both tires simultaneously. As soon as the tires rose from the concrete, the truck rolled forward slightly, so I let it back down and checked on the front cups. Surprisingly, the coffee cups had not broken, even though they were both titled with only one point on their rims supporting the truck.
I quickly jacked the front end up again, and supported it slightly above the cups with jack stands. Next, I jacked the rear end up again and successfully installed the cup and wood ‘sandwiches’ under each tire. Then I used the jack to remove the jack stands at each front wheel, thus getting all four wheels supported on cups.
After leaving the truck on the cups for the entire, windy night and most of the next day, I decided to test the cups further by jumping up and down in the truck bed. The cups seemed to be magically strong, so to prove to myself and others that these were ordinary ceramic cups, I used my phone to record a video clip of me breaking one of them. Wearing safety glasses and using a glass shield for the phone proved to be a wise decision, because the weight of the truck helped create an intense explosion of ceramic pieces when I tapped the cup with a hammer. The video clearly demonstrates that the cup is indeed ceramic and that the truck’s weight is substantial.
I asked John whether he often takes up ‘extracurricular’ experiments like this. He said, “I do not usually think of them as “experiments,” more of just an “I wonder if” idea put into action.”
Once, for example, he and a buddy wondered whether they could harness some of Texas’ high winds to pull their bicycles down the road using parachute-like kites. Another time he and some pals decided that $200 was over their budget for a small catamaran mast float. Instead, they gathered up some floating duck decoys and modified them into a workable substitute.
A self-described tinkerer John says, “I’m always “doing something” which I find much more interesting than merely sitting in front of a TV or video games.”
In fact, this coffee mug experiment made him wonder what would happen if he did the same experiment using unopened soft drink cans. That experiment can be viewed here, and in the background you can here him definitively state his conclusion, “OK. Soda cans do not work.”
He spends his spare time helping out the local high school and middle school robotics teams or restoring his 1978 CJ7 Jeep. In the future, plans to pursue a MS in mechanical engineering and hopes to work on robotics-related technology such as unmanned ground or aerial vehicles.
This summer he’ll be working for Boeing in Mesa, Ariz., on tooling mechanisms for Apache helicopters.
I hope they can provide a coffee cup for him. He’s running out.
The textbook that triggered the experiment was The Science and Engineering of Materials, Sixth Edition, Askeland, D. R., Pradeep, P. F., and Wendelin, J. W. 2006, Cengage Learning, Stamford, CT, pp. 220.