Discovery Channel - Smash Lab

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Hi all...

I'm Mary, the Discovery vice president overseeing both MythBusters and Smash Lab.  I've been reading all your posts with real interest.  With regards to MythBusters, I feel so lucky to be involved with a show that sets such a high benchmark for popular science storytelling.

Smash Lab is a different program set around a concept we call "dangerous experiments for a safer world." Our Smash Lab team uses cutting-edge technology to make our lives a little safer.  We're a brand new show with a big idea and we're working hard to get the science and storytelling as good as we can as fast as we can. I'm paying attention to all your messages-- even the "ouch" ones-- to figure out ways to make it better.  We'd love your ideas on how to make our experiments stronger.  What would you do differently?  What innovative materials would you use? Let us know and keep watching while we work with you to make Smash Lab a show you love to watch.

Vice President, Creative Content/Talent
Discovery Channel

Railway Smash

Episode 4: Train Crash
The Challenge: Could giant air bags on the front of a train push a car stuck on the tracks out of harm’s way?

The Material: Air bags. The same ones used inside cars to protect us during a car crash, just attached to the front of an 8,000-ton train.

What to Watch For: The lopsided face-off between an 8,000-ton train and a 2-ton car.

When to Watch: Wednesday, Jan. 30, at 10 p.m. ET/PT. Get a reminder.

A Swirl of Questions, Calculations and Tests

Deanne writes:
A lot of interesting questions on the topics of mobile home construction and the practicalities of carbon fiber came up for us during the testing for this show. We had our own theories, but it would be interesting to find out what you think.

1. How would you shape a mobile home to give it the most defense against hurricane force winds? And make it architecturally functional/practical?
2. Do you think that the mass production of carbon fiber will ever drive down cost enough to see this as a potential solution for mobile homes, perhaps in 10 years? (The high cost of this application was a big concern for us, but our show is about testing proof of concepts, so we proceeded nonetheless. Many airplanes will be made of carbon fiber soon enough, and manufacturers are increasing its production, so it was an interesting debate.)
3. Carbon fiber is extremely lightweight. It has high tensile strength, but only low to moderate impact resistance. Can you think of a lightweight material that may work even better in our application?
4. Mobile homes are elevated and rest on blocks. If you could put up a temporary cladding around the open space below the home, would you? And what would you use that is removable after the storm?
5. I’ve met two guys who tried to make diamonds out of carbon fiber. I’ve never tried it and they couldn’t get it to work, but could it be done?
6. The Smash Lab team met Burt Rutan, the creator of Spaceship One, at a small, local diner at the Spaceport in Mojave. Would you go into space if you had the chance?

Now, for my unofficial lab notebook pages. Our challenge for this episode was to find out if carbon fiber cloth could protect a mobile home against hurricane force winds. We limited our tests to carbon fiber and only testing the effects of high-speed wind.

Note that many alternative building materials are available and that a hurricane is comprised of not only strong winds, but also immense rain,  flying debris, storm surge and, of course, potentially long duration, which equals structural fatigue.

Material:
Carbon Fiber Cloth and Resin.

Tensile strength of our woven carbon fiber fabric is 150,000 psi. A mild steel, ASTM A36, has a tensile strength of 36,000 psi. Unidirectional cloth is often used in hoop stress applications such as reinforcing pipelines. Bidirectional cloth is the better choice for application in a hurricane because the winds may come from any direction. We used bidirectional cloth in our test, which has an equivalent strength of a 1/16-inch-thick plate of steel.

Hypothesis:
Carbon fiber has incredible potential when applied to conditions requiring tensile reinforcement, so its ability to minimize deflection of panels due to high pressure wind is almost certain. On the other hand, carbon fiber is not very impact resistant, but may prove to have some minor improvement regarding flying debris damage. The focus of our debris failure is solely linked to wind, and how wind may further damage a home once debris initiates damage to the home.

Testing:
Qualitative tests were performed for the audience to describe carbon fiber cloth's tensile strength and impact resistance qualities. (We used old samples that were falling apart, but they still worked.)

Wind tunnel tests were conducted (and omitted from the final show) that studied the flow of air over a 1/12-scale model of our trailer.  Of course, a wind tunnel creates laminar, smooth flow, but a mobile home would be mainly subjected to turbulent winds during a hurricane. Nonetheless, here's a list of the major failure points of a mobile home:

1. Hurricane force winds create positive pressure along the windward face and low pressure on the leeward face. Basically, this creates a huge force along the windward face of the mobile home and can cause deflection or even shear fracture – much like we saw on the shed test.
2. Large flow separation occurs at the corner of the front wall and roof.  This creates a negative pressure region along the roof that creates suction and  can cause the roof to peel back at the corners.
3. The wind along the front face causes a moment/torque, giving it a tendency to tumble as opposed to shift backward.
4. Even though we could barely see them, a research specialist in hurricane structure damage told me that hairpin vortices along the roof corners of the home are one of the most significant causes of damage.

We also explored various ways to reshape/retrofit an existing mobile home to make it more aerodynamic during a hurricane and/or create a downward force toward the ground, but found that the shape change would have to be very drastic to have any effect. There are two main issues:

1. Hurricane winds can come from any direction.
2. Since the fluid dynamics of any wind is that it has a velocity of zero on the ground (standard boundary layer stuff) and the velocity increases as you go up in altitude, a change in roof shape would have little to no effect in pushing the home down. The only potential change we decided on would be to change the entire structure to have more of an ellipsoid profile, to create a shape with a lower drag coefficient, thus minimizing the stress on the corners. (The classic Airstream trailers got their name for a reason ...)

The shed tests were fun. Nick and I made weak structures to see where the wind damage occurs first. The front wall of the shed cracked in half, shearing at a nail.  If there is one thing we have reaffirmed on this show it’s that fasteners are the most common failure point … over and over again. We’ve seen it on planes, buildings, cars and everything else. (So, choose your fasteners wisely!)

Calculations:
Kinetic energy (N*m) = 1/2 * mass * v^2

For a gas, the mass is spread out over volume, so we replace it with a density yielding:

Stagnation Pressure applied to the exterior of a structure (N/m^2) = 1/2 * density * v^2

At a height of 10 meters (33 feet), the standard atmosphere (defined in 1976) says that the density is 1.22 kg/m^3.

Let’s assume a wind speed of 150 mph (67.056 m/s). The quick and easy version, which rolls all of the above assumptions into a coefficient-style formula, uses this equation:

Stress = 0.00256 * v^2, where v is in mph and p is in lbs/ft^2

In English units, this equates to .4 psi. It doesn’t sound like much; however, a person has a cross-sectional area of 6 ft^2, which means s/he gets blasted with 346 pounds of force in a category 4 storm. It’s not easy to stand in that -- and Kevin proved it!

I won’t do more math, but knowing that carbon fiber has a tensile strength around 150,000 psi, Nick and I were obviously confident in our design.

Application:
The home that was purchased for us to use was literally rotting. So, in order to give the carbon fiber a realistic substrate, we added a thin plywood cladding on the outside of the mobile home. Carbon fiber strapping was then applied around every corner at 3-foot intervals, and carbon fiber sheets were applied to the entire façade of the home with at least a 6-inch overlap between panels.

To prevent the mobile home from rolling we came prepared with anchor straps. Unfortunately, we assumed we would be on a concrete foundation, but Kevin and Chuck’s secret locale was a spaceport that allowed us to anchor to sand, and only sand. We improvised a set of welded spikes, since that was our only resort due to time constraints.

Final Test:
Airplane thrust ranging from category 1 to category 5 winds and debris from an amazing 2x4 air cannon.

Results:
As suspected, carbon fiber was successful at structurally reinforcing the mobile home, but it still suffered from impact resistance exerted by flying debris.

We also learned the hard way that anchors are critically important in saving a mobile home from hurricane damage. If you don’t anchor the mobile home down, it may even become debris itself that destroys other nearby structures. While Nick and I  had to improvise on the spot since we were anchoring the structure to sand, not a concrete slab foundation, homeowners should not improvise if their mobile home is at risk. Buy the proper anchors, check them annually for corrosion, and no matter where you live, listen to your local emergency manager’s advice and orders to evacuate during serious storms.

Hurricane Facts:
One of the best ways to find out more about how hurricanes work is to collect meteorological data from them such as wind speed, temperature, pressure and precipitation – from an airplane! Flying an airplane into a storm  is a very effective way to get observations of the hurricane, since it can directly measure the data needed even when the storm is far away from land. The U.S. Air Force and National Oceanic and Atmospheric Administration (NOAA) "hurricane hunters" fly into several storms every season, collecting data that is used by researchers, forecasters and numerical weather models to help predict hurricane tracks and intensity. I know this because my brother happens to be a meteorologist who flies into the eyes of these storms. He’s flown in Katrina, Rita and many other types of weather phenomena to deposit dropsondes, little GPS-enabled parachutes, which measure useful meteorological data.

Another interesting thing that I’ve learned from my brother is that monetary assessment of hurricane damage has been estimated to be proportional to the wind speed anywhere from the 3rd power up to the 9th power. So, the difference in damage of a category 4 and category 5 storm is HUGE in comparison to the damage between a category 1 and 2.

For tons more info about hurricanes, go to the following Web site: http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html

Gale Force Testing

Episode 3: Hurricane Proof House
The Challenge: Attempt to protect a mobile home from hurricane-force winds with material used to reinforce concrete beams.

The Material: Carbon fiber cloth is a tough, new material designed to reinforce concrete beams and other structures to make them stronger. Could it be wrapped around a mobile home before a hurricane hits?

What to Watch For: A wind machine blowing gusts of 150 mph.

What Happened Behind the Scenes: Deanne is back with more calculations and insider hurricane tidbits from her daredevil meteorologist brother.

When to Watch: Wednesday, Jan. 23, at 10 p.m. ET/PT. Get a reminder.

Car-Stopping, Concrete-Crushing Calculations

Deanne writes:
With every simple test you see on TV, there are lots of calculations being done behind the scenes. To pick the proper densities of aerated concrete, we needed to figure out some general numbers for the energies we were dealing with. The general idea is to use work and energy principles.

The Calculations
Initial kinetic energy of the vehicle — rolling and crushing energy — equals final kinetic energy of the vehicle. The calculation looks like this: ½ mv^2 - µmgd – (area under the concrete stress strain curve)x(volume of crushed material) = 0

Now for the geeked out definitions: M is mass of the vehicle; v is velocity of the vehicle; mu is the coefficient of rolling friction; g, you know as our friend gravity; d is the distance we are solving for, and the other two get into really complicated integrals real quick.

As an aside, wind resistance and the change in potential energy due to the vehicle dropping into the bed were neglected. It was assumed that the accelerator was off once the vehicles entered the arrestor bed.

Using these calculations, we chose three different densities of concrete to test. Since I’m no concrete expert, we had to consult our concrete team about approximate air percentage mixtures. More importantly, we needed to know how those percentages correlate to our desired compressive strengths, and what that translates to in terms of cure, or solidifying, time. Another big factor we had to deal with was a seven-day cure time, which is significantly shorter than a regular concrete pour. This means that you have to approximate what the strength of the concrete will be mid-cure.

As you can tell, things get complicated fast and it doesn’t translate well on TV. So, our calculations get us in the ballpark and then allow us to do the tests that you see. Since the calculations get us in the ballpark, the tests help us to hit a home run.

Once we picked three densities of concrete, it was onto our tests.

Concrete Compression Tests
This day was our first introduction to using high-speed cameras. Oh my goodness, people! These things are amazing. I am convinced that you could film anything in high speed and be amazed when you play it back in slow motion. High speed of a person laughing would be doubly hilarious. High speed of someone dropping something would seem doubly as clumsy. And, of course, high speed of me punching a calculator would no doubt be doubly as geeky.

The footage showed us that our middle density concrete was the way to go, but we had to scale the numbers a bit. We made it slightly less dense, and added an entrance ramp to the design because we wanted to make sure that the crushing would initiate. We had to figure out the depth, which was a huge decision and required another test that didn’t make it to TV. All to stop a vehicle going really fast -- and we have one shot and one shot only. Engineers don’t usually have one shot, unless you’re designing the Mars Rover or something. (I have so much more respect for challenges like that now.)

Pour Day
Nick and I were a bit bummed because we didn’t get to see Chuck and Kevin’s car crashes, but our day ended up being a blast. We went all the way out to the test site in the canyons. The concrete trucks started rolling in and we had one more chance to second-guess our decision on the concrete, but we stuck with it. Then we suited up and got our hands dirty. We started pouring and pouring, and pouring, (put on sunscreen) and pouring, (learned the trucker lingo) and pouring, (sun went down) and pouring, (called Chuck and Kevin) and pouring, (put up lights) and pouring. OK, you get the picture. It was A LOT of concrete. But it was fun to pour and the concrete guys were awesome. Now it was a waiting game. Hopefully it sets up like the arrestor bed we are hoping for.

Crash Test Day
This is it.  Vehicles will be crashed! Concrete will be crushed! Chuck and Kevin haven’t got a chance against our arrestor bed. =) Now, while I razz them on TV, I’m really a big fan of success in general, so I just like to push their buttons sometimes in friendly contest. We all get along so well. Freakishly well.

There is one thing you need to know about high-speed cameras. They need an absurd amount of sunlight. Lots and lots of light to get good footage. And they take forever to set up. So preparation keeps going, the time is ticking, the sun is dropping, and our bus has to get moving or we lose our final shot. So once it was set, it was GO, GO, GO!

First is testing the arrestor bed. I was nervous. This was it. What if it fails miserably? Will I be amused or horribly disappointed? The truth is, both.

Car Test on the Arrestor Bed:
The car starts moving. I got really nervous right before Mike Ryan, our stunt driver, hit the concrete, because I wanted to make sure he was safe. We were testing a proof-of-concept after all. But once he blazed over the bed and avoided every camera obstacle in his way, I remembered that he was a professional. But our bed was way too dense for a car to sink in, so it was time to go BIG and bring in a bus.

Bus Test on the Arrestor Bed:
After some very “Sandra Bullock/Keanu Reeves moments" driving a bus at high speeds, Nick and I prepared for the big test. Nick practiced driving the bus via remote control and I practiced, well, nothing. I just prayed to the gods of concrete for success.

The final test was sooo dramatic. Way more so than on TV.

The bus starts moving. It looks so slow from far away, and then once it gets closer, the nerves kick in. It’s fast, really fast. Then BOOM! It goes off the ramp, into the concrete, it isn’t stopping. Then it slows down, veers to the right, just misses the cars, and stops. Whoa! I was ecstatic. We ran to inspect the wreckage and we found a huge track of pulverized concrete – the exact width of the tires. The helicopters had my hair in a mess. It was a rush of excitement. So much so, that I had to do a snow angel in the concrete, just to celebrate our success. Our final test worked! Well, mostly ... So, we would have barely hit oncoming traffic, and if I had to do it all over again, I would definitely use a lower density of concrete. While we didn’t do an ASTM (American Society for Testing and Materials) standard compressive strength test of the final arrestor bed, I believe our mode of failure was that the compressive strength of the concrete was above the contact pressure of the bus tires (around 54 psi). We were hoping that the entrance ramp would help us overcome this by initiating crushing, but we just didn’t manage to sink into our full depth and achieve full energy absorption. Considering our short time span and short cure time, we managed to absorb a significant amount of energy, and the test was a success. The technology proved that it could work.

Bus Barrier Test:
You don’t get to see this one on the show. They were great crashes, but the bus obviously didn’t perform any better than the car barriers did. The drama, though, was like a real action movie.

The barriers were in place. The cameras were set. The helicopter started swirling. Our director of photography started running up the hill to film us. The bus started driving ... and then our cameraman’s camera ran out of tape! The sun is halfway down, the bus is picking up speed, and a guy with a fresh tape is running up the hill as fast as he possibly can. The tape was put in the camera about three seconds before the bus hit the barrier. The camera swings to us, and BOOM! The bus hits the barrier and it annihilates it. Completely. Ahh, it makes me energized just thinking about it! Then to make things even crazier, we run down the hill to see the wreckage with a helicopter swirling 75 feet above us. For the first time in my life, I wanted to pinch myself. I do a lot of crazy things, and often times think they are too good to be true, but this was an experience that made me question my own reality. Am I really doing this? Crashing buses? Performing huge scientific experiments that work, with a helicopter flying above me?

The answer is yes.

A Crumbly, Crushing Crash

Episode 2: Crash Absorbing Concrete
The Challenge: Use the latest aviation breakthrough technology to prevent a car or bus from crossing a median and smashing into oncoming traffic.

The Material: Aerated concrete, a crumbly, crushable material laid at the end of runways at 18 select airports across America. Right now, it’s used to stop a plane that has overshot the runway, but what if the concrete was laid in the central median strip on a highway or used to make some new kind of barrier?

What to Watch For: A car weighing 4,000 pounds crashing into an aerated concrete barrier, producing 9 Gs of force.

What Happened Behind the Scenes: KE=1/2mv^2 = Fd… Stay tuned for Deanne’s behind-the-scenes calculations and post-experiment thoughts.

When to Watch: Wednesday, Jan. 16, at 10 p.m. ET/PT. Get a reminder.

Keep telling us what you think.