Diversions

Engineering the Perfect Crash Test Dummy

May 12, 2014

If you’ve ever been in a serious auto accident, chances are you owe your life to Sierra Sam and his descendants. But crash test dummies aren’t just store mannequins with stickers on their heads: they’re highly sophisticated precision engineering tools that can cost hundreds of thousands of dollars and take years to design and perfect.

A Crash Test Dummy Doesn’t Splat

The first crash tests, back in the 1930s and 1940s, were carried out using human cadavers. There are very good reasons why we don’t do that any more. Apart from the ethical issues of using dead people, especially children, cadavers don’t actually move like live humans. Crash testing is, by its very nature, destructive, so each cadaver can only be used once, and testing is a messy, unpleasant business. Most importantly, unless you’re prepared to open them up in all sorts of gruesome ways, experimenters are limited to visual observation and very limited stress testing.

From an engineering point of view, crash test dummies are superior in many ways. They are filled with sensors that generate far more usable data than a real body. They’re much more pleasant to work with, and damaged parts can be replaced, allowing the dummy to be reused many times.

How Dummies are Designed

Modern crash test dummies have come a long way since Sierra Sam was developed in 1949 to test ejection seats. They have to conform to a complex and demanding set of design requirements. To start with, they have to simulate skeletal articulation and body composition using plastics, leather, steel, springs, and other materials.  Humanetics, the world’s leading supplier of dummies, based in Plymouth, Michigan, offers dummies in varying shapes and sizes, representing different heights and weights. The petite female Hybrid III 5% is just 4’11” and 108lb, while the large male Hybrid III 95% clocks in at 6’2” and 223lb. They also have a range of child dummies, ranging from newborns up to ten years of age.

Different types of dummies are designed for specific types of crash tests. The required testing regime (explained here by Citroen) includes frontal impact, side impacts, rear impacts, and objects entering a vehicle. The efficacy of the seatbelts, airbags and the integrity of the structure all need to be checked. Occupants may be ejected from vehicles, or trapped inside a rolling car.  Riders may be thrown from motorcycles, and pedestrians may also be struck. There is a specialized crash test dummy for each of these tests, each designed to measure specific forces and look for specific types of injury.

And don’t forget that it’s not just humans who travel in cars – a lot of us like to bring our canine companions with us when we travel. They, too, can be thrown around in the event of a collision or other incident, causing serious injury or death to themselves or the human occupants. To address this, Sleepypod designed Max and Duke, two crash test dogs.

In order to get accurate measurements of exactly what goes on in an accident, the dummies are filled with sensors such as accelerometers, potentiometers and strain gages. Researchers can see to the millisecond exactly what forces a body is subjected to, and at what point a rib would break or how fast a skull would strike a door. A Hybrid III records over 30,000 individual measurements on 58 data channels during a crash lasting just 0.2 seconds. The data is stored on a computer located safely in the dummy’s chest.

Testing the Testers

Every crash test dummy has to be designed and built to an extreme standard of ruggedness. Both the dummy and the inbuilt sensors have to be able to stand repeated heavy impacts that would quite literally tear a real person apart. They also have to conform to highly demanding technical standards. The Society of Automotive Engineers (SAE) oversees and approves all crash test dummies to ensure compliance with current standards. In addition, the National Highway Safety Transportation Administration (NHSTA) and other national and international bodies around the world specify requirements such as the exact placement of calibration markings on the dummy to ensure standardized observations.

Completed dummies are then beaten with metal poles and pendulums, thrown around on test platforms, and stabbed with various objects to ensure that the neck and spine flex correctly, the leather skin punctures realistically, and that the ribs move as expected. Only then are they ready for a real simulated crash.

So next time you step on the brakes a little harder than usual, say a quiet thank you to the engineers who created the crash test dummies. Their work may be all that stands between you and tragedy.

 

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