Anatomy of a Crash-Test Dummy
We've been learning a lot from dummies
PHOTO: Chris Mueller/Redux
HALF A DUMMY
The vinyl flesh was removed from half of this dummy to expose its skeleton and sensors. Its maker, Denton ATD, normally assigns only serial numbers to its dummies, but this special unit, used in trade shows all over the world, was nicknamed Fred.
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His bare buttocks rest on the cold steel shelf; the smooth, hairless skin has a ghastly pinkish-orange hue. His toeless feet lie nearby, alongside his head, rib cage, arms, hands, and legs. Could this be the grisly scene of some ritualistic slaying?
Not quite. A white-coated technician enters the room and transports the body parts to a wooden workbench. He takes an Allen wrench and screws the feet to the legs, the hands to the arms, and then the limbs and head to the torso. When he's finished, another Hybrid III midsize adult male anthropomorphic test device has begun to come to life. Or at least what passes for life for a crash-test dummy.
This Hybrid III is the handiwork of Denton ATD, a 170-employee company with facilities in Michigan and Ohio that manufactures some of today's most advanced crash-test dummies. These human surrogates simulate how a real person's body would respond in a car crash and help ensure that a new car's seat belts, air bags, head and armrests, structural frame, interior padding, and other elements provide good protection.
In a few days this new Hybrid III unit will be instrumented with force, torque, and acceleration sensors and then shipped to an undisclosed automaker in the Detroit area. There he'll be placed into brand-new cars and endure a torturous range of injury and insult: head-on collisions, rollovers, rear and side crashes--all to certify that the carmaker's vehicles can protect their human occupants in the event of an accident.
The dummy's ordeal, in other words, could someday save your life. But you'll probably never get to meet this electromechanical marvel. He doesn't even have a name. In the records that register the dummy's parts, his crash-test history and, ultimately, his retirement date, he'll simply be known as No. 0200-137.
This past summer, I visited Denton to see how the company makes its extraordinary dummies. Denton's assembly plant sits amid cornfields just outside the picturesque town of Milan, Ohio (population 1445), birthplace of Thomas Edison.
When I step inside the company's unassuming building, the first things I see are body parts--everywhere. ”Here's a thorax,” says Mike Beebe, a senior vice president at Denton and one of the world's leading experts on the art and science of making dummies. ”There's a spine box, with all the different pieces. That's an abdomen. Those are arms. Legs. Heads.” I try to mentally arrange a full body out of the disordered parts, but what springs to mind is something alarmingly Picasso-esque.
Beebe points to a photo showing a group of dummies. ”Family portrait,” he quips. The family includes the most widely used dummy, the Hybrid III 50th-percentile male, meant to represent the average North American man. He weighs 78 kilograms and is 1.75 meters tall--or would reach that height if he could stand, which he can't, because he's in permanent sitting mode. Hybrid III has a petite wife (Hybrid III 5th-percentile female), three kids (Hybrid III 10-year-old, 6-year-old, and 3-year-old), and an oversized cousin (Hybrid III 95th-percentile male), who tips the scales at 100 kg--the ”big guy,” as Beebe puts it.
PHOTO: Chris Mueller/Redux
Denton's most complex force sensor, the pelvis load cell of a WorldSID dummy, can record 12 data variables.
This family of dummies is designed for use in crash tests simulating frontal impacts: cars running squarely into other cars, trees, walls--that kind of thing. Also in Denton's catalog of 40 dummies are models for testing side impacts, rear impacts, accidents involving pedestrians, and air-bag blows on small children. Denton's customers include Chrysler, Ford, Honda, Hyundai, Nissan, Porsche, Volkswagen, India's Tata Motors, and China's FAW. The company ships 20 to 25 dummies a month.
Beebe explains that in a crash test, a dummy's sensors register a range of parameters: the force of a blow to the thigh, the torque on the neck during sudden deceleration, the compression of the chest against a seat belt. These measurements are then converted into injury criteria, which reveal the harm--anything from minor concussion to death--that would have been done to the vehicle's occupants had they been human. Such injury knowledge comes mostly from researchers studying how Newtonian mechanics applies to the human body, usually by performing impact and deceleration tests on cadavers, pig carcasses, or eager graduate students.
But Denton's dummies do more than car crashes. They've been used in roller coaster tests in Iowa and in simulated train wrecks in India. They've been dropped out of airplanes, strapped into crashing helicopters, and shot out of cannons. They've checked out school-bus seats, motorcycle air bags, and ski-slope protection nets. An Australian clothing company ordered a ”perfect size 10” dummy to try on its new styles. And in a TV show, a Denton Hybrid III was punched in the face by a professional boxer and held in a neck lock by a Brazilian jujitsu fighter.
”There were some applications where we had no clue what they were doing,” Beebe says. ”It was proprietary or government related. The dummies left brand-new. They came back in parts.”
A dummy like No. 0200-137 consists of 350 metal and plastic parts. Denton fabricates most of them itself, and just about everything is done by hand.
First comes the skin, the salmon-colored flexible plastic that covers a dummy's body. To make the feet, for example, a worker pours a milkshake-like substance--liquid vinyl--into an aluminum mold the size of a brick. The mold's interior is shaped like a foot (that is, a dummy's toeless foot), and the vinyl will solidify, or cure, when it goes into an oven. The skin for the dummy's head, upper arms, lower arms, hands, thighs, and shins is made the same way.
In another part of the factory, a group of workers fabricates steel and aluminum parts for the dummy's skeleton. One technician loads some specs into a computer numerical control, or CNC, machine, which automatically cuts, drills, and mills a steel part--in this case, an intricate disk for the dummy's shoulder. Over in another corner, a worker bends long strips of steel that will form No. 0200-137's ribs. Co-workers call this guy ”Rib Man.”
As the workers weld the smaller parts to the larger ones, pieces of the skeleton begin to take shape: skull, spine, hips, ankles, knees, elbows. The dummy's neck is more intricate. A large fraction of car accidents, especially rear collisions, result in severe neck injuries. To create a structure that can mimic the movement of a human neck, a worker mixes together natural rubber, polyacrylates, nitriles, neoprene, and butyl to obtain precise damping characteristics. He injects the mixture into a press that molds a handful of disk-shaped pieces, which will be alternated with metal rings to form the Hybrid III's characteristic segmented neck.
From different sectors of the plant, No. 0200-137's vinyl and metal parts converge in the assembly area, where they wait for the white-coated technician. The technician starts by measuring and weighing the head, limbs, and torso, and with a special scale he determines each section's center of gravity, which has to match that of a real person. To assemble the dummy, all it takes is a bunch of hex screws and a wrench. But No. 0200-137 is not ready yet. He needs some sensors.
On my second day at Denton, I head out to its headquarters in Rochester Hills, Mich. From Beebe's remarks, I already have an inkling that the company appreciates the humor in the otherwise serious work it does. My suspicions are soon confirmed: dummy bobbleheads greet visitors at the reception desk; a poster of a dummy posing as Rodin's The Thinker hangs in a corridor.
PHOTO: Chris Mueller/Redux
FOCUS, an enhanced dummy face, has multiple load cells behind its eyes and facial bones.
When I walk into the corner office of Denton's president and CEO, David Stein, I get still more. ”I spend my day with dummies!” is one of his favorite tension breakers. Stein, an electrical engineer turned dummy-industry executive, shows me his collection of crash-test miniature toys and dummy dolls bought on eBay.
The goal of my visit is to find out how the company is pushing the envelope of dummy design, and I had anticipated that Stein wouldn't be forthcoming with details. A dummy's specs, I reasoned, are probably like the formula for Coca-Cola or the blueprints for the Boeing 787--secreted away in a locked vault under heavy guard.
Not so. Dummy specifications in the United States are public, Stein tells me. You can walk into the offices of the National Highway Traffic Safety Administration in Washington, D.C., and request docket 74-14; in it you'll find schematic drawings, assembly descriptions, performance requirements, and a 16-page parts list for the Hybrid III 50th percentile.
The rationale behind keeping dummy specs open is so that automakers, safety equipment suppliers, dummy makers, and the NHTSA, which crash-tests most new models of vehicles before they can go on the U.S. market, are all on the same page. (The European Union and other countries have similar regulations.)
So in principle, anyone can get the specs and build a Hybrid III dummy. The challenge, Stein says, is consistency--meeting the requirements while making your next dummy indistinguishable from the previous one. Fashioning dummies that are like clones takes a lot of expertise. In fact, only two companies in the world have the know-how to build the most advanced dummies: Denton and First Technology Safety Systems, in Plymouth, Mich.
Making the dummy specs public and official also has a downside: you can't improve a given dummy model once the government freezes its design. The Federal Motor Vehicle Safety Standard No. 208, Occupant Crash Protection, which dictates how dummies should be built, among other things, was promulgated in the United States back in 1972 and hasn't changed substantially since then. So dummy makers have to stick with some 30-year-old designs and materials.
In fact, certain fabrication techniques date back to just after World War II, when the U.S. military developed the first modern dummies to test ejection seats in airplanes. Colonel John Stapp, a U.S. Air Force medical officer, pioneered the field of biomechanics with research that involved subjecting volunteers, including himself, to death-defying deceleration runs on sleds. He later realized it was more productive to develop and use crash-test dummies. An annual meeting named after him, the Stapp Car Crash Conference, is still the key gathering of car-crash testers, biomechanics researchers, and other safety industry experts.
In the late 1960s and early 1970s, with traffic accidents killing more than 50 000 people on U.S. roads each year, demand for safer vehicles grew stronger. In 1971, General Motors, which had been developing some dummy prototypes, decided to combine elements from two competing designs, one from Alderson Research Laboratories and the other from Sierra Engineering. GM named the resulting hybrid dummy, aptly, Hybrid I.
All the while, different makers created a myriad of other dummies, some now long retired, others still in active duty. The aerospace variety includes Model T Parachute Dummy, Torso, and Dynamic Dan. The medical profession has Rando for Radiotherapy, Dexter Dental Dummy, and the Phantom family--Cardiac Chest Phantom, Nuclear Phantom, and Organ Scanning Phantom.
The automotive sector raised its own dummy families: the now-retired Sierra Family (Sierra Sam, Sierra Stan, Sierra Susie, Sierra Saul, little Sierra Sammy, and Sierra Toddler) and the Hybrid clan (Hybrid I, II, and III--this last variety created by GM for the NHTSA, which made the design official in the late 1970s). More recent are the side-impact units: SID, EuroSID, BioSID, and WorldSID. These dummies, like the Hybrids, have specifications set by government agencies, and Denton and other makers follow such designs to manufacture and sell them to customers.
PHOTO: Chris Mueller/Redux
Waiting to receive new parts, a Hybrid III family sits in the Dummy Emergency Room at Denton’s assembly plant in Ohio.
Today, WorldSID is by far the most advanced dummy. It was the first to be designed by a worldwide consortium of industry, government, and academic experts, with the goal of harmonizing test protocols and safety standards, which can vary widely from country to country. Loaded with sensors, it can record 258 different measurements in a single crash test. One unit can run close to US $350 000--more than twice the price of a Hybrid III.
Denton didn't start out as a dummy maker. The company originally focused on making force and torque sensors, called load cells, which are used in crash-test dummies but also in many other pieces of equipment, such as power tools and digital scales. Robert A. Denton founded the company in 1969. A quiet and creative engineer, he produced his first load cells at his home near Troy, Mich., using his kitchen oven to cure the components. Denton and his engineers went on to design many of today's most widely used automotive load cells--including the ones used in the Hybrid III.
After its mechanical parts and skin have been assembled, No. 0200-137 is shipped from Denton's Ohio plant to the company's load cell unit, adjacent to its Michigan headquarters.
In a vast, high-ceilinged hall, half a dozen milling machines hum away. Occasionally, a machine stops and a worker retrieves the newly milled part. These parts, made of aluminum and steel, come in all shapes and sizes and will form the structural elements of the load cells.
No. 0200-137's femur load cell, for example, is encased in a cylinder. Inside, a small metal beam traverses the cylinder's length. If you compress the cylinder, the beam will deform. To measure the extent of deformation, the load cell uses a thin zigzagging wire of brittle metal such as a titanium alloy. The electrical resistance of this wire, or gauge, changes when you compress or stretch it. When the gauge is glued to the beam, it converts the beam's deformation into a variable voltage. Add more beams and gauges, and your load cell can measure force in additional directions, and because you know the dimensions of the beams, you can also measure torque.
The metal parts are carted to Denton's electronics lab, where they will be outfitted with gauges. These need to be precisely glued to the center of the beam or the measurements will be distorted. Whereas the making of the dummy so far has required lots of heavy lifting, hammering, and milling, the alignment and gluing tasks require great finesse and hand-eye coordination. Fourteen women are on the job. Sitting in cubicles decorated with flowers and children's drawings, they peer intently into microscopes and nimbly maneuver tiny tweezers and wire cutters.
Like other Hybrid III dummies, No. 0200-137 will receive two other types of sensors: accelerometers and potentiometers. To measure accelerations experienced by the dummy's head, for example, three uniaxial accelerometers are installed inside the skull at the center of gravity. The potentiometers measure deflection by translating their movement into voltage; the dummy receives one of these units behind the sternum to measure forces exerted by the seat belt or other object against the chest.
Now fully instrumented, No. 0200-137 has one last stop before it can leave the factory. It must be thoroughly checked out in the certification lab. Considering what goes on here, you could just as easily call this place the dummy torture chamber.
First comes the Head Drop Test--and the name pretty much says it all. A technician detaches No. 0200-137's head from the neck and hangs it from shafts at a precise height of 37.6 cm above a heavy block of steel. A magnetic release mechanism drops the head, which hits the block with a thud. This test ensures that the head has the right weight and damping properties.
Next, the technician reattaches the head to the body and places the dummy on a platform, positioning him so that his chest is in line with a 23-kg steel cylinder--the thorax impactor probe--hanging from above. Three, two, one! The probe swings down and connects with the dummy's sternum, sending No. 0200-137 flying backward into a net. The impact deflects the potentiometer, and the technicians check that the data fall within a certain range.
Minutes later, the dummy is getting his neck bent in an evil-looking contraption, and his knees whacked by another swinging probe. When it's all done, No. 0200-137 receives a certification stamp on his records and is ready to meet his future owner. Which means he gets packed into a cardboard box and trucked away.
The dummies of the future-- what will they look like? Answering that question would require visiting the many organizations that in one way or another are advancing dummy technology--automakers such as GM and Ford, the NHTSA and its counterparts in other countries, research groups at places such as Wayne State University, the University of Virginia, and the University of Michigan, and the dummy manufacturers, of course.
PHOTO: Chris Mueller/Redux
A dummy’s vinyl and metal parts converge in the assembly area.
But since I'm here at Denton, I pose the question to Randy Kelly, the company's sales vice president and a dummy spokesman of sorts. Kelly has been on television a bunch of times talking about dummies. The dummy of the future, he declares, is already here--in Rochester Hills. He's got two examples to show me.
One of the long-standing goals of biomechanics has been to find out just what goes on inside the rib cage during an accident, Kelly says. That's especially important in a side-impact collision, where the armrest, a door, or an SUV fender can hit passengers on the side, snapping their ribs. In current side-impact dummies, potentiometers attached to each rib register the rib's movement. But the device is tracking deflections only in one direction, so it's somewhat crude. Denton engineers came up with a better way to capture all that rib action.
”This is RibEye,” Kelly says, pointing to a dummy's torso. Nothing appears unusual, but he explains that instead of potentiometers, each of the dummy's 12 ribs is equipped with an LED, and two light-angle sensors are mounted on the spine. ”The sensors track the position of each LED or of a point on the rib,” Kelly says. ”It's just like celestial navigation that the sailors did back then.”
The advantage of RibEye over existing methods is that it measures movement in all three dimensions, with an accuracy of 1 millimeter. Denton, which partnered with Boxboro Systems of Boxborough, Mass., to develop the system, has installed it in several dummies. Customers are now testing RibEye in R&D programs.
The second project Kelly mentions is FOCUS (facial and ocular countermeasure for safety headform), developed by Denton with the U.S. Army Aeromedical Research Laboratory and the Center for Injury Biomechanics, run jointly by Virginia Tech College of Engineering, in Blacksburg, and Wake Forest University School of Medicine, in Winston-Salem, N.C. FOCUS consists of an enhanced dummy face, with synthetic eyeballs made of a silicon-like material to register penetrating injuries and load cells at the back of each eye socket to measure nonpenetrating impacts. The face also has custom-made multiaxis load cells behind the frontal bone above the eyes, the zygomatic bones on each side of the eyes, the nasal bone, and the upper and lower jawbones.
What's FOCUS good for? Eye injuries to soldiers have increased dramatically since World War II, Kelly explains, so the Army plans to use FOCUS to evaluate helmets, goggles, and the protective features of its vehicles. The sensor-packed face could also be used to study air-bag face impacts, motorcycle-related injuries, and sports injuries. Oh, and popping corks. Turns out they account for about 10 percent of eye-related hospital admissions in Europe.
I encounter No. 0200-137 on a muggy afternoon in June at Autoliv, in Auburn Hills, Mich. Autoliv, one of the world's largest suppliers of air bags, seat belts, and other car safety systems, also performs crash tests for customers that don't have their own crash-test facilities. One such customer--No. 0200-137's owner--is conducting a frontal crash test today. The customer allows me to observe the test as long as I omit certain details that might reveal the automaker's identity and ”stay away from the vehicle.” In exchange, I get to watch a brand-new $40 000 car get totaled. Sounds like a fair trade to me.
The test takes place in a temperature- and humidity-controlled hangar. Eight other men and I sit inside a viewing room above the test track, kind of like a VIP box at a Formula One race. Except this race lasts about 10 seconds, and the track is just 200 meters long.
The car, a greenish-gray four-door sedan, sits at the head of the track. To the bottom of the vehicle, technicians attach a cable that will tow it down the center of the course. At the opposite end is a 45-metric-ton barrier made of reinforced concrete. It's 1.8 meters high, 1.8 meters thick, and 3.6 meters wide.
No. 0200-137 sits in the driver's seat, his expressionless face registering none of the last-minute preparations going on around him. The technicians carefully adjust the angle of his head, the space between his torso and the steering wheel, and the inclination of his thighs. The dummy wears a formfitting cotton short-sleeve shirt, above-the-knee shorts, and a pair of $125 size 11 black oxfords. It's all to reproduce real driving conditions (people usually drive with their clothes on, after all).
Suddenly a horn goes off. An orange light flashes. Huge light panels flood the test bay. Fifteen high-speed video cameras begin rolling. We hear the noise of the tow cable dragging down the track. In just 3 seconds, the sedan accelerates from 0 to 48 km/h, and for another 7 seconds it maintains that exact speed. An instant before impact, the tow cable is released, and in the next instant, the car crashes into the barrier. Boom! Headlight fragments fly off in all directions. The back wheels almost jump from the ground. Then--just silence.
Measurements from the dummy will be transferred to computers, processed, and translated into an injury criteria report, which will tell the carmaker how real passengers would have fared in such a crash. I'm not allowed to see No. 0200-137 afterward. But odds are he's still in good shape. He may need a replacement part or two or a realignment or maybe some new clothes--but little more than that. For the next decade or so, this will be his routine. Until the day a new dummy takes his place.
To Probe Further
To see more photos of dummies along with a video of a rib-impact test, visit http://www.spectrum.ieee.org/oct07/dummies.
For technical details about Denton's dummies, go to http://www.dentonatd.com.
Accidental Injury: Biomechanics and Prevention, edited by Alan M. Nahum and John W. Melvin (Springer-Verlag, 2001), has several chapters on how dummies are used in crash tests.
For an entertaining view of the field of biomechanics, see Stiff: The Curious Lives of Human Cadavers, by Mary Roach (W.W. Norton and Co., 2003).