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They go through the pain – so we can survive Photo courtesy Denton ATD Inc. Crash Test Dummies By Peter Holtham Ever seen those video clips of car crash tests where the dummies are thrown about like rag dolls? The dummies are highly engineered to simulate the effect of crashes on human bodies and they carry lots of instrumentation to record the pain (forces & deflections) they suffer. 24  Silicon Chip siliconchip.com.au W orldwide, car accidents kill about 400,000 people and injure 12 million more every year. Despite these grim statistics our roads are much safer than they were 50 years ago. The reason is simple. New cars are repeatedly crashtested by their makers, until they are safe as can be made for the price. Inside almost every doomed car sits one or more very expensive and very life-like anthropomorphic test devices. You and I call them crash test dummies. Packed inside each dummy are sensors that record the accelerations, forces and movements felt by its head and body throughout the crash. This data allows engineers to see what happens to the driver and passengers millisecond by millisecond. It enables them to pinpoint how particular injuries occur. Such complex capability did not appear overnight. Sixty years of development has taken crash test dummies from simple mannequins to today’s complex biomechanical marvels. Sierra Engineering built the first test dummy, for the United States Air Force, in 1949. Christened ‘Sierra Sam’, he tested ejection seats in jet aircraft. Weighing over 90kg, Sam was not very life-like and so the air force also used human volunteers. Strapped into seats on a rocket-powered sled, the volunteers experienced up to 45Gs of deceleration while testing harness designs and seating positions. In the mid 1950s, General Motors got to hear about the air force work. Shortly afterwards, GM started to use mannequin-like dummies in a simple crash test program. They soon discovered that their dummies were not able to survive repeated crashes. Nor would apparently similar dummies behave in the same way in similar crashes. By the 1960s, road safety was becoming a big issue for US politicians. In 1966 the United States Congress passed an Act setting minimum safety standards for new cars. To help GM meet the standards, the company started serious development Hybrid III head and neck (photo courtesy Denton ATD Inc.) siliconchip.com.au of a new crash dummy. They took components from two crude dummies then commercially available and combined them to create Hybrid I. Hybrid I was a 50th percentile male dummy, meaning its body (1.75m tall) and mass (77kg) represented an average US adult male. Although much improved compared with the early mannequins, Hybrid I was still not particularly life-like. GM kept up the research and development effort. In 1972 they introduced Hybrid II, with improved shoulders, spine and knees. By careful calibration they standardised its design and performance. Then, rather than keeping the knowledge locked away inside the company, GM made the drawings and calibration data freely available to anyone. GM introduced a third generation, the Hybrid III, in 1976. Now for the first time crash test dummies had a scientific foundation. Hybrid III’s builders used biomechanics, the study of how a human body responds mechanically to impact, to guide their design. Foot accelerometer and X-axis potentiometer wiring (source THOR documentation). The dummy family Hybrid III formed the basis for a whole family of dummies. Next came a petite 5th percentile female, followed by her ten, six and three-year old children. Reflecting the super-sizing of America, there is also a 1.88m tall, 101kg 95th percentile male. As with Hybrid II, GM made the plans and calibration data for Hybrid III publicly available. Several companies worldwide now manufacture Hybrid IIIs to the GM specification. In 1991 the International Standards Organisation (ISO) adopted Hybrid III as the standard crash test dummy for frontal impact testing. Whatever their size, all Hybrid III dummies are built in the same way. Each consists of over 300 component parts. The skin for the head, arms, and legs is made from pink coloured vinyl plastic while the flesh is made from urethane foam. The vertebrae of the neck are made up of rubber and plastic disks sand- Wire routing and strain relief, THOR main bundle of instrumentation wires (source THOR documentation) June 2008  25 Table 1: Hybrid III Sensors Location Type Amplitude Channels Head Accelerometer 250G 3 Neck Load cell Rotation 14kN 290Nm 3 3 Chest Accelerometer Deflection 150G 100mm 3 1 Pelvis Accelerometer 150G 3 Thigh (L & R) Load cell 20kN 2 Knee (L & R) Deflection 19mm 2 Lower leg top (L & R) Load cell Rotation 12kN 400Nm 4 4 Lower leg bottom (L & R) Load cell Rotation 12kN 400Nm 4 4 wiched between steel rings. The consistency of the disks is carefully controlled so that the structure mimics the rotation, stretching and bending movements of the human neck. The upper body has six high-strength steel ribs with polymer-based damping material. This arrangement simu- lates how a human chest responds to the crushing forces of an impact. The lower body has a curved cylindrical rubber spine; typical of a person slouched in their seat. The pelvis is an aluminium casting fixed in a sitting position. A ball-jointed thigh bone mimics human hip to upper leg movement and rotation. Knee, lower leg and ankle movements are all reproduced. Feeling the pain If you have any empathy at all you will shudder when you see the impacts that crash test dummies are exposed to. And they do the feel the pain. Or at least they have electronic sensors which register the forces which would cause extreme pain if the dummy was alive. Dummy manufacturers supply little or no instrumentation themselves, just the spaces where it can be fitted. Sensors are supplied by specialist instrument companies and are selected and fitted for a particular crash test. Hybrid III dummies have four different types of sensor built in, as shown in Table 1. Load sensors record the forces on different body parts during a crash, while rotation sensors measure twisting moments. Load and rotation sensors are built into the thigh and shin bones, for example. Accelerometers are fitted all over the body to measure acceleration in a particular direction. The head has accelerometers for three directions: front to back, side to side and up and down. Female Hybrid III with her two children on the back seat (photo courtesy Denton ATD Inc.) 26  Silicon Chip siliconchip.com.au Movement sensors record deflections during a crash. A linear potentiometer is fitted inside the chest to measure the amount of compression caused by a seat belt for example. Another, called a ‘knee-slider’, is used to measure forces transmitted through the dummy’s knees, particularly if they hit the lower facia. No instrumentation is built into the arms. In a head-on crash the arms flail around uncontrollably but serious injuries are rare and worthwhile protection is difficult to achieve. Table 2: THOR Sensors Location Type Channels Head Accelerometer Tilt sensor 9 1 Face Load cell 5 Upper neck Load cell 6 Lower neck Load cell 6 Front neck Load cell 1 Recording the data Rear neck Load cell 1 Data from the sensors is of no value if it cannot be recorded for later analysis. In the early days of crash testing, data logging systems were too bulky to fit in the car. Umbilical cables connected the few instruments in the test car and the dummy to a remote data recording system. Data was stored as analog signals on tape for later playback and analysis. Carmakers do not want to fill up test cars with bulky or heavy instrumentation as it might affect the outcome of the crash. Yet they want all the data they can possibly get from the crash test dummies, as well as any other sensors mounted on the car. Companies specialising in crash test data loggers now produce on-board units with as many as 96 data channels. Mass per channel is less than 150g and sampling rates reach as high as 22000 samples per second. These rugged, battery-powered on-board data loggers amplify, filter, digitise and store in flash memory all the signals from the dummy’s sensors. Multiple data acquisition units can be daisy-chained together when the test car is carrying a family of dummies. The whole data logging system is cabled to a laptop Head rotation Potentiometer 1 Chest Accelerometer Deflection 1 12 Upper abdomen Accelerometer Deflection 1 1 Lower abdomen Deflection 6 Spine Accelerometer Load cell Tilt sensor 2 1 4 Pelvis Accelerometer Load cell 1 8 Thigh (L & R) Load cell 2 Knee (L & R) Deflection Rotation 2 2 Load cell Accelerometer 8 2 Load cell Ankle rotation Leg accelerometer Foot accelerometer 12 6 2 6 Lower leg top (L & R) Lower leg bottom, ankle and foot (L & R) Location of sensors in THOR 50th percentile male dummy (source THOR documentation). siliconchip.com.au June 2008  27 computer while it is programmed for a specific test. Once the test is set up, the cable is removed and the car is ready to be crashed. Data from the sensors is recorded from the moment the car starts moving until it comes to rest after the crash. Not content with this level of miniaturisation, data loggers are now moving from on-board to in-dummy. The loggers can be connected together by Ethernet through a central hub. There is a single cable from the dummy for network communication, trigger, and off board power if necessary. In-dummy batteries allow the dummy to run completely cable-free during a test. Each sensor is cabled through the dummy in small channels in the flesh and spine. What of the future? Hybrid III is now over 30 years old and is beginning to show its age. It does not measure injuries to the abdomen, there is only a single chest deflection measurement, and its leg bones are rigid. It is just not sensitive enough to crash test modern cars fitted with seatbelt pre-tensioners, seatbelt load limiters and multistage airbags. The latest dummy Development of a new front impact test dummy called THOR (Test device for Human Occupant Restraint) started in the late 1990s. Designing THOR involves the efforts of carmakers, research groups and governments worldwide. The current version of THOR was released in late 2001. A spine and pelvis that allows it to sit in different poBelow right: the WorldSID 50th percentile male. By contrast, the CAD image opposite is WorldSID 5th percetile dummy (images courtesy of WorldSID Task Group). 28  Silicon Chip sitions is just one of THOR’s many improvements. Its face has five load sensors to measure facial injuries while its rib cage measures deflections in four places compared with Hybrid III’s one. Three deflection sensors are fitted inside the abdomen to assess soft tissue damage. The legs have bushings to simulate the elasticity of real bone. Up to 21 sensors on the leg bones measure loads, accelerations and ankle rotation. These additional sensors require THOR to have as many as 134 data channels, four times as many as Hybrid III (Table 2). Despite the millions spent on its d e s i g n , T H O R ’s drawings and operating manual can be downloaded by anyone from the US Department of Transportation website. See www-nrd. nhtsa.dot.gov/departments/nrd-51/thornt/ THORNT.htm Different dummies Not all crashes are siliconchip.com.au THOR head components (source THOR documentation). frontal impact. Many are side impacts (T-bones!) caused by drivers running red lights. Because the injuries are different, the requirements of dummies for side impact tests are different. Carmakers need to measure the risk of injury to the ribs, spine and internal organs such as the liver. Head and neck injuries are also common and carmakers need crash test data for head airbag development. Hundreds of scientists and engineers from over 45 organisations worldwide have just spent eight years and US$14 million designing WorldSID (World Side Impact Dummy). Companies from the Netherlands, France and Britain designed WorldSID’s head, neck and pelvis while companies from the USA developed the rib cage, spine, arms and legs, as well as the sensors and data loggers. The result is the most life-like crash test dummy ever created. WorldSID’s 212 built-in sensors record accelerations of the head, upper and lower spine, shoulder, ribs, pelvis and arms. It also logs compression of the shoulders and individual ribs, as well as rotation of the head, torso, pelvis and ankles. But whether it’s one of the Hybrid III family, a THOR or a WorldSID, the procedure for using a dummy remains identical. International standard test protocols are followed exactly. Technicians first assemble the dummy, carefully testing and calibrating each individual ‘body part’. They dress the dummy in shorts, a short-sleeved shirt and shoes, and precisely position it in the car. They stick yellow and black adhesive targets to the sides of the head to serve as reference points for the crash films. The eyebrows, nose, chin, knees and lower legs are painted with patches of different colours. Any contacts with the car during the crash will then show up as coloured smears. Once the instrumentation in the dummy and the car has been checked, the test can start. The test bay is flooded with light and high-speed film cameras start up. A tow cable pulls the car towards the crash barrier at 64km/h (40 mph). Just before impact the cable is released and the car smashes into the barrier. In just 10 seconds the test is over, although the megabytes of data recording the dummy’s ‘injuries‘ will take weeks to SC analyse. Ultimately, the result is safer cars for us all. Radio, Television & Hobbies: ONLY the COMPLETE 00 $ 62 archive on DVD &P +$7 P • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to Electronics Australia. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you're an old timer (or even young timer!) into vintage radio, it doesn't get much more vintage than this. If you're a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you're just an electronics dabbler, there's something here to interest you. NB: Requires a computer with DVD reader to view – will not work on a standard audio/video DVD player the handy handy order order form form Use the on page 57 of this issue on page 81 of this issue. siliconchip.com.au June 2008  29