Crash test dummies, ever more sophisticated since their introduction in 1949, have also become more lifelike, with the entire family now represented: male, female, child and infant. It's important, after all, to understand how a car crash might affect different body types and sizes.
That's especially true for elderly passengers, who research shows are more likely to sustain internal injuries in certain crashes because their bones are more fragile and soft tissues less robust. So it was only a matter of time before Humanetics, the Michigan-based company that designs, develops and builds virtually every test dummy in the world, came up with a body-double for Grandma.
She is 70 years old, 161 cm tall (about 5 feet, three inches) and 73 kg (about 161 pounds). Her body mirrors that of a typical elderly woman, with more flesh around the abdominal area, which affects the body's interaction with the seatbelt.
The first elderly dummy also represents a technological advancement: she is the first anthropomorphic test device (ATD) developed using additive manufacturing. The entire torso, from the pelvis to the head assembly, was 3D-printed using new materials and techniques.
"This is the first look at the future," said Mike Beebe, chief technical officer at Humanetics. "We'd been exploring the latest technologies and materials. But none of us knew at the time whether the materials could hold up in a crash."
Design engineers wanted to see whether some of the expensive steel components - the ribcage assembly, for instance - could be replaced with cheaper 3D-printed plastic and rubber components. "If we could tackle the ribs, that would open up the door for some other organs," said Beebe.
But they were having difficulty finding a material with the durability to withstand the forces and impacts of their unique crash-testing environment.
The traditional process creates the rib out of a piece of spring steel that is formed and heat treated. Then a piece of damping material is glued to the inside of the rib to control the response to impact. The rib is left to set, then tested, and the damping material is trimmed several times to achieve the desired performance. But the process is expensive and inconsistent; steel parts degrade over time, plastic and vinyl components are subject to hardening and shrinkage—and it all impacts the accuracy of the many sensors loaded onto a crash dummy.
The first 3D printed ribs, using a plastic/rubber compound, matched many of the properties they were looking for, but they didn't survive the rigors of crash testing. “We 3D printed some ribs out of the plastic,” said design engineer Kris Sullenberger. “But after 20 hits, the ribs started to crack.”
Humanetics then turned to Adaptive Corporation, a digital-to-physical product lifecycle company, which suggested using Onyx, a carbon-composite material reinforced with continuous Kevlar fibers, developed by MarkForged, a Massachusetts-based maker of 3D printers.
“We’ve inflicted over 150 impacts to those Markforged-produced ribs to date,” Sullenberger said. “And we haven’t broken a rib yet.”
That led Humanetics to print other body parts, including the shoulder, spine, lumbar, scapula, sternum and arms. The 3D-printed parts cost about the same as the steel ones but they are three times more durable and can be made more quickly. Manufacturing a set of ribs conventionally used to take two to three weeks. Now they can print a single rib in 24 hours and a full set in a week.
Humanetics has also found it can save 40 percent to 60 percent in assembly and labor costs by 3D-printing molds for complex components rather than producing them from machined steel.
The company is also exploring the use of 3D printing to create specific organs for test dummies. Humanetics typically creates test systems to represent overall regions of the body (such as the thoracic or abdominal area) rather than an individual heart or lung. By 3D printing organs like a liver or a spleen, researchers can better understand how each one is affected by an impact.
So far, Humanetics has made just two of the elderly dummies, which are undergoing further testing. But amid a growing, aging population, the focus on elderly passengers seems to be justified. Baby Boomers now in their 60s and 70s are often heavier than they were on average just a few decades ago, yet healthy enough to be driving into their 80s and beyond. In 2015, there were more than 40 million licensed drivers aged 65 and older in the United States, representing one in every five drivers on American roads.
