While the original automotive crash test dummies mimicked only adult males, more recent models of the anthropomorphic test device (ATD) have diversified to include female, child, infant and, most recently, elderly body types. The newest dummy from Humanetics ATD (humaneticsatd.com
) mimics a 160-pound, five-foot, three-inch, 70-year-old female. Given that the crash test dummies are expensive and reusable, the volumes produced by Humanetics is comparatively low, so the company has developed a new process for building this new model, using 3D printing for much of the construction.
The approach for creating this female ATD began with a rib: Humanetics Design engineer Kris Sullenberger was looking for a way to use plastic components to replace the elderly dummy’s steel ribcage assembly.
The traditional multi-stage 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. Not only complex and time-consuming, the process is also 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.
Sullenberger’s first attempt at 3D-printing ribs failed. The plastic/rubber compound they tried had many of the properties they were looking for, but when tested wasn’t strong enough. “After 20 hits, the ribs started to crack,” he says.
Sullenberger reached out to Adaptive Corp. (adaptivecorp.com
), a digital-to-physical product lifecycle company with expertise in 3D printing through its use of Markforged (markforged.com
) 3D printers. Markforged’s Onyx, a carbon-composite material reinforced with continuous Kevlar fibers, was recommended and a sample rib was made for dynamic testing purposes.
The piece met Humanetics’ specifications, so they ordered a complete set of ribs, put them on an elderly dummy and conducted impact tests. According to Sullenberger, “We’ve inflicted over 150 impacts to those Markforged-produced ribs . . . And haven’t broken a rib yet.”
(It is worth noting that Kevlar, invented by DuPont, is used to produce military body armor, so there is something to be said for its impact-resistance.)
After the successful trial, Humanetics purchased its own Markforged Mark Two 3D printer. Material costs are comparable to the previously used steel, and processing time gains are significant: while it used to take as many as three weeks to produce a set of ribs, they’re now able to produce a set in a week.
Of course, a body—elderly or otherwise—is more than a skeletal structure. There are organs contained within. So now that they’ve gotten the printing of bones down pat, they’re now starting on 3D printing livers and spleens and the like. Explains Humanetics CTO Mike Beebe, “We’re also looking for a deeper understanding of the relationship between the outside flesh and these organs. Representing all these characteristics in our crash test dummies will provide better test results.”
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