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The crash test dummy has come of age over many decades as the gold standard for safety testing of automobiles. Organizations like the National Highway Traffic Safety Administration (NHTSA), the Insurance Institute for Highway Safety (IIHS), and other agencies throughout the world continually update the requirements for driver and passenger protection. These updates require automakers to invest significant resources to ensure that their vehicles pass muster and that the crash dummies they use in their cars realistically reflect what happens in the types of collisions these groups will be testing.

An “elderly” crash-test dummy. (Image courtesy of Humanetics)

Crash test dummies should reflect the full variety of human body types. Going beyond the first male-only dummies, the family has been expanded to include female, child, infant, and most recently, elderly bodies, which have turned out to be a unique challenge for Humanetics, a leading manufacturer of crash dummies.

Humanetics’ elderly dummy, introduced in December 2017, represents an important development in vehicle-testing technology, and is designed to meet the unique characteristics of the world's growing aging population. Research has shown that elderly occupants are more likely to sustain internal injuries during certain crash scenarios since bones are more fragile and soft tissues are less robust. To reflect this, Humanetics’ newest dummy captures the biofidelic nature of a 70-year-old female — 161 cm in height and 73 kg in weight — and is expected to have a significant impact on how the vehicle-safety community measures impact responses in crash events.

Due to the nature of the industry (crash test dummies are very expensive and can be re-used multiple times, so vehicle makers tend to order them in small quantities), Humanetics is often asked to produce custom products in low volumes. As they worked to cost-effectively develop their latest elderly dummy model, Humanetics decided to look into 3D printing (additive manufacturing) to more quickly fulfill their needs for small-batch production, less expensive replacement parts, and faster turnaround times. Now, all of the components of the new elderly dummy, from the pelvis to the head assembly, are additively manufactured.

3D Printing Provides Solutions

As the elderly dummy project began, Humanetics’ design engineers felt that some of the expensive steel components in their crash dummies could be replaced with 3D-printed plastic and rubber components. But they were having difficulty finding a material with the durability to withstand the forces and impacts of their unique crash-testing environment.

Design engineer Kris Sullenberger is responsible for day-to-day 3D printing operations at the Humanetics ATD manufacturing facility in Huron, OH. He operates several 3D printing machines from different manufacturers and was looking for a way to use plastic components to replace the elderly dummy's steel ribcage assembly.

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.

Sullenberger tried using a plastic/rubber compound from one leading 3D printer manufacturer, but while the part matched many of the properties they were looking for, it wasn't strong enough. After 20 hits, the ribs started to crack.

He researched other solutions and reached out to Adaptive Corporation, a digital-to-physical product lifecycle company that provides Markforged 3D printers. Adaptive suggested Humanetics consider using Markforged's Onyx, a carbon-composite material reinforced with continuous Kevlar fibers. A part was made for dynamic testing. The piece met Humanetics’ specifications, so they ordered a complete set of ribs, put them on an elderly dummy, and conducted 60-70 impacts with no visible deformation or damage.

After the successful trial, Humanetics purchased their own Markforged Mark Two 3D printer to make ribs and other skeletal components. Humanetics is seeing Onyx material costs similar to those of the previous steel, and significant efficiencies are now coming from those threefold gains in rib durability over the plastic/rubber alternative they considered. Manufacturing a set of ribs conventionally used to take two to three weeks. With the Mark Two, a single rib can be printed in 24 hours and a full set in a week.

Crash dummy torso showing 3D-printed components. (Image courtesy of Humanetics)

Most of the more complex parts on the dummy are molded. Producing the molds out of machined steel can be expensive and time-consuming. In comparison, a 3D-printed mold can be replaced in a day or two, saving between 40% and 60% in assembly and labor costs.

Humanetics’ models also include the softer internal organs that are represented in terms of regions (such as the thoracic or abdominal). Test systems are created to represent each overall region, rather than an individual heart or lung. While regional data is important, researchers would like to have a more in-depth understanding of the characteristics of the specific organs within those regions — which is where 3D printing is providing new answers for the elderly crash dummy in particular.

In the abdominal region, the liver is on one side of the body and the spleen is on the other. To better understand the different deflection characteristics of each organ, Humanetics has begun 3D-printing organs individually to see how their qualities contribute to overall regional crash-test readings. Elderly people tend to have more flesh in front of the bones, which affects how a person moves within a seatbelt system and how the belt interacts with the passenger's body during a crash. The ability to generate new organs using 3D printing technology will lead to shorter lead times, improved restraint systems, and safer vehicles.

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