Lattice Structures in Military Helmets: Why Configuration Matters

Traumatic brain injury (TBI) remains one of the most debilitating, long-lasting effects of blunt, blast, and ballistic trauma that our soldiers face on the battlefield. There is a growing need for better safety solutions for our soldiers, as many are faced with life-altering injuries that reduce their ability to live normal lives post-deployment. Even now, countless clinical research studies are trying to understand how best to treat the effects of combat on our soldiers, such as the ongoing ADNI-DOD clinical trial. Some are trying to improve diagnostics, making it easier for physicians to diagnose TBI by way of cutting-edge neuroimaging techniques like electroencephalography.

However, we’re more interested in prevention, designing solutions that prevent or mitigate head injuries to the soldier.

Windpact is in the business of safety, and one of the most exciting new technologies in the field of safety science is the hierarchical lattice structure. They are made possible by an iterative, additive manufacturing approach that allows for many types of lattice structures configurations. These structures are unique because the struts that make up the core lattice are made up of lattices themselves. Lattices within lattices, lattice-ception, if you will. Lattices have notable benefits when placed inside of protective equipment, and their applications to military use are powerful.

What are lattice structures?

Lattices are interweaved materials that form arrays of interconnected struts, and they are a relatively novel introduction to materials science due to their wide range of possible applications. Lattices can be designed with unique properties dependent on the density of the array; when the array is large, lattices are interchangeable with many other types of engineering materials due to their size and stiffness. Smaller lattices exhibit properties of meshes and are generally less stiff. Still, this property is dependent on the density of the array itself (e.g., how many interlocked weaves the lattice forms determines its density gradient).

Why do lattice structures perform well?

Additive manufacturing techniques make the lattice possible, and by way of 3D printing, optimized, customizable solutions are made possible.

Lattice structures perform well when impacted due to their ability to manage energy efficiently, as well as their unique strength compared to their overall stiffness; this ratio between strength and stiffness is specific to lattices. Their geometry is their hidden strength. It is well known that more compact, denser material configurations may not be well suited for all types of impacts. Constant thickness in helmets has been shown to perform poorer than materials that are complex; however, many helmet designs incorporating constant thickness padding persist.

Finite element frameworks have shown that hierarchical lattice liners may be a compelling choice for reducing head injuries by comparison; FEA examines impact in a component-wise manner, and it is effective at simulating the mechanical and kinematic properties of hits on the head.

Additive lattice structures have numerous advantages, including:

• Customization: lattice structures hold up well when configured in multiple different ways, especially hierarchical structures. The additive nature of the design allows for precise tuning of the model, something that is hard to achieve using other types of materials.
• Impact performance: lattice configurations outperform structures that lack variance, with models demonstrating that their gradient is part of their strength.
• Flexibility: lattices can be 3D printed to fit nearly any design, well beyond the human imagination, with special considerations for human factors like comfort and fit. It removes the dilemma many product engineers experience when they have to consider functionality and wearability.
• Cost: because lattices are 3D printed, the need for expensive tooling to manufacture the parts is eliminated.
• Speed to market: Weeks to months of the development process are saved by removing the tooling portion of the manufacturing process.

How is Windpact leading the charge towards better lattice structures for our military?

So now we know how powerful lattice structures are, especially in a hierarchical formation. The main roadblock many groups face, however, is the task of incorporating cutting-edge design configurations like hierarchical lattices into their solution. This is where Team Windpact comes in.

We have partnered with Ohio State University (OSU) to commercialize and scale this exciting new technology. Edward Herderick, PhD is the Director of Additive Manufacturing at the College of Engineering CDME (Center for Design and Manufacturing Excellence) at OSU.

Dr. Herderick states, ““The intersection of design and additive manufacturing offers the possibility for a step change in improving personal protection. Tailoring lattices across length scales from microns to millimeters with the full rate production capability of modern additive manufacturing machines will absolutely be a game changer for our service members. The Windpact x OSU collaboration brings together modeling, design, and printing to bring to life new customized protection solutions that couldn’t be made any other way.”

By remaining process-oriented, we elevate designs by way of optimization and remove the workload of constant testing, iteration, and tuning. Windpact’s main mission is to provide engineers with accurate, tunable materials and modeling by way of our proprietary materials characterization process that allows for precise customization no matter what kind of specs our clients are looking for. The process that affords Windpact a competitive edge involves the use of a finite element (FE) model combined with our pedigreed materials data. These tools allow us to predict, and therefore, optimize performance. Using the United States military combat helmet as an example (i.e., the ECH and ACH combat helmets), Windpact solved for a 17 feet per second impact versus the previous 10 feet per second impact standard for these ballistic shells.

The computational underpinnings of our optimization process are made possible through continued innovation in materials science; as more materials become 3D printing compatible, we are able to quickly update and improve our clients products. The predictive computational model we apply is triple-fold:

• Design model for workable hierarchical lattice structures
• Manipulate the various characteristics of the structure against multiple metrics
• Optimize as the product’s impact attenuation performance improves, and take into consideration the human factors that apply to the real-world solution

The lattice structures we output are thus tailored to individual needs by way of our customizable development pipeline. One of the greatest strengths of this pipeline is the ability to remain relatively materials-agnostic; we are not married to a certain subset of materials so long as the physical 3D printing capabilities are there.

We are able to predict how different rules and scenarios apply to the materials we work with, and lattices are no different.