NEWS | Jan. 6, 2021

Carderock Patent Spotlight – Multilayer Composite Structure

By Benjamin McKnight III, NSWCCD Public Affairs

The earliest documentation of armor designed with ballistic protection in mind can be traced back to the Bullet-proof Cuirass in 1908 (U.S. Patent No. 1003270A).

In the 100-plus years since that initial patent, the technological advancements in ballistic protective materials have improved exponentially. More discoveries are being made to this day, and a duo of engineers at Naval Surface Warfare Center, Carderock Division, recently earned a patent for their recent development in the field.

U.S. Patent No. 10,751,983, “Multilayer Composite Structure Having Geometrically Defined Ceramic Inclusions,” was awarded to Brandon Good of Carderock’s Emerging Technology Branch and Jonathan Kruft of the Non-Metallic Materials Research and Engineering Branch in August 2020. This achievement was a culmination of nearly three years of dedicated research and experimentation by the two.

While many inventions are jumpstarted by a triggering event, Good said that the origins of their work was nothing more than the natural progression of conversations in the ballistic research circles.

“There wasn’t that news event or something that occurred,” he said. “It just kind of came out of those different communities indicating this is something they could potentially use.”

According to the patent, while composite structures are typically designed with the structural supportability as the main focus, modern-day practices encourage dual functionality or more. Stopping bullets are the first function that comes to mind when thinking of armored material, but the second property the duo decided was a necessary addition was electromagnetic energy absorption. Creating a structure with both ballistic and electromagnetic functionality is no easy task, but the duo appears to have found a solution by introducing a geometrical inclusion methodology in their addition of ceramics to the composite structure.

“We began this project surveying the ballistic and ballistic material community for ‘rules of thumb’ to defeating the target projectile and velocity,” said Kruft, who worked with the Navy’s armor experts in Carderock’s Hull Response and Protection Branch to develop these rules of thumb. “The biggest challenge was staying true to these ballistic concepts while tailoring the composite to control electromagnetic energy propagation.”

Determining the electromagnetic properties of the material took priority once the duo started the fabrication process. To reach a satisfactory level of electromagnetic response performance, Good said the structure needed to effectively minimize reflection from electromagnetic waves. This was done utilizing an iterative design process. After each constituent layer was measured for electromagnetic properties, they were imported into a model which Kruft said was again adjusted to optimize performance. The fabrication was broken down into six phases where partial prototypes were evaluated and measured against the model at each phase’s conclusion.  

“We came up with an anti-reflective surface for our ceramic by trying to minimize the reflection of the side of the ceramic,” Good said. “Essentially, we measured the ceramic and a bunch of different geometrical layers. Then, working with our electromagnetic codes at Carderock, we were able to build up a design that achieved anti-reflective properties for that ceramic.”

Following the prototype creations, Kruft said that ballistics testing was conducted at the Aberdeen Test Center ballistics range. Kruft worked with Joe Walther in the Hull Response and Protection Branch to ensure that the test methodology was sufficient for comparative evaluation of the ballistic performance to legacy materials. The samples were subjected to three shots in an equilateral triangle pattern of 120mm per side.

Kruft and Good took a risk in assuming that, by saving ballistic testing until after the prototypes were complete, the material would pass the latter assessments. In fact, they were initially unsure if the project was even possible when they discovered the required thickness and ceramic density needed to defeat projectiles.

“I think that was the biggest thing to overcome, learning ballistics,” Good said. “Like anything, there’s a bit of nuance to what works, and people don’t always understand exactly why. We had to do a lot of learning in regards to what was unique, and what had or hadn’t been done.”

The end result was the creation of a five-layer structure containing the following: low-density, high-strain-rate polymer 850; hybrid composite fabric 820; inventive composite 650 with ceramic inclusions 50; ceramic plate 830; and high-strain-rate polymer ballistic fabric 840. Although there is not an immediate demand for the invented structure, understanding the techniques behind creating this form of structure is something Kruft said will benefit material designers – and the Navy as a whole – in the future. The materials and processes developed during prototype development are now part of the core competencies and library of techniques the Navy can adopt to any number of customer electromagnetic applications.

“When the challenge arises, we want to be able to address it,” Good said. “When does that critical need come into play? Will it be five years from now? We don’t know, but we have seen people trying to address multifunctional materials, and this is a method that we have confidence will address both ballistic and electromagnetic issues.