Topic 1:
Armor

The first workshop topic focused on armor and featured presentations by K.T. Ramesh of the Hopkins Extreme Materials Institute, Rod Heiple of Alcoa, and Vikram Deshpande of Cambridge University in the United Kingdom. The speakers gave separate presentations and took questions during and after their individual presentations.

THE SCIENCE OF MATERIALS IN EXTREME DYNAMIC ENVIRONMENTS

K.T. Ramesh, Hopkins Extreme Materials Institute

K.T. Ramesh started his presentation by noting that it is possible to reduce weight by several methods, including materials substitution, structural design, and manufacturing and optimization, all of which are often linked in intricate ways. The key question is whether the designed system can survive the application environment. Ramesh noted that when it comes to the military environment, one of the most important aspects is kinetic impacts.

Ramesh explained that in late 2010 the Army Research Laboratory solicited proposals to establish a Collaborative Research Alliance (CRA) for Materials in Extreme Dynamic Environments (MEDE), and in May 2012 this was awarded to a consortium led by Johns Hopkins University (JHU).

He said that JHU has established the Hopkins Extreme Materials Institute (HEMI) with the Center for Materials in Extreme Dynamic Environments (CMEDE) as one of its research centers. Funding began in mid-2012. CMEDE

performs strategically driven fundamental science. The MEDE CRA objective, Ramesh noted, is to establish the capability to design materials for use in specific dynamic environments. This includes developing fundamental understanding in multiscale materials and ultra-high loading rate environments, executing a basic research program, and enhancing and fostering cross-disciplinary and cross-organizational collaboration. The MEDE CRA is considering materials that include ceramics, metals, polymers, and their respective hybrids or composites, but they are not limited to those materials. They are not developing process-ready models or industrial-scale materials and structures.

Ramesh said the program elements include the following: modeling and simulation, bridging the scales, advanced experimental techniques, multiscale material metrics and characterization, and processing and synthesis. The model material systems include metals such as magnesium, ceramics such as boron carbide, polymers such as ultrahigh molecular weight Polyethylene, and composites such as S2 glass/epoxy. The MEDE CRA funds many scientific approaches at once—synthesis and processing, experiments and modeling. This simultaneous funding is crucial for accelerating materials design. The CRA is not, however, developing process-ready models or industrial-scale materials and structures.

Ramesh explained that the way of thinking about new materials and how they can be used is more important than the specific material that is designed. He discussed the importance of seeing the event—the specific mechanisms that are activated within the application environment. He said that they need experimental techniques to see those mechanisms. “Once you can see it, you can build a model for it,” he explained. The goal is to understand the mechanism through modeling and then control the mechanism through material synthesis and processing so as to design the material for the extreme dynamic results.

Ramesh noted that the problem with seeing the events is that “everything interesting is a millisecond and below . . . actually, 100 microseconds and below.” These extremely short time intervals present great difficulties for observation techniques. In addition, he noted that what you see during the event may be different from what you see after the event, so that merely observing the outcome may not be sufficient for understanding what has happened and how it happened.

He talked about the other issues involved in scaling materials up—a small amount of material can be designed with the microstructure very well. But when entering the manufacturing process on an industrial scale of relevance to vehicle production, problems can appear. Ramesh noted that there is a lack of understanding of how effects scale up, from small laboratory-scale samples to much larger samples. Researchers who work on modeling often do not focus on this scale-up, even though it could be very important to developing better materials. He said that one question they are dealing with at HEMI is how to help change the culture.

Ramesh ended his talk by noting that no armor system is just one material; it is many materials, and the interactions among the materials may be crucial.

LIGHTER, FASTER, AND STRONGER MATERIALS

Rod Heiple, Alcoa

Rod Heiple started his presentation by discussing what Alcoa is and does. The company was founded in 1888 and currently has more than 200 locations in 30 countries. In 2013, he said, it had $23 billion in sales. The company is involved in every stage of aluminum production and has approximately 60,000 employees around the world, including 26,000 in the United States.

He talked about the company’s technical centers being located in Pittsburgh, Pennsylvania, Whitehall, Michigan, and Carson, California. The Alcoa Technical Center in Pittsburgh is the world’s largest light metals research facility and focuses on aluminum, titanium, and nickel-based alloys, as well as ceramics and polymers. It has a full range of laboratory and pilot capabilities. The Whitehall center focuses on turbofan engine components.

Heiple noted that in the past Alcoa has adapted naval materials for armored use. The company is currently working on Advanced Armor Materials known as ArmX™, developing functional gradient product (FGP) armor. The FGP armor effort includes ingot casting technology and a pilot-scale facility at ATC-Pittsburgh, which Heiple noted could have major implications for providing improved protection for armored vehicles.

Heiple said that one of the company’s current goals is to achieve titanium performance from aluminum at half the cost, and it is also looking at the possibility of developing a monolithic hull structure for combat vehicles. Instead of welding multiple pieces together, Heiple said the hull would be formed from a single piece. He briefly discussed the possibility of “continuous structures” which could reduce the number of joints and increase survivability (see Figure 3).

Heiple noted that a major part of a vehicle’s lifetime will be training, not combat. He said that aluminum corrodes and pits over time—a problem they have to consider. Alcoa is currently working with the third generation of aluminum lithium alloys, which provide a big improvement in corrosion resistance. Heiple added that commercial aerospace has performed a lot of work on corrosion performance that the armored vehicle industry may be able to learn from. (Later speakers also addressed this issue.)

Heiple also discussed a number of the improvements over the years. For instance, some of the latest aluminum alloys have armor piercing and fragment threat

performance equivalent to or even a little better than titanium, all using existing processes.¹

Some of the participants then discussed the view that the Army sometimes is a difficult customer and what the Army can do to be a better customer. A few participants believed that the Army changes requirements and can be very bureaucratic. In addition, the size of the market drives the technology, and the military is too

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¹ Even today there are situations where both materials might not meet a desired level of protection. However, there is a continuous and ongoing development of both protection materials as well as threats.

small of a customer to really drive the development of new materials technology.² Some participants at the workshop also noted that the military needs to be clearer about requirements. “How will we inspect it, certify, and qualify it?” one participant asked. This participant also said that, at the moment, the military is not clear about what it expects from the customer (i.e., materials producers) on these issues.

Some participants also discussed the claim that aluminum catches fire, a story that has persisted since the attack on the destroyer HMS Sheffield during the 1982 Falklands War. Although this story has been distorted, Heiple noted that aluminum does melt at a lower temperature than steel. But a few participants pointed out that both the M113 and Bradley armored vehicles use aluminum, and both have been around for a long time. They said that the M113 was first fielded by the Army in the early 1960s and the Bradley in the early 1980s, albeit each requiring significant armor upgrades to survive current shaped charge, explosively formed penetrator, mine, and improvised explosive device threats. One participant noted that if aluminum really did catch fire, the military would not have used it for so long. He also noted that every combat vehicle in the Army, with the exception of the M1 Abrams tank, is made of aluminum. He continued to say that the systems have performed very well, but ammunition and fuel are still dangers to the vehicle and crew if ignited.

THE MECHANICAL BEHAVIOR OF PROTECTION MATERIALS

Vikram Deshpande, Cambridge University, United Kingdom

Vikram Deshpande began his talk by explaining that it is possible to develop armor from “sandwich” panels that consist of a honeycomb core panel. These sandwich panels can perform as well as solid panels when subjected to an explosive shock. He noted that a recent development is how the panels are connected. The panels are separated by lattices, and new construction techniques enable the use of new lattices. Deshpande explained that, more broadly, the key to developing materials is to find unique opportunities, because designers cannot simply increase the performance of all properties at once.

Deshpande also explained the possibilities of graphene composites. He said they can potentially serve as ballistic materials and could provide very good ballistic protection. However, unlike materials like steel and aluminum, he noted that

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² See, for example, archive.defense.gov/dodreform/briefs/Road-Ahead-without-appendix.doc, accessed on March 9, 2016: “[I]n the technology era of today, the Department, and the U.S. Government at large, are no longer the driving forces behind the development of most new technology, including many critical new technologies required by the Department to meet its mission” (p. 5).

graphene composites cannot serve a structural role, so they would still have to be integrated with other materials.

Deshpande noted that it is possible to manufacture quasi-ductile composites. He said these represent a new class of “seamless” structures with 3D fiber arrangements; they have the potential to revolutionize the next generation of vehicle structures but only if the challenges of production scale-up can be addressed to make them affordable.