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Designer Materials

Advances in materials science hold the promise of revolutionary improvements in supportability, maintainability, reliability, and deployability.

Editor’s note: This is the third in a series of five articles on future logistics innovations identified by the Army Logistics Innovation Agency’s Futures Group. The second article in the series—on telepresence— begins on page 22 of this issue. The final two articles in the series will appear in the January-February 2007 issue of Army Logistician.

Imagine a world where materials are engineered from the “ground up,” atom by atom, rather than from the “top down.” Imagine having the ability to create entirely new types of materials and to tailor the properties of existing materials, thereby minimizing sustainment requirements and reducing demand. Advances in designer materials will allow attainment of these capabilities, thereby revolutionizing
future logistics.

Designer materials encompass that realm of materials science that is concerned with the design, development, and optimization of materials to reduce wear, friction, corrosion, radiation, oxidation, and fatigue. The Joint Logistics (Distribution) Joint Integrating Concept describes the need for the Future Force to have increased speed and agility. Advances in metallic alloys, composites, ceramics, electro-optic and photonic materials, and polymers promise to provide those improvements. Ultralightweight, amorphous, and multifunctional materials will reduce the weight and increase the performance of aircraft and ground vehicles and therefore greatly minimize the logistics burden of warfighters in the field. The new and exciting field of nanoscale technology, including molecular manufacturing, will yield materials that dramatically improve the reliability and durability of equipment, supplies, and infrastructure.

In this article, we discuss designer materials and their properties in an effort to inform the logistics community of the exciting possibilities designer materials offer for the future of Army logistics. We also present some basic concepts of nanoscale technology and nanoscale materials. Logisticians in today’s Army will need an understanding of these concepts so they can advocate and plan for the introduction of these new materials into the Future Force. Familiarity with the implications of advances in the various fields of materials science will enable logisticians to communicate their requirements to the research, development, test, and evaluation community.

Nanotechnology and Nanomaterials

The National Nanotechnology Initiative describes nanoscale technology as “the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications.” [A nanometer is 10-9 meter, or one-billionth of a meter.] Scientists and engineers employing nanoscale technologies seek to build materials from the ground up, atom by atom. To appreciate the marvels of emerging nanoscale technologies, consider the human hair. A piece of hair is approximately 50,000 nanometers thick; this is equivalent to the length of 500,000 atoms placed side by side. Couple the small size of nanoscale particles with the fact that these particles cannot be seen with the unaided eye, and we can begin to appreciate the complex task of manipulating nanoscale particles to design advanced materials.

Scientific and technological advances in nanoscale technologies provide the underpinnings of designer materials by allowing the deliberate manipulation and manufacture of nanoscale structures. Materials designed at the nanoscale level exhibit properties that do not exist in their macroscale counterparts. [“Macroscale” refers to matter greater than 100 nanometers in size.]

Take carbon as an example. The carbon in a lead pencil is a soft material. However, reconfiguring carbon on the molecular scale to form cylindrical carbon molecules (carbon nanotubes) yields one of the strongest materials known to mankind (stronger than steel, yet six times lighter). Carbon nanotubes also can be fabricated in the form of concentric cylinders, known as multiwalled carbon nanotubes, that exhibit dynamic properties. Imagine a nanoscale carbon cylinder within another nanoscale carbon cylinder of slightly larger radius. Such a configuration creates a telescoping property in which the inner tube can slide within the outer tube almost without friction; the result is ultralow-friction nanoscale linear bearings. These carbon nanotubes may constitute near-perfect, wear-free surfaces and offer an example of molecular nanoscale technology with potentially significant logistics benefits. They represent precise manipulation of atoms to manufacture useful materials with functional capabilities.

Emerging nanoscale technologies for the manipulation and manufacture of novel advanced materials are quite remarkable. Rodney Brooks, Director of the Artificial Intelligence Laboratory at the Massachusetts Institute of Technology, observed, “Our thirty-year goal is to have such exquisite control over the genetics of living systems that instead of growing a tree, cutting it down, and building a table out of it, we will ultimately be able to grow the table.”

Perhaps even more remarkable, however, is the fact that molecules can self-assemble without external guidance. Molecular self-assembly is a process that occurs in nature by which a material can spontaneously build itself (biological self-assembly). The construction of cell membranes is a common example. Self-assembly also can occur in the laboratory. Scientists and engineers have succeeded recently in imitating biologically self-assembled systems by “encoding” molecules to self-assemble into larger molecular assemblies (nanoscale materials) with desired shapes and properties. Once scientists and engineers gain adequate control over the scale and speed of molecularly self-assembled materials, they will set the stage for molecular manufacturing: the effective and economically viable tailoring of the properties and attributes of materials. Think of the possibilities for solving many of the logistics challenges of the future. The molecular manufacturing of supplies and equipment at or near the point of need in the battlespace may become a real possibility. This would eliminate much of the demand for distribution across hazardous terrain or airspace.

Multifunctional Materials

While nanoscale technologies have the promise to revolutionize materials of the future, materials with multifunctional abilities undoubtedly will affect almost every military activity from communications to sensing to power generation. As military systems and missions become more complex, the ability of materials to adapt to their environment—to be dynamic in both shape and function—will become critical. Multi-functional materials—specifically engineered materials that can behave both structurally and functionally (for example, actuating, or putting into action; functioning electrically, magnetically, or thermally; or performing self-diagnosis and self-healing actions)—will offer extraordinary capabilities for military logistics.

Smart, or intelligent, materials form a class of multifunctional materials that have intrinsic information-processing capabilities, such as sensing, actuating, and controlling. The ultimate goal of using smart materials is to provide materials that can respond autonomously and intelligently to dynamically changing environmental conditions in the best way possible. This requires materials (and structures) that can respond to stimuli in an appropriate time interval and return to their normal state once the stimuli are removed. For example, future military mobile bridges constructed of smart materials will be able to sense strain, alter their structure when subjected to heavy loads, and provide self-diagnosis and self-repair in response to any damages incurred. Some advanced smart materials with intrinsic intelligence include shape-memory materials and active polymers.

Shape-Memory Materials

Shape-memory materials (SMMs) can sense magnetic, electrical, thermal, and mechanical changes and respond to those stimuli. SMMs also can be tuned, or adjusted, to respond to predetermined changes in position, strain, shape, stiffness, damping (reducing excess vibrations), natural frequency of vibration, and even friction. SMMs include alloys, ceramics, polymers, and gels and can be fabricated into wires, fibers, thin films, and other forms that allow for numerous applications.

Certain SMMs, such as shape-memory alloys (SMAs), exhibit the “shape-memory effect.”Temperature-dependent SMAs, for example, have a certain shape above a particular temperature (called the transformation temperature), but they can be deformed easily below that temperature. Returning the material to its original temperature after heating will return the material to its original shape. In a sense, the material “remembers” its shape before deformation. This shape change is a result of a change in the crystal structure of the material and is called the shape-memory effect. SMAs are also pseudo-elastic, have a high damping capacity and good chemical resistance, and are biocompatible. As a result, they are attracting a great deal of attention for use in smart and functional materials and are very attractive for use in microelectromechanical systems (MEMS).

MEMS combine advanced electronics with mechanical systems at the microscale (10-6 meter, or one-millionth of a meter) to sense and control changing conditions within larger systems. MEMS is an enabling technology that facilitates the development of smart products and augments the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators. MEMS devices, which already are being developed to monitor environmental factors to determine the health and shelf life of equipment and supplies (such as medical supplies), can use SMAs and other nanoscale improvements to increase their own effectiveness, versatility, and durability.

The most prominent SMA is nickel-titanium (NiTi). NiTi not only exhibits the shape-memory effect but also has very good mechanical properties, is fairly easy to process, and demonstrates excellent corrosion and fatigue resistance. Because of these attributes, NiTi is used for medical implants, smart materials, and smart structure systems with amazing success. One particular feature of NiTi, which has plagued its use in applications, is its slow response time to changes in temperature. Recently, however, NiTi has been used in robotics applications to mimic smooth, human-like motions; it may be usable in robots that require human physiological characteristics. Thin-film NiTi has been shown to yield very fast actuation response times and is finding increased use as a core technology for some MEMS applications, including micropumps, microvalves, microsprings, and micropositioners.

In addition to SMAs, shape-memory ceramics (SMCs) and shape-memory polymers (SMPs) are being applied in a number of areas not suitable for SMAs. SMCs can transition under both temperature and stress and have additional attributes such as improved toughening and plasticity, making them particularly attractive for uses calling for increased reliability and structural integrity. Perhaps the biggest drawbacks to using SMCs are the presence of microcracks, which are inherent in some ceramic materials, and a limited ability to recover from deformation (in other words, they can recover from only a low level of strain).

SMPs have recently gained much attention because of their ability to regain their original shape after severe deformation. Rubber and plastic are examples of polymer materials. The fact that polymers exhibit shape memory at all is quite amazing considering the very large deformations they undergo at certain temperatures. A rubber bushing (an insulating lining), for example, is rubbery and pliable at high temperatures, yet it becomes glassy and stiff when cooled to low temperatures. If an ordinary piece of rubber is bent at high temperature and its temperature then is lowered, the deformation of the rubber can be frozen in a glassy state. Reheating the rubber usually will not allow it to completely return to its normal shape. In contrast, SMPs can recover all of their residual deformation after undergoing such a process; strains of more than 400 percent can be recovered in most SMPs. A car bumper made out of an SMP, for example, can be shaped at high temperatures and then cooled to room temperature for installation on a car. If the bumper is dented, then one simply would have to heat the bumper to return it to its original shape.

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Active Polymers

Certain polymers, known as electroactive polymers, undergo shape changes when subjected to an applied voltage, so they are distinguished from SMPs. Applying a voltage to an electroactive polymer causes it to undergo a deformation in one direction, while reversing the voltage polarity causes it to reverse its deformation. This motion can be done repetitively, and the response time is fairly quick. These materials are finding applications in the field of robotics as “artificial muscles.” They also are being used in supercapacitors and superbatteries, transistors, chemical and biological sensors, molecular electronics, photovoltaics, and corrosion protection.

The use of electroactive polymers as anticorrosion coatings is particularly attractive, considering that the majority of the Department of Defense’s (DOD’s) military assets are subjected to environments in which corrosion causes deterioration. A 2001 study indicated that direct costs of corrosion for military systems and infrastructure are $10 billion to $20 billion annually. Corrosion was found to be one of the largest components of life-cycle costs for military weapon systems; corrosion also substantially reduces readiness by increasing equipment downtime. Recent studies on the use of electroactive polymers for corrosion prevention are quite promising. In this application, a conducting electroactive polymer film is produced directly on the surface of a metal through a procedure known as “anodic oxidation.” Conventional metal coatings, such as paint, form a temporary barrier to the environment and slow the corrosion of metals. Conductive polymers, on the other hand, do not create physical barriers but actually react with metals to create a layer of pure iron oxide on the metal surface that halts corrosion. In field tests, these coatings have been shown to be 3 to 10 times more effective than conventional coatings. They may play a substantial role in corrosion mitigation for future military systems.

Research on SMMs is ongoing, and many applications are yet to be discovered. The development and design of new SMMs to meet demanding applications with strict tolerance requirements are crucial. SMMs are not without shortcomings, but widespread use undoubtedly will increase in the future if low-cost SMMs become available, design and modeling complexity issues are overcome, pretuning of SMMs to respond to exacting environmental changes is achieved, and better understanding of material properties and behaviors is gained. For military applications, SMMs that can withstand extreme deformations, extreme temperature variations, and enormous stresses are highly desirable. The main applications of SMMs include actuation, memory, energy storage, sensing, switching, vibration control, and surface coatings. The ultimate goal for these materials is to offer complete end-to-end design of composite SMMs to help meet the future demands of our military.

New Composite Materials

New composite materials will yield significant advances for future material designs and functions. A composite material is an engineered material consisting of two or more constituent materials. The constituent materials consist of a matrix material (similar to glue) and a reinforcement material. The custom blending of these distinct components yields a composite with improved properties that allows the composite to outperform its constituents. One particularly useful property of composites is their high strength-to-weight ratio, which allows lightweight materials to be designed that reduce the weight of military platforms and thus increase fuel efficiency. Composites can be molded into complex shapes to further reduce weight (for example, by eliminating fasteners). Composites also resist corrosion, thereby reducing maintenance requirements.

While composites have been around for a number of years, advances in nanoscale and wireless technologies will create incredible opportunities to develop composite multifunctional materials at reduced costs. Composites will allow for the design of materials and structures based on the desired functionality of the materials. This may help remove constraints imposed by a material’s intrinsic properties. The ability to embed sensors, actuators, and nanoscale particles into composites will permit creation of materials with built-in health monitoring and control (self-diagnosis and self-repair), surveillance, and stealth-like functions.

The ability to control, organize, and integrate nanoscale particles into composite materials will offer tremendous potential for applications. Polymer-based composite materials with embedded chemical microcapsules, for example, have been shown to self-repair after cracking. In the future, composite materials embedded with microscale and nanoscale capsules that sense thermal, mechanical, and electrical stresses will wirelessly trigger additional embedded microscale and nanoscale capsules to initiate self-repair with near-instantaneous response. Recent estimates indicate that increased research efforts in composite materials will achieve an average 20- to 25-percent improvement in strength, toughness, stiffness, density, environmental resistance, and high-temperature capabilities in these materials by 2020. This, in turn, will lead to enhanced mobility, maneuverability, survivability, and transportability of DOD systems.

Logistics Implications

The application of designer materials within the Army likely will have enormous logistics benefits. Equipment readiness will increase in real terms as component parts achieve enhanced reliability. Development of lubrication-free bearings for quiet, efficient, high-performance electric motor drives on vehicles and aircraft will increase maintainability and reduce the need to stock and transport lubricants in the battlespace. The use of surface coatings will contribute to increased maintainability and reduced downtime by reducing friction and wear, increasing reliability, and creating superior resistance to corrosion. Material developments will reduce the weight and volume of equipment and systems, enhance mobility and durability, and reduce friction.

Low-power, highly reliable electronic and integrated circuits will be designed for logistics command and control decision support systems and their communications backbones. The use of advanced, novel materials to support efforts like telepresence will serve to remove Soldiers from the battlespace yet let them participate fully in ongoing operations. (See the article beginning on page 22.) Advanced manufacturing and fabrication capabilities will allow for deployment of molecular replication equipment to support onsite production of consumables (such as food, water, and fuels) in a theater of operations.

Nanoscale technology will permit the creation of materials with structurally superior shear strength, tensile strength, and compression characteristics. These and other novel characteristics will yield increased reliability of parts, thereby reducing sustainment and distribution requirements. Designer materials also may enhance human performance by augmenting human skills, attributes, or competencies. Human-embedded nanoscale materials and machines, for example, may revolutionize medicines and therapies designed to replace or increase performance.

Future advances in materials science will yield maintenance-free, highly durable materials capable of enduring harsh battlespace and other environmental conditions. Ultrahigh temperature ceramic materials that can withstand extremely high temperatures (4,000 degrees Fahrenheit) have been developed in the laboratory, and strong, electrically and thermally conductive carbon nanotube-based materials currently exist. Revolutionary advances in newer and better materials will lead to new structures, vehicles, armor, munitions, and equipment. These advances will greatly affect supportability, maintainability, reliability, and deployability, leading to reductions in logistics footprint and life-cycle costs as well as increased effectiveness for sustained combat.

So when you hear the expression, “don’t sweat the small stuff,” think again. Because of the small stuff resulting from designer materials, logisticians in the future may have to do less sweating about the big stuff needed to support the Soldier.

Dr. Keith Aliberti is a research physicist in the Sensors and Electron Devices Directorate at the Army Research Laboratory at Adelphi, Maryland. He currently serves as the laboratory’s liaison officer to the Army Logistics Innovation Agency at Fort Belvoir, Virginia. He has a B.S. degree in physics from Rensselaer Polytechnic Institute and M.S. and Ph.D. degrees from the State University of New York at Albany.

Thomas L. Bruen is a logistics management specialist at the Army Logistics Innovation Agency at Fort Belvoir, Virginia. He has a bachelor’s degree in engineering from the U.S. Military Academy and is a graduate of the Army Management Staff College’s Sustaining Base Leadership Management Program.