Materials Research to Meet 21st-Century Defense Needs (2003) / Chapter Skim
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3 Structural and Multifunctional Materials
3 Structural and Multifunctional Materials
Pages 27-54
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From page 27... ...
An example might be a composite material in which both the matrix and filaments serve several functions: The matrix might contain microcapsules sensitive to mechanical stress that, upon breaking, would highlight the damaged area by changing color. The strengthening filaments might have two different compositions which, when imbedded in a conducting polymer matrix, would produce a galvanic current.
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From page 28... ...
Using data presented by many outstanding scientists and engineers, the panel identified four broad R&D opportunities; in order of priority they are original design. Materials design assisted by computation, Service-induced material changes, Composite materials design and development, and Integration of nondestructive inspection and evaluation into These opportunities, if exploited, can produce many DoD materials of the future.
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From page 29... ...
Thus, "materials design assisted by computation" is a major opportunity to · Design better materials, Better understand their behavior, Design better structures with them, and Shorten the development cycle from concept to i Implementation. As a result of the improved understand)
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From page 30... ...
These points are especially relevant for polymer matrix composites where very high specific properties can be obtained for nominal temperature applications. Thus "composite materials design and development" is a compelling approach that merits study and refinement, because reduced weight is a primary design criterion in many structures.
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From page 31... ...
The following sections describe applications of computational approaches to materials design, the integration and optimization of materials systems, multifunctional materials, materials with self-healing abilities, materials with thermal or electrical conductivity spanning the range from conductors to insulators, and advanced coatings and adhesives. The chapter concludes by drawing out crosscutting materials R&D opportunities that will be vital to critical DoD systems in the coming decades.
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From page 32... ...
Also, materials costs for complex composite structures are as little as 2-5 percent of the total fabricated cost. The importance of reducing materials weight is that all vehicles, engines, and aircraft can be lighter and require less energy to run, thus saving fuel or enabling them to carry larger payloads.
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From page 33... ...
. Weight reduction coupled with strength increase is doubly imoortant for vehicle or engine weight and for allowable engine size.
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From page 34... ...
Because ceram ic or polymer matrix materials can produce very strong, I ightweightstructu res, research on these materials is of pri mary i Importance. The drawbacks are that the fabrication costs of composite materials often exceed those of metals and alloys, and their ductility and fracture toughness are usually lower.
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From page 35... ...
More recently, new higher temperature alloys contain increasing amounts of Ta and Re, both heavy elements, so the density of these blade materials has increased by about 25 percent (Antolovich, 1 992; Kissinger, 1 996; Pollock, 2000~. Finally, thermal barrier coatings are used to insulate metallic material from the heat of flowing gases.
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From page 36... ...
Thus, the disk, the shaft, and the bearing support structure must be strengthened, adding still more weight to the engine. Significant progress in turbine engine efficiency is likely to come from materials that allow engine weight to decrease.
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From page 37... ...
Processing of structural materials is critical because the microstructure developed during processing is a primary determinant of the resultant mechanical properties. Complicating the design process is the fact that a material has many mechanical and physical properties, e.g., elastic modulus, yield strength, ductility, fracture toughness, fatigue resistance, density, weldability, and corrosion resistance.
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From page 38... ...
Development of computational materials science would enable mechanistic constitutive materials models to replace the empirical models now used in FEM simulations. The result will be a predictive tool that would allow materials designers to shorten the experimental synthesis and testing stages, and hence development cycle time and cost, by at least one order of magnitude.
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From page 39... ...
..................................................... performance ,` \,reliability cost safety Systems Model Schematic of materials and systems interactions through a series of models at various size scales.
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From page 40... ...
The key to lifetime design is a sophisticated systems model that can predict system performance and reliability throughout service lifetime; system costs, including initial, maintenance, and disposal costs; and system safety both in normal operation and under threat conditions. This panel's view of the future has a systems engineer optimizing all these requirements, not only by changing conventional design parameters (e.g., geometry)
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From page 41... ...
The vision is to have a sufficiently fundamental understanding of phenomena like corrosion, creep, stress and creep rupture, galvanic action, radiation effects, and long-term temperature effects on a wide range of engineering materials to enable the development of in situ and other real-time property sensors and mechanistic sciencebased performance models. This will allow us to predict the life-cycle 41
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From page 42... ...
Multifunctional Materials Multifunctionality in the context of materials applications is often referred to as "structure +," because one of the functions of the material is typically structural to carry load or define shape. The other functions can be as varied as actuation (to control position, shape, or load)
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From page 43... ...
The following subsections will briefly discuss the future of multifunctionality, mentioning first the general area of smart materials, then the possibi I ities i n composites. Smart Materials Smart or intelligent materials where revolutionary improvements in material design or application are likely are piezoelectric materials, shape memory alloys (SMAs)
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From page 45... ...
In · o · · ~n o · To m By ~n o ._ ._ o In m U or.
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From page 46... ...
Their conductivity and color can be reversed by controlled chemical or electrical stimuli. Electroactive polymers can be used both as light and chemical sensors and as actuators, but because of their low elastic modulus they are not typically used as structural members Nevertheless, they are certainly multifunctional materials with enormous growth potential and could play a role in self-healing composite materials.
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From page 47... ...
Much greater progress is likely with amorphous metals, where the best properties might be found in composite materials formed of an amorphous metal matrix with ductile dendritic phase reinforcements. Use of simple and fast thermoplastic forming techniques for these materials, the known glass transition temperature, and the thermal stability of the final amorphous composite merit further study.
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From page 48... ...
In polymers and polymer composites, the effect has been achieved by chemical triggers (catalyst) and microcapsules of fluid repair agent in the polymer matrix.
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From page 49... ...
Adhesives are also used as matrix materials for all types of composites, including solid propellants and explosives as well as high-performance structural materials. Advances in the science and engineering of adhesion, including how such systems fail, will continue to yield improvements in adhesion performance and reliability.
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From page 50... ...
Because most polymeric glasses, such as epoxies, all have about the same shear modulus and the spatial sizes are so small, attempts to improve matrix stiffness via composite reinforcement have not been pursued. With the advent of nanosized reinforcement, such as carbon nanotubes, it should be possible to substantially improve the stiffness of matrix materials by reinforcing them at the nanoscale level, 50
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From page 51... ...
Investment in these priority areas should provide enabling materials technologies to DoD for use by 2020. Materials Design Assisted by Computation In the design of materials assisted by computation, the goal is to implement new materials by integrating constitutive models into a framework that employs FEM calculations.
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From page 52... ...
Other benefits are robust multidisciplinary virtual design environments that reduce cost and speed design, testing, prototyping, manufacturing, and deployment. The results would be reduced vehicle weight, enhanced performance, and fuel savings.
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From page 53... ...
Integrating Nondestructive Inspection and Evaluation into Design As a complement to composite material development, this panel believes that there are opportunities for integrating NDI/NDE into the original design of both materials and structures. This would allow for continuous health monitoring of all new structures.
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From page 54... ...
2001. Autonomic healing of polymer composites.
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