The University of Texas at Austin
College of Engineering

Nanoscale Properties: Mechanical

Making a Nanowire
Making a Nanowire

Mechanical Properties of Nanomaterials

Scientific challenges in nanoscience and nanotechnology include the development of nanomaterials with novel mechanical properties. The need for scratch, mar and/or abrasion resistance is well established in various markets, including fingernail polishes, flooring, plastic glazing, headlamp covers and other automotive parts, transportation windows and optical lenses, where clear scratch-resistant coatings are used. Because the nanosize, many of their mechanical properties of the materials is modified, among others, hardness and elastic modulus, fracture toughness, scratch resistance, fatigue strength, and hardness. Energy dissipation, mechanical coupling within arrays of components, and mechanical nonlinearities are influenced by structuring components at the nanometer scale. This includes also the interpretation of unusual mechanical behavior (e.g., strengths approaching the theoretical limit) and the exploration of new ways to integrate diverse classes of mechanically functional materials on the nano-size.

Applications of Mechanical Properties of Nanomaterials

Tougher and harder cutting tools
Cutting tools made of nanomaterials, such as tungsten carbide, tantalum carbide, and titanium carbide, are much harder, much more wear-resistant, erosion-resistant, and last longer than their conventional (large-grained) counterparts. Also, for the miniaturization of microelectronic circuits, the industry needs micro drills (drill bits with diameter less than the thickness of an average human hair or 100 µm) with enhanced edge retention and far better wear resistance. Since nanocrystalline carbides are much stronger, harder, and wear-resistant, they are currently being used in these micro drills.

Automobiles with greater fuel efficiency
In automobiles, since nanomaterials are stronger, harder, and much more wear-resistant and erosion-resistant, they are envisioned to be used in spark plugs. Also, automobiles waste significant amounts of energy by losing the thermal energy generated by the engine. So, the engine cylinders are envisioned to be coated with nanocrystalline ceramics, such as zirconia and alumina, which retain heat much more efficiently that result in complete and efficient combustion of the fuel.

Aerospace components with enhanced performance characteristics
One of the key properties required of the aircraft components is the fatigue strength, which decreases with the component’s age. The fatigue strength increases with a reduction in the grain size of the material. Nanomaterials provide such a significant reduction in the grain size over conventional materials that the fatigue life is increased by an average of 200-300%. In spacecrafts, elevated-temperature strength of the material is crucial because the components (such as rocket engines, thrusters, and vectoring nozzles) operate at much higher temperatures than aircrafts and higher speeds. Nanomaterials are perfect candidates for spacecraft applications, as well.

Ductile ceramics
Ceramics are very hard, brittle, and hard to machine even at high temperatures. However, with a reduction in grain size, their properties change drastically. Nanocrystalline ceramics can be pressed and sintered into various shapes at significantly lower temperatures. Zirconia, for example, is a hard, brittle ceramic, has even been rendered superplastic, i. e., it can deformed to great lengths ( up to 300% of its original length). However, these ceramics must possess nanocrystalline grains to be superplastic. Ceramics based on silicon nitride (Si3N4) and silicon carbide (SiC), have been used in automotive applications as high-strength springs, ball bearings, and valve lifters, and because they possess good formability and machinabilty combined with excellent physical, chemical, and mechanical properties. They are also used as components in high-temperature furnaces.

Better insulation materials
Aerogels are nanocrystalline porous and extremely lightweight materials and can withstand 100 times their weight. They are currently being used for insulation in offices, homes, etc. They are also being used as materials for "smart” windows, which darken when the sun is too bright and they lighten themselves otherwise.

 


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