Nanomaterials on Earth and Beyond Series
Steel is another important building material used as cables, joints, bolts, reinforcement and pre-cast concrete tensioning. Fatigue especially during cyclic loading is a major problem while using steel and can lead to structural failure (9). Adding copper nano-particles to steel reduces the unevenness in the surface of the steel, which in turn reduces the amount of stress risers i.e. locations where stresses are concentrated, thus lowering fatigue cracking. Another issue with steel arises during welding. The area affected by heat during welding can be brittle and fail without warning at times. The addition of magnesium and calcium nano-particles makes the heat affected zone (HAZ) grains (microscopic crystallites inside the material) finer (about 1/5th the size of conventional material) thereby reducing the chances of the sudden failure of steel plates (9).
In high rise structures the joints and the bolts need to be of high strength. Current steel bolts are limited in their strength to 1,000 – 1,200 N/mm2 due to a phenomenon called delayed fracture. Quenching and tempering is usually used to realize high strength bolts. During tempering if the tensile strength of steel exceeds 1,200 N/mm2 , even a small amount of hydrogen embrittles the grain boundaries and causes the steel to fail during usage. This delayed fracture problem associated with high strength bolts can be overcome by using vanadium and molybdenum nano-particles. The nanoparticles reduce the effect of inter-granular fracture during cementite phase thereby reducing the effects of hydrogen embrittlement (9).
Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen. Hydrogen embrittlement is often the result of unintentional introduction of hydrogen into susceptible metals during forming or finishing operations and increases cracking in the material.
A significant challenging issue with steel is the trade off between steel strength and ductility; the forces in modern construction require high strength, whereas safety (especially in seismic areas) and stress redistribution require high ductility. Sandvik Nanoflex (22) (produced by Sandvik Materials Technology) is currently being used in the production of parts as diverse as medical instruments and bicycle components and has both the desirable qualities of a high Young’s Modulus and high strength, and is also resistant to corrosion due to the presence of very hard nanometer-sized particles in the steel matrix. MMFX2 steel (23) (produced by MMFX Steel Corp) is a lower cost alternative, it has the same mechanical properties of conventional steel, however has a modified nano-structure that makes it corrosion resistant.
Space launch pads use a combination of concrete and steel and are the key for a successful rocket launch (24). A Stronger concrete supporting material using some of techniques mentioned earlier, will help more powerful and sophisticated rockets to be launched.