Tao Zheng Supervisor: Professor Harry Bhadeshia Richard Kemp Configurational Entropy as a function of Material Dimensions: A theory for strong ropes Tao Zheng Supervisor: Professor Harry Bhadeshia Richard Kemp

Outline space elevator. are carbon nanotube ropes ideal materials for space elevator project? 1 Configurational entropy 2 Stored energy and energy release rate 3 size-dependence of materials strength Conclusion

D.V.Smitherman 2005

High strength Lightweight > 62.5 GPa Carbon nanotubes Steel Kevlar Density 1300 kg m-3 7900 kg m-3 1440 kg m-3 Tensile strength 130 GPa < 5 GPa 3.6 GPa Bradley C. Edwards 2004

Steven L.Mielke et al (2004)

Equilibrium defect density Fromhold,Albert Thomas (1976)

Regular or ideal solution model Quasichemical solution model Lecture notes of Thermodynamics H K D H Bhadeshia (2004)

Energy release rate ( sound velocity): Stored energy Energy release rate ( sound velocity):

strength 130 GPa modulus 0.63 TPa Stored energy (J g-1) Energy release rate (m s-1) Dynamite 4650 6000 Nanotube 5420 21500 Bradley C. Edwards 2004

Different tensile strength value with different ropes length. Data from M.-F. Yu et al (2000); Min-Feng et al (2000); Z. W. Pan et al (1999)

Conclusion 1. By applying quasichemical solution model, more accurate configurational entropy and equilibrium defect density can be obtained. 2. Because of high strength and low density, carbon nanotubes have quite high stored energy and energy release rate which may make them not very safe in engineering application. 3. Strength of nanotube ropes will decrease sharply with increase of length of ropes.

Thank you!