1. Nanoscience: Mechanical Properties Olivier Nguon CHEM *7530/750 Feb 21st 2006

2. Outline I. Classic Mechanical Properties II. Nanostructured Materials III. Conclusions and Applications

3. Tensile test Determination of mechanical properties Stress: σ = F/S Strain: ε = Δl / l 0

4. Tensile Test curve Max stress : tensile strength Max elasticity: Yield strength Stress, σ (Mpa) Necking Strain, ε (%) Elastic deformationPlastic deformation Fracture Typical Tensile Test curve or Strain Stress curve

5. Modulus = slope Strain Elastic Deformation Hooke’s law: σ = E ε E = Young modulus (Pa) Stiffness of material Non linear models exist (visco-elastic behaviour) Stress, σ

6. Mechanical properties Yield strength: maximum stress before permanent strain Tensile strength: maximum stress Ductility: measure of deformation (L f – L o )/ L o Toughness: ability to absorbe energy: area under curve

7. Hardness Resistance to plastic deformation Measure of depth or size of indentation

8. II. Nanostructured materials

9. Nanoparticles Conventional materials: Grain size micron to mm Nanoparticles increase grain boundaries Influence on mechanical properties: Increased hardness, yield strength, elastic modulus, toughness

10. Comparison tensile curves Comparison: Al Mg cryomilled (20 nm) Al Mg ultra fine grain (80 nm) Al Mg coarse (2 mm) Cryomilling: Milling in liquid N 2 Ultrafine grain: electrodeposition B. Han, Red.Adv.Mater.Sci; 9 (2005) 1-16

11. Mechanical properties of nanomaterials compared to coarse grain materials Higher Young modulus and tensile strength (to 4 times higher) Lower plastic deformation More brittle

12. Strength and Hardness with grain size Strength and Hardness of nanostructured material increases with decreasing size Grain boundaries deformation

13. Comparison of Young modulus MaterialYoung modulus (GPa) Rubber0.1 Al70 Fe200 SiC440 Fe nanoparticles (100 nm)800 C nanotubes1000 Diamond1200

14. Elongation nanostructured materials Elongation decreased Lower density of mobile dislocations Short distance of dislocation movement

15. III. Conclusions

16. Mechanical properties Mechanical properties: Strength, toughness, hardness increased Materials more brittle Due to increased grain boundaries density and less dislocations density

17. Important factors on mechanical properties History of the material: Temperature, strain: influence on amount of dislocations, grain size Impurities: segregate at high temperature and affect mechanical properties

18. Applications Biomedical: bones, implants, etc. High strength, strong, long-lasting materials: automotives, electronics, aerospace, etc. Composites materials