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Nanoscience: Mechanical Properties

Nanoscience: Mechanical Properties. Olivier Nguon CHEM *7530/750 Feb 21st 2006. Outline. I. Classic Mechanical Properties II. Nanostructured Materials III. Conclusions and Applications. Tensile test. Determination of mechanical properties Stress: σ = F/S Strain: ε = Δ l / l 0.

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Nanoscience: Mechanical Properties

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  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 / l0

  4. Stress, σ (Mpa) Max stress : tensile strength Necking Max elasticity: Yield strength Fracture Strain, ε (%) Elastic deformation Plastic deformation Tensile Test curve 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 (Lf – Lo)/ Lo • 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 N2 • 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

  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

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