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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

Nanoscience: Mechanical Properties

Olivier Nguon

CHEM *7530/750

Feb 21st 2006

outline
Outline
  • I. Classic Mechanical Properties
  • II. Nanostructured Materials
  • III. Conclusions and Applications
tensile test
Tensile test
  • Determination of mechanical properties
  • Stress: σ = F/S
  • Strain: ε = Δl / l0
tensile test curve
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

elastic deformation
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

mechanical properties
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
hardness
Hardness
  • Resistance to plastic deformation
  • Measure of depth or size of indentation
nanoparticles
Nanoparticles
  • Conventional materials: Grain size micron to mm
  • Nanoparticles increase grain boundaries
  • Influence on mechanical properties: Increased hardness, yield strength, elastic modulus, toughness
comparison tensile curves
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

mechanical properties of nanomaterials compared to coarse grain materials
Mechanical properties of nanomaterials compared to coarse grain materials
  • Higher Young modulus and tensile strength (to 4 times higher)
  • Lower plastic deformation
  • More brittle
strength and hardness with grain size
Strength and Hardness with grain size
  • Strength and Hardness of nanostructured material increases with decreasing size
  • Grain boundaries deformation
elongation nanostructured materials
Elongation nanostructured materials
  • Elongation decreased
  • Lower density of mobile dislocations
  • Short distance of dislocation movement
mechanical properties16
Mechanical properties
  • Mechanical properties: Strength, toughness, hardness increased
  • Materials more brittle
  • Due to increased grain boundaries density and less dislocations density
important factors on mechanical properties
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
applications
Applications
  • Biomedical: bones, implants, etc.
  • High strength, strong, long-lasting materials: automotives, electronics, aerospace, etc.
  • Composites materials
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