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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 l.jpg

Nanoscience: Mechanical Properties

Olivier Nguon

CHEM *7530/750

Feb 21st 2006


Outline l.jpg
Outline

  • I. Classic Mechanical Properties

  • II. Nanostructured Materials

  • III. Conclusions and Applications


Tensile test l.jpg
Tensile test

  • Determination of mechanical properties

  • Stress: σ = F/S

  • Strain: ε = Δl / l0


Tensile test curve l.jpg

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 l.jpg

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 l.jpg
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 l.jpg
Hardness

  • Resistance to plastic deformation

  • Measure of depth or size of indentation



Nanoparticles l.jpg
Nanoparticles

  • Conventional materials: Grain size micron to mm

  • Nanoparticles increase grain boundaries

  • Influence on mechanical properties: Increased hardness, yield strength, elastic modulus, toughness


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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 l.jpg
Mechanical properties of nanomaterials compared to coarse grain materials

  • Higher Young modulus and tensile strength (to 4 times higher)

  • Lower plastic deformation

  • More brittle


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Strength and Hardness with grain size grain materials

  • Strength and Hardness of nanostructured material increases with decreasing size

  • Grain boundaries deformation



Elongation nanostructured materials l.jpg
Elongation nanostructured materials grain materials

  • Elongation decreased

  • Lower density of mobile dislocations

  • Short distance of dislocation movement


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III. Conclusions grain materials


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Mechanical properties grain materials

  • Mechanical properties: Strength, toughness, hardness increased

  • Materials more brittle

  • Due to increased grain boundaries density and less dislocations density


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Important factors on mechanical properties grain materials

  • History of the material: Temperature, strain: influence on amount of dislocations, grain size

  • Impurities: segregate at high temperature and affect mechanical properties


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Applications grain materials

  • Biomedical: bones, implants, etc.

  • High strength, strong, long-lasting materials: automotives, electronics, aerospace, etc.

  • Composites materials


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