Mechanical properties of Biomaterials Flashcards
Define Hooke’s Law
The ratio of force and displacement are constant (for elastic deformation). F = k* change in horizontal displacement
Define ‘stress’
The force per unit area.
S = F/area.
Unit = N/m^2 = Pa
Define ‘Strain’
Proportion of change in length, with respect to the Original length.
Strain (e) = change in L / Original length.
Unitless.
Define ‘ Young’s Modulus’ (elastic modulus)
Ratio of stress to strain in the elastic region. E = Stress / Strain. - Units = Pa. (pascal) - Larger E = Stiffer material. - Slope of Stress-strain graph
Define ‘elastic region’
Material returns to initial length after stress is removed (fully reversible deformation).
Define ‘plastic region’
Material is permanently deformed after stress is removed.
Define ‘proportional limit’
Highest stress within elastic region.
Define ‘ultimate stress’
Highest stress before fracture of material.
Define ‘elongation’.
Maximum strain before material fracture.
Define ‘toughness’.
Area under entire stress-strain curve; total energy that is absorbed by material before fracture.
Define ‘ resilience’
Area under elastic region of curve; energy absorbed by elastic deformation.
Define ‘ductile’
Material that has large plastic region.
Define ‘brittle’
Material with very short plastic region.
Define ‘shear stress’
Force applied parallel to a surface, per unit area.
A = Cross-sectional area of material with area parallel to the applied force vector.
Define ‘shear strain’
Displacement of the parallel surface, with respect to the length of the normal surface.
Define ‘ shear modulus (G)’
Shear stress/shear strain.
Define ‘fatigue’
Failure of a material after repeated loading cycles of stresses BELOW the ultimate stress.
Define ‘hardness’
Resistance of a material to indentation, penetration, or scratching; determines wear.
Define ‘viscosity’
Resistance of a liquid to flow. Viscosity = shear stress/ flow rate.
Define ‘Newtonian liquid’
Flow rate of liquid is directly proportional to shear stress.
Define ‘creep’
Strain of material under constant stress due to temperature alone.
Describe the Maxwell Body of viscoelastic response
This is a series configuration.
- Elastic deformation
- Gradual viscous deformation.
- Permanent deformation; only elastic deformation is recovered.
Describe the Kelvin-Voigt Body model of viscoelastic response
This is a parallel configuration.
- Deformation and recovery start linearly and quickly.
- Slows down as viscous properties kick in.
- No permanent strain.
