Biomechanical properties

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Biomechanical properties
Material properties of device materials and
tissues. Stress, strain, and constitutive
relationships.
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Basic testing for determination of material
properties

• Elastic modulus
• Yield strength
• Ultimate tensile strength
• Fracture Strength
• Toughness
• Ductility
• Engineering vs. True Stress-Strain testing

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Types of Behavior

• Elastic
• Non-linear elastic
• Visco-elastic
• Plastic
• Isotropic vs. Anisotropic
• Brittle (fracture before yield)
• Ductile (yield before fracture)

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Viscoelastic and Anisotropic Mechanical Behavior
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Stress and Strain

• In biomedical devices it is necessary to consider
  3-D states of loading
• Stress is typically thought of as a force acting
  on an area and strain as the change in size and
  shape--stress is cause and strain is effect
• In 3-d loading we must recognize stress and
  strain as tensor quantities

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Stress

• Stress relates a force vector to the plane it
  acts upon (defined by its normal)
• Different planes have different stress vectors
  that can be resolved into its normal and shear
  components

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Stress vectors
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3-D State of Stress
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Transformations and principal stresses
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Equivalent stress states
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Strain
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How do we relate stress and strain?
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Isotropy vs. Anisotropy