5.4 Strain

5.4.1 Normal strain

Normal strain

  • Normal strain is the change in length over the original length

\[{\varepsilon}= \frac{\Delta l}{l}\]

5.4.2 Shear strain

Shear strain

  • Shear strain (\(\gamma\)) is proportional to the shear angle (\(\alpha\)) \[\gamma = \alpha\]

5.4.3 Strain

Note

  • Strain is defined by deformation
  • It is possible to have strain without stress
    • Tissues expand with moisture content
    • PMMA shrinkage during polymerization

5.4.4 A chain of relationships in biomechanics

Constraints
\(\Updownarrow\)
Deformation
\(\Updownarrow\)
Strain
\(\Updownarrow\)
Stress
\(\Updownarrow\)
Equilibrium
\(\Updownarrow\)
Applied Loads
  • Each arrow represents a relationship that must be understood and properly accounted