# Strain

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Strain, abbreviated as $$\epsilon$$ (Greek symbol epsilon), a dimensionless number, also known as linear strain or longitudinal strain, is the deformation, stretched or compressed, of a material compared to its original length.

## strain Types

• Elastic Strain  -  A transitory dimensional change that exists only while the initiating stress is applied and disappears immediately upon removal of the stress.
• Plastic Strain  -  A dimensional change that does not go away when the initiating stress is removed.

## strain formula

 $$\large{ \epsilon = \frac{ \Delta l }{ l_i } }$$ $$\large{ \epsilon = \frac{ l_f \;-\; l_i }{ l_i } }$$

### Where:

 Units English Metric $$\large{ \epsilon }$$  (Greek symbol epsilon) = strain $$\large{\frac{in}{in}}$$ $$\large{\frac{mm}{mm}}$$ $$\large{ \Delta l }$$ = length change $$\large{ ft }$$ $$\large{ m }$$ $$\large{ l_f }$$ = final length $$\large{ ft }$$ $$\large{ m }$$ $$\large{ l_i }$$ = initial length $$\large{ ft }$$ $$\large{ m }$$

## Related formulas

 $$\large{ \epsilon = \frac { \sigma } { \lambda } }$$ (elastic modulus) $$\large{ \epsilon = \frac { \sigma } { E } }$$ (Young's modulus)

### Where:

$$\large{ \epsilon }$$  (Greek symbol epsilon) = strain

$$\large{ \lambda }$$  (Greek symbol lambda) = elastic modulus

$$\large{ \sigma }$$  (Greek symbol sigma) = stress

$$\large{ E }$$ = Young's modulus