Longitudinal strain is the longitudinal deformation expressed as a dimensionless constant and is defined as the ratio of change in length to the initial length.
e = δL/L
Lateral strain is the lateral deformation expressed as a dimensionless constant and is defined as the ratio of change in lateral dimension to the initial lateral dimension Lateral strain = Change in lateral dimension/Original lateral dimension
= Change in diameter/Original diameter; For circular bar
= Change in width or depth/Original width or depth; For rectangular bar
LATERAL STRAIN = POISSON'S RATIO X LONGITUDINAL STRAIN
