Measurements of Strain

Strain measures the deformation or displacement in a material. Normal strain is calculated by comparing lengths before and after a load is applied.

A more accurate method for measuring normal strains involves using electrical strain gauges consisting of a thin wire cemented to two pieces of paper.

When the material elongates, the wire's length increases, and its diameter decreases, causing an increase in electrical resistance. Measuring this change in current determines accurate strain.

Strain components at a given point can be determined by measuring the normal strain across the axes drawn through that point. A third measurement along the bisector of the angle formed by the axes determines the shearing strain.

Strain measurements are made along three lines drawn through a point, forming respective angles with the horizontal axis.

The corresponding strain measurements are substituted into the normal strain equation to form three strain measurement equations.

The arrangement of strain gauges used to measure strains is called a strain rosette, typically in 45° or 60° configurations.