Measure and record the length of each
side, the angle between each side, and the orientation angle for each
square.
Digital and Dial Calipers
Vernier Caliper
Sandwich both ends of the specimen between the specimen
shields as the sample is loaded into the universal testing machine.
Remove the slack, and
measure the distance between the crossheads.
Elongate the sample, at 1.5 to 2.0 inches/min, until the distance between the crossheads has increased
approximately 1.5 to 2.0 inches. This will ensure a sufficiently large
size change in the squares once the
load has been removed.
Remove the sample from the testing
machine. Be careful not to touch the printed squares, as the ink
will now be broken and easily wiped off.
Remeasure the lengths and angles, excluding the orientation angle for
each square.
Calculate the average normal and shear
strain experienced by each square.
Use the strain values to calculate the
principle-axis angle of rotation, the principal strains,
and the maximum shear strain, thereby determining the
direction and magnitude of the applied strain field.