For uniaxial tests, the displacement is typically held at a constant rate, and displacement
and resulting load are recorded. The load is measured by a series of strain gages, or “load cell,”
while the displacement can be recorded as displacement of the crosshead, or the beam on which
the specimen load frame is mounted. For more precise load measurements, strain gages or an
extensometer can be directly fixed to the specimen. To make direct comparisons between
materials, loading responses must be normalized against sample geometry. Therefore, the
dimensions of each sample are noted to compute stress and strain from load and displacement,
respectively. Engineering strain can be calculated as: