Compression
testing involves a self-supporting sample being compressed under a flat
probe large enough to cover the whole sample.
The
loading arm (attached to the probe) moves down at a constant speed to
deform the sample, first deforming it elastically then plastically (if
it is not completely brittle). If the force required to break the sample
is within the limit of the load cell, fracture may occur. However, this
is not always the case in compression as many samples are stronger (or
tougher) in compression than in tension, especially ceramic samples.