While in EN 826 and ISO 844 the movement of the compression platen is typically measured by the crosshead travel of the testing machine with a defined minimum accuracy, ASTM D1621 describes an additional method that compensates for the self-deformation of the testing machine.
Alternately, all standards permit direct displacement measurement of the compression platen.
ISO 844, Method B also describes direct compressive deformation measurement of the specimen. Method B provides deformation data and a compression modulus that is less influenced by force application effects. If deformations are significant, the measured deformations differ significantly from those in other methods because of the compression sphere that forms and do not provide reproducible results.
