Compression Properties ASTM D695, ISO 604
Understand compression strength and modulus of plastics materials used in various engineering applications using ASTM D695.
Compressive properties describe the behavior of a material when it is subjected to a compressive load. Loading is at a relatively low and uniform rate. Compressive strength and modulus are two common values generated by the test.
The specimen is placed between compressive plates parallel to the surface. The specimen is then compressed at a uniform rate. The maximum load is recorded along with stress-strain data. An extensometer attached to the front of the fixture is used to determine modulus.
Specimens can either be blocks or cylinders. For ASTM, the typical blocks are 12.7 x 12.7 x 25.4mm (½ by ½ by 1 in). and the cylinders are 12.7mm (½ in) in diameter and 25.4mm (1 in) long. For ISO, the preferred specimens are 50 x 10 x 4mm for modulus and 10 x 10 x 4mm for strength.
Compressive strength and modulus are two useful calculations.
Compressive strength =
maximum compressive load/
minimum cross-sectional area
Compressive modulus =
change in stress/
change in strain
This test method covers the determination of the mechanical properties of unreinforced and reinforced rigid plastics, including high-modulus composites, when loaded in compression at relatively low uniform rates of straining or loading. Test specimens of standard shape are employed. This procedure is applicable for a composite modulus up to and including 41,370 MPa (6,000,000 psi).