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.

Test Procedure:
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.

Specimen size:
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 

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Due to copyright restrictions, we are not able to provide copies of standards. Standards can be obtained from appropriate standards authorities.
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