Scope:

ASTM D695 test method is used to evaluate compressive properties of rigid plastic materials used in various engineering applications. A plastic material behaves in a certain way when subjected to a compressive load, and this particular behaviour defines the compressive properties of that plastic. This test provides compressive strength and modulus as the two standard values for the test plastic material.

Test Procedure:

A compression properties test is done by using a compression fixture designed to crush the material put between the compressor plates. Compressive loading is done slowly at a uniform rate. First, the crosshead of the upper portion of the compressor is adjusted to touch the rigid plastic specimen placed between two surfaces of the compressor. Next, the sample is compressed at a steady rate till failure is observed. Finally, the stress-strain data and the maximum load applied are recorded. The front portion of the fixture contains an extensometer that records the modulus.

Specimen size:

Blocks or cylinders of test material are used as a specimen. For ASTM test, usually 12.7 × 12.7 × 25.4 mm (½ by ½ by 1 inch) blocks are used. Also, 25.4 mm (1 inch) long cylinders having 12.7 mm (½ in) diameter can be used. For the ISO test, the ideal specimens used are 50 × 10 × 4 mm for determining modulus and 10 × 10 × 4 mm specimens for determining strength.

Data:

This test reports maximum load, maximum stress, modulus of elasticity and yield by offset (stress). Units for compressive strength are usually given in megapascals or pounds per square inch.

Compressive strength = maximum compressive load/minimum cross-sectional area

Compressive modulus = change in stress/change in strain