Compression set

The compression set (ASTM D395) of a material is the permanent deformation remaining after squashing it.[1] In specific methods, temperatures and percent compression are specified. The term is normally applied to soft materials such as elastomers and foams. Compression is normally measured in two ways: compression set A and compression set B.[2]

Compression Set A

A diagram of the compression set A experiment (under constant force in air).

This has the formal name compression set under constant force in air. In compression set A a force of 1.8 kN is applied to the specimen for a set time at a set temperature. Compression set A is defined as the percentage of original specimen thickness after the specimen has been left in normal (uncompressed) conditions for 30 minutes. C_A, the compression set A is given by C_A = [(t_o - t_i) / t_o] * 100 where t_o is the original specimen thickness and t_i is the specimen thickness after testing.[2]

Compression Set B

A diagram of the compression set B experiment (under constant deflection in air).

This has the formal name compression set under constant deflection in air. The specimen is compressed to 75% of its original height for a set time and at a set temperature (sample is compressed to .75 of its original height). Compression set B is (like Compression set A) defined as the percentage of specimen deflection after it has been left in normal (uncompressed) conditions for 30 minutes. C_B, the compression set B is given by C_B = [(t_o - t_i) / (t_o - t_n)] * 100 where t_o is the original specimen thickness, t_i is the specimen thickness after testing and t_n is the spacer thickness or the specimen thickness during the test.[2]

References

Carroll, Gregory T.; Jongejan, Mahthild G. M.; Pijper, Dirk; Feringa, Ben L. (2010). "Spontaneous generation and patterning of chiral polymeric surface toroids". Chemical Science. 1 (4): 469. doi:10.1039/c0sc00159g. ISSN 2041-6520.
"Compression Set - ASTM D395 Plastic Test Standard". IDES. Integrated Design Engineering Systems. Archived from the original on 28 December 2011. Retrieved 15 June 2012.

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[1] Carroll, Gregory T.; Jongejan, Mahthild G. M.; Pijper, Dirk; Feringa, Ben L. (2010). "Spontaneous generation and patterning of chiral polymeric surface toroids". Chemical Science. 1 (4): 469. doi:10.1039/c0sc00159g. ISSN 2041-6520.

[IDES-2] "Compression Set - ASTM D395 Plastic Test Standard". IDES. Integrated Design Engineering Systems. Archived from the original on 28 December 2011. Retrieved 15 June 2012.