compression set
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The compression set (ASTM D395) of a material is the permanent deformation remaining after compressing it.{{Cite journal |last1=Carroll |first1=Gregory T. |last2=Jongejan |first2=Mahthild G. M. |last3=Pijper |first3=Dirk |last4=Feringa |first4=Ben L. |date=2010 |title=Spontaneous generation and patterning of chiral polymeric surface toroids |url=http://xlink.rsc.org/?DOI=c0sc00159g |journal=Chemical Science |language=en |volume=1 |issue=4 |pages=469 |doi=10.1039/c0sc00159g |s2cid=263769377 |issn=2041-6520}} 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.{{cite web | title = Compression Set - ASTM D395 Plastic Test Standard | url = http://www.ides.com/property_descriptions/ASTMD395.asp | accessdate = 15 June 2012 | work = IDES | publisher = Integrated Design Engineering Systems | url-status = dead | archive-url = https://web.archive.org/web/20111228181315/http://www.ides.com/property_descriptions/ASTMD395.asp| archive-date = 28 December 2011}}
Compression Set A
File:Compression Set A Diagram.gif
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. CA, the compression set A is given by CA = [(to - ti) / to] * 100
where to is the original specimen thickness and ti is the specimen thickness after testing.
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Compression Set B
File:Compression Set B Diagram.gif
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. CB, the compression set B is given by CB = [(to - ti) / (to - tn)] * 100
where to is the original specimen thickness, ti is the specimen thickness after testing and tn is the spacer thickness or the specimen thickness during the test.