Compression Set - ASTM D395
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The permanent deformation remaining after release of a compressive stress. Compression set is expressed as the percentage of the original specimen thickness for Method A (constant force) or the percentage of the original deflection for Method B (constant deflection). Compression set is an important property for elastomers and cushioning materials.
Compression Set Methods
| Method |
Name |
Test Description |
Calculation |
Diagram |
| A |
Compression Set Under Constant Force in Air |
A constant compressive force of 1.8 kN (400 lbf) is applied to the specimen for a specified time at a specified temperature. Compression set is taken as the percentage of the original specimen thickness after the material is allowed to recover at standard conditions for 30 minutes. |
CA = [(to - ti) / to] * 100
where to is the original specimen thickness and ti is the specimen thickness after testing. |
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| B |
Compression Set Under Constant Deflection in Air |
Specimen is compressed 25% for a specified time at a specified temperature. Compression set is taken as the percentage of the original deflection after the material is allowed to recover at standard conditions for 30 minutes. |
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. |
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Two different specimens may be used for testing. Test specimens are cylindrical disks cut from a slab of the testing material.
Compression Set Specimens
| Specimen Type |
Diameter (mm) |
Thickness (mm) |
Used for Method |
| 1 |
29.0 |
12.9 |
A and B |
| 2 |
13.0 |
6.0 |
B |
Similar Standards
Property information for specific grades of resin are available in the Prospector.
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