Compression Hardness
Stauchhärte | A service provided by |
|---|
|
| Polymer Service GmbH Merseburg |
| Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de |
| Our further education offers: https://www.psm-merseburg.de/weiterbildung |
| PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg |
Compresssion hardness
Compression hardness
This test technique is similar to the compression test and is used to determine the compression hardness of foams. To determine the compression hardness, a square test specimen (parallelepiped) is compressed between two plates and the force required to compress the specimen to a specific percentage of its original height (e.g. 40 %) is measured. The test specimens usually have dimensions of 100 x 100 x 50 mm³. This force value is then related to the tested area, resulting in the compressive strength or compression resistance of the foam in kPa.
The operating principle of the compression hardness test is illustrated in Fig. 1.
| Fig. 1: | Functional principle of compression hardness testing |
Indentation hardness
Unlike indentation hardness, where the pressure plates (see: compression test arrangement) are larger than the test specimen (Fig. 1), indentation hardness or compression resistance is determined using smaller pressure plates that are rounded to prevent excessive shearing (Fig. 2). In this case, a foam test specimen is compressed by 25, 40 and 65 % of its initial thickness, and the indentation hardness or compression resistance is then expressed in N.
| Fig. 2: | Functional principle of indentation hardness |
Compression hardness curves using PUR foams as an example
If the force required to compress the material is not merely determined when a specified deformation is reached, but a force-deformation diagram is plotted, this results in the spring characteristic curve or compression stiffness curve of the foam under investigation. This spring characteristic curve is generally non-linear, and when the unloading process is taken into account, a hysteresis loop results (Fig. 3), which is caused by the delayed return deformation. The area of this hysteresis loop is a measure of the foam’s elastic damping [1].
| Fig. 3: | Compressive stress–deformation diagrams of soft-elastic PUR foams [1], Type A: PUR foam with normal energy absorption, Type B: PUR foam with high energy absorption, and Type C: PUR foam with low energy absorption |
The material parameters of this test are:
- Compressive stress at 40 % compression = compressive modulus σd40
- Spring characteristic curve σ(ε)
- Elastic energy dissipation = area under the hysteresis curve
See also
- Hardness
- Rebound resilience elastomers
- Compressive strength
- Compression test
- Compression test arrangement
References
| [1] | Oertel, G. (Ed.), Abele, L.: Kunststoff-Handbuch, Volume 7, Polyurethane. Carl Hanser, Munich Vienna (1993), ISBN 978-3-446-16263-1 |
| [2] | ISO 3386-1 (2025-07): Polymeric Materials, Cellular Flexible – Determination of Stress–Strain Characteristics in Compression – Part 1: Low-density Materials |
| [3] | ISO 3386-2 (1997-06): Flexible Cellular Polymeric Materials – Determination of Stress–Strain Characteristics in Compression – Part 2: High-density Materials |