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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Stauchhärte}} {{PSM_Infobox}} Compresssion hardness __FORCETOC__ ==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..."

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{{Language_sel|LANG=ger|ARTIKEL=Stauchhärte}}
{{PSM_Infobox}}
Compresssion hardness
__FORCETOC__

==Compression hardness==

This test technique is similar to the [[Compression Test|compression test]] and is used to determine the compression hardness of foams. To determine the compression hardness, a square test [[Specimen|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|compressive strength]] or compression resistance of the foam in kPa.

{|
|-
|width="20px"|
|width="500px" | <math> \sigma =\frac{F}{A_{0}}</math>
|}

The operating principle of the compression hardness test is illustrated in '''Fig. 1'''.

[[File:Stauchhaerte_1.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Functional principle of compression hardness testing
|}

==Indentation hardness==

Unlike indentation hardness, where the pressure plates (see: [[Compression Test Arrangement|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.

[[File:Stauchhaerte_2.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |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|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 [[Deformation#Anisotropic deformation|hysteresis]] loop is a measure of the foam’s elastic damping [1].

[[File:Stauchhaerte_Bild2a.JPG]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px" |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 Parameter|material parameters]] of this test are:

* Compressive stress at 40 % compression = compressive modulus ''σ''d40
* Spring characteristic curve ''σ''(''ε'')
* Elastic energy dissipation = area under the hysteresis curve

==See also==

* [[Hardness]]
* [[Rebound Resilience Elastomers|Rebound resilience elastomers]]
* [[Compressive Strength|Compressive strength]]
* [[Compression Test|Compression test]]
* [[Compression Test Arrangement|Compression test arrangement]]

==References==

{|
|-valign="top"
|[1]
|Oertel, G. (Ed.), Abele, L.: Kunststoff-Handbuch, Volume 7, Polyurethane. Carl Hanser, Munich Vienna (1993), ISBN 978-3-446-16263-1
|-valign="top"
|[2]
|ISO 3386-1 (2025-07): Polymeric Materials, Cellular Flexible – Determination of Stress–Strain Characteristics in Compression – Part 1: Low-density Materials
|-valign="top"
|[3]
|ISO 3386-2 (1997-06): Flexible Cellular Polymeric Materials – Determination of Stress–Strain Characteristics in Compression – Part 2: High-density Materials
|}

[[Category:Compression Test]]
[[Category:Hardness]]

Compression Hardness - Revision history