Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Überlagerung Kriechen Relaxation}} {{PSM_Infobox}} Tensile test overlapping creep relaxation FORCETOC ==Stress–strain behaviour without superimpositions== The characteristic value level of plastics depends largely on the test speed and temperature. These viscoelastic properties of plastics are evident..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Überlagerung Kriechen Relaxation}} {{PSM_Infobox}} Tensile test overlapping creep relaxation __FORCETOC__ ==Stress–strain behaviour without superimpositions== The characteristic value level of plastics depends largely on the test speed and temperature. These viscoelastic properties of plastics are evident..."

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{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Überlagerung Kriechen Relaxation}}
{{PSM_Infobox}}
Tensile test overlapping creep relaxation 
__FORCETOC__

==Stress–strain behaviour without superimpositions==

The characteristic value level of [[Plastics|plastics]] depends largely on the [[Test Speed|test speed]] and temperature. These [[Viscoelastic Material Behaviour|viscoelastic properties]] of plastics are evident in the [[Creep Plastics|creep]] and [[Relaxation Plastics|relaxation]] effects of these [[Material & Werkstoff|materials]], which influence the dimensional stability of [[Plastic Component|plastic components]] or the durability of the connection in force-bound constructions. In [[Tensile Test|tensile tests]] on plastics, these effects are superimposed by the rapid [[Stress|stressing]] of this test. Assuming a hypothetical plastic that shows no tendency to creep or relax, the stress-strain behaviour shown in '''Fig. 1''' would be recorded in the tensile test, whereby only the [[Tensile Strength|tensile strength]] ''σ''m and the elongation at break ''ε''b (see: [[Tensile Strength|tensile strength]]) are used here to compare the material behaviour.

[[File:Z_ueberlagerung_1.jpg|300px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Stress–strain behaviour in [[Tensile Test|tensile testing]] without creep and relaxation effects
|}

==Influences due to creep and relaxation==

The influence of [[Creep Plastics|creep]] behaviour superimposed on the tensile test can be seen in '''Fig. 2a'''. As a result of creep during the tensile test, the elongation at break increases compared to the material in '''Fig. 1''', since the elongation is composed of ''ε''b and the time-dependent elongation ''ε''(''t'').

[[File:Z_ueberlagerung_2.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Stress–strain behaviour in tensile testing with creep (a) and relaxation effects (b)
|}

It can be seen from this that the slower the [[Test Speed|test speed]] in the tensile test, the stronger this effect is. If the [[Tensile Test|tensile test]] is superimposed by pure [[Relaxation Plastics|relaxation]] behaviour, the stress–strain behaviour shown in '''Fig. 2b''' results. As a result of the stress reduction occurring simultaneously in the tensile test due to [[Relaxation Plastics|relaxation]], the [[Tensile Strength|tensile strength]] is reduced by the time-dependent stress component ''σ''(''t''), whereby the elongation at break itself is not affected. In a real tensile test, both components occur simultaneously, so that the [[Tensile Strength|tensile strength]] and elongation at break both show significant changes ('''Fig. 3''') with increasing stress time or reduced [[Strain Rate Basics|strain rate]].

[[File:Z_ueberlagerung_3.jpg|300px]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px" |Stress–strain behaviour in [[Tensile Test|tensile testing]]
|}

In general, the following statements can be made regarding the influence of test conditions [1]:

# As the test temperature increases ('''Fig. 4a'''), the behaviour changes from predominantly brittle to ductile.

# At higher [[Test Speed|test speeds]] or [[Strain Rate Basics|strain rates]], the stress–strain behaviour changes from predominantly ductile to brittle ('''Fig. 4b'''). Both test influences have opposite effects, which is specifically exploited in the [[Time–Temperature Shift Law|time–temperature shift principle]].

[[File:Z_ueberlagerung_4.jpg|450px]]
{|
|- valign="top"
|width="50px"|'''Fig. 4''':
|width="600px" |Influence of test speed and test temperature in tensile testing
|}

'''Figure 5''' shows a practical example of tensile tests with varying [[Test Speed|test speeds]] on a short glass fibre reinforced polyamide 6 material (see also: [[Short-fibre Reinforced Plastics|short-fibre reinforced composites]]). The [[Crosshead Speed|crosshead speeds]] correspond in part to the values specified in ISO 527-2 [2]. It can be seen that in this comparatively small speed interval, the [[Tensile Strength|tensile strengths]] double and the elongation at break decreases by approx. 25 %.

[[File:Tensile Test Overlapping 5.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 5''':
|width="600px" |Influence of [[Test Speed|test speed]] in [[Tensile Test|tensile testing]] of PA6 with 30 wt.-% GF
|}

[[Quasi-static Test Methods|Quasi-static mechanical tests]], such as [[Tensile Test|tensile]], [[Bend Test|bending]] or [[Compression Test|compression tests]], as well as [[Hardness|hardness]] measurements, always represent a superposition of rapid [[Stress|stress]] with [[Relaxation Plastics|relaxation]] and [[Creep Plastics|retardation]] effects in [[Plastics|plastics]], whereby the absolute proportion is influenced by the test conditions.

==See also==

* [[Test Speed|Test speed]]
* [[Creep Plastics|Creep plastics]]
* [[Relaxation Plastics|Relaxation plastics]]
* [[Deformation|Deformation behaviour]]
* [[Time–Temperature Shift Law|Time–temperature shift law]]

==References==

{|
|-valign="top"
|[1]
|[[Bierögel, Christian|Bierögel, C.]]: Tensile Tests on Polymers. In: [[Grellmann,_Wolfgang|Grellmann, W.]], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 106–123 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-806-5; see AMK-Library under A 22)
|-valign="top"
|[2]
|ISO 527-2 (2025-06): Plastics – Determination of Tensile Properties – Part 2: Test Conditions for Moulding and Extrusion Plastics
|}

[[Category:Creep Behaviour Plastics]]
[[Category:Tensile Test]]

Tensile Test Overlapping Creep Relaxation - Revision history