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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Kriechverhalten Zeitstandzugversuch}} {{PSM_Infobox}} Creep behaviour – Tensile creep test __FORCETOC__ ==General== The creep behaviour of plastics can be determined under tensile, bending and Compression Test|compressive loads]], or by means of Instrumented Hardness Testing – Method & Material Parameters|instrument..."

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{{Language_sel|LANG=ger|ARTIKEL=Kriechverhalten Zeitstandzugversuch}}
{{PSM_Infobox}}
Creep behaviour – Tensile creep test
__FORCETOC__

==General==

The [[Creep Plastics|creep behaviour]] of [[Plastics|plastics]] can be determined under [[Tensile Test|tensile]], [[Bend Test|bending]] and Compression Test|compressive loads]], or by means of [[Instrumented Hardness Testing – Method & Material Parameters|instrumented hardness testing]]. The [[Tensile Creep Test|tensile creep test]] has become the most important method for the experimental determination of creep or long-term behaviour [1].

==Determination of time-dependent strain==

The key measurement requirement is to determine the time-dependent strain on the [[Specimen|test specimen]], which is measured using mechanical extensometers (clip-on gauges) or optoelectronic strain measurement systems ('''Fig. 1'''). In rare cases, crosshead displacement measurement may also be used; however, in such cases, the [[Machine Compliance|machine compliance]] of the configuration should be known.

[[File:Tensile_Creep_Test_Fig-1.jpg|400px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Schematic illustration of the measurement of time-dependent strain in [[Plastics|plastics]] during a [[Tensile Creep Test|tensile creep test]] using a time-dependent testing station
|}

==Conducting the tensile creep test==

To achieve the required loading levels, creep test stands or [[Material Testing Machine|universal testing machines]] may be used; however, to ensure constant test conditions, these must be equipped with temperature-controlled chambers. For reasons of cost-effectiveness and time efficiency, at least 10 individual test stands should be available, which are operated either with variable loading at a constant temperature or with an identical loading level but at varying temperatures. When using universal testing machines, the tests must be carried out under [[Tensile Test Control|force control]], as otherwise the simultaneous [[Relaxation Plastics|stress relaxation]] would alter the test conditions, particularly the load level. On creep test stands, the load stress is applied using mass blocks, in which case a catch device is required ('''Fig. 1'''). To determine the strain at specified time points, each test system must be equipped with mechanical or, preferably, non-contact optoelectronic extensometers ([[Video Extensometry|video extensometers]] or [[Laser Extensometry|laser extensometers]]), which are read out via an online computer in multiplex mode ('''Fig. 2''').

[[File:Tensile_Creep_Test_Fig-2.jpg|400px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Schematic arrangement of the creep test stand (a) and a universal testing machine for [[Tensile Creep Test|tensile creep tests]] (b)
|}

==Definition of time-dependent creep strain==

For the [[Testing|tests]], Type 1A or 1B [[Specimen|test specimens]] are used in accordance with ISO 527-1 [2] and ISO 3167 [3], as well as ISO 293 to ISO 295 [4–6]. The test specimens should be prepared in accordance with ISO 2818 [7]. The tensile creep tests are usually carried out in accordance with the standard ISO 899-1 [8] or, in some cases, also with DIN 53 44 [9] and ASTM D 2990 [10]. Following the application of a non-impact load, the test specimen’s strain or elongation is then continuously recorded until [[Fracture|failure]] or a specified time value is reached. The applied load stress is defined in accordance with '''Eq. (1)''' via the applied force or the equivalent mass. The time-dependent creep strain is calculated according to '''Eq. (2)'''.

{|
|-
|width="20px"|
|width="500px" | <math>\sigma _{t0}=\frac{F}{A_0}</math>
|width="50px" |(1)
|}

{|
|-
|width="20px"|
|width="500px" | <math>\varepsilon _{t}=\varepsilon (t)=\frac{\Delta L_{0}(t)}{L_{0}} 100 \ \%</math>
|width="50px" |(2)
|}

==Characteristic values of tensile creep test==

The recorded creep curves (time–strain lines) are converted, in accordance with the evaluation procedure [8], into the creep diagram, the isochronous stress–strain diagram and the creep modulus curves (see: [[Creep Behaviour – Determination|creep behaviour – determination]]). From these curves, the characteristic values of the [[Tensile Creep Test|tensile creep test]] – such as the 1-minute strain, the residual and permanent strain, the tensile creep strength or the time–strain stress, as well as the creep modulus according to '''Eq. (3)''' – can then be calculated. An example for polypropylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PP) for a stress duration of up to 104 h is shown in '''Fig. 3'''. Further information on graphical and tabular creep data can be found in [11]. A simplified creep test for assessing the creep behaviour of [[Plastics|plastics]] is the [[Creep Behaviour – Recovery Test|recovery test]], which takes considerably less time but does not provide the full range of characteristic values.

{|
|-
|width="20px"|
|width="500px" | <math>E_c(t)=\frac{\sigma }{\varepsilon (t)}</math>
|width="50px" |(3)
|}

[[File:Tensile_Creep_Test_Fig-3.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px" |Tensile creep behaviour of polypropylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PP) under various loads [1]: creep curves (a), isochronous stress–strain diagram (b), creep diagram (time – stress diagram) (c) and creep modulus curves (d)
|}

==See also==

* [[Creep Plastics|Creep plastics]]
* [[Linear-viscoelastic Behaviour|Linear-viscoelastic behaviour]]
* [[Viscoelastic Material Behaviour|Viscoelastic material behaviour]]
* [[Creep Behaviour – Determination|Creep behaviour – Determination]]
* [[Tensile Test Overlapping Creep Relaxation|Tensile test overlapping creep relaxation]]
* [[BOLTZMANN's Superposition Principle|BOLTZMANN's superposition principle]]
* [[VOIGT-KELVIN Model|VOIGT-KELVIN model]]
* [[Instrumented Hardness Measurement – Creep|Instrumented hardness measurement – Creep]]
* [[Stepped Isothermal Method, Tensile Stress|Stepped isothermal method, Tensile stress]]
* [[Creep Behaviour – Recovery Test|Creep behaviour – Recovery test]]

==References==

{|
|-valign="top"
|[1]
|Höninger, H.: Long-term static behavior. In: [[Grellmann,_Wolfgang|Grellmann, W.]], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 167–177 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Library]] under A 22)
|-valign="top"
|[2]
|ISO 527-1 (2019-07): Plastics – Determination of Tensile Properties – Part 1: General Principles
|-valign="top"
|[3]
|ISO 3167 (2014-08): Plastics – Multipurpose Test Specimens
|-valign="top"
|[4]
|ISO 293 (2023-02): Plastics – Compression Moulding of Thermoplastic Materials
|-valign="top"
|[5]
|ISO 294-1 (2017-05): Plastics – Injection Moulding of Test Specimens of Thermoplastic Materials – Part 1: General Principles, and Moulding of Multipurpose and Bar Test Specimens
|-valign="top"
|[6]
|ISO 295 (2004-02): Plastics – Compression Moulding of Test Specimens of Thermosetting Materials
|-valign="top"
|[7]
|ISO 2818 (2018-12): Plastics – Preparation of Test Specimens by Machining
|-valign="top"
|[8]
|ISO 899-1 (2017-09): Plastics – Determination of Creep Behaviour –Part 1: Tensile Creep
|-valign="top"
|[9]
|DIN 53444 (1990-01): Testing the Tensile Creep of Plastics (withdrawn)
|-valign="top"
|[10]
|ASTM D 2990 (2017): Standard Test Methods for Tensile, Compression, and Flexural Creep and Creep-Rupture of Plastics
|-valign="top"
|[11]
|[[Bierögel, Christian|Bierögel, C.]], [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.]: Long-term loading test. In: [https://de.wikipedia.org/wiki/Wolfgang_Grellmann Grellmann, W.], [https://www.researchgate.net/profile/Sabine-Seidler Seidler, S.] (Eds.): Mechanical and Thermomechanical Properties of Polymers. Landoldt Börnstein. Volume VIII/6A2, Springer, Berlin (2014) pp. 286−331 (ISBN 978-3-642-55165-9; see [[AMK-Library]] under A 16)
|-valign="top"
|[12]
|DIN EN 12814-3 (2014-07): Testing of Welded Joints of Thermoplastics Semi-finished Products – Part 3: Tensile Creep Test
|}

[[Category:Creep Behaviour Plastics]]

Creep Behaviour – Tensile Creep Test - Revision history