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{{Language_sel|LANG=ger|ARTIKEL=Biegeversuch und Lichtmikroskopie}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Bend test and light microscopy</span>
__FORCETOC__

==Methods for determining damage limits at deformation==

The further development of [[Hybrid Methods|hybrid methods]] for [[Polymer Diagnostic|polymer diagnostics]] always pursues the goal of increasing the informative value of individual classic testing methods. Numerous [[Hybrid Methods, Examples|examples]] from our own research work [1‒3] demonstrate the possibilities of quantifying [[Micro-Damage Limit|micro-damage limits]] and the associated description of local microdeformation processes during the [[Stress|stressing]] of [[Plastic Component|plastic components]]. The in-situ R-curve method under [[Quasi-static Test Methods|quasi-static]] loading was developed to elucidate the relationships between mechanical and [[Fracture Behaviour|fracture mechanical behaviour]] and [[Microscopic Structure|microstructure]] on the basis of quantitative structure (morphology)–property correlations.

==In-situ technique for recording crack resistance (R) curves under static bend loading==

In order to determine [[Fracture Mechanics|fracture mechanics]] values taking into account physical [[Crack Initiation|crack initiation]], in-situ observation of the deformation phenomena at the [[Crack|crack]] tip is necessary. One experimental option is to combine the [[Quasi-static Test Methods|quasi-static]] [[Fracture Mechanical Testing|fracture mechanics test]] with classical light microscopy ('''Fig. 1'''). With the aid of this in-situ technique, [[Crack Resistance (R) Curve|crack resistance (R) curves]] can be recorded using single-sample measurement technology, as the respective applied force and the corresponding [[Crack Opening|crack opening]] and [[Crack Propagation|crack growth]] values can be assigned to each load condition.

==Physical crack initiation and the stretch zone==

The evaluation of the microscopic images obtained in-situ makes it possible to determine qualitative and quantitative information about the respective shape of the crack tip in the propagation and blunting state and to specify a physical crack initiation value. In addition, statements about the deformation processes taking place are also possible. A particular advantage of the in-situ technique is the direct measurement of the extent of the [[Stretch Zone|stretch zone]] as a result of [[Deformation#Plastic deformation|plastic deformation]] on the [[Fracture Surface|fracture surface]]. A disadvantage of the usually subsequent recording of the stretch zone height, e.g. with the aid of [[Scanning Electron Microscopy|scanning electron microscopy]], is the strong underestimation of the expansion due to the non-consideration of the [[Deformation#Elastic deformation|elastic]] and [[Viscoelastic Material Behaviour|viscoelastic deformation parts]].

==Test setup for recording in-situ R curves==

For this hybrid method, a special bending test arrangement known as the ‘inverse’ [[Bend Test|bending test]] was developed at the Chair of Non-Metallic Materials (https://www.tuwien.at/mwbw/wwwt ) at the Vienna University of Technology [4]( https://www.tuwien.at/). The test arrangement ensures that the area of interest at the crack tip does not move out of the field of view of the light microscope, with the [[Support Distance|supports]] moving in the direction of the fixed bending punch ('''Fig. 1a'''). The test arrangement enables the recording of force–time and deflection–time signals and the in-situ video recording of the crack opening displacement ''δ'' and the stable crack growth Δ''a'' ('''Fig. 1b'''). The direct assignment of the recorded measured values enables the construction of [[Crack Resistance (R) Curve|crack resistance (R) curves]] in the form of ''J''–Δ''a'' and ''δ''–Δ''a'' curves, whereby the ''δ''–Δ''a'' curves are preferable due to their direct assignment to the crack tip deformation processes ('''Fig. 1c''').

[[File:Bend_Test_and_Light_Microscopy_Fig1.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Schematic test setup for recording in-situ R curves under quasi-static loading (a); crack tip of isotactic polypropylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: iPP) with determination of the direct measured variables ''δ'' and Δ''a'' (b) and example of an in-situ ''δ''–Δ''a'' crack resistance curve (c)
|}

==Development trends in the evaluation of damage mechanisms at the crack tip==

In addition to light microscopy, [[Electron Microscopy|electron microscopy]] ([[Scanning Electron Microscopy|SEM]], [[Environmental-SEM (ESEM)|ESEM]]) can also be used due to the geometric expansion of the stretch zone. The use of light microscopes for in-situ observation of crack initiation and crack propagation processes under quasi-static stress is relatively widespread due to its comparatively simple and cost-effective feasibility. There are two variants: either a light microscope is attached to commercial [[Material Testing Machine|material testing machines]] (see '''Fig. 1a'''), or special in-situ testing devices are installed in a horizontal arrangement in a microscope, whereby a stereomicroscope is generally used in both cases. Such investigations into crack initiation and crack propagation behaviour allow the observation of micromechanical processes (see: [[Micromechanics & Nanomechanics|micromechanics & nanomechanics]]) at the crack tip and conclusions to be drawn about the material-specific microdeformation mechanisms. The disadvantage of in-situ testing is that, due to the low thickness of the test specimens, it is limited to the area of [[Plane Stress and Strain State|plane stress state]] and comparatively low [[Deformation Rate|deformation rates]]. To evaluate the damage kinetics, [[Quasi-static Test Methods|quasi-static]] in-situ tensile tests can be performed on [[Notch Geometry|notched]] [[Specimen|test specimens]] in an [[Environmental-SEM (ESEM)|environmental scanning electron microscope (ESEM)]], whereby a schematic representation of a [[Specimen Clamping|clamped test specimen]] and additionally applied acoustic emission sensors (see: [[In-situ Tensile Test in ESEM with AE|in-situ tensile test in ESEM with SEA]]) are described in the literature by Zankel [5, 6] and Schoßig [7, 8].

==See also==

* [[Bend Test|Bend test]]
* [[Bend Loading|Bend loading]]
* [[In-situ Tensile Test in ESEM with AE|In-situ tensile test in ESEM with AE]]
* [[Hybrid Methods, Examples|Hybrid methods, Examples]]
* [[Bend Test and Sound Emission Analysis|Bend test and sound emission analysis]]
* [[Micromechanics & Nanomechanics]]

==References==

{|
|-valign="top"
|[1]
|[[Grellmann,_Wolfgang|Grellmann, W.]]: New Developments in Toughness Evaluation of Plymers and Composites by Fracture Mechanics. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], [[Seidler, Sabine|Seidler, S.]] (Eds.): Deformation and Fracture Behaviour of Polymers. Springer, Berlin Heidelberg (2001) pp. 3–26; ISBN 3-540-41247-6; see [[AMK-Library]] under A 7)
|-valign="top"
|[2]
|[[Bierögel, Christian|Bierögel, C.]]: Hybrid Methods of Polymer Diagnostics. In: [https://de.wikipedia.org/wiki/Wolfgang_Grellmann Grellmann, W.], Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 497–513 (ISBN 978-1-56990-8066-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Library]] under A 22)
|-valign="top"
|[3]
|Grellmann, W., Langer, B.: Methods for Polymer Diagnostics for the Automotive Industry. Materialprüfung 55 (2013) pp. 17–22 [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Methods_for_Polymer_Diagnostics_for_the_Automotive_Industry__Grellmann_Langer_2013_.pdf Download as pdf]
|-valign="top"
|[4]
|Seidler, S., Koch, T., Kotter, I., Grellmann, W.: Crack Tip Deformation of PP-materials. In: Miannay D.; Cost, P.; Francois, D.; Pineau, A. (Eds.): Advances in Mechanical Behaviour, Plasticity and Damage. Volume 1. Elsevier Science Ltd, Oxford (2000) pp. 255–260; E-Book: ISBN 978-0-0805-5275-0
|-valign="top"
|[5]
|Zankel, A., Pölt, P., Ingolic, E., Gahleitner, M., Grein, C.: The Fracture Behaviour of Polymers – in situ Investigations in the ESEM. Imaging & Microscopy 7 (2005) 16–18; [https://analyticalscience.wiley.com/content/article-do/fracture-behaviour-polymers---situ-investigations-esem https://analyticalscience.wiley.com/content/article-do/fracture-behaviour-polymers---situ-investigations-esem] (Access: 17.04.2026)
|-valign="top"
|[6]
|Zankel, A., Pölt, P., Gahleitner, M., Ingolic, E., Grein, C.: Tensile Tests of Polymers at Low Temperatures in the Environmental Scanning Electron Microscope: An Improved Cooling Platform. Scanning 29 (2007) 261–269; https://doi.org/10.1002/sca.20075
|-valign="top"
|[7]
|Schoßig, M.: Schädigungsmechanismen in faserverstärkten Kunststoffen – Quasistatische und dynamische Untersuchungen. Teubner Poublishing House, Wiesbaden (2010), (see [[AMK-Library]] under B 1–21) [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Schossig_Promotion_Inhaltsverzeichnis.pdf Content as pdf]
|-valign="top"
|[8]
|Schoßig, M., Zankel, A., Bierögel, C., Pölt, P., Grellmann, W.: Acoustic Emission Analysis for Assessment of Damage Kinetics of Short-glass Fibre-reinforced Thermoplastics – ESEM Investigations and Instrumented Charpy Impact Test. In: Grellmann, W., Langer, B. (Eds.): Deformation and Fracture Behaviour of Polymer Materials. Springer, Berlin (2017) pp. 126‒149 (ISBN 978-3-319-41877-3; see [[AMK-Library]] under A 19)
|}

'''Additional literature'''

* Bierögel, C.: Bend Test on Polymers. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Munich (2022), 3rd Edition, pp. 133–143 (ISBN 978-1-56990-806-8; see [[AMK-Library]] under A 22)

[[Category:Hybrid Methods]]

Bend Test and Light Microscopy - Revision history