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{{Language_sel|LANG=ger|ARTIKEL=Ausgangsrisslänge}}
{{PSM_Infobox}}
Initial crack length
__FORCETOC__

==Manual notch insertion==

In the [[Fracture Mechanical Testing|fracture mechanics testing]] of [[Plastics|plastics]] with the aim of specifying geometry-independent plastic-specific [[Material Value|characteristic values]] (see also: [[Geometry Criterion|geometry criterion]]), the mechanically introduced [[Notch|notch]] plays a decisive role (see: [[Notching|notching]]). In contrast to metallic [[Material & Werkstoff|materials]], where [[Fatigue|fatigue]] [[Crack|cracks]] are preferably generated, mechanical notches or cracks, e.g. with metal or razor blades, are applicable for plastics. These initial cracks can be introduced directly with a metal blade, either pneumatically or manually, for small ''a''/''W''-ratios ('''Fig. 1''').

[[File:Initial_Crack_Length-Fig1.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Notching equipment from [[Polymer Service GmbH Merseburg]]
|}

==Motorised notch insertion==

In testing practice, particularly for larger [[Specimen|test specimens]], motorised notch insertion ('''Fig. 2''') has proven effective, where, for example, a notch can be planed in using a special device. For larger ''a''/''W''-ratios, a V-notch is first milled in and then the required sharp notch is created using a metal blade.

[[File:Initial_Crack_Length-Fig2.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Motorised Notchvis notch device from Instron/Ceast, Italy
|}

==Determination of the initial crack length==

The notch produced with a metal blade is preferably measured under a light microscope, and the notch length is referred to as the initial crack length or true crack length (see: [[Effective Crack Length|effective crack length]]). If plastic phenomena, e.g. in the form of [[Plastic Zone|plastic zones]], are detected on the [[Fracture Surface|fracture surface]] using light or [[Scanning Electron Microscopy|scanning electron microscopy]] (SEM) methods as an expression of stable [[Crack Propagation|crack propagation]], the initial crack length a must be extended by the microscopically measured length of the stable crack growth ''r''pl.

==See also==

* [[Effective Crack Length|Effective crack length]]
* [[Notching]]
* [[Fracture Surface|Fracture surface]]
* [[Plastic Zone|Plastic zone]]
* [[Notch]]

==References==

{|
|-valign="top"
|[1]
|[[Blumenauer, Horst|Blumenauer, H.]], Pusch, G.: Technische Bruchmechanik, Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1993), (ISBN 3-342-00659-5; see [[AMK-Library]] under E 29-3)
|-valign="top"
|[2]
|[[Grellmann,_Wolfgang|Grellmann, W.]], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 235/236 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Library]] under A 22)
|}

[[Category:Fracture Mechanics]]

Initial Crack Length - Revision history